CYTOPLASMIC DESMOSOME FORMATION BY H-7 AND EGF TREATMENT IN CULTURED FETAL-RAT KERATINOCYTES

Cytoplasmic desmosomes (CD) are classically found in dyskeratotic cell s of many epithelial tumors. Their significance and mechanism of forma tion remain largely speculative. Recently, we have reported the induct ion of these structures in rat keratinocytes following a brief treatme nt with acrylamide, and proposed that protein kinase inhibition may be implicated in their formation. In the present study, we show that pro tein kinase inhibitor H-7 in the presence of EGF is able to induce CD in rat keratinocytes within half an hour. in-serum free medium contain ing 20 ng/ml of EGF, desmosomal structures at different stages of asse mbly were obtained using H-7 at concentrations ranging between 20 and 80 mu M No such structures were found at lower concentrations. The pla que diameters were significantly small in comparison with plasma membr ane plaques. EGF induced plakoglobin positive membrane invaginations a nd in the presence of H-7, desmosomal plaques assembled on these membr anes as either half desmosomes or as symmetric ones. The present resul ts implicate protein kinase inhibition in CD formation and suggest tha t EGF provides tubular membrane structures in the cytoplasm on which d esmosomes may assemble.