IL‐6 is a growth and survival factor for prostate cancer cells through autocrine pathways. Here, we have systematically examined the transcriptional regulation mechanisms of IL‐6 in autocrine prostate cancer cells.

RT‐PCR and immunohistochemical staining were used to determine IL‐6 production in the cells. Serial mutant IL‐6 promoter luciferase reporters were generated and their transcriptional activities were examined. The transcription factors involved in IL‐6 regulation were identified with super‐shift EMSA. Overexpression of NFκB p65 and C/EBP‐β, and blockade of NFκB with IκBα or CAPE were performed to demonstrate the cooperation between NFκB p65 and C/EBP‐β in activation of IL‐6.

Transcription factor regulatory sites IL6‐NFκB, IL6‐C/EBP, IL6‐CREB, and IL6‐AP1, are responsive to constitutively activated IL‐6 production in autocrine prostate cancer cell lines. Among these sites, IL6‐AP1 and IL6‐C/EBP appear most important, while IL6‐NFκB shows the least effect for IL‐6 promoter activity as determined by mutant IL‐6 promoter luciferase reporter assay. Nevertheless, nuclear factor NFκB is activated and required. Such activation is minimally dependent upon the IL6‐NFκB site, occurring through cooperation with other transcription factors that bind the IL‐6 promoter. Cooperation between NFκB p65 and C/EBP‐β did not require a functional IL6‐NFκB binding site.

These data support a unique role for NFκB p65 as the primary trigger in autocrine production of IL‐6 in prostate cancer cells. Furthermore, we describe a novel transcriptional activation mechanism for NFκB that is independent of its regulatory binding site, occurring through cooperation with other transcription factors that facilitate the neighboring regulatory site. © 2004 Wiley‐Liss, Inc.