AbstractBone metastasis is the primary cause of death in human prostate cancer. Disseminated from primary tumor and distributed via the bloodstream, a proportion of prostate carcinoma cells eventually reach the skeleton and develop into metastases, requiring adhesion to inner bone surfaces lined by osteoblasts. The crosstalk of tumor cells with osteoblasts is a critical but poorly characterized step in the metastatic process. Using an in vitro metastasis model system, we have been examining effects of osteoblast‐released factors on gene expression of prostate carcinoma cells. Here, we show by large‐scale transcript profiling and quantitative RT‐PCR that osteoblast‐released factors target in particular the proliferation and adhesion regulons of tumor cells. Genes encoding components of the cell‐cycle control machinery and connected pathways are predominantly repressed and cell proliferation is slowed down, resembling in vivo observations assumed to render commonly used chemotherapeutic measures ineffective. Genes encoding anchoring junction components are predominantly elevated, and the adhesion properties of tumor cells are altered. Moreover, prostate carcinoma cells are provoked to undergo osteomimicry, i.e., to express bone cell–related genes. The data indicate that the crosstalk with osteoblasts induces expressional changes in prostate carcinoma cells favoring the bone colonization process. © 2004 Wiley‐Liss, Inc.