Activation of connective tissue growth factor gene by the c-Maf and Lc-Maf transcription factors

Abstract

The Maf family of transcription factors is expressed during development of various organs and tissues, and is involved in a variety of developmental and cellular differentiation processes. We previously found that c-maf and mafB are strongly expressed in hypertrophic chondrocytes during cartilage development. Connective tissue growth factor (CTGF) is also expressed in hypertrophic chondrocytes. Adenovirus mediated introduction of c-maf gene into the mouse fibroblast cell line C3H10T1/2 strongly induced CTGF expression. CTGF can be induced by TGF-β via the SMAD pathway; however, the c-Maf could not induce TGF-β, nor could TGF-β induce the c-Maf, suggesting that activation of CTGF by Maf is TGF-β independent. Reporter transfection analysis using C3H10T1/2 cells shows that c-Maf stimulates a CTGF reporter gene. Lc-Maf, a splice variant of c-Maf containing an extra 10 amino acids in the carboxyl terminus, was a stronger inducer of the CTGF reporter gene than c-Maf. Chromatin immunoprecipitation analysis showed that c-Maf binds to the promoter region of the CTGF gene, indicating that Maf directly activates the CTGF gene. Gel mobility shift assays indicated that c-Maf binds to the region near the transcription initiation site of CTGF gene. Taken together, these data indicate that the CTGF gene is a target of c-Maf and Lc-Maf in cartilage development

Alteration of Smad3 signaling in ischemic rabbit dermal ulcer wounds

“…To the best of our knowledge, the effect of an adenoviral Smad3 vector on CTGF protein levels in vivo has not yet been reported in the context of wound healing. Moreover, there is increasing evidence that CTGF is regulated to a significant extent by other intermediates, such as the transcriptional factors c‐Maf and Lc‐Maf independent of the canonical Smad‐dependent TGF‐β pathway 32 . We speculate that these Smad‐independent pathways might be enhanced under ischemic conditions affecting CTGF expression in vivo.…”

“…Moreover, there is increasing evidence that CTGF is regulated to a significant extent by other intermediates, such as the transcriptional factors c-Maf and Lc-Maf independent of the canonical Smad-dependent TGF-b pathway. 32 We speculate that these Smad-independent pathways might be enhanced under ischemic conditions affecting CTGF expression in vivo. The profibrotic role of CTGF is more relevant in scarring than in wound healing and CTGF levels tend to increase after POD 15.…”

The transcription factor Lc-Maf participates in Col27a1 regulation during chondrocyte maturation

“…Because the Lc-Maf protein is translated from a splice variant of c-Maf , both the c-Maf and Lc-Maf proteins were absent in these null mice [17]. Analysis of tibiae at various stages of embryonic and post-natal development showed that at E15.5, the number of hypertrophic chondrocytes was decreased.…”

“…Lc-Maf was shown to synergize with SOX9 to increase the expression of the cartilage-specific Col2a1 gene in 10T1/2 cells and MC615 chondrocytes by binding within a Col2a1 enhancer element to the short, 7-bp recognition element GGCTCTG [7]. Lc-Maf is a splice variant of c-Maf, it has a different 3′UTR region and the protein has an additional 10 amino acids at the carboxyl terminus [7, 17]. Using a probe from the 3′UTR of Lc-Maf, northern hybridizations revealed RNA expression in various mouse tissues, including cartilage [7, 17].…”

“…Lc-Maf is a splice variant of c-Maf, it has a different 3′UTR region and the protein has an additional 10 amino acids at the carboxyl terminus [7, 17]. Using a probe from the 3′UTR of Lc-Maf, northern hybridizations revealed RNA expression in various mouse tissues, including cartilage [7, 17]. It has been demonstrated that the presence of Lc-Maf and c-Maf in cartilage plays a vital role for correct skeletal development: mice lacking these proteins exhibited decreased fetal bone length and had improper hypertrophic chondrocyte differentiation [18].…”