Modulation of the epidermal growth factor receptor by the human papillomavirus type 16 E5 protein in raft cultures of human keratinocytes

It has been shown that the E5 protein of the human papillomavirus type 16 m odulates epidermal growth factor receptor downregulation in monolayer cultu res of human keratinocytes and mouse fibroblasts, We have now analysed the effect of this protein on the expression, the distribution and the activati on of EGF receptors in raft cultures derived from an E5-transfected human k eratinocyte cell line, The epithelia generated in these cultures were strat ified and exhibited suprabasal expression of cytokeratins 1 and 10, which a re known markers of early epidermal differentiation. In situ hybridization with an antisense riboprobe to the human papilloma virus type 16 E5 protein revealed a homogeneous gene expression within the entire epithelium of ES- transfected but not empty vector-transfected control cultures, Treatment of serum-starved rafts with EGF for 48 hours led to a strong decrease of supr abasal EGF receptors in control cultures, but not in rafts of ES-expressing cells, Under these conditions, no activated receptors were observed in con trol cultures, but activated receptors were still present in ES-raft cultur es, Our results indicate that human papilloma virus type 16 E5-mediated mod ulation of EGF receptor expression occurs in a time- and structure-dependen t manner in epithelial equivalents of human keratinocytes.