Overexpression of regenerating islet-derived type 4 isoform 2 increases colorectal cancer cell proliferation.

Regenerating islet-derived type 4 (REG4) is highly expressed in various cancers, including colorectal cancer (CRC). REG4 has been reported to promote cancer cell proliferation, contribute to treatment resistance, and be associated with poor prognosis in CRC. In humans, this protein has two isoforms that are translated from three RNA-splicing variants. However, previous studies have primarily focused on isoform 1 and have not examined the function of isoform 2. Therefore, in the present study, we aimed to investigate the effects of REG4 isoform 2 on colon cancer cell proliferation. Real-time polymerase chain reaction (RT-qPCR) revealed higher REG4 isoform 2 expression in colon cancer cell lines (DLD-1, HCT116, and HT29) than in normal tissue-derived cell lines (HDLECs, HME1, HUVECs, and TIG114), similar to that of REG4 isoform 1. Moreover, REG4 isoform 2 overexpression significantly enhanced the proliferation of colon cancer-derived HCT116 cells in a WST-1 assay under low-serum conditions and in a soft agar colony formation assay. In NOD/SCID mice, tumor volumes tended to be larger in the REG4 isoform 2-overexpressing group than in the controls, although the difference did not reach statistical significance. Furthermore, in a subset of patients, the expression of this isoform in CRC tissues was higher than that in the adjacent normal tissues in human specimens. These results suggest that REG4 isoform 2, similar to isoform 1, is associated with enhanced proliferative properties of colon cancer cells and highlight the need for further investigation of isoform 2 in future studies.