Krüppel-like Factor 4 Mediates p53-dependent G1/S Cell Cycle Arrest in Response to DNA Damage

Abstract

The tumor suppressor p53 is required for the maintenance of genomic integrity following DNA damage. One mechanism by which p53 functions is to induce a block in the transition between the G 1 and S phase of the cell cycle. Previous studies indicate that the Krüppel-like factor 4 (KLF4) gene is activated following DNA damage and that such activation depends on p53. In addition, enforced expression of KLF4 causes G 1 /S arrest. The present study examines the requirement of KLF4 in mediating the p53-dependent cell cycle arrest process in response to DNA damage. We show that the G 1 population of a colon cancer cell line, HCT116, that is null for the p53 alleles (−/−) was abolished following γ irradiation compared with cells with wild-type p53 (+/+). Conditional expression of KLF4 in irradiated HCT116 p53−/− cells restored the G 1 cell population to a level similar to that seen in irradiated HCT116 p53+/+ cells. Conversely, treatment of HCT116 p53+/+ cells with small interfering RNA (siRNA) specific for KLF4 significantly reduced the number of cells in the G 1 phase following γ irradiation compared with the untreated control or those treated with a nonspecific siRNA. In each case the increase or decrease in KLF4 level because of conditional induction or siRNA inhibition, respectively, was accompanied by an increase or decrease in the level of p21 WAF1/CIP1 . Results of our study indicate that KLF4 is an essential mediator of p53 in controlling G 1 /S progression of the cell cycle following DNA damage.The mammalian cell cycle is operationally divided into five distinct phases: gap 1 (G 1 ), DNA synthesis (S), gap 2 (G 2 ), mitosis (M), and growth arrest phase (G 0 ), also called quiescence (1). Complex networks of control mechanisms called "checkpoints" are responsible for the orderly progression of these events within the cell cycle. Defects in checkpoint control increase genetic instability, thereby contributing to uncontrolled proliferation (2). For example, damage to the DNA elicits a series of signal transduction pathways that result in an arrest of the cell cycle at various checkpoints (3). Much of the DNA damage-induced signals are funneled through p53, which directs further downstream actions that lead to inhibition of G 1 to S and G 2 to M transitions, among other events such as apoptosis (4). Therefore, it is not surprising that p53 is the most frequently mutated tumor suppressor gene in human cancers (5).The arrest in the transition between the G 1 and S phase of the cell cycle elicited by p53 requires in part the transcriptional activation of the gene encoding the cyclin-dependent kinase (Cdk) 1 inhibitor p21 WAF1/CIP1 (6,7). p21 WAF1/CIP1 binds to several G 1 cyclin-Cdk complexes and * This work was supported in part by Grants DK52230 and CA84197 from the National Institutes of Health. ¶ Recipient of a Georgia Cancer Coalition Distinguished Cancer Clinician Scientist award. To whom correspondence should be addressed: 201 Whitehead Biomedical Research Bldg., Emory University School of Medicine, 61...

KLF4, p21 and context-dependent opposing forces in cancer

“…This argues that the suppression of p53 expression represents a primary oncogenic function of KLF4. Conversely, KLF4 has also been placed downstream in the p53 pathway, as KLF4 is required for p53-mediated induction of CDKN1A in response to DNA damage, which leads to cell-cycle arrest 23,62 (FIG. 4,5).…”

“…Both Krüppel-like transcription factor 4 (KLF4) and p21 (also known as CIP1/WAF1) are targets of multiple tumour-suppressor pathways. KLF4 has been shown to mediate p53-p21 signalling in response to DNA damage 23,62 . We speculate that KLF4 is also a mediator of transforming growth factor-β (TGFβ)-p21 and adenomatosis polyposis coli (APC)-p21 signalling, thereby relaying signals elicited by multiple key tumour-suppressor pathways.…”

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

“…DNA damage caused by methyl methanesulfonate (MMS) [16] or γ irradiation [17] leads to the induction of KLF4 expression in a p53-dependent manner. The increase in KLF4 mRNA level parallels the increase in the level of p21 WAF1/Cip1 mRNA, a major cyclin-dependent kinase inhibitor [16].…”

“…A consequence of the p53-dependent activation of p21 WAF1/Cip1 expression following DNA damage is an arrest in the cell cycle at both the G 1 /S and G 2 /M transition points. KLF4 was shown to be necessary and sufficient in mediating the checkpoint function of p53 at both of these transition points [17,18]. KLF4 accomplishes this task both through its transcriptional activation of p21 WAF1/Cip1 and through direct suppression of cyclin D1 [19] and cyclin B1 expression [18], which are required for the G 1 /S and G 2 /M transitions, respectively.…”

Mutant p53 subverts p63 control over KLF4 expression in keratinocytes

“…Cell-cycle block by DNA-damaging agents activates KLF4 expression, but apoptotic doses decrease it (Yoon et al, 2003). Interestingly, maintaining elevated levels of KLF4 prevents apoptosis mediated by p53 (Ghaleb et al, 2007), and elimination of KLF4 induction leads to apoptosis in cells treated with nonapoptotic doses of DNA-damaging agents (Zhou et al, 2009).…”