Identification of Krüppel-like factor 4 as a potential tumor suppressor gene in colorectal cancer

Abstract

Krüppel-like factor 4 (KLF4 or GKLF) is an inhibitor of the cell cycle. The gene encoding KLF4 is localized on chromosome 9q, previously shown to exhibit allelic loss in colorectal cancer (CRC). In this study, we show that the mean level of KLF4 mRNA in a panel of 30 CRC was 52% that of paired normal colonic tissues. Similarly, the levels of KLF4 mRNA and protein in a panel of six established CRC cell lines were significantly lower than those of an untransformed colonic epithelial cell line. Using highly polymorphic DNA markers that .ank the KLF4 locus, we found evidence for loss of heterozygosity (LOH) in two of eight surgically resected CRC specimens. In addition, LOH was observed in .ve of six CRC cell lines with one additional cell line exhibiting hemizygous deletion in the KLF4 gene. We also found that the 5′-untranslated region of KLF4 was hypermethylated in a subset of resected CRC specimens and cell lines. Lastly, the open-reading frame of KLF4 in two of three CRC cell lines examined contained several point mutations that resulted in a diminished ability to activate the p21 WAF1/Cip1 promoter. These findings indicate that KLF4 is a potential tumor suppressor gene in CRC.

Krüppel-like factor 4 exhibits antiapoptotic activity following γ-radiation-induced DNA damage

“…KLF4 has a dual function -to synergistically induce the expression of p21 WAF1/CIP1 with p53, leading to cell cycle arrest (Zhang et al, 2000) and to suppress BAX expression, both directly and indirectly by inhibiting activation of BAX by p53, thus reducing apoptosis (this study). This model may explain the context-dependent nature by which KLF4 functions as either a tumor suppressor or an oncogene as reported by various groups (Foster et al, 1999(Foster et al, , 2005Zhao et al, 2004;Rowland et al, 2005;Wei et al, 2005;Rowland and Peeper, 2006). It may also explain the recent finding that inactivation of p21 WAF1/CIP1 by oncogenic RAS V12 neutralizes the cytostatic action of KLF4, converting the latter to a transforming protein owing to its antiapoptotic activity (Rowland et al, 2005) Materials and methods…”

“…Expression of KLF4 in RKO cells is negligible owing to hemizygous deletion of one KLF4 allele and silencing of the other allele by hypermethylation Zhao et al, 2004). We previously established a derivative of RKO cells containing a stably transfected KLF4 cDNA under the control of an inducible promoter that responds to the insect hormone, ecdysone.…”

“…These results indicate that KLF4 is an important factor in mediating the checkpoint functions of p53 following DNA damage. Accordingly, KLF4 has been shown to be a potential tumor suppressor in tumors of the gastrointestinal tract (Zhao et al, 2004;Katz et al, 2005;Wei et al, 2005).…”

Krüppel-like factors 4 and 5: the yin and yang regulators of cellular proliferation

“…A similar reduction in KLF4 mRNA levels is seen in colorectal cancer specimens when compared to matched normal colonic tissues [23]. Moreover, there is evidence for loss of heterozygosity (LOH) in the KLF4 locus in a subset of colorectal cancer specimens [23]. Conversely, re-expression of KLF4 in a colorectal cancer cell line results in diminished tumorigenecity [24].…”

“…Indeed, the levels of KLF4 mRNA are significantly reduced in intestinal adenomas in the Apc MIN/+ mice and familial adenomatous polyposis (FAP) patients when compared to matched normal tissues [22]. A similar reduction in KLF4 mRNA levels is seen in colorectal cancer specimens when compared to matched normal colonic tissues [23]. Moreover, there is evidence for loss of heterozygosity (LOH) in the KLF4 locus in a subset of colorectal cancer specimens [23].…”