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The aryl hydrocarbon receptor interacting protein (AIP) is a tumor-suppressor gene underlying the pituitary adenoma predisposition. Thus far, the exact molecular mechanisms by which inactivated AIP exerts its tumor-promoting action have been unclear. To better understand the role of AIP in pituitary tumorigenesis, we performed gene expression microarray analysis to examine changes between Aip wild-type and knockout mouse embryonic fibroblast (MEF) cell lines. Transcriptional analyses implied that Aip deficiency causes a dysfunction in cyclic adenosine monophosphate (cAMP) signaling, as well as impairments in signaling cascades associated with developmental and immune-inflammatory responses. In vitro experiments showed that AIP deficiency increases intracellular cAMP concentrations in both MEF and murine pituitary adenoma cell lines. Based on knockdown of various G protein α subunits, we concluded that AIP deficiency leads to elevated cAMP concentrations through defective Gαi-2 and Gαi-3 proteins that normally inhibit cAMP synthesis. Furthermore, immunostaining of Gαi-2 revealed that AIP deficiency is associated with a clear reduction in Gαi-2 protein expression levels in human and mouse growth hormone (GH)-secreting pituitary adenomas, thus indicating defective Gαi signaling in these tumors. By contrast, all prolactin-secreting tumors showed prominent Gαi-2 protein levels, irrespective of Aip mutation status. We additionally observed reduced expression of phosphorylated extracellular signal-regulated kinases 1/2 and cAMP response element-binding protein levels in mouse and human AIP-deficient somatotropinomas. This study implies for the first time that a failure to inhibit cAMP synthesis through dysfunctional Gαi signaling underlies the development of GH-secreting pituitary adenomas in AIP mutation carriers.

Hereditary leiomyomatosis and renal cell cancer (HLRCC) is a syndrome predisposing to cutaneous and uterine leiomyomatosis as well as renal cell cancer and uterine leiomyosarcoma. Heterozygous germline mutations in the fumarate hydratase (FH, fumarase) gene are known to cause HLRCC. On occasion, no FH mutation is detected by direct sequencing, despite the evident HLRCC phenotype in a family. In the present study, to investigate whole gene or exonic deletions and amplifications in FH mutation-negative patients, we used multiplex ligation-dependent probe amplification technology. The study material comprised 7 FH mutation-negative HLRCC patients and 12 patients affected with HLRCC-associated phenotypes, including papillary RCC, early-onset RCC, uterine leiomyomas, or uterine leiomyosarcoma. A novel FH mutation, a deletion of FH exon 1 that encodes the mitochondrial signal peptide, was detected in one of the HLRCC patients (1/7). The patient with the FH mutation displayed numerous painful cutaneous leiomyomas and papillary type renal cell cancer. Our finding, together with the two patients with whole FH gene deletion who had been detected previously, suggests that exonic or whole-gene FH deletions are not a frequent cause of HLRCC syndrome.

