Loss of Protein Kinase Cδ from Human HaCaT Keratinocytes upon Ras Transfection Is Mediated by TGFα

Abstract

The spontaneously immortalized human skin keratinocytes HaCaT contain protein kinase C (PKC)α, -δ, -ϵ, and -ζ. All PKC isoenzymes except PKCζ are down-regulated by TPA as well as by bryostatin. However, with PKCδ, bryostatin but not TPA was found to be much less effective at high concentrations than at low ones. PKCδ expression at the protein and mRNA level is significantly suppressed in HaCaT cells I-7 and II-4, which are transfected with mutated c-Ha-ras. The expression of the other isoenzymes remains essentially unchanged in the ras-transfected cells compared to normal ones. PKCδ is lost when growing HaCaT cells in a medium obtained from the cultivation of ras-transfected cells ("ras-conditioned" medium). The factor secreted into the medium by the ras-transfected cells that is responsible for this effect appears to be TGFα, since the action of ras-conditioned medium on PKCδ expression can be overcome by the addition of an anti-TGFα antibody. Moreover, treatment of HaCaT cells with TGFα suppresses selectively the expression of the PKC isoenzyme δ.