Serum response factor is alternatively spliced in colon cancer

Abstract

Introduction: Serum response factor (SRF) is a transcription factor important 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 forms during tumorigenesis. We hypothesized that there is a change in expression of splice variants during intestinal tumorigenesis, and that this change in splice variant expression promotes the tumor phenotype. Methods: The expression of SRF was determined by western blotting of normal intestinal cells and human colon cancer cell lines. To determine the effect of alternatively spliced forms of SRF on intestinal growth and proliferation, the major alternatively spliced isoform of SRF (SRF▵5) seen in cancer cells was transfected into IEC-6 cells. IEC-6 and IEC-6SRF▵5 cells were plated on matrigel on day 0. Cell numbers were determined at four timepoints. Results: Western blotting demonstrates that full length SRF is the predominant form of SRF in IEC-6 cells and the well-differentiated human colon cancer cell line HT-29. In poorly differentiated human colon cancer cells (WiDr, HCT 116, LoVo, and SW480) SRF▵5 is the dominant form expressed (Figure 1). There was a marked increase in cell growth kinetics in IEC-6 cells transfected with SRF▵5 compared to the parental cells (Figure 2). Conclusion: This data demonstrates that an alternatively spliced form of SRF, SRF▵5 is expressed in human colon cancer cell lines. Additionally, this data demonstrates that expression of SRF▵5 may contribute to the tumor phenotype by affecting cell growth. This is the first study to document a change in alternative splicing of SRF in human malignancy.