CYTOPATHIC EFFECT IN HUMAN PAPILLOMAVIRUS TYPE-1 INDUCED INCLUSION WARTS - IN-VITRO ANALYSIS OF THE CONTRIBUTION OF 2 FORMS OF THE VIRAL E4PROTEIN

Myrmecia warts induced by human papillomavirus type 1 (HPV1) are chara cterized by abundant eosinophilic inclusions associated with HPV1 E4 g ene products. The major HPV1 E4 proteins are a 17-kilodalton (kDa) E1- E4 fusion protein and a 16-kDa species lacking the five El aminoacids and a few E4 residues. To study the contribution of E4 proteins to the formation of myrmecia inclusions, we used a previously designed trans ient expression system in the rabbit VX2-R keratinocyte line. We find that the E1-E4 and an E4 protein without the E1 residues (E4-3200) for m eosinophilic inclusions. Ultrastructural and immunoelectron microsco pic studies show that the electron-dense, keratohyalin-like myrmecia i nclusions are recognized by anti-E4 antibodies. They are associated wi th tonofilament bundles at their periphery in the cytoplasm or free of filaments in the nucleus. The E1-E4 inclusions formed in vitro are al so homogeneously electron dense, and are usually associated with tonof ilaments at their periphery in the cytoplasm and free of filaments in the nucleus. The E4-3200 inclusions are exclusively cytoplasmic and he terogeneously electron dense, with a fibrillar structure made of entan gled 10-nm filaments. The expression of either protein in VX2-R cells does not result in the collapse of the cytokeratin network, as shown b y immunofluorescence double-labeling experiments. This is in contrast to data reported for the HPV16 E1-E4 protein. Our findings indicate th at the E1-E4 protein by itself accounts for the formation of myrmecia inclusions, and suggest that the five N-terminal E1 aminoacids play a major role in the interaction of E4 proteins with intermediate filamen ts.