Phosphorylation of Kruppel-like factor 5 (KLF5/IKLF) at the CBP interaction region enhances its transactivation function

Abstract

The Kruppel-like factor 5 (KLF5/IKLF) belongs to the Kruppel family of genes which bind GC-rich DNA elements and activate or repress their target genes in a promoter context and/or cellular environment-dependent manner. In the present study, we used the Gal4 fusion assay system to characterize the mechanism of transactivation by KLF5. We demonstrated that the transactivation function of KLF5 was enhanced by CREB-binding protein (CBP) and blocked by wild-type but not mutant E1A. Over expression of CBP reversed the inhibition effect of E1A. With various lengths of KLF5 fusion protein, the transactivation functions were localized to 156 amino acid residues at the N-terminal region and 133 amino acid residues adjacent to the Zn finger motif. We mapped the CBP and KLF5 interaction domain to the N-terminal region of CBP (amino acids 1-232) and the N-terminal region of KLF5 (amino acids 1-238) where one of the activation functions resides. The histone acetyltransferase (HAT) activity of CBP does not play a role in the transactivation function of KLF5 nor does it acetylate KLF5 in vitro. However, phosphorylation is important in KLF5 transactivation activity. Inhibition of protein kinase activity by H7 or calphostin C blocked both full-length and N-terminal fragment (amino acids 1-238) KLF5 activities. Mutation at a potential protein kinase C phosphorylation site within the CBP interaction domain of KLF5 reduces its transactivation function. Furthermore, using the GST pull-down approach, we showed that phosphorylation of KLF5 enhances its interaction with CBP. The results of the present study provide a mechanism for KLF5 transactivation function.

Krüppel-like factor KLF9 regulates PPARγ transactivation at the middle stage of adipogenesis

“…29 Several KLFs were reported to be phosphorylated and their transcriptional activities were changed by the modifications. [30][31][32] We found that when several serines on the KLF9 protein were mutated to alanines, its transcriptional activities detected by luciferase report assay for the PPARg2 promoter were greatly enhanced (unpublished data). However, whether post-translational modifications really happened to endogenous KLF9 in adipogenesis needs to be further investigated.…”

Ubiquitin–proteasome degradation of KLF5 transcription factor in cancer and untransformed epithelial cells

“…Tightly controlled protein regulation is a common feature to many transcription factors critically involved in cell growth control, such as p53 (Haupt et al, 1997), HIF-1a (Huang et al, 1998), c-myc (Salghetti et al, 1999), and E2F (Campanero and Flemington, 1997). In addition, instability of KLF5 protein has been suggested in two previous studies (Zhang and Teng, 2003;Bateman et al, 2004). In this study, we tested if and how KLF5 protein is regulated in epithelial cells.…”

“…Other factors also regulate the transcription of KLF5 (Chen et al, 2004). Furthermore, KLF5 undergoes post-translational modifications including phosphorylation (Zhang and Teng, 2003) and acetylation (Miyamoto et al, 2003). Tightly controlled protein regulation is a common feature to many transcription factors critically involved in cell growth control, such as p53 (Haupt et al, 1997), HIF-1a (Huang et al, 1998), c-myc (Salghetti et al, 1999), and E2F (Campanero and Flemington, 1997).…”

Krüppel-like factor 5 promotes breast cell proliferation partially through upregulating the transcription of fibroblast growth factor binding protein 1

“…Like other Sp/KLF transcription factors, KLF5 binds to GC-rich DNA sequences, such as the Sp1 site, GC box and CACCC box (Sogawa et al, 1993;Kojima et al, 1997;Zhang and Teng, 2003) through three zinc-finger domains. KLF5 has been shown to regulate transcription of a number of genes, such as the platelet-derived growth factor-a (PDGF-a) (Aizawa et al, 2004), CyclinD1 (Bateman et al, 2004), Pim1 (Zhao et al, 2008) and PPARg in different cell models.…”