Interleukin 1β mediates the modulatory effects of monocytes on LNCaP human prostate cancer cells

Proliferative and secretory responses in androgen-sensitive prostate cancer LNCaP cells are regulated by steroid and peptide hormones and by differentiation-promoting substances. In the present study, we evaluated whether peripheral blood monocytes that exhibit anti-tumour activity in haematopoietic and solid tumours influence growth and secretion in the LNCaP cell line. For this purpose, LNCaP cells were incubated with monocyte-conditioned medium (MCM), and proliferation as well as expression of androgen receptor (AR) and secretion of prostate-specific antigen (PSA) were assessed. Conditioned medium from monocytes reduced proliferation in a dose-dependent manner. Incubation with 40% MCM caused a 50% reduction in cell proliferation. AR protein decreased by 70% and PSA levels in supernatants from LNCaP cells were reduced by approximately 80% following treatment with MCM. We focused on the contribution of two major products of activated monocytes, prostaglandin E(2) and interleukin 1 beta (IL-1 beta), to the MCM modulatory action. LNCaP cells treated with prostaglandin E(2) showed neither a reduction in proliferation nor a down-regulation of AR and PSA levels. The effects of MCM on cellular proliferation, AR protein and PSA secretion were abolished by pretreatment of MCM with a neutralizing anti-IL-1 beta antibody, In addition, recombinant IL-1 beta was able to replace MCM for the inhibition of proliferation and down-regulation of AR and PSA proteins. LNCaP cells were shown to express the IL-1 beta receptor type I, which transduces IL-1 beta signal. Our findings reveal that monocyte-derived IL-1 beta inhibits the proliferation of androgen-responsive prostate tumour cells and reduces AR and PSA levels.