The keratinocyte-specific POU transcription factor hSkn-1a is believed to trigger and regulate the differentiation of keratinocytes. To find genes regulated by hSkn-1a, we compared mRNAs in a HeLa clone (HeLa/hSkn-1a) that contains an inducible hSkn-1a gene between before and after the induction. RNA was screened for binding to DNA microarrays and candidate RNAs were further examined by two PCR methods. Quantitative RT-PCR showed that hSkn-1a up-regulated Cx43 and ARHH genes, besides the two genes of differentiation markers K10 and TG1, and down-regulated Mx2 and RALGDS genes in the HeLa cells. To know whether this finding is applicable to keratinocyte differentiation, we examined in human primary keratinocyte cultures the mRNAs for those six genes, along with the hSkn-1a gene, before and after the cells achieved confluence. Quantitative RT-PCR showed that in the differentiating confluent cells mRNAs increased for hSkn-1a, K10, TG1, Cx43, ARHH, and RALGDS, but decreased for Mx2. Thus, it appears that in keratinocyte differentiation Cx43, ARHH, and RALGDS genes were newly identified as up-regulated by hSkn-1a and Mx2 gene, as down-regulated. To study how hSkn-1a regulates those genes we cloned and sequenced putative transcriptional control regions for Cx43, ARHH, and Mx2 genes, in which several hSkn-1a-binding sequences were located. Expression of the luciferase gene from the isolated ARHH promoter was enhanced by the induction of hSkn-1a in HeLa/hSkn-1a and deletion or substitution mutation of the hSkn-1a-binding sequences reduced the expression, suggesting that hSkn-1a activates ARHH gene by binding to its promoter. (C) 2003 Elsevier Science (USA). All rights reserved.