Hoxb13 Up-regulates Transglutaminase Activity and Drives Terminal Differentiation in an Epidermal Organotypic Model

Judith A Mack,Ling Li,Nobuyuki Sato,Vincent C Hascall,Edward V Maytin

doi:10.1074/jbc.m505262200

Judith A Mack, Ling Li + Show 3 more

Open Access

https://doi.org/10.1074/jbc.m505262200

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Abstract

Hox genes act to differentiate and pattern embryonic structures by promoting the proliferation of specific cell types. An exception is Hoxb13, which functions as a proapoptotic and antiproliferative protein during development of the caudal spinal cord and tail vertebrae and has also been implicated in adult cutaneous wound repair. The adult epidermis, which expresses several Hox genes including Hoxb13, is continually renewed in a program of growth arrest, differentiation, and a specialized form of apoptosis (cornification). Yet little is known about the function(s) of these genes in skin. Based on its role during embryogenesis, Hoxb13 is an attractive candidate to be involved in the regulation of epidermal differentiation. Here, we demonstrate that Hoxb13 overexpression in an adult organotypic epidermal model recapitulates actions of Hoxb13 reported in embryonic development. Epidermal cell proliferation is decreased, apoptosis increased, and excessive terminal differentiation observed, as characterized by enhanced transglutaminase activity and excessive cornified envelope formation. Overexpression of Hoxb13 also produces abnormal phenotypes in the epidermal tissue that resemble certain pathological features of dysplastic skin diseases. Our results suggest that Hoxb13 functions to promote epidermal differentiation, a critical process for skin regeneration and for the maintenance of normal barrier function.

Highlights

During development, the skin begins as a single layer of multipotent ectodermal cells capable of producing either hair follicles or epidermis
Wound healing studies conducted on human fetal and adult skin explants transplanted onto SCID mice revealed that Hoxb13 expression is significantly down-regulated in fetal skin that heals without a scar, but its expression does not change in adult wounds [23]
Hoxb13 Is Differentially Expressed in rat epidermal keratinocytes (REKs) Lift Cultures—To begin our study of Hoxb13 in epidermal differentiation, we examined the expression pattern of Hoxb13 in REK lift cultures over time (Fig. 1A)

Summary

Introduction

The skin begins as a single layer of multipotent ectodermal cells capable of producing either hair follicles or epidermis. In contrast to the vector-only controls, overexpression of Hoxb13 in lift culture, as shown with clones 13 and 36, profoundly affected the overall epidermal phenotype (see Fig. 2, B, BЈ and C, CЈ). We utilized immunohistochemistry, RT-PCR, and Western blot analyses to examine the effects of Hoxb13 overexpression upon epidermal marker expression in REK 5-day lift cultures.

Results

Conclusion