Interferon treatment enhances the expression of underphosphorylated (biologically-active) retinoblastoma protein in human papilloma virus-infected cells through the inhibitory TGF beta 1/IFN beta cytokine pathway.
Interferons (IFN) regulate transcription of certain genes playing a role in cell proliferation. Targets of IFN action may include tumor suppressor genes such as the retinoblastoma (RB) gene and cytokines such as transforming growth factor beta 1 (TGF beta 1) and IFN beta which are inhibitors of epithelial cell proliferation. Using reverse transcription followed by PCR amplification, an increase of those growth inhibitory gene mRNA levels (TGF beta 1, IFN beta and RB) were found after interferon treatment in condylomas harboring non-oncogenic human papilloma virus (HPV 6/11) types, in an oncogenic HPV 16-containing cell line, and in a HPV negative, epidermoid carcinoma cell line. In addition, immunodetection by Western blot demonstrated a higher proportion of underphosphorylated (active form) retinoblastoma gene protein (pRB) after IFN treatment due to the decrease in the phosphorylating cdc2 kinase levels. Changes in the phosphorylation pattern of pRB together with the increased expression of those inhibitory genes represent a growth inhibited state in those cells as demonstrated by diminished c-myc expression. Since the extent of c-myc inhibition was significantly lower in the case of oncogenic HPV infection, a role of viral oncoproteins in abrogation of the antiproliferative effect of IFN therapy could be considered. These results demonstrate a new mechanism via which IFNs exert their antiproliferative effect on HPV-infected cells by affecting the expression and phosphorylation of the RB tumor suppressor gene, through the inhibitory TGF beta 1/IFN beta cytokine pathway.
Arany
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Department of Microbiology, University of Texas Medical Branch, Galveston 77555.
Rady
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Tyring
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D015153:Blotting, Western; D042846:CDC2-CDC28 Kinases; D003218:Condylomata Acuminata / Q000382:microbiology / Q000628:therapy*; D006801:Humans; D016898:Interferon-alpha / Q000627:therapeutic use; D016899:Interferon-beta / Q000096:biosynthesis* / Q000235:genetics; D007371:Interferon-gamma / Q000627:therapeutic use; D007372:Interferons / Q000494:pharmacology* / Q000627:therapeutic use; D009856:Oncogene Proteins, Viral / Q000096:biosynthesis / Q000235:genetics; D027383:Papillomaviridae / Q000187:drug effects*; D050725:Papillomavirus E7 Proteins; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D017346:Protein Serine-Threonine Kinases / Q000032:analysis; D016271:Proto-Oncogene Proteins c-myc / Q000096:biosynthesis; D012367:RNA, Viral / Q000032:analysis; D016160:Retinoblastoma Protein / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000096:biosynthesis* / Q000235:genetics; D014407:Tumor Cells, Cultured
D016898:Interferon-alpha; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; D016271:Proto-Oncogene Proteins c-myc; D012367:RNA, Viral; D016160:Retinoblastoma Protein; D016212:Transforming Growth Factor beta; C059731:oncogene protein E7, Human papillomavirus type 16; D016899:Interferon-beta; D007371:Interferon-gamma; D007372:Interferons; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases