Parathyroid hormone-related protein (PTHrP) is expressed by human prostatic tissue and prostate cancer cell lines, and enhances prostate tumor cell growth both in vivo and in vitro. PTHrP expression also plays a role in the development of bone metastasis, which is a frequent complication in patients with prostate carcinoma. Tumor cell adhesion to extracellular matrix (ECM) components is mediated via integrin subunits, and plays a major role in the invasion and metastasis of tumor cells. We previously showed that PTHrP overexpression increases adhesion of the human prostate cancer cell line PC-3 to the ECM molecules collagen type I, fibronectin, and laminin. Increased adhesion is accompanied by upregulation in the expression of alpha1, alpha5, alpha6, and beta4 integrin subunits. We used the same cell line to study the mechanism via which PTHrP upregulates integrin expression. Clonal PC-3 cells were established overexpressing wild-type PTHrP or PTHrP mutated in the nuclear localization sequence (NLS). Mutation of the NLS negated the effects of PTHrP on alpha1, alpha5, alpha6, and beta4 integrin expression, indicating that these effects are mediated via an intracrine pathway requiring nuclear localization. Expression of the alpha2, alpha3, alphav, and beta1 integrin subunits were comparable in wild-type and NLS-mutated PTHrP transfectants. These findings indicate that PTHrP may play a role in prostate tumor invasion and metastasis by upregulating the expression of specific integrin subunits via an intracrine pathway.