ENHANCEMENT OF EGF-MEDIATED AND PMA-MEDIATED MAP KINASE ACTIVATION INCELLS EXPRESSING THE HUMAN-PAPILLOMAVIRUS TYPE-16 E5 PROTEIN

In this report we demonstrate that cells expressing the human papillom avirus type 16 E5 open reading frame (HPV16-E5) show a greatly enhance d transcription of the immediate early genes after EGF or PMA treatmen t compared to control cells. This enhancement is due to amplification of the signal transduction pathways in response to growth factors or p horbol esters. Upon short-time EGF treatment of the E5-expressing cell s we observed an increase in the activation of EGF receptors, resultin g in a stronger activation of MAP kinases ERK1/2 compared to control-t ransfected cells. We also observed that in E5-expressing cells, treatm ent with PMA results in an increase in membrane-associated PKC activit y, and a superactivation of the ERK1/2 MAP kinases. This superactivati on is PKC-dependent, since pretreatment of the cells with the PKC inhi bitor Ro 31-8220 inhibits MAP kinase activation and early gene transcr iption almost completely. Furthermore, treatment with genistein strong ly reduces the PMA-mediated superactivation of ERK1/2 kinases, demonst rating a PKC-mediated, tyrosine kinase-dependent pathway in the superi nduction of MAP kinase activation. Thus, HPV16-E5 effects superactivat ion of MAP kinases over at least two different pathways, a PKC-mediate d, and another, receptor tyrosine-kinase mediated, PKC-independent one .