HOXA5 inhibits keratinocytes growth and epidermal formation in organotypic cultures in vitro and in vivo

Abstract

Homeobox transcription factors play important roles in epidermal renewal. Among them HOXA5 emerges as a promising member. However, its direct effect on epidermal biology, either to promote or to inhibit growth, is still controversial. We proposed to unravel the role of HOXA5 in modulating keratinocytes growth and epidermal formation in organotypic cultures both in vitro and in vivo. We transfected HaCaT cells with lentivirual vectors which over-expressed either wild-type or mutant HOXA5 cDNAs with deleted homeodomain. Subsequently we propagated the cells in organotypic cultures (OTCs) and then transplanted them into nude mice. Cell proliferation and cell cycle progression were detected. Epidermal morphogenesis and stratification were investigated by immunohistochemistry and immunofluorescence staining of a series of epidermal markers. HaCaT cells transfected with HOXA5 cDNAs displayed lower growth rate and delayed G1-S transition. HOXA5-transfected OTC exhibited an aberrantly organized epithelium with significantly increased TUNEL staining as well as decreased PCNA and K5 staining, while expression of differentiation markers as K10, involucrin and filaggrin were somewhat enhanced. However, under in vivo environment in nude mice which had great paracrine regulatory mechanisms, the aberrant phenotype was ameliorated as shown by a more regular tissue organization and normal expression of PCNA and K5. Inversely, cells transfected with the homeodomain-deleted protein exhibited accelerated growth and produced a more proliferative and better-orchestrated epidermis, as shown by well-expressed proliferation and differentiation markers. HOXA5 can suppress keratinocytes growth and epidermal formation. It probably activated antagonist genes against growth factors release, which depends on its homeodomain.