Defects in the mismatch repair system lead to microsatellite instability (MSI), a feature observed in ∼ 15% of all colorectal cancers (CRCs). Microsatellite mutations that drive tumourigenesis, typically inactivation of tumour suppressors, are selected for and are frequently detected in MSI cancers. Here, we evaluated somatic mutations in microsatellite repeats of 790 genes chosen based on reduced expression in MSI CRC and existence of a coding mononucleotide repeat of 6–10 bp in length. All the repeats were initially sequenced in 30 primary MSI CRC samples and whenever frameshift mutations were identified in >20%, additional 70 samples were sequenced. To distinguish driver mutations from passengers, we similarly analyzed the occurrence of frameshift mutations in 121 intronic control repeats and utilized a statistical regression model to determine cut-off mutation frequencies for repeats of all types (A/T and C/G, 6–10 bp). Along with several know target genes, including TGFBR2, ACVR2, and MSH3, six novel candidate driver genes emerged that harbored significantly more mutations than identical control repeats. The mutation frequencies in 100 MSI CRC samples were 51% in G8 of GLYR1, 47% in T9 of ABCC5, 43% in G8 of WDTC1, 33% in A8 of ROCK1, 30% in T8 of OR51E2, and 28% in A8 of TCEB3. Immunohistochemical staining of GLYR1 revealed defective protein expression in tumors carrying biallelic mutations, supporting a loss of function hypothesis. This is a large scale, unbiased effort to identify genes that when mutated are likely to contribute to MSI CRC development. Defects in the mismatch repair system lead to microsatellite instability (MSI), a feature observed in ∼15% of all colorectal cancers (CRCs). Microsatellite mutations that drive tumourigenesis, typically inactivation of tumour suppressors, are selected for and are frequently detected in MSI cancers. Here, we evaluated somatic mutations in microsatellite repeats of 790 genes chosen based on reduced expression in MSI CRC and existence of a coding mononucleotide repeat of 6-10 bp in length. All the repeats were initially sequenced in 30 primary MSI CRC samples and whenever frameshift mutations were identified in >20%, additional 70 samples were sequenced. In order to distinguish driver mutations from passengers we similarly analyzed the occurrence of frameshift mutations in 121 intronic control repeats and utilized a statistical regression model to determine cut-off mutation frequencies for repeats of all types (A/T and C/G, 6-10 bp). Along with several know target genes, including TGFBR2, ACVR2, and MSH3, six novel candidate driver genes emerged that harbored significantly more mutations than identical control repeats. The mutation frequencies in 100 MSI CRC samples were 51% in G8 of GLYR1, 47% in T9 of ABCC5, 43% in G8 of WDTC1, 33% in A8 of ROCK1, 30% in T8 of OR51E2, and 28% in A8 of TCEB3. Immunohistochemical staining of GLYR1 revealed defective protein expression in tumours carrying biallelic mutations, supporting a loss of function hypothesis. This is a large scale, unbiased effort to identify genes that when mutated are likely to contribute to MSI CRC development.

Uterine leiomyomas, or fibroids, are benign tumors that affect millions of women worldwide and that can cause considerable morbidity. To study the genetic basis of this tumor type, we examined 18 uterine leiomyomas derived from 17 different patients by exome sequencing and identified tumor-specific mutations in the mediator complex subunit 12 (MED12) gene in 10. Through analysis of 207 additional tumors, we determined that MED12 is altered in 70% (159 of 225) of tumors from a total of 80 patients. The Mediator complex is a 26-subunit transcriptional regulator that bridges DNA regulatory sequences to the RNA polymerase II initiation complex. All mutations resided in exon 2, suggesting that aberrant function of this region of MED12 contributes to tumorigenesis.

A strong clustering of Hodgkin lymphoma in certain families has been long acknowledged. However, the genetic factors in the background of familial Hodgkin lymphoma are largely unknown. We have studied a family of 4 cousins with a rare subtype of the disease, nodular lymphocyte predominant Hodgkin lymphoma. We applied exome sequencing together with genome-wide linkage analysis to this family and identified a truncating germline mutation in nuclear protein, ataxia-telangiectasia locus (NPAT) gene, which segregated in the family. We also studied a large number of samples from other patients with Hodgkin lymphoma, and a germline variation leading to the deletion of serine 724 was found in several cases suggesting an elevated risk for the disease (odds ratio = 4.11; P = .018). NPAT is thus far the first gene implicated in nodular lymphocyte predominant Hodgkin lymphoma predisposition.

Hereditary leiomyomatosis and renal cell cancer (HLRCC, also known as multiple cutaneous and uterine leiomyomatosis, MCUL) is a highly penetrant autosomal dominant tumor predisposition syndrome characterized by benign leiomyomas of the skin and the uterus. Renal cell carcinomas, occurring in a subset of the HLRCC families, are exceptionally aggressive. Therefore careful, frequent surveillance strategies are recommended. Association of malignant smooth-muscle tumors, leiomyosarcomas, with HLRCC has been observed but the risk appears to be smaller than initially estimated. To date inactivating heterozygous mutations in the fumarate hydratase (FH, fumarase) gene, predisposing to HLRCC, have been found in approximately 180 families worldwide. The most extensively studied hypothesis on molecular mechanisms of HLRCC tumorigenesis is activation of the hypoxia pathway due to aberrant stabilization of the HIF1 transcription factor. HIF1 regulates transcription of genes relevant for vascularization, glucose transport and glycolysis, processes that facilitate tumor growth. However, additional mechanisms underlying tumor formation are likely to exist.

