Neuropeptides (e.g. bombesin) are small regulatory peptides localized in the neurons of the central and peripheral nervous system as well as in