THE PROMOTER OF THE HACAT KERATINOCYTE DIFFERENTIATION-RELATED GENE KERATIN-4 CONTAINS A FUNCTIONAL AP-2 BINDING-SITE

The nuclear transcription factor AP-2 appears to be a key regulator me diating programmed gene expression during embryonic morphogenesis and adult cell differentiation. AP-2 has also been considered to be involv ed in epidermal gene regulation, but its precise role is not yet defin ed, The level of AP-2 transcripts increases during culturing of HaCaT keratinocytes preceding the expression of the differentiation-related gene keratin 4 (K4), The current study was aimed at investigating whet her AP-2 transactivates K4 transcription, We cloned and sequenced the promoter region of K4 and found, in addition to canonical sequences, a n AP-2 consensus site in the vicinity of the transcriptional start, In order to provide functional evidence for a regulation of K4 transcrip tion by AP-2, we cloned various parts, which did or did not contain th e AP-2 site of the K4 upstream sequence, into Cat reporter plasmids, T hese constructs were ballistically transfected into differentiating Ha CaT keratinocytes, The determination of the resulting Cat activity rev ealed that the AP-2 site in the vicinity of the transcriptional start was functional for K4 transcription, Thus, the role of AP-2 in the pro cess of keratinocyte differentiation appears to be considerable, In ad dition, further regulatory elements were found to be necessary for ful l transcription of K4.