Prolactin stimulates cell proliferation through a long form of prolactin receptor and K+ channel activation

PRL (prolactin) has been implicated in the proliferation and differentiation of numerous tissues, including the prostate gland. However, the PRL-R (PRL receptor) signal transduction pathway, leading to the stimulation of cell proliferation, remains unclear and has yet to be mapped. The present study was undertaken to develop a clear understanding of the mechanisms involved in this pathway and, in particular, to determine the role of K⁺ channels. We used androgen-sensitive prostate cancer (LNCaP) cells whose proliferation is known to be stimulated by PRL. Reverse transcriptase PCR analysis showed that LNCaP cells express a long form of PRL-R, but do not produce its intermediate isoform. Patch-clamp techniques showed that the application of 5 nM PRL increased both the macroscopic K⁺ current amplitude and the single K⁺-channel open probability. This single-channel activity increase was reduced by the tyrosine kinase inhibitors genistein, herbimycin A and lavandustine A, thereby indicating that tyrosine kinase phosphorylation is required in PRL-induced K⁺ channel stimulation. PRL enhances p59^fyn phosphorylation by a factor of 2 after a 10 min application in culture. In addition, where an antip59^fyn antibody is present in the patch pipette, PRL no longer increases K⁺ current amplitude. Furthermore, the PRL-stimulated proliferation is inhibited by the K⁺ channel inhibitors α-dendrotoxin and tetraethylammonium. Thus, as K⁺ channels are known to be involved in LNCaP cell proliferation, we suggest that K⁺ channel modulation by PRL, via p59^fyn pathway, is the primary ionic event in PRL signal transduction, triggering cell proliferation.