121 The role of Runx family in the murine epidermis

Abstract

Keratinocytes contribute to the epidermal homeostasis mainly. Keratinocytes regularly undergo differentiation and proliferation so that the homeostasis is maintained normally. Many factor are involved in these regulation. However, the regulatory mechanism of keratinocytes is complicated and its full picture has not been found out. Runt-related transcription factor (RUNX) proteins belong to a family of metazoan transcription factors that serve as master regulators. The RUNX gene family has three members, Runx1(R1), Runx2 and Runx3(R3). RUNX functions have been unclear in keratinocytes in detail. In this study, we focused on the roles of RUNX in keratinocyte. First, we confirmed whether R1 and R3 (R1/3) are expressed in keratinocytes. We used primary culture of mouse keratinocytes. The transcripts of R1/3 were detected by RT-PCR. Keratinocytes expressed R1/3. Next, we overexpressed R1/3 in primary mouse keratinocytes. R1/3 overexpression decreased the amounts of keratin1 and keratin10 (K1/10). Conversely, R1/3 knockdown increased the amounts of K1/10. R1/3 inhibited the induction of K1/10, which were early differentiation markers. We analyzed the mechanism to modulate K1/10 by R1/3. We tried to immunostain R1/3. Immunohistological analysis showed that R1/3 were detected in the nuclear of immatured keratinocytes but moved out of the nuclear of differentiated keratinocytes. ChIP assay showed that R1/3 bound to Runx consensus sequences of K1/10 genome in undifferentiated state but not in differentiated state. R1/3 directly regulated the expressions of K1/10. We assessed the role of R1/3 to proliferation. R1/3 overexpression induced keratinocytes growth arrest. R1/3 knockdown did not advance proliferation. We generated transgenic mice lacking R1(or R3) in basal kerationocytes. In these mice, K1/10 were detected in basal keratinocytes, but the proliferation did not changed. Last we applied Imiquimod to these mice. However there was no difference between transgenic mice and wild type. Taken together, we propose that R1/3 regulate partially differentiation and proliferation of keratinocytes.