MAF

Official Full Name

MAF bZIP transcription factor

Organism

Homo sapiens

GeneID

4094

Background

The protein encoded by this gene is a DNA-binding, leucine zipper-containing transcription factor that acts as a homodimer or as a heterodimer. Depending on the binding site and binding partner, the encoded protein can be a transcriptional activator or repressor. This protein plays a role in the regulation of several cellular processes, including embryonic lens fiber cell development, increased T-cell susceptibility to apoptosis, and chondrocyte terminal differentiation. Defects in this gene are a cause of juvenile-onset pulverulent cataract as well as congenital cerulean cataract 4 (CCA4). Two transcript variants encoding different isoforms have been found for this gene. [provided by RefSeq, Jan 2010]

Synonyms

CCA4; AYGRP; c-MAF; CTRCT21;

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Detailed Information

The Maf family protein is derived from the original member of the family, v-Maf, a protein encoded by the avian musculoaponeurotic fibrosarcoma virus (AS42) oncogene v-maf. Maf can bind to other family transcription factors containing b-Zip motifs in the nucleus to form homologous or heterodimers, and then bind to the specific sequence Mafre recognition elements (MARE) on DNA to regulate the corresponding Gene transcription. Later, many structurally similar Maf family proteins were found, including large Maf family proteins (greater than 200 amino acid residues) c-Maf, MafB, MafA/L-Maf/SMaf, Nrl and small Maf family proteins (less than 200 amino acid residues) MafK, MafF, MafG, and MafT. Maf family proteins play a key role in the proliferation, metastasis and differentiation of embryonic maternal erythrocytes, the development of eye lens, the polarization of Th2 cells, insulin production, and apoptosis.

Maf Structure

At present, several Maf family genes have been cloned in different species, including humans, mice, clawed frogs, chickens and zebrafish. The Maf family encodes a protein with a highly conserved basic region, a bZIP domain at the carboxy terminus that binds the Maf protein to its target DNAs, typically through a T-MARE or C-MARE recognition site. The bZIP that binds to the Maf protein can also form a dimer with itself or other proteins containing the bZIP domain.

Figure 1. A LncRNA-MAF:MAFB Transcription Factor Network Regulates Epidermal Differentiation. （Lopez-Pajares, et al. 2015）

The function of the Maf

MafB is selectively expressed in monocytes and macrophages. For example, during macrophage differentiation, MafB is not expressed in pluripotent progenitor cells, expressed at appropriate levels in myeloid bud cells, and expressed at high levels in mature monocytes and macrophages. Further studies have shown that MafB can bind to the promoter of macrophage growth factor f4/80, which also has a MARE semi-similar sequence on the promoter to promote its expression. If MafB is absent, the expression of f4/80 will also be inhibited. Other studies have shown that when alveolar macrophages are subjected to oxidative stress by free radicals, oxidants and lipid peroxides, their function changes and their survival is prolonged. In the study of numerous transcription factors inside alveolar macrophages, only MafB expression was up-regulated and it was responsible for inhibiting apoptosis of macrophages.

MafB also plays an important role in the differentiation and development of islet α cells and β cells. Embryonic MafB is expressed in both α cells and β cells. If MafB is mutated during embryonic stage, the number of insulin cells and glucagon cells is reduced. MafB expression was reduced in beta cells after birth, and MafB was not detected after 3 weeks. After maturity, MafB is expressed only in the alpha cells of islets, selectively binding to the G1 control region of the glucagon gene, regulating the activation of the glucagon gene.

ELMO1（engulfment and cell motility 1） and tumor invasive growth

Other small Maf family proteins were found in the defense response of the studied cells. When cells are stimulated by certain chemicals, oxidants, and antioxidants, Keap1 (Kelch-like ECH-associated protein 1) first senses these substances and resolves with Nrf2. Dissociated Nrf2 accumulates in the nucleus and forms a heterodimer with the small Maf proteins MafG and MafK in the nucleus, and then binds to the antioxidant response element ARE, ultimately regulating the ARE-dependent phase II detoxification enzyme gene and antioxidant The transcription of the genes NQO1, GSTYa, g-GCS, HO-1 and ferritin-L has extensive cytoprotective functions in anti-tumor, neuroprotective, and anti-inflammatory responses. Overexpression of MafG and MafK can inhibit the transcription of genes such as NQO1, GSTYa, and g-GCS.

References:

Lopez-Pajares, V. , Qu, K. , Zhang, J. , Webster, D. , Barajas, B. , & Siprashvili, Z. , et al. (2015). A lncrna-maf:mafb transcription factor network regulates epidermal differentiation. Developmental Cell, 32(6), 693-706.
Y Katsuoka, F. , & Yamamoto, M. . (2016). Small maf proteins (maff, mafg, mafk): history, structure and function. Gene, S0378111916302487.
Zhang, C. , & Guo, Z. M. . (2015). Multiple functions of maf in the regulation of cellular development and differentiation. Diabetes/Metabolism Research and Reviews, 31(8), 773-778.

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