Krüppel-Like Factor 5 Mediates Cellular Transformation During Oncogenic KRAS-Induced Intestinal Tumorigenesis

Background & Aims: Krüppel-like factor 5 (KLF5) is a zinc finger–transcription factor that regulates cell proliferation. Oncogenic KRAS mutations are commonly found in colorectal cancers. We aimed to determine whether KLF5 mediates KRAS functions during intestinal tumorigenesis. Methods: The effects of KLF5 on proliferation and transformation were examined in IEC-6 intestinal epithelial cells stably transfected with inducible KRAS^V12G. KLF5 expression was examined in intestinal tumors derived from transgenic mice expressing KRAS^V12G under villin promoter and in human colorectal cancers with mutated KRAS. Results: Induction of KRAS^V12G in IEC-6 cells resulted in increased expression of KLF5, accompanied by increased rates of proliferation and anchorage-independent growth. Inhibition of KLF5 expression by mitogen-activated protein kinase/extracellular signal–regulated kinase (MEK) inhibitors or KLF5-specific small interfering RNA reduced proliferation and anchorage-independent growth despite KRAS^V12G induction. Human colorectal cancer cell lines with mutated KRAS contained high levels of KLF5 and reduction of KLF5 by MEK inhibitors or KLF5 small interfering RNA also led to reduced proliferation and transformation. In vivo, both intestinal tumors derived from mice transgenic for villin-KRAS^V12G and human primary colorectal cancers with mutated KRAS contained high levels of KLF5 and increased staining of the proliferative marker Ki67. Conclusions: Elevated levels of KLF5 protein are strongly correlated with activating KRAS mutations in intestinal tumors in vitro and in vivo. Inhibition of KLF5 expression in tumor cells resulted in significantly reduced rates of proliferation and transforming activities. We conclude that KLF5 is an important mediator of oncogenic KRAS transforming functions during intestinal tumorigenesis.

Abbreviations used in this paper: DMSO, dimethyl sulfoxide, ERK, extracellular signal–regulated kinase, IPTG, isopropyl-1-thio-β-d-galactopyranoside, KLF5, Krüppel-like factor 5, MAPK, mitogen-activated protein kinase, MEK, mitogen-activated protein kinase/extracellular signal–regulated kinase, siRNA, small interfering RNA