AUTOCRINE IL-6 PRODUCTION BY HUMAN TRANSITIONAL CARCINOMA CELLS UPREGULATES EXPRESSION OF THE α5β1 FIBRONECTIN RECEPTOR

Abstract

Purpose: Studies have demonstrated elevated expression and secretion of IL-6 by transitional cell carcinomas (TCC) following bacillus Calmette-Guerin (BCG) therapy. At present, the role of IL-6 on the biology of TCC is poorly understood. This study evaluated the influence of IL-6 expression on a critical variable regulating BCG-tumor interaction, the tumor expression of α5β1 integrin. Materials and Methods: A human TCC cell line (253J) was transfected with an expression vector containing the full-length IL-6 cDNA sequence. Overexpression of IL-6 mRNA and protein was confirmed by Northern analysis and ELISA, respectively. Clones found to overexpress IL-6 were then assayed for α5β1 expression using Northern analysis and flow cytometry. The effect of alterations in α5β1 expression on tumor adherence to fibronectin (FN), and BCG adherence to tumor cells was determined using specific adherence assays. Results: mRNAs for both the α5 and β1 subunits of the FN receptor were increased an average of 9.4 fold and 125.7 fold respectively in the IL-6 overexpressing transfectants relative to the parental 253J cells. Increased mRNA of α5 and β1 was associated with increased cell surface expression of both proteins. Increased protein expression resulted in greater FN substrate binding affinity and increased adherence of BCG to tumor cells. Conclusions: Autocrine expression of IL-6 upregulates the expression of FN receptor subunits in TCC. Increased α5β1 expression increases cellular adherence to FN, and BCG adherence to tumor cells. These results suggest a role for IL-6 in mediating the antitumor activity of BCG by influencing BCG's adherence to TCC.