Frameshift mutations frequently accumulate in microsatellite-unstable colorectal cancers (MSI CRCs) typically leading to downregulation of the target genes due to nonsense-mediated messenger RNA decay. However, frameshift mutations that occur in the 3′ end of the coding regions can escape decay, which has largely been ignored in previous works. In this study, we characterized nonsense-mediated decay-escaping frameshift mutations in MSI CRC in an unbiased, genome wide manner. Combining bioinformatic search with expression profiling, we identified genes that were predicted to escape decay after a deletion in a microsatellite repeat. These repeats, located in 258 genes, were initially sequenced in 30 MSI CRC samples. The mitotic checkpoint kinase TTK was found to harbor decay-escaping heterozygous mutations in exon 22 in 59% (105/179) of MSI CRCs, which is notably more than previously reported. Additional novel deletions were found in exon 5, raising the mutation frequency to 66%. The exon 22 of TTK contains an A 9 –G 4 –A 7 locus, in which the most common mutation was a mononucleotide deletion in the A 9 (c.2560delA). When compared with identical non-coding repeats, TTK was found to be mutated significantly more often than expected without selective advantage. Since TTK inhibition is known to induce override of the mitotic spindle assembly checkpoint (SAC), we challenged mutated cancer cells with the microtubule-stabilizing drug paclitaxel. No evidence of checkpoint weakening was observed. As a conclusion, heterozygous TTK mutations occur at a high frequency in MSI CRCs. Unexpectedly, the plausible selective advantage in tumourigenesis does not appear to be related to SAC.

Mutations in the aryl hydrocarbon receptor-interacting protein (AIP) gene have been shown to predispose to pituitary adenoma predisposition, a condition characterized by growth hormone (GH)-secreting pituitary tumors. To study AIP-mediated tumorigenesis, we generated an Aip mouse model. Heterozygous mice developed normally but were prone to pituitary adenomas, in particular to those secreting GH. A complete loss of AIP was detected in these lesions, and full penetrance was reached at the age of 15 months. No excess of any other tumor type was found. Ki-67 analysis indicated that Aip-deficient tumors have higher proliferation rates compared with Aip-proficient tumors, suggesting a more aggressive disease. Similar to human AIP-deficient pituitary adenomas, immunohistochemical studies showed that expression of aryl hydrocarbon receptor nuclear translocator 1 or 2 (ARNT or ARNT2) protein was lost in the mouse tumors, suggesting that mechanisms of AIP-related tumorigenesis involve aberrant ARNT function. The Aip(+/-) mouse appears to be an excellent model for the respective human disease phenotype. This model constitutes a tool to further study AIP-associated pituitary tumorigenesis and may be potentially valuable in efforts to develop therapeutic strategies to treat pituitary adenomas.

Hereditary leiomyomatosis and renal cell cancer (HLRCC) is a tumor predisposition syndrome with cutaneous and uterine leiomyomatosis as well as renal cell cancer (RCC) as its clinical manifestations. HLRCC is caused by heterozygous germline mutations in the fumarate hydratase (fumarase) gene. In this study, we used array comparative genomic hybridization to identify the specific copy number changes characterizing the HLRCC‐associated RCCs. The study material comprised formalin‐fixed paraffin‐embedded renal tumors obtained from Finnish patients with HLRCC. All 11 investigated tumors displayed the papillary type 2 histopathology typical for HLRCC renal tumors. The most frequent copy number changes detected in at least 3/11 (27%) of the tumors were gains in chromosomes 2, 7, and 17, and losses in 13q12.3‐q21.1, 14, 18, and X. These findings provide genetic evidence for a distinct copy number profile in HLRCC renal tumors compared with sporadic RCC tumors of the same histopathological subtype, and delineate chromosomal regions that associate with this very aggressive form of RCC.

Hereditary leiomyomatosis and renal cell cancer (HLRCC) is a tumor predisposition syndrome caused by mutations in the fumarate hydratase (FH) gene. HLRCC is characterized by uterine and cutaneous leiomyomas, renal cell cancer, and uterine leiomyosarcoma. Typically, renal cell cancers in HLRCC are unilateral and display a papillary type 2 or ductal histology. We describe here a 23-year-old patient carrying a novel FH mutation (N330S) with a bilateral renal cell center. Carcinoma of the right kidney showed papillary structure, but the left tumor was diagnosed as a conventional (clear cell) renal carcinoma, a type not previously described in HLRCC. The clear cell renal carcinoma also displayed loss of the normal FH allele and the FH immunostaining. Our finding extends the number of cases in which HLRCC can be suspected, and the FH immunohistochemistry may serve as a useful tool to screen for HLRCC in young individuals with clear cell renal carcinoma.

