Serum response factor is alternatively spliced in human colon cancer

Serum response factor (SRF) is a transcription factor that plays an important role in cellular differentiation and cell cycle regulation. SRF function is regulated in part by alternative splicing. Little is known about the expression or role of these alternatively spliced isoforms during tumorigenesis. We hypothesized that there is a change in the splice variants during intestinal tumorigenesis and that this change promotes the tumor phenotype.

SRF expression was determined by Western blotting of benign intestinal cells and human colon cancer cell lines. To determine the effect of alternative splicing of SRF on intestinal growth and proliferation, the predominant alternatively spliced isoform of SRF that we identified in colon cancer cells, SRFDelta5, was transfected into IEC-6 cells. IEC-6 and IEC-6SRFDelta5 cells were plated and cell numbers were determined at four time points.

Western blotting demonstrates that full-length SRF is the predominant form of SRF in rat IEC-6 cells, normal human colonic mucosa, and HT-29 cells, derived from a well-differentiated human colonic adenocarcinoma. In the colon cancer cell lines derived from poorly differentiated tumors (WiDr, HCT 116, LoVo, and SW480), SRFDelta5 is the predominant isoform expressed. There was a significant increase in cell survival in IEC-6 cells transfected with SRFDelta5 compared to parental cells.

Our data demonstrate that an alternatively spliced isoform of SRF, SRFDelta5, is expressed in human colon cancer cell lines. Additionally, these data demonstrate that expression of SRFDelta5 may contribute to the tumor phenotype by affecting cell survival. This is the first study to document a change in expression of the alternatively spliced isoform of SRF in human malignancy.