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Background: PRDM (PRDI-BF1 and RIZ domain containing) proteins are zinc finger proteins involved in multiple cellular regulations by acting as epigenetic modifiers. We studied a recently identified PRDM member PRDM5 for its epigenetic abnormality and tumor suppressive functions in multiple tumorigeneses. Methodology/Principal Findings: Semi-quantitative RT-PCR showed that PRDM5 was broadly expressed in human normal tissues, but frequently silenced or downregulated in multiple carcinoma cell lines due to promoter CpG methylation, including 80% (4/5) nasopharyngeal, 44% (8/18) esophageal, 76% (13/17) gastric, 50% (2/4) cervical, and 25% (3/12) hepatocellular carcinoma cell lines, but not in any immortalized normal epithelial cell lines. PRDM5 expression could be restored by 5-aza-2'-deoxycytidine demethylation treatment in silenced cell lines. PRDM5 methylation was frequently detected by methylation-specific PCR (MSP) in multiple primary tumors, including 93% (43/46) nasopharyngeal, 58% (25/43) esophageal, 88% (37/42) gastric and 63% (29/46) hepatocellular tumors. PRDM5 was further found a stress-responsive gene, but its response was impaired when the promoter was methylated. Ectopic PRDM5 expression significantly inhibited tumor cell clonogenicity, accompanied by the inhibition of TCF/β-catenin-dependent transcription and downregulation of CDK4, TWIST1 and MDM2 oncogenes, while knocking down of PRDM5 expression lead to increased cell proliferation. ChIP assay showed that PRDM5 bound to its target gene promoters and suppressed their transcription. An inverse correlation between the expression of PRDM5 and activated β-catenin was also observed in cell lines. Conclusions/Significance: PRDM5 functions as a tumor suppressor at least partially through antagonizing aberrant WNT/β-catenin signaling and oncogene expression. Frequent epigenetic silencing of PRDM5 is involved in multiple tumorigeneses, which could serve as a tumor biomarker. [ABSTRACT FROM AUTHOR]

Background: Identification of tumor suppressor genes (TSGs) silenced by CpG methylation uncovers the molecular mechanism of tumorigenesis and potential tumor biomarkers. Loss of heterozygosity at 11q25 is common in multiple tumors including nasopharyngeal carcinoma (NPC). OPCML, located at 11q25, is one of the downregulated genes we identified through digital expression subtraction. Methodology/Principal Findings: Semi-quantitative RT-PCR showed frequent OPCML silencing in NPC and other common tumors, with no homozygous deletion detected by multiplex differential DNA-PCR. Instead, promoter methylation of OPCML was frequently detected in multiple carcinoma cell lines (nasopharyngeal, esophageal, lung, gastric, colon, liver, breast, cervix, prostate), lymphoma cell lines (non-Hodgkin and Hodgkin lymphoma, nasal NK/T-cell lymphoma) and primary tumors, but not in any non-tumor cell line and seldom weakly methylated in normal epithelial tissues. Pharmacological and genetic demethylation restored OPCML expression, indicating a direct epigenetic silencing. We further found that OPCML is stress-responsive, but this response is epigenetically impaired when its promoter becomes methylated. Ecotopic expression of OPCML led to significant inhibition of both anchorage-dependent and -independent growth of carcinoma cells with endogenous silencing. Conclusions/Significance: Thus, through functional epigenetics, we identified OPCML as a broad tumor suppressor, which is frequently inactivated by methylation in multiple malignancies. [ABSTRACT FROM AUTHOR]

Ras has achieved notoriety as an oncogene aberrantly activated in multiple human tumors. Approximately 30% of all human tumors express an oncogenic form of this GTPase that is locked in an active conformation as a result of being insensitive to Ras GTPase- activating proteins (GAPs), proteins that normally regulate the inactivation of Ras by enhancing its intrinsic GTPase activity. Besides oncogenic mutations in Ras, signaling by wild-type Ras is also frequently deregulated in tumors through aberrant coupling to activated cell surface receptors. This indicates that alternative mechanisms of aberrant wild-type Ras activation may be involved in tumorigenesis. Here, we describe another mechanism through which aberrant Ras activation is achieved in human cancers. We have established that Ras GTPase-activating-like protein (RASAL), a Ca2+-regulated Ras GAP that decodes the frequency of Ca2+ oscillations, is silenced through (pG methylation in multiple tumors. With the finding that ectopic expression of catalytically active RASAL leads to growth inhibition of these tumor cells by Ras inactivation, we have provided evidence that epigenetically silencing of this Ras GAP represents a mechanism of aberrant Ras activation in certain cancers. Our demonstration that RASAL constitutes a tumor suppressor gene has therefore further emphasized the importance of Ca2+ in the regulation of Ras signaling and has established that deregulation of this pathway is an important step in Ras-mediated tumorigenesis. [ABSTRACT FROM AUTHOR]