BACKGROUND Amplification and overexpression of EIF3S3 gene has been demonstrated in breast and prostate cancer. Here, our goal was to study the effect of EIF3S3 on cell growth. METHODS The effect of EIF3S3 on growth of NIH 3T3 murine fibroblasts as well as breast (SK-Br-3 and ZR-75-1) and prostate (PC-3 and LNCaP) cancer cell lines was examined by using transfection with inducible pTet-Off system and siRNAs. RESULTS NIH 3T3 cells with overexpression of EIF3S3 grew significantly faster than cells transfected with empty vector and survived longer when grown in soft agar. The EIF3S3 overexpression was associated with increased fraction of cells in S-phase and with phosphorylation of retinoblastoma (Rb) protein. siRNA treatment inhibited significantly (P = 0.0022) the growth of all breast and prostate cancer cell lines studied. CONCLUSIONS The results suggest that EIF3S3 regulates cell growth and viability, and that overexpression of the gene may provide growth advantage to the cancer cells. Prostate © 2006 Wiley-Liss, Inc.

Microsatellite instability can be found in approximately 15% of all colorectal cancers. To detect new oncogenes we sequenced the exomes of 25 colorectal tumors and respective healthy colon tissue. Potential mutation hot spots were confirmed in 15 genes; ADAR, DCAF12L2, GLT1D1, ITGA7, MAP1B, MRGPRX4, PSRC1, RANBP2, RPS6KL1, SNCAIP, TCEAL6, TUBB6, WBP5, VEGFB, and ZBTB2; these were validated in 86 tumors with microsatellite instability. ZBTB2, RANBP2, and PSRC1 also were found to contain hot spot mutations in the validation set. The form of ZBTB2 associated with colorectal cancer increased cell proliferation. The mutation hot spots might be used to develop personalized tumor profiling and therapy.

Gastrointestinal polyposis is a common clinical problem, yet there is no consensus on how to best manage patients with moderate-load polyposis. Identifying genetic features of this disorder could improve management and especially surveillance of these patients. We sought to determine the prevalence of hamartomatous polyposis-associated mutations in the susceptibility genes PTEN, BMPR1A, SMAD4, ENG, and STK11 in individuals with ≥5 gastrointestinal polyps, including at least 1 hamartomatous or hyperplastic/serrated polyp.We performed a prospective, referral-based study of 603 patients (median age: 51 years; range, 2-89 years) enrolled from June 2006 through January 2012. Genomic DNA was extracted from peripheral lymphocytes and analyzed for specific mutations and large rearrangements in PTEN, BMPR1A, SMAD4, and STK11, as well as mutations in ENG. Recursive partitioning analysis was used to determine cutoffs for continuous variables. The prevalence of mutations was compared using Fisher's exact test. Logistic regression analyses were used to determine univariate and multivariate risk factors.Of 603 patients, 119 (20%) had a personal history of colorectal cancer and most (n = 461 [76%]) had30 polyps. Seventy-seven patients (13%) were found to have polyposis-associated mutations, including 11 in ENG (1.8%), 13 in PTEN (2.2%), 13 in STK11 (2.2%), 20 in BMPR1A (3.3%), and 21 in SMAD4 (3.5%). Univariate clinical predictors for risk of having these mutations included age at presentation younger than 40 years (19% vs 10%; P = .008), a polyp burden of ≥30 (19% vs 11%; P = .014), and male sex (16% vs 10%; P = .03). Patients who had ≥1 ganglioneuroma (29% vs 2%; P.001) or presented with polyps of ≥3 histologic types (20% vs 2%; P = .003) were more likely to have germline mutations in PTEN.Age younger than 40 years, male sex, and specific polyp histologies are significantly associated with risk of germline mutations in hamartomatous-polyposis associated genes. These associations could guide clinical decision making and further investigations.

