Positive- and Negative-acting Krüppel-like Transcription Factors Bind a Transforming Growth Factor β Control Element Required for Expression of the Smooth Muscle Cell Differentiation Marker SM22α in Vivo

Abstract

Transforming growth factor ␤ (TGF-␤) is implicated in the regulation of smooth muscle cell (SMC) differentiation. We previously identified a novel TGF-␤ control element (TCE) in the promoters of SMC differentiation marker genes, including ␣-smooth muscle actin and SM22␣. In this study, the importance of the TCE in regulation of SM22␣ gene expression in vivo was investigated by mutating it within the context of a mouse SM22␣ promoter-lacZ transgenic construct. Mutation of the TCE completely abolished SM22␣ promoter activity in arterial SMCs as well as in developing heart and skeletal muscle. To identify the transcription factor(s) binding to the TCE, we performed yeast one-hybrid cloning analysis and identified gut-enriched Krü ppellike factor (GKLF). However, cotransfection studies in cultured cells showed that GKLF repressed the TGF-␤-dependent increases in SM22␣ and ␣-smooth muscle actin promoter activities. Furthermore, GKLF was not highly expressed in differentiated SMCs in vivo, and TGF-␤ down-regulated GKLF expression in dedifferentiated cultured SMCs. In contrast, overexpression of a related factor (BTEB2) transactivated SM22␣ promoter activity. Thus, our findings suggest a reciprocal role for related Krü ppel-like transcription factors in the regulation of SMC differentiation through a TCE-dependent mechanism.

Overexpression of Krüppel-like factor 4 in the human colon cancer cell line RKO leads to reduced tumorigenecity

“…However, in vivo growth suppression remains sustained, actually becoming more marked with time. This observation suggests that KLF4 overexpression may also affect the tumor microenvironment in addition to epithelial cell growth in vivo, and would be consistent with previous reports of KLF4 localization and function in smooth muscle and vascular endothelial cells (Yet et al, 1998;Adam et al, 2000;Nickenig et al, 2002). Thus, again, context appears to contribute to KLF4 function.…”

“…KLF4 is also highly expressed in the testes, specifically in the postmeiotic germ cells and somatic Sertoli cells, suggesting an important role in testicular differentiation (Behr and Kaestner, 2002). Finally, KLF4 is expressed in vascular endothelial cells (Yet et al, 1998), and may function to inhibit TGF-bmediated differentiation of vascular smooth muscle cells (Adam et al, 2000).…”

Induction of KLF4 in basal keratinocytes blocks the proliferation–differentiation switch and initiates squamous epithelial dysplasia

“…Interactions between KLF4 and cell fate determinants such as TGFb (Adam et al, 2000;King et al, 2003), Wnt (van de Wetering et al, 2002;Sancho et al, 2003), or others may account for its distinct role in different tissues, as cell type-specific effects are common for these important signaling molecules (Engel et al, 1998;Taipale and Beachy, 2001;Maillard and Pear, 2003). In developing colonic epithelium, KLF4 exerts its effects after cell migration; the proliferation-differentiation switch and several binary cell fate decisions are made in response to molecules such as Wnt, Notch, Hes, and Neurogenin (Sancho et al, 2003).…”

Proteasomal degradation of the KLF5 transcription factor through a ubiquitin‐independent pathway

“…KLF5 modulates multiple cellular processes, such as proliferation [6], differentiation [7,8], cell cycle [4], and apoptosis [9] through regulating expression of multiple important target genes including PDGFa [10], PPARc [8], NF-jB [11], and cyclinD1 [12,4].…”