Cytopathic Effect in Human Papillomavirus Type 1-induced Inclusion Warts: In Vitro Analysis of the Contribution of Two Forms of the Viral E4 Protein

J Invest Dermatol. 1993 Dec;101(6):843-51. doi: 10.1111/1523-1747.ep12371705.


Myrmecia warts induced by human papillomavirus type 1 (HPV1) are characterized by abundant eosinophilic inclusions associated with HPV1 E4 gene products. The major HPV1 E4 proteins are a 17-kilodalton (kDa) E1-E4 fusion protein and a 16-kDa species lacking the five E1 amino acids and a few E4 residues. To study the contribution of E4 proteins to the formation of myrmecia inclusions, we used a previously designed transient 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) form eosinophilic inclusions. Ultrastructural and immunoelectron microscopic studies show that the electron-dense, keratohyalin-like myrmecia inclusions are recognized by anti-E4 antibodies. They are associated with tonofilament bundles at their periphery in the cytoplasm or free of filaments in the nucleus. The E1-E4 inclusions formed in vitro are also homogeneously electron dense, and are usually associated with tonofilaments at their periphery in the cytoplasm and free of filaments in the nucleus. The E4-3200 inclusions are exclusively cytoplasmic and heterogeneously electron dense, with a fibrillar structure made of entangled 10-nm filaments. The expression of either protein in VX2-R cells does not result in the collapse of the cytokeratin network, as shown by immunofluorescence double-labeling experiments. This is in contrast to data reported for the HPV16 E1-E4 protein. Our findings indicate that the E1-E4 protein by itself accounts for the formation of myrmecia inclusions, and suggest that the five N-terminal E1 amino acids play a major role in the interaction of E4 proteins with intermediate filaments.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenovirus E4 Proteins / analysis
  • Adenovirus E4 Proteins / physiology
  • Amino Acid Sequence
  • Animals
  • Cell Line
  • Cytopathogenic Effect, Viral
  • Cytoplasmic Granules / drug effects
  • Cytoplasmic Granules / ultrastructure
  • Fluorescent Antibody Technique
  • Humans
  • Inclusion Bodies / chemistry
  • Keratinocytes / cytology
  • Keratins / physiology
  • Microscopy, Immunoelectron / methods
  • Molecular Sequence Data
  • Papillomaviridae / physiology*
  • Papillomaviridae / ultrastructure
  • Rabbits
  • Tumor Cells, Cultured


  • Adenovirus E4 Proteins
  • Keratins