Alternative splicing of the OCC-1 gene generates three splice variants and a novel exonic microRNA, which regulate the Wnt signaling pathway

作者：Najafi Hadi; Soltani Bahram M^*; Dokanehiifard Sadat; Nasiri Shirzad; Mowla Seyed Javad

来源：RNA-A Publication of the RNA Society, 2017, 23(1): 70-85.

DOI：10.1261/rna.056317.116

• colorectal cancer
• Wnt pathway
• alternative splicing
• microRNA
• OCC-1
• APPL2

The Wnt signaling pathway is hyperactivated in most colorectal cancers (CRC). Finding new regulators of this pathway represents the potential for cancer diagnosis or treatment. OCC-1 was initially reported as an up-regulated gene in colon carcinoma, without knowing its mechanism of action. Here, two novel transcript variants and an exonic microRNA that originated from the OCC-1 gene are reported, showing positive effects on Wnt activity. Up-regulation of the known OCC-1 variant (assigned as OCC-1A/B) was limited to CRC, and its overexpression increased survival of CRC-originated SW480 cells (Wnt(+)), while resulting in apoptosis of Wnt-suppressed SW480 cells or HeLa cells (Wnt(-)) detected by PI staining. Immunocytochemistry showed that the OCC-1A/B-encoded peptide was localized to the nucleus, where its overexpression resulted in Wnt signaling up-regulation, detected by TOP/FOPflash assay. The noncoding portion of the OCC-1A/B transcript had a suppressive effect on Wnt activity and had a negative correlation with APPL2 neighboring gene expression. Unlike OCC-1A/B, the novel OCC-1C splice variant had no expression alteration in CRC, and it seemed to encode a smaller peptide with cytoplasmic localization. A 60-nucleotide (nt) fragment containing an AUG start codon is spliced out to produce an OCC-1D noncoding RNA variant. The 60-nt RNA was validated as the precursor of a novel microRNA, which we named miR-ex1. Both OCC-1D and miR-ex1 were coordinately up-regulated in CRC. MiR-ex1 functional analysis revealed that it is targeting the APC2 tumor suppressor gene and is an activator of the Wnt signaling pathway. Overall, the OCC-1 gene is now introduced as a novel Wnt signaling regulator and as a potential therapeutic target.

• 出版日期2017-1