Background: The antiapoptotic and epithelial-mesenchymal transition activities of Twist have been implicated in the neoplastic transformation and the development of metastasis, respectively. Upregulation of Twist, described in several types of human cancer, also acts as a prognostic marker of poor outcome. Aim: To investigate Twist expression in oesophageal squamous cell carcinoma (SCC) and its prognostic value in a Chinese cohort of patients with oesophageal SCC. Methods: Twist expression in primary oesophageal SCC of 87 Chinese patients was investigated by immunohistochemical staining. Twist protein level in one immortalised normal oesophageal epithelial cell line and six oesophageal SCC cell lines was measured by western blot analysis. Twist mRNA level in 30 pairs of frozen specimens of primary oesophageal SCC and non-neoplastic oesophageal epithelium from the upper resection margin of corresponding oesophagectomy specimen was also determined by semiquantitative reverse transcription-PCR. Results: It was found that Twist was upregulated in oesophageal SCC cell lines, and its mRNA and protein levels were both increased in oesophageal SCC and the non-neoplastic oesophageal epithelium (p<0.001). In addition, a high level of Twist expression in oesophageal SCC was significantly associated with a greater risk for the patient of developing distant metastasis within 1 year of oesophagectomy (OR 3.462, 95% CI 1.201 to 9.978; p=0.022). Conclusions: Our results suggest that upregulation of Twist plays a role in the neoplastic transformation to oesophageal SCC and subsequent development of distant metastasis. Twist may serve as a useful prognostic marker for predicting the development of distant metastasis in oesophageal SCC. [ABSTRACT FROM AUTHOR]

Epigenetic silencing of tumour suppressor genes (TSG) inactivates TSG functions. Previously, we identified PCDH10 as a methylated TSG in carcinomas. Here, we detected its frequent silencing and methylation in lymphoma cell lines including 100% Burkitt, 100% diffuse large B cell, 86% Hodgkin, 100% nasal natural killer/T-cell lymphoma and 1/3 of leukaemia cell lines, and in primary tumours but not in normal peripheral blood mononuclear cells or lymph nodes. PCDH10 silencing could be reversed by demethylation with 5-aza-2′-deoxycytidine. Methylation was further detected in 14% of Hodgkin lymphoma sera. Thus, PCDH10 methylation is frequently involved in lymphomagenesis and could serve as a tumour-specific biomarker. [ABSTRACT FROM AUTHOR]

The key genes involved in the development of esophageal squamous cell carcinoma (ESCC) remain to be elucidated. Previous studies indicate extensive genomic alterations occur on chromosome 9 in ESCC. Using a monochromosome transfer approach, this study provides functional evidence and narrows down the critical region (CR) responsible for chromosome 9 tumor suppressing activity to a 2.4?Mb region mapping to 9q33-q34 between markers D9S1798 and D9S61. Interestingly, a high prevalence of allelic loss in this CR is also observed in primary ESCC tumors by microsatellite typing. Allelic loss is found in 30/34 (88%) tumors and the loss of heterozygosity (LOH) frequency ranges from 67 to 86%. Absent to low expression of a 9q32 candidate tumor suppressor gene (TSG), DEC1 (deleted in esophageal cancer 1), is detected in four Asian ESCC cell lines. Stably expressing DEC1 transfectants provide functional evidence for inhibition of tumor growth in nude mice and DEC1 expression is decreased in tumor segregants arising after long-term selection in vivo. There is 74%LOH in the DEC1 region of ESCC primary tumors. This study provides the first functional evidence for the presence of critical tumor suppressive regions on 9q33-q34. DEC1 is a candidate TSG that may be involved in ESCC development.Oncogene (2005) 24, 697-705. doi:10.1038/sj.onc.1208179 Published online 6 December 2004 [ABSTRACT FROM AUTHOR]