Background: Mediator complex participates in transcriptional regulation by connecting regulatory DNA sequences to the RNA polymerase II initiation complex. Recently, we discovered through exome sequencing that as many as 70% of uterine leiomyomas harbour specific mutations in exon 2 of mediator complex subunit 12 (MED12). In this work, we examined the role of MED12 exon 2 mutations in other tumour types. Methods: The frequency of MED12 exon 2 mutations was analysed in altogether 1158 tumours by direct sequencing. The tumour spectrum included mesenchymal tumours (extrauterine leiomyomas, endometrial polyps, lipomas, uterine leiomyosarcomas, other sarcomas, gastro-intestinal stromal tumours), hormone-dependent tumours (breast and ovarian cancers), haematological malignancies (acute myeloid leukaemias, acute lymphoid leukaemias, myeloproliferative neoplasms), and tumours associated with abnormal Wnt-signalling (colorectal cancers (CRC)). Results: Five somatic alterations were observed: three in uterine leiomyosarcomas (3/41, 7%; Gly44Ser, Ala38_Leu39ins7, Glu35_Leu36delinsVal), and two in CRC (2/392, 0.5%; Gly44Cys, Ala67Val). Conclusion: Somatic MED12 exon 2 mutations were observed in uterine leiomyosarcomas, suggesting that a subgroup of these malignant tumours may develop from a leiomyoma precursor. Mutations in CRC samples indicate that MED12 may, albeit rarely, contribute to CRC tumorigenesis.

Background & Aims Familial visceral myopathy (FVM) is a rare inherited form of myopathic pseudo-obstruction; little is known about the genetic factors that cause this disorder. FVM is characterized by impaired functions of enteric smooth muscle cells, resulting in abnormal intestinal motility, severe abdominal pain, malnutrition, and even death. We searched for genetic factors that might cause this disorder. Methods We performed whole-exome sequence analysis of blood samples from 2 individuals in a family that had 7 members diagnosed with FVM. Sanger sequencing was used to analyze additional family members and 280 individuals without this disorder (controls). Intestinal tissue samples from 4 patients and 2 controls were analyzed by immunohistochemistry. Functional studies, including immunofluorescence, cell contractility, and actomyosin structure analyses, were performed using CRL-1976 and U2OS sarcoma cell lines. Results Whole-exome sequence analysis of DNA from 2 siblings identified 83 gene variants that were shared between the siblings and considered as possible disease-causing changes. A heterozygous variant, R148S in enteric smooth muscle actin γ-2 ( ACTG2 ), segregated with disease phenotype. Intestinal smooth muscle (muscularis propria) from individuals with FVM had reduced levels of cytoplasmic ACTG2 and abnormal accumulation of the protein into intracellular inclusions compared with controls. Sarcoma cells that expressed exogenous ACTG2 R148S incorporated reduced amounts of this protein into actin filaments compared with cells expressing ACTG2 wt ( P R148S also interfered with actin cytoskeleton organization and the contractile activities of the cells, indicating a dominant-negative effect. These findings, along with the site of the variation in the protein, indicate that ACTG2 R148S interferes with actin filament assembly. Conclusions We identified the R148S variant in ACTG2 as a cause of FVM in one family. The altered ACTG2 protein appears to aggregate, rather than form actin filaments, in intestinal smooth muscle tissue. This defect could impair contraction of the visceral smooth muscle cells and reduce bowel motility.

Germline mutations in the FH gene encoding the Krebs cycle enzyme fumarate hydratase predispose to hereditary leiomyomatosis and renal cell cancer (HLRCC) syndrome. FH-deficient cells and tissues accumulate high levels of fumarate, which may act as an oncometabolite and contribute to tumourigenesis. A recently proposed role for fumarate in the covalent modification of cysteine residues to S-(2-succinyl) cysteine (2SC) (termed protein succination) prompted us to assess 2SC levels in our existing models of HLRCC. Herein, using a previously characterized antibody against 2SC, we show that genetic ablation of FH causes high levels of protein succination. We next hypothesized that immunohistochemistry for 2SC would serve as a metabolic biomarker for the in situ detection of FH-deficient tissues. Robust detection of 2SC was observed in Fh1 (murine FH)-deficient renal cysts and in a retrospective series of HLRCC tumours (n = 16) with established FH mutations. Importantly, 2SC was undetectable in normal tissues (n = 200) and tumour types not associated with HLRCC (n = 1342). In a prospective evaluation of cases referred for genetic testing for HLRCC, the presence of 2SC-modified proteins (2SCP) correctly predicted genetic alterations in FH in every case. In two series of unselected type II papillary renal cancer (PRCC), prospectively analysed by 2SCP staining followed by genetic analysis, the biomarker accurately identified previously unsuspected FH mutations (2/33 and 1/36). The investigation of whether metabolites in other tumour types produce protein modification signature(s) that can be assayed using similar strategies will be of interest in future studies of cancer.

