c-Maf, the gammaD-crystallin Maf-responsive element and growth factor regulation

Abstract

The transcription factor c-Maf has been suggested to regulate the activity of gamma-crystallin promoters in lens fibre cells. We here show that the transactivation potential of c-Maf and MafB for the rat gammaD-crystallin Maf-responsive element (gammaD MARE) is dependent upon the cellular context and, using chimeric and single domain mutants, that c-Maf is most likely to be the cognate factor for the gammaD MARE in the lens. Transactivation of the gammaD MARE by c-Maf in lens cells was not enhanced by c-Fos or c-Jun and was not blocked by dominant negative c-Fos or c-Jun constructs. c-Maf can activate the gammaD MARE as a homodimer since activation of the gammaD-crystallin promoter in P19 embryonic carcinoma cells required only c-Maf, but none of a number of c-Fos and c-Jun family members tested. Transactivation by c-Maf was inhibited by activation of protein kinase A (PKA) (by signal transduction agonist forskolin) or of protein kinase C (PKC) (by signal transduction agonist tetradecanoyl phorbol acetate). Site-directed mutagenesis showed that this effect is not mediated by phosphorylation of the consensus PKA/PKC site in the extended DNA-binding domain, but likely involves activation of MAP kinase kinase, as inhibition by PD98059 increased transactivation by c-Maf.

CD13/APN transcription is regulated by the proto-oncogene c-Maf via an atypical response element

“…The mechanisms regulating activation of Maf family proteins have been investigated (Gardner and Montminy, 2005) and include a model invoking bFGF/MEK/ERK-induced phosphorylation that triggers proteosome-dependent degradation (Ochi et al, 2003) to explain L-Maf's decreased stability in neural retinal cells. In contrast, inhibition of the MAPK, MEK, increased c-Maf transactivation of the gammaD crystallin gene (Civil et al, 2002), while we observe that a similar MEK inhibition decreases c-Maf transactivation of the CD13 promoter in endothelial cells to a similar extent as mutation of Ser 15 (unpublished observations, Mahoney and Shapiro). Therefore, in endothelial cells the Ras/MAPK signal transduction pathway appears to activate c-Maf and CD13 transcription but inhibits L-Maf (and c-Maf) activity in primary neural retinal cells (Ochi et al, 2003).…”

“…Sequence alignment of the large Maf proteins showed that numerous putative phosphorylation sites in the amino terminal transactivation domain are highly conserved (Civil et al, 2002) a region we find critical for maximal activation of the CD13 promoter in endothelial cells. We chose to focus on two ERK phosphorylation sites which are strictly conserved in all of the large Maf proteins (serines 15 and 70 in the c-Maf sequence, Fig.…”

“…bZip transcription factor activity is controlled via phosphorylation of serine and/or threonine residues (Civil et al, 2002,Kawauchi et al, 1999. Sequence alignment of the large Maf proteins showed that numerous putative phosphorylation sites in the amino terminal transactivation domain are highly conserved (Civil et al, 2002) a region we find critical for maximal activation of the CD13 promoter in endothelial cells.…”

“…We chose to focus on two ERK phosphorylation sites which are strictly conserved in all of the large Maf proteins (serines 15 and 70 in the c-Maf sequence, Fig. 5A) and functionally regulate the related protein L-Maf, yet are uncharacterized in c-Maf (Civil et al, 2002,Kawauchi et al, 1999. We introduced mutations into the c-Maf expression plasmid to alter these serine residues (Ser 15 and Ser 70 , analogous to Ser 14 and Ser 65 in LMaf/MafA) to alanine residues, either individually or in combination and confirmed the expected expression profile by western blot analysis (Fig.…”

c‐Maf interacts with c‐Myb to down‐regulate Bcl‐2 expression and increase apoptosis in peripheral CD4 cells

“…These include the L7 gene in Purkinje cells [14] and the detoxifying enzyme gene quinone oxidoreductase l in hepatocytes [15], which are activated and repressed by c-Maf, respectively. In vitro, c-Maf transactivates the cyclin D2 promoter in myeloma cell lines [16] and the cD-crystallin promoter in lens epithelial cell explants [17]. A novel long form of c-Maf, Lc-Maf, regulates type II collagen via interactions with Sox9 [11].…”