Connective tissue growth factor (CTGF/CNN2) is a novel APF target gene. A novel mechanism is described by which the APF cellular receptor, cytoskeleton-associated protein 4 (CKAP4), mediates APF-induced CTGF transcription.

Antiproliferative factor (APF) is a sialoglycopeptide elevated in the urine of patients with interstitial cystitis—a chronic, painful bladder disease. APF inhibits the proliferation of normal bladder epithelial and T24 bladder carcinoma cells in vitro by binding to cytoskeleton associated protein 4 (CKAP4) and altering the transcription of genes involved in proliferation, adhesion, and tumorigenesis; however, specific molecular mechanisms and effector genes that control APF's antiproliferative effects are unknown. In this study, we found that there was a 7.5‐fold upregulation of connective tissue growth factor (CTGF/CCN2) expression in T24 bladder carcinoma cells treated with APF, and Western blot revealed a dose‐dependent increase in CCN2 protein levels with secretion into the culture medium following APF treatment. CCN2 overexpression enhanced APF's antiproliferative activity while CCN2 knockdown by siRNA diminished it. Using a luciferase reporter construct, we found that APF treatment resulted in a 5‐fold activation of the CCN2 proximal promoter and that siRNA‐mediated knockdown of CKAP4 inhibited CCN2 upregulation. Additionally, we show that CKAP4 translocates to the nucleus and binds to the CCN2 proximal promoter in an APF‐dependent manner, providing evidence that CCN2 regulation by APF involves CKAP4 nuclear translocation and binding to the CCN2 promoter. NIH 1R03AR057193‐01; KIZ grant