The circadian clock regulates daily variations in physiologic processes. CLOCK acts as a regulator in the circadian apparatus controlling the expression of other clock genes, including PER1. Clock genes have been implicated in cancer-related functions; in this work, we investigated CLOCK as a possible target of somatic mutations in microsatellite unstable colorectal cancers. Combining microarray gene expression data and public gene sequence information, we identified CLOCK as 1 of 790 putative novel microsatellite instability (MSI) target genes. A total of 101 MSI colorectal carcinomas (CRC) were sequenced for a coding microsatellite in CLOCK. The effect of restoring CLOCK expression was studied in LS180 cells lacking wild-type CLOCK by stably expressing GST-CLOCK or glutathione S-transferase empty vector and testing the effects of UV-induced apoptosis and radiation by DNA content analysis using flow cytometry. Putative novel CLOCK target genes were searched by using ChIP-seq. CLOCK mutations occurred in 53% of MSI CRCs. Restoring CLOCK expression in cells with biallelic CLOCK inactivation resulted in protection against UV-induced apoptosis and decreased G2-M arrest in response to ionizing radiation. Using ChIP-Seq, novel CLOCK-binding elements were identified near DNA damage genes p21, NBR1, BRCA1, and RAD50. CLOCK is shown to be mutated in cancer, and altered response to DNA damage provides one plausible mechanism of tumorigenesis. Mol Cancer Res; 8(7); 952–60. ©2010 AACR.

Hereditary leiomyomatosis and renal cell carcinoma (HLRCC) is caused by mutations in the Krebs cycle enzyme fumarate hydratase (FH). It has been proposed that “pseudohypoxic” stabilization of hypoxia-inducible factor-α (HIF-α) by fumarate accumulation contributes to tumorigenesis in HLRCC. We hypothesized that an additional direct consequence of FH deficiency is the establishment of a biosynthetic milieu. To investigate this hypothesis, we isolated primary mouse embryonic fibroblast (MEF) lines from Fh1-deficient mice. As predicted, these MEFs upregulated Hif-1α and HIF target genes directly as a result of FH deficiency. In addition, detailed metabolic assessment of these MEFs confirmed their dependence on glycolysis, and an elevated rate of lactate efflux, associated with the upregulation of glycolytic enzymes known to be associated with tumorigenesis. Correspondingly, Fh1-deficient benign murine renal cysts and an advanced human HLRCC-related renal cell carcinoma manifested a prominent and progressive increase in the expression of HIF-α target genes and in genes known to be relevant to tumorigenesis and metastasis. In accord with our hypothesis, in a variety of different FH-deficient tissues, including a novel murine model of Fh1-deficient smooth muscle, we show a striking and progressive upregulation of a tumorigenic metabolic profile, as manifested by increased PKM2 and LDHA protein. Based on the models assessed herein, we infer that that FH deficiency compels cells to adopt an early, reversible, and progressive protumorigenic metabolic milieu that is reminiscent of that driving the Warburg effect. Targets identified in these novel and diverse FH-deficient models represent excellent potential candidates for further mechanistic investigation and therapeutic metabolic manipulation in tumors. Cancer Res; 70(22); 9153–65. ©2010 AACR.

