Paracrine Calcitonin in Prostate Cancer is Linked to CD44 Variant Expression and Invasion

Abstract

Background: Calcitonin (CT) exerts an autocrine/paracrine influence on prostatic tumor invasion through coupling to transduction protein G_sα. Cell adhesion glycoprotein CD44 variant v7-v10 also faciliates invasion, but its modulation by the CT-G_sα system was unexplored. Materials and Methods: LnCaP, PC-3 and metastasis-derived PC-3M cell lines were studied, including cells modified therefrom: G_sα-QL, expressing mutant constitutively active G_sα protein, and CT+, overexpressing CT. CD44 variant expression was evaluated in vivo after orthotopic implantion into nude mice, and in vitro by real-time RT-PCR and Western blotting. Results: Both mRNA and protein levels of the CD44 variant were minimal in PC-3M tumor implants, but elevated in G_sα-QL. Exogenous CT stimulated invasion into Matrigel strongly in LnCaP and CT+, and less in PC-3 and G_sα-QL. By Western blot analysis, untreated G_sα-QL and CT+ cells overexpressed CD44 variant compared with LnCaP or PC-3. By quantitative RT-PCR, exogenous CT dose-dependently increased CD44 variant mRNA to seven-fold. Pharmacologic agents that stimulated or inhibited G_sα activity or stimulated adenylyl cyclase produced proportionate dose-dependent effects on both CD44 variant expression and Matrigel invasion. Conclusion: This paracrine factor, acting though cyclic AMP, regulates the expression of CD44v7-10, which modulates the tumor phenotype.