RESUMEN
Dysregulated expression of Maf proteins (namely c-Maf, MafA and MafB) leads to multiple myeloma in humans and oncogenic transformation of chicken embryonic fibroblasts. Maf proteins are transcriptional activators of tissue-specific gene expression and regulators of cell differentiation. For example, MafA is a critical regulator of crystallin genes and the lens differentiation program in chickens. In mammals, MafA is essential for the development of mature insulin-producing beta-cells of pancreas. It has been shown that MafA protein stability is regulated by phosphorylations at multiple serine and threonine residues. Here, we report that Maf proteins are also post-translationally modified by small ubiquitin-like modifier (SUMO) proteins at a conserved lysine residue in the amino-terminal transactivator domain. A SUMOylation-deficient mutant of MafA (K32R) was more potent than wild-type MafA in transactivating luciferase reporter construct driven by alphaA-crystallin or insulin gene promoter. In ovo electroporation into developing chicken embryo showed that the K32R mutant induced ectopic delta-crystallin gene expression more efficiently than the wild-type MafA. We also demonstrated that the K32R mutant had enhanced ability to induce colony formation of a chicken fibroblast cell line DF-1. Therefore, SUMOylation is a functional post-translational modification of MafA that negatively regulates its transcriptional and transforming activities.
Asunto(s)
Transformación Celular Neoplásica/genética , Factores de Transcripción Maf de Gran Tamaño/genética , Sumoilación , Transcripción Genética/genética , Animales , Línea Celular , Línea Celular Tumoral , Embrión de Pollo , Fibroblastos/citología , Fibroblastos/metabolismo , Regulación del Desarrollo de la Expresión Génica , Células HeLa , Humanos , Lisina/genética , Lisina/metabolismo , Factores de Transcripción Maf de Gran Tamaño/metabolismo , Factor de Transcripción MafB/genética , Factor de Transcripción MafB/metabolismo , Ratones , Mutación , Células 3T3 NIH , Proteínas Modificadoras Pequeñas Relacionadas con Ubiquitina/genética , Proteínas Modificadoras Pequeñas Relacionadas con Ubiquitina/metabolismo , Transfección , delta-Cristalinas/genéticaRESUMEN
BACKGROUND: The hair follicle of mammalian skin consists of a group of concentric epithelial cell layers. The inner root sheath (IRS), which surrounds the hardening hair shaft beneath the skin surface, is subdivided into three layers, termed the cuticle of the IRS, Huxley's layer, and Henle's layer. The IRS forms a follicular wall in the hair canal and helps guide the developing hair shaft. c-Maf and MafB, members of the Maf family of transcription factors, play important roles in the developmental processes of various tissues and in cell type-specific gene expression. OBJECTIVE: The aim of this study is to reveal the pattern of expression and functional roles of c-Maf and MafB in the hair follicle. METHODS: We determined the precise location of c-Maf and MafB expression using immunofluorescent staining of mouse skin sections with layer-specific markers. We also analyzed whiskers of c-maf- and mafB-null mice (c-maf(-/-) and mafB(-/-), respectively) using scanning electron microscopy. RESULTS: c-Maf and MafB were differentially expressed in the Huxley's and Henle's layers of the IRS. Scanning electron microscopic analysis showed irregular cuticle patterning of whiskers of c-maf(-/-) and mafB(-/-) mice. The cuticles of mafB(-/-) mice were also thinner than those of wild-type mice. CONCLUSION: c-Maf and MafB are expressed in the IRS layers in a lineage-restricted manner and are involved in hair morphogenesis.