Germline mutations in the aryl hydrocarbon receptor interacting protein (AIP) gene predispose to the development of pituitary adenomas. Here, we characterized AIP mutation positive (AIPmut+) and AIP mutation negative (AIPmut-) pituitary adenomas by immunohistochemistry. The expressions of the AIP-related proteins aryl hydrocarbon receptor (AHR), AHR nuclear translocator (ARNT), cyclin-dependent kinase inhibitor 1B encoding p27(Kip1), and hypoxia-inducible factor 1-alpha were examined in 14 AIPmut+ and 53 AIPmut- pituitary adenomas to detect possible expression differences. In addition, the expression of CD34, an endothelial and hematopoietic stem cell marker, was analyzed. We found ARNT to be less frequently expressed in AIPmut+ pituitary adenomas (P = 0.001), suggesting that AIP regulates the ARNT levels. AIP small interfering RNA-treated HeLa, HEK293, or Aip-null mouse embryonic fibroblast cells did not show lowered expression of ARNT. Instead, in the pituitary adenoma cell line GH3, Aip silencing caused a partial reduction of Arnt and a clear increase in cell proliferation. We also observed a trend for increased expression of nuclear AHR in AIPmut+ samples, although the difference was not statistically significant (P = 0.06). The expressions of p27(Kip1), hypoxia-inducible factor 1-alpha, or CD34 did not differ between tumor types. The present study shows that the expression of ARNT protein is significantly reduced in AIPmut+ tumors. We suggest that the down-regulation of ARNT may be connected to an imbalance in AHR/ARNT complex formation arising from aberrant cAMP signaling.

Fumarate hydratase (FH) is an enzyme of the mitochondrial tricarboxylic acid cycle (TCAC). Here we report the characterization of a novel FH variant (FHv) that contains an alternative exon 1b, thus lacking the mitochondrial signal sequence. Distinct from mitochondrial FH, FHv localized to cytosol and nucleus and lacked FH enzyme activity. FHv was expressed ubiquitously in human fetal and adult tissues. Heat shock and prolonged hypoxia increased FHv expression in a cell line (HTB 115) by nine- and fourfold, respectively. These results suggest that FHv has an alternative function outside the TCAC related to cellular stress response.

Germline mutations in nuclear genes encoding mitochondrial enzymes fumarate hydratase (FH) and succinate dehydrogenase (subunits SDHB/C/D) have been implicated in the development of tumor syndromes referred to as hereditary leiomyomatosis and renal cell cancer (HLRCC) and hereditary paragangliomatosis (HPGL), respectively. FH and SDH are operating in the tricarboxylic acid cycle (the TCA cycle, the Krebs cycle). In the FH and SDH deficient tumors, accumulation of the substrates, fumarate and succinate, has been shown to cause stabilization of hypoxia inducible factor 1 alpha (HIF1 alpha). According to recent studies, HIF1 alpha could contribute to the hypoxia induced genomic instability seen in many cancers, through repression of mismatch repair (MMR) protein MSH2. In this study, in agreement with previous works, we found HIF1 alpha to be moderately or highly stabilized in 67% (16/24) and 77% (48/62) of HLRCC tumors and SDHB/C/D paragangliomas (PGL) and pheochromocytomas (PHEO), respectively. In addition, a set of 54 other familial and nonfamilial PGLs/PHEOs were studied. Moderately or highly stabilized HIF1 alpha was present in 68% (26/38) of the PGLs but in PHEOs (n = 16) no such pattern was observed. We then analyzed the suggested link between HIF1 alpha stabilization and MSH2 repression, in HLRCC and HPGL tumor material. No microsatellite instability (MSI) or lack of MSH2 expression was, however, observed. Thus we failed to provide in vivo evidence for the proposed link between HIF1 alpha stabilization and functional MMR deficiency, in TCAC deficient tumors.

Germline mutations in fumarate hydratase (FH) gene at 1q43 predispose to hereditary leiomyomatosis and renal cell cancer (HLRCC) syndrome. In HLRCC, the most common clinical features are leiomyomas of the skin and uterus, and in a subset of the families, renal cell cancer (RCC) and uterine leiomyosarcoma (ULMS) occur frequently at young age. This study was conducted to evaluate the possible contribution of FH mutations in a population-based series of early onset (< or = 45 years) ULMSs. Eighty-one cases were identified through the national cancer registry, and samples from 67 cases (83%) were available for FH mutation screening and analysis of allelic imbalance (AI) at the FH locus. Seventeen percent of tumors showed AI. In the mutation analysis, a novel missense mutation K424R was found. The mutation was also found from the patient's normal tissue. To study whether this variant has functional consequences, FH enzyme activity assay was performed in a cell model. The activity of the mutated protein was significantly reduced as compared to wild type (p = 0.009). This study shows that FH germline mutations can occur in seemingly nonsyndromic cases of ULMS (1/67, 1.5%). It appears that on the population level hereditary FH defects do play a role in pathogenesis of sporadic early onset ULMSs, albeit rarely.