Loss of heterozygosity at 3p21 is common in various cancers including nasopharyngeal carcinoma (NPC). BLU is one of the candidate tumor suppressor genes (TSGs) in this region. Ectopic expression of BLU results in the inhibition of colony formation of cancer cells, suggesting that BLU is a tumor suppressor. We have identified a functional BLU promoter and found that it can be activated by environmental stresses such as heat shock, and is regulated by E2F. The promoter and first exon are located within a CpG island. BLU is highly expressed in testis and normal upper respiratory tract tissues including nasopharynx. However, in all seven NPC cell lines examined, BLU expression was downregulated and inversely correlated with promoter hypermethylation. Biallelic epigenetic inactivation of BLU was also observed in three cell lines. Hypermethylation was further detected in 19/29 (66%) of primary NPC tumors, but not in normal nasopharyngeal tissues. Treatment of NPC cell lines with 5-aza-2'-deoxycytidine activated BLU expression along with promoter demethylation. Although hypermethylation of RASSF1A, another TSG located immediately downstream of BLU, was detected in 20/27 (74%) of NPC tumors, no correlation between the hypermethylation of these two TSGs was observed (P=0.6334). In addition to methylation, homozygous deletion of BLU was found in 7/29 (24%) of tumors. Therefore, BLU is a stress-responsive gene, being disrupted in 83% (24/29) of NPC tumors by either epigenetic or genetic mechanisms. Our data are consistent with the interpretation that BLU is a TSG for NPC.Oncogene (2004) 23, 4793-4806. doi:10.1038/sj.onc.1207632 Published online 3 May 2004 [ABSTRACT FROM AUTHOR]

Epigenetic inactivation of RASSF1A, a putative tumor suppressor with proapoptotic activity, is frequently observed in a number of solid tumors, including a variety of epithelial cancers, but has not been described in hematopoietic tumors. We have analysed the expression and methylation status of RASSF1A in Hodgkin's lymphoma (HL)-derived cell lines, primary HL tumors and serum samples from HL patients. RASSF1A transcription was detectable in only 2/6 HL cell lines. Methylation-specific PCR and bisulfite genomic sequencing revealed that the RASSF1A promoter was hypermethylated in all four RASSF1A-nonexpressing cell lines. 5-aza-2'-deoxycytidine treatment resulted in demethylation of the promoter and RASSF1A expression in these lines. Hypermethylation of RASSF1A was also detected in 34/52 (65%) primary HL tumors and in 2/22 serum samples from these patients. Microdissection of Hodgkin/Reed-Sternberg (HRS) cells from several of these cases confirmed that the RASSF1A hypermethylation we detected in the analysis of whole tumor originated from the tumor cell population. Although hypermethylation of RASSF1A was detected in 5/6 non-Hodgkin's lymphoma (NHL)-derived cell lines, only rare primary NHL (1/10 of Burkitt's lymphoma, 1/12 of post-transplant lymphoma, 1/12 diffuse large B-cell lymphoma, 0/27 of nasal lymphoma, 0/8 follicular center cell lymphoma, 0/4 mantle cell lymphoma, 0/4 anaplastic large cell (Ki-1+) lymphoma, 0/2 MALT lymphoma) showed hypermethylation of the promoter. No methylation was detected in any of the 14 normal PBMC. These results point to an important role for epigenetic silencing of RASSF1A in the pathogenesis of HL. Inactivation of RASSF1A could be one mechanism by which HRS cells escape the apoptosis that should occur following nonproductive immunoglobulin gene rearrangements.Oncogene (2004) 23, 1326-1331. doi:10.1038/sj.onc.1207313 [ABSTRACT FROM AUTHOR]

Chick embryo liver mitochondrial matrix protein, 5-aminolaevulinate synthase, is synthesised initially as a larger cytosolic precursor. In this report we present the complete nucleotide sequence of a cDNA clone coding for the precursor together with corresponding confirmatory amino acid sequence of peptides derived from purified mature mitochondrial enzyme. The deduced amino acid sequence shows that the precursor consists of mature enzyme of 579 amino acids and an N-terminal extension of 56 amino acids. The latter presequence is highly basic in character as found with other mitochondrial preproteins. [ABSTRACT FROM AUTHOR]

