Background: Recent evidence suggests that muscarinic receptors induce mitogenesis in cells capable of undergoing cell proliferation. Human prostate gland is innervated by the autonomic nervous system and muscarinic receptors have been localized in the prostate gland.
Methods: Effects of carbachol (a stable analog of acetyl choline) on DNA synthesis of LNCaP cells (a human prostate cancer cell line) and primary prostate cells was examined. The DNA synthesis in the cultured cells was assessed using techniques of 3H-thymidine incorporation and bromodeoxyuridine (BrdU) incorporation immunocytochemistry.
Results: Carbachol induced a significant increase in BrdU- and 3H-thymidine incorporation of LNCaP cells. The effect of carbachol was completely reversed by atropine, a selective muscarinic antagonist. Subtypes of muscarinic receptors mediating carbachol-induced DNA synthesis were identified using selective receptor subtype antagonists. Pirenzepamine and gallamine did not affect carbachol action on LNCaP cells but diphenylpyralamine, an M3 receptor antagonist, completely blocked carbachol-induced DNA synthesis. Carbachol also stimulated DNA synthesis in primary prostate cells. Prostate carcinoma (PC)-derived primary prostate cells displayed a dramatically greater response to carbachol (a ten-fold increase in DNA synthesis) as compared to benign prostate hypertrophy (BPH)-derived cells (a two-fold increase in DNA synthesis).
Conclusions: M3 receptors stimulate the proliferation of LNCaP cells, BPH-derived and PC-derived primary prostate cells. A dramatically higher response to carbachol by PC-derived prostate cells suggests that M3 receptors may be up-regulated in PC. M3 receptors may play a significant role in PC tumors growth and androgen-independent tumor progression.