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Background & Aims: Regenerating (Reg) gene IV is predominantly expressed in gastrointestinal cells and highly up-regulated in many gastrointestinal malignancies, including colorectal cancer (CRC). Human CRC cells expressing higher levels of Reg IV gene and its protein product (Reg IV) are resistant to conventional therapies, including irradiation (IR). However, the underlying mechanism is not well defined., Methods: A murine model of IR-induced intestinal injury and in vitro and in vivo models of human CRC were used to determine the role of Reg IV in regulation of normal intestinal and colorectal cancer cell susceptibility to IR-induced apoptosis., Results: Treatments of recombinant human Reg IV (rhR4) protein protected normal intestinal crypt cells from IR-induced apoptosis by increasing the expression of antiapoptotic genes Bcl-2, Bcl-XL, and survivin. However, overexpression of Reg IV in human CRC cells was associated with increased resistance to IR-induced apoptosis. Therefore, we used antagonism of Reg IV as a tool to increase CRC cell susceptibility to IR-induced cell death. Two complementary approaches using specific monoclonal antibodies and small interfering RNAs were tested in both in vitro and in vivo models of human CRC. Both approaches resulted in increased apoptosis and decreased cell proliferation, leading to decreased tumor growth and increased animal survival. Furthermore, these approaches increased CRC cell susceptibility to IR-induced apoptosis., Conclusions: These results implicate Reg IV as an important modulator of gastrointestinal cell susceptibility to IR; hence, it is a potential target for adjunctive treatments for human CRC and other gastrointestinal malignancies.

Background & Aims: MicroRNAs (miRNAs) are non-coding RNAs that regulate gene expression. The tumor suppressor miRNA let-7a has been reported to be inhibited posttranscriptionally in embryonic stem cells and in human cancers. Microtubule-associated kinase DCAMKL-1 is a putative intestinal stem cell marker that is expressed in Apc(Min/+) adenomas. We investigated the role of DCAMKL-1 on expression of let-7a miRNA and the oncogene c-Myc and in tumorigenesis., Methods: Human tissue microassay slides were immunostained for DCAMKL-1. HCT116 and SW480 cells were transfected with DCAMKL-1 small interfering RNA (siRNA) (si-DCAMKL-1) and analyzed for DCAMKL-1, c-Myc (using immunoblot and real-time reverse-transcription polymerase chain reaction [RT-PCR]), and pri-let-7a miRNA (using real-time RT-PCR) levels. A liposomal preparation of si-DCAMKL-1 was administered into HCT116 xenografts in nude mice, and tumor volumes were measured. A luciferase reporter assay, with a plasmid containing a let-7a-binding site at the 3' untranslated region, was utilized to measure let-7a in cell lines. Cells were isolated from normal mouse intestine using DCAMKL-1 and fluorescence-activated cell sorting (FACS) and subjected to pri-let-7a miRNA analysis., Results: Expression of DCAMKL-1 was increased in human colorectal cancers. siRNA-mediated blockade of DCAMKL-1 resulted in H tumor xenograft growth arrest, increased pri-let-7a miRNA, a corresponding decrease in luciferase activity, and decreased expression of the oncogene c-Myc. DCAMKL-1(+) cells isolated by FACS demonstrated a significant decrease in pri-let-7a miRNA, compared with more differentiated cells., Conclusions: DCAMKL-1 is a negative regulator of let-7a miRNA biogenesis in intestinal stem and colorectal cancer cells; it could represent a novel target for anti-cancer stem cell-based strategies.

Background & Aims: In the gut, tumorigenesis is thought to arise from the stem cell population located near the base of intestinal and colonic crypts. The RNA binding protein musashi-1 (Msi-1) is a putative intestinal and progenitor/stem cell marker. Msi-1 expression is increased during rat brain development and in APC(min/+) mice tumors. This study examined a potential role of Msi-1 in tumorigenesis., Methods: Msi-1 small interfering RNA (siRNA) was administered as a liposomal preparation to HCT116 colon adenocarcinoma xenografts in athymic nude mice and tumor volume was measured. Cell proliferation was assessed by hexosaminidase and 3-(4,5-dimethylthiazol 2-yl)-2,5-diphenyltetrazolium bromide MTT assays. siRNA-transfected cells were subjected to 12 Gy gamma-irradiation. Apoptosis was assessed by immunoreactive activated caspase-3 and mitosis was assessed by phosphorylated histone H3 staining. The tumor xenografts were stained similarly for phosphorylated histone H3, activated caspase-3, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling, Notch-1, and p21(WAF1). Furthermore, siRNA-transfected cells were subjected to cell-cycle analysis and Western blot analyses for Notch-1 and p21(WAF1)., Results: Knockdown of Msi-1 resulted in tumor growth arrest in xenografts, reduced cancer cell proliferation, and increased apoptosis alone and in combination with radiation injury. siRNA-mediated reduction of Msi-1 lead to mitotic catastrophe in tumor cells. Moreover, there was inhibition of Notch-1 and up-regulation of p21(WAF1) after knockdown of Msi-1., Conclusions: Our results show the involvement of Msi-1 in cancer cell proliferation, inhibition of apoptosis, and mitotic catastrophe, suggesting an important potential mechanism for its role in tumorigenesis.

Background and Aims: Cyclooxygenase-2 (COX-2) expression is regulated at the levels of messenger RNA (mRNA) stability and translation by AU-rich elements (ARE) located in its 3' untranslated region (3'UTR). Although structurally homologous RNA binding proteins HuR and CUGBP2 stabilize COX-2 mRNA, HuR induces whereas CUGBP2 inhibits COX-2 mRNA translation. This study aimed to determine the antagonism between these proteins on COX-2 expression., Methods: COX-2 ARE binding activity was determined by nitrocellulose filter binding and UV cross-linking assays using recombinant glutathione S-transferase (GST)/HuR and GST/CUGBP2. Protein:protein interactions were determined by GST pull-down, yeast 2-hybrid, and immunocytochemistry assays. Nucleocytoplasmic shutting was determined by heterokaryon analyses. The effect of CUGBP2 and HuR on COX-2 ARE-dependent translation was shown by a chimeric luciferase mRNA containing COX-2 3'UTR. HT-29 cells were subjected to 12 Gy gamma-irradiation in a cesium irradiator., Results: CUGBP2 and HuR bind with similar affinities to COX-2 ARE, but CUGBP2 competes with HuR for binding. In vitro, HuR and CUGBP2 heterodimerize. Furthermore, FLAG-tagged HuR and myc-tagged CUGBP2 colocalize in the nucleus of HCT-116 cells. Moreover, both proteins shuttled between the nucleus and cytoplasm. In vitro, HuR enhanced whereas CUGBP2 inhibited translation of the chimeric luciferase COX-2 3'UTR mRNA. Furthermore, CUGBP2 competitively inhibited HuR-mediated translation of the transcript. In HT-29 cells transfected with HuR and CUGBP2, a switch in COX-2 mRNA binding from predominantly HuR to CUGBP2 occurred after radiation treatment, which was coupled with increased silencing of the COX-2 mRNA., Conclusions: CUGBP2 overrides HuR and suppresses COX-2 mRNA translation.