Interleukin-6 induces G1 arrest through induction of p27(Kip1), a cyclin-dependent kinase inhibitor, and neuron-like morphology in LNCaP prostate tumor cells

Prostate carcinoma cells express high levels of interleukin-6 (IL-6) and IL-6 receptor. In this study, we examined the effect of IL-6 on LNCaP human prostate carcinoma cells. IL-6 induces G1 growth arrest of LNCaP. Following IL-6 treatment of LNCaP, Western blot analysis showed that the protein levels of cyclin-dependent kinase-2 (CDK2), CDK4, and CDK6 were decreased, while accumulation of CDK inhibitor p27(Kip1) was rapidly and markedly induced. In vitro kinase assays revealed that the CDK-associated histone H1 and CDK4- and CDK6-associated pRb kinase activities were significantly inhibited in IL-6-treated LNCaP. Further, a significant amount of p27(Kip1) was co-precipitated with CDK2, CDK4 and CDK6, as detected in immunoprecipitation experiments. Thus, IL-6-induced G1 arrest appears to be due to the accumulation of p27(Kip1). In addition, IL-6-treated LNCaP cells induced neuron-like morphological changes. Since neuroendocrine differentiation is observed in most prostate carcinomas, these findings raise the possibility that IL-6 may be involved in neuroendocrine differentiation in vivo.