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

Abstract

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.

Long noncoding RNA OCC-1 suppresses cell growth through destabilizing HuR protein in colorectal cancer

“…The lack of OCC-1 polypeptide, in some extent, may due to the high GC-content of OCC-1 5′UTR and the highly stable hairpin structure around the initial codon, which would lower the translational efficiency dramatically ( 38 ). In addition, a novel noncoding OCC-1 splice variant (OCC-1D) was also discovered in CRC, in which a 60-nucleotide RNA fragment containing the initial codon of OCC-1 ORF was spliced out ( 39 ). Thus, we supposed that OCC-1 RNA has noncoding function independent of its polypeptide product in CRC cells.…”

COPD is accompanied by co-ordinated transcriptional perturbation in the quadriceps affecting the mitochondria and extracellular matrix

“…In COPD, up-regulation of follistatin may represent a compensatory mechanism aiming to sustain muscle mass in response to energy deficit. The only protein-coding gene to show a large magnitude reduction in abundance was C12orf75 , which binds the insulin receptor substrate 4 protein (IRS4) to promote insulin signalling in rat hypothalamic and human embryonic kidney cells 28 , and undergoes alternative splicing with products differentially regulating Wnt signalling 29 . This may similarly be a mechanism co-ordinating energy status and muscle growth/regeneration in COPD.…”

The expression and significance of microRNA in different stages of colorectal cancer

“…In addition, some of these signaling pathways are involved in the development of colorectal cancer, such as the Wnt and Ras signaling pathways. [ 25 , 26 ] Based on the previous research, the identification of some tumor-related signaling pathways, including the p53, Wnt, and TGF-β signaling pathways, which were mapped to some pathways in CRC, such as cell cycle and survival, [ 27 ] showed that microRNAs and their target genes were directly involved in the biological process of CRC and that CRC cell carcinogenesis was indirectly inhibited by the cell signaling pathways in different stages of CRC. Therefore, intervening in these signaling pathways may provide a new method for individualized treatment for and diagnosis of CRC.…”