Hepatic 5-aminolevulinate synthase was induced in chick embryos by administration of the porphyrinogenic drugs 2-allyl-2-isopropylacetamide and 3,5-diethoxycarbonyl-l,4-dihydrocollidine. A cDNA library was constructed from drug-induced liver mRNA and clones containing sequences coding for 5-aminolevulinate synthase were identified by hybrid-selected translation. The identity of these clones was confirmed by comparing DNA sequence data with the amino acid sequence of peptides from purified 5-aminolevulinate synthase. From Northern blot analysis the size of the m R N A for 5-aminolevulinate synthase was estimated to be 2800 base pairs, approximately 600 base pairs more than that required to code for the primary translation product of relative molecular mass 74000. [ABSTRACT FROM AUTHOR]

The induction of cytochrome P450 in chick embryo liver has been studied using three different porphyrinogenic drugs, 2-allyl-2-isopropylacetamide, 3,5-diethoxycarbonyl-1,4-dihydrocollidine and Phenobarbital. Pulse-labelling studies have shown that for each drug the cytochrome P450 synthesized either in ovo or in a wheat germ translation system reacted immunologically with antibody raised against the purified 2-allyl-2-isopropylacetamide-induced enzyme (Mr = 50000). To investigate whether this is due to the three drugs inducing the same protein or different proteins with common immunological determinants, nucleic acid hybridization studies have been carried out using a recently characterized 2-allyl-2-isopropylacetamide-induced cytochrome P450 cloned cDNA probe [Brooker, J. D. et al. (1982) Eur. J. Biochem. 129, 325 – 333]. It has been shown that the mRNA induced by each drug hybridizes with this probe and all are of similar size. The melting profile of the mRNA·cDNA hybrids indicates that the mRNAs induced by the three drugs have at least 98% homology with the cDNA probe. Restriction endonuclease digestions of total chick embryo genomal DNA and a chick cytochrome P450 genomal clone indicates that the cytochrome P450 gene homologous with the cDNA probe is represented in the genome only once. These results strongly suggest that the three drugs cause increased levels of the same cytochrome P450 mRNA, possibly due to enhanced expression of the same gene. Results are also presented which show that other cytochrome-P450-inducing drugs, 3-methylcholanthrene, β-naphthoflavone or pregnenolone-16α-carbonitrile do not increase the level of the 2-allyl-2-isopropylacetamide-inducible mRNA but rather reduce it to a level which was lower than that of the untreated controls. [ABSTRACT FROM AUTHOR]

5-Aminolaevulinate synthase from chick-embryo liver mitochondria has, for the first time, been purified to homogeneity in its native non-degraded form by molecular sieve chromatography, chromatofocusing and affinity chromatography. The enzyme has a minimum molecular weight of 68000 as determined by sodium dodecylsulphate/polyacrylamide gel electrophoresis and a specific activity of 35000 units/mg of protein. This result conflicts with the previous report of Whiting, M. J. and Granick, G. [(1976) J. Biol. Chem. 251, 1340-1346] that the chick embryo enzyme has a molecular weight of 49000. We show here that the purified form can be degraded proteolytically to a smaller form of molecular weight around 50000 while retaining full enzymatic activity. It seem evident, therefore, that the enzyme isolated by Whiting & Granick (1976) was degraded. We have further established by pulse-labelling studies and immunoprecipitation that the enzyme isolated by our new and rapid procedure has the same minimum molecular weight as that which exists in vivo. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented regarding post-rituximab burkitt transformation of PTLD in the June 9, 2009 issue.

The structure of chick embryo liver 5-aminolaevulinate synthase has been examined by electron mciroscopic studies using negative staining. From the different projections of the enzyme particles observed in electron micrographs, a model for the enzyme molecule has been proposed. In this model, an enzyme molecule consists of two curved and identical subunits associated in opposite polarities. From the dimensions of an enzyme molecule subunit measured from electron micrographs, the relative molecular mass of each subunit is estimated to be 70000. [ABSTRACT FROM AUTHOR]