Impaired alpha-interferon signaling in transitional cell carcinoma: Lack of p48 expression in 5637 cells

The limited success of IFN-alpha therapy for clinical treatment of transiti onal cell carcinoma (TCC) has prompted us to investigate the responsiveness of TCC lines to IFN-alpha. The response to IFN-alpha in terms of 561 gene induction. an IFN-stimulated response element-containing IFN-alpha/beta -in ducible gene, and IFN-stimulated gene Factor 3 (ISGF3) formation was normal in primary human urothelial tells. We tested the antiproliferative effects of IFN-alpha in three TCC lines as a measure of IFN-alpha responsiveness, and variable patterns of growth inhibition were observed in three TCC lines . More than 90% growth inhibition was noted in TCCSUP cells. whereas only 4 0% and 10% inhibition by IFN-alpha was observed in 5637 and HT1197 tells, r espectively. IFN-alpha treatment formed extremely low levels of ISGF3 in el ectrophoretic mobility shift assays in these later two relatively insensiti ve cells. In addition, expression of the 561 gene was significantly reduced in these two TCC lines by Northern blots. We have further identified a low expression level or Tyk2 in HT1197 cells compared with two other TCCs. Thi s suggests that an extremely low ISGF3 level after IFN-ol treatment mar be due to low Tyk2 expression or other unidentified defects. In 5637 cells, p4 8 protein expression was undetectable. This undetectable p48 expression is not due to a deletion in the coding region because the correct size protein is detected following IFN-gamma treatment. Consequently, the ISGF3 complex formation and 561 gene induction were restored by IFN-gamma pretreatment p lus IFN-a treatment. Introduction of p48 expressing plasmid into 5637 cells was sufficient to Form the ISGF3 complex by IFN-cu treatment, suggesting t he defect lies in the expression of p48 protein in 5637 cells. Detailed mec hanistic understanding of the action of IFNs in bladder cancer cell lines m ay explain the abrogated therapeutic response of IFN-alpha in the clinical treatment of TCCs.