title: BAG-1L promotes keratinocyte differentiation in organotypic culture models and changes in relative BAG-1 isoform abundance may lead to defective stratification.
abstract: In keratinocytes the human Bag-1 gene produces three different protein isoforms from a single messenger RNA, BAG-1L, BAG-1M and BAG-1S. In this study we questioned whether BAG-1L or the shorter isoforms would promote keratinocyte differentiation in organotypic cultures of HaCaT. HaCaT parental and vector cells showed stratification, but terminal differentiation was not complete. Cultures overexpressing BAG-1L isoform-specifically were of increased thickness, demonstrated pronounced expression of basal cytokeratin 5 and β1-integrin, suprabasal involucrin, cytokeratin 1 and plasma membrane-localised filaggrin, and a marked keratinized layer of cells at the surface. We were unable to overexpress BAG-1S and BAG-1M isoform-specifically. Overexpression of BAG-1M gave rise to organotypic cultures intermediate in differentiation to controls and those overexpressing BAG-1L. Cells overexpressing BAG-1S also exhibited elevated endogenous BAG-1. These produced slow growing cultures with high levels of basal cytokeratin 5, but little involucrin or cytokeratin 1. Suprabasal β1-integrin and Ki67 positive cells indicated defective stratification. The results suggest that BAG-1L potentiates epidermal differentiation, but disruption in the relative balance of isoforms towards overexpression of BAG-1S can lead to defective tissue patterning. Hence, a delicate balance of BAG-1 isoforms may be required to regulate normal epidermal stratification and differentiation, with important implications for aberrant differentiation in cancer.
authors: University of Bristol, School of Oral and Dental Sciences, Lower Maudlin Street, Bristol, UK.
authors: C A M
authors: CA
authors: Hinitt
authors: T M
authors: TM
authors: Benn
authors: S
authors: S
authors: Threadgold
authors: J
authors: J
authors: Wood
authors: A C
authors: AC
authors: Williams
authors: A
authors: A
authors: Hague
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism*; D000091344:Filaggrin Proteins; D006801:Humans; D039641:Integrin beta Chains / Q000378:metabolism; D015603:Keratinocytes / Q000166:cytology* / Q000378:metabolism; D009924:Organ Culture Techniques; D020033:Protein Isoforms / Q000378:metabolism; D051381:Rats; D014157:Transcription Factors / Q000378:metabolism*; D014162:Transfection
chemical_list: C091732:BCL2-associated athanogene 1 protein; D004268:DNA-Binding Proteins; C000717249:FLG protein, human; D000091344:Filaggrin Proteins; D039641:Integrin beta Chains; D020033:Protein Isoforms; D014157:Transcription Factors