Udgivelsesdato: Januar 1 Defects in mitochondrial enzymes predispose to severe developmental defects as well as tumorigenesis. Heterozygous germline mutations in the nuclear gene encoding fumarate hydratase (FH), an enzyme catalyzing the hydration of fumarate in the Krebs tricarboxylic acid cycle, cause hereditary leiomyomatosis and renal cell cancer; yet the connection between disruption of mitochondrial metabolic pathways and neoplasia remains to be discovered. We have used an expression microarray approach for studying differences in global gene expression pattern caused by mutations in FH. Seven uterine fibroids carrying FH mutations were compared with 15 fibroids with wild-type FH. The two groups showed markedly different expression profiles, and multiple differentially expressed genes were detected. The most significant increase in FH mutants was seen in the expression of carbohydrate metabolism- and glycolysis-related genes. Other significantly up-regulated gene categories in FH mutants were, for example, iron ion homeostasis and oxidoreduction. Genes with lower expression in FH-mutant fibroids belonged to groups such as extracellular matrix, cell adhesion, muscle development and cell contraction. We show that FH mutations alter significantly the expression profiles of fibroids, most strikingly increasing the expression of genes involved in glycolysis.

Hereditary leiomyomatosis and renal cell cancer (HLRCC) is a tumour predisposition syndrome caused by heterozygous germline mutations in the fumarate hydratase (FH) gene. The condition is characterised by predisposition to benign leiomyomas of the skin and the uterus, renal cell carcinoma (RCC), and uterine leiomyosarcoma (ULMS). To comprehensively examine the cancer risk and tumour spectrum in Finnish FH mutation positive families, genealogical and cancer data were obtained from 868 individuals. The cohort analysis of the standardised incidence ratios (SIR) was analysed from 256 individuals. FH mutation status was analysed from all available individuals (n = 98). To study tumour spectrum in FH mutation carriers, loss of the wild type allele was analysed from all available tumours (n = 22). The SIR was 6.5 for RCC and 71 for ULMS. The overall cancer risk was statistically significantly increased in the age group of 15-29 years, consistent with features of cancer predisposition families in general. FH germline mutation was found in 55% of studied individuals. Most RCC and ULMS tumours displayed biallelic inactivation of FH, as did breast and bladder cancers. In addition, several benign tumours including atypical uterine leiomyomas, kidney cysts, and adrenal gland adenomas were observed. The present study confirms with calculated risk ratios the association of early onset RCC and ULMS with FH germline mutations in Finns. Some evidence for association of breast and bladder carcinoma with HLRCC was obtained. The data enlighten the organ specific malignant potential of HLRCC.

DNA mismatch repair (MMR)–deficient cells typically accumulate mutations in short repetitive DNA tracts. This microsatellite instability (MSI) facilitates malignant transformation when affecting genes with growth-related and caretaker functions. To date, several putative MSI target genes have been proposed mainly based on high mutation frequency within their coding regions. However, some intronic repeat mutations have also been suggested to associate with MSI tumorigenesis, indicating the need for additional analyses on noncoding repeats. Here we have analyzed an intronic T9 repeat of semenogelin I (SEMG1) and report mutation frequencies of 51% (75 of 146) and 62% (8 of 13) in MMR-deficient primary colorectal cancers and cell lines, respectively. The putative effect of the SEMG1 mutations was assessed by RNA and protein level analyses, but no differences were detected between colorectal cancer cell lines with different SEMG1 status. Subsequently, the general background mutation frequency of MSI colorectal cancers was assessed by screening for intergenic T9 repeat alterations. One of 10 examined repeats was mutated in 70% (102 of 145) of the colorectal cancers evaluated. The frequencies observed here are notably higher than previously published in noncoding repeats shorter than 10 bp in MMR-deficient primary tumors. Our results indicate that high mutation frequencies, similar or higher than those observed in proposed and approved target genes, can be detected in repeat tracts of MSI tumors without any apparent selection pressure. These data call for urgent and thorough large-scale evaluation of mutation frequencies in neutral short repetitive sequences in MMR-deficient tumors.