Secreted caveolin-1 stimulates cell survival/clonal growth and contributes to metastasis in androgen-insensitive prostate cancer

Caveolin-1 is an integral protein of caveolae, known to play important roles in signal transduction and lipid transport. We demonstrate that caveolin-1 expression is significantly increased in primary and metastatic human prostate cancer after androgen ablation therapy. We also show that caveolin-1 is secreted by androgen-insensitive prostate cancer cells, and that this secretion is regulated by steroid hormones. Significantly, caveolin-1 was detected in the MDL₃ fraction of serum specimens from patients with advanced prostate cancer and to a lesser extent in normal subjects. Conditioned media from high passage caveolin-1 secreting, androgen-insensitive, LNCaP cells stimulated increased viability and clonal growth of low passage, caveolin-1-negative, androgen-sensitive, LNCaP cells in vitro, and this effect was blocked by treating the media with caveolin-1 antibody. i.p. injections of caveolin-1 antibody suppressed the orthotopic growth and spontaneous metastasis of highly metastatic, androgen-insensitive caveolin-1-secreting mouse prostate cancer. Overall, our results establish caveolin-1 as an autocrine/paracrine factor that is associated with androgen-insensitive prostate cancer. We demonstrate the potential for caveolin-1 as a therapeutic target for this important malignancy.