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 ro le in cell proliferation. Targets of IFN action may include tumor supp ressor genes such as the retinoblastoma (RB) gene and cytokines such a s transforming growth factor beta 1 (TGF beta 1) and IFN beta which ar e inhibitors of epithelial cell proliferation. Using reverse transcrip tion followed by PCR amplification, an increase of those growth inhibi tory gene mRNA levels (TGF beta 1, IFN beta and RB) were found after i nterferon treatment in condylomas harboring non-oncogenic human papill oma virus (HPV 6/11) types, in an oncogenic HPV 16-containing cell lin e and in a HPV negative, epidermoid carcinoma cell line. In addition, immunodetection by Western blot demonstrated a higher proportion of un derphosphorylated (active form) retinoblastoma gene protein (pRB) afte r IFN treatment due to the decrease in the phosphorylating cdc2 kinase levels. Changes in the phosphorylation pattern of pRB together with t he increased expression of those inhibitory genes represent a growth i nhibited state in those cells as demonstrated by diminished c-myc expr ession. Since the extent of c-myc inhibition was significantly lower i n the case of oncogenic HPV infection, a role of viral oncoproteins in abrogation of the antiproliferative effect of IFN therapy could be co nsidered. These results demonstrate a new mechanism via which IFNs exe rt their antiproliferative effect on HPV-infected cells by affecting t he expression and phosphorylation of the RB tumor suppressor gene, thr ough the inhibitory TGF beta 1/IFN beta cytokine pathway.