1. ¹Department of Radiation Oncology, Cancer Center, University of Virginia Health Sciences Center, Charlottesville, VA, USA
2. ²Department of Microbiology, Cancer Center, University of Virginia Health Sciences Center, Charlottesville, VA, USA
3. ³Department of Biology, Mary Baldwin College, Staunton, VA, USA

Correspondence: Dr SJ Parsons, Department of Microbiology, University of Virginia Health System, PO Box 800734, Charlottesville, VA 22908-0734, USA. E-mail: sap@virginia.edu

Received 28 February 2006; Revised 2 June 2006; Accepted 2 June 2006; Published online 24 July 2006.

Abstract

Neuroendocrine (NE)-like cells are hypothesized to contribute to the progression of prostate cancer by producing factors that enhance the growth, survival or metastatic capabilities of surrounding tumor cells. Many of the factors known to be secreted by NE-like cells, such as neurotensin (NT), parathyroid hormone-related peptide, serotonin, bombesin, etc., are agonists for G-protein-coupled receptors, but the signaling pathways activated by these agonists in prostate tumor cells are not fully defined. Identification of such pathways could provide insights into novel methods of treating late-stage disease. Using conditioned culture medium (CM) from LNCaP-derived NE-like cells (as a source of these agonists) or NT (a prototypical component of CM) to treat PC3 cells, we found that the epidermal growth factor (EGF) receptor (EGFR) was transactivated and that such activation was required for maximal PC3 cell mitogenesis, as measured by 5-bromo-2'-deoxy-uridine incorporation or cell number. NT also induced a time-dependent increase in EGFR Tyr⁸⁴⁵ phosphorylation and phosphorylation of c-Src and signal transducer and activator of transcription 5b (Stat5b) (a downstream effector of Tyr⁸⁴⁵), events that were blocked by specific inhibition of c-Src (which mediates Tyr⁸⁴⁵ phosphorylation of EGFR) or of EGFR. Introduction of mutant forms of EGFR (Tyr⁸⁴⁵) or Stat5b in PC3 cells, or treatment with selective, catalytic inhibitors of EGFR, c-Src and matrix metalloproteinases (MMPs) resulted in the loss of NT-induced stimulation of DNA synthesis, relative to wild-type controls. These data indicate that the mitogenic effect of NT on prostate cancer cells requires transactivation of the EGFR by MMPs and a novel downstream pathway involving c-Src, phosphorylation of EGFR Tyr⁸⁴⁵ and activation of Stat5b.