Parathyroid hormone-related protein induces interleukin 8 production by prostate cancer cells via a novel intracrine mechanism not mediated by its classical nuclear localization sequence

PTHrP (parathyroid hormone-related protein) overexpression by prostate carc inoma cells has been implicated in tumor progression. Although the biologic al effects of PTHrP can be mediated by the G-protein-coupled PTH/PTHrP rece ptor, PTHrP also has intracrine actions mediated by a nuclear localization sequence at residues 87-107, We investigated the effect of PTHrP transfecti on and treatment on production by prostate carcinoma cells of IL (interleuk in)-8, which fan regulate prostate cancer growth by angiogenic activity and growth-promoting effects. Six prostate cancer cell lines exhibited constit utive expression of PTHrP and IL-8 that were significantly correlated (r = 0.93; P < 0.01), We transfected wild-type and mutant PTHrP into these tells . Wild-type PTHrP1-173 and PTHrP33-173 lacking the PTH/PTHrP receptor-bindi ng domain induced a 3-fold stimulation of IL-8 production but nut productio n of another angiogenic factor, vascular endothelial growth factor, Transfe ction of the COOH-terminal truncation mutant PTHrP1-87 induced a 5-fold sim ulation of IL-8 and a 3-fold increase in IL-8 mRNA, Cells transfected with PTHrP1-87 and 1-173 also showed increased cell proliferation, In contrast, exogenous PTHrP1-34 and 1-86 peptides did not significantly affect IL-8 pro duction; moreover, PTHrP-neutralizing antibodies did not inhibit the produc tion of IL-8 by transfected PTHrP, Additional transfection studies with pro gressively COOH-terminally truncated PTHrP1-87 defined a 23-amino acid sequ ence, PTHrP65-87, required for PTHrP1-87 to robustly stimulate IL-8 in pros tate cancer cells. Confocal microscopy and immunoassay demonstrated PTHrP1- 87 nuclear localization. Our results demonstrate that PTHrP acts to induce IL-8 production in prostate cancer cells via an intracrine pathway independ ent of its classical nuclear localization sequence. This novel pathway coul d mediate the effects of PTHrP on the progression of prostate cancer.