Involvement of protein kinase C in the transcriptional regulation of 12-O-tetradecanoylphorbol-13-acetate-inducible genes modulated by AP-1 or non-AP-1 transacting factors.

Abstract

The involvement of protein kinase C (PKC), a 12-O-tetradecanoylphorbol-13-acetate (TPA) receptor, in the transcriptional regulation of TPA-inducible genes was determined. Expression plasmids harboring full-length or kinase domain of PKC alpha and PKC delta (PKC alpha K and PKC delta K) were constructed. Transient transfection of PKC alpha K and PKC delta K into COS cells resulted in approximately 20- and 16-fold increase in phospholipid-, calcium-independent protein kinase activity. To determine the effects of overexpression of PKC alpha K and PKC delta K on the AP-1-mediated TPA-inducible genes, we transfected into COS cells the PKC alpha K or PKC delta K expression plasmids with collagenase chloramphenicol acetyltransferase (CAT) reporter construct containing one TPA responsive element (TRE), or a construct containing five synthetic TRE linked to a thymidine kinase promoter. PKC alpha K or PKC delta K overexpression resulted in a comparable increase (approximately 4-fold) in CAT activity. However, CAT activity was not increased after transfection of PKC constructs with non-TPA responsive thyroid hormone responsive elements CAT construct (delta MTV-TyRE-pCAT). We also found that deletion of the AP-1-like motif in the SV40 promoter abolished the PKC alpha K or PKC delta K-induced activity of luciferase (luc) reporter constructs. Overexpression of full-length PKC delta in COS cells also increased the activity of the CAT construct with TRE after TPA treatment. We determined the effects of overexpression of PKC alpha K and PKC delta K on transcription of the ornithine decarboxylase (ODC) gene, which has a non-AP-1 TRE. Cotransfection of PKC alpha K or PKC delta K expression plasmids with a TPA-inducible ODC luc construct (-72/+130-ODC-luc) into HeLa cells resulted in an increased luc activity. These results indicate that both PKC alpha (calcium dependent) and PKC delta (calcium independent) may mediate the transcription of TPA-inducible genes through both AP-1 and non-AP-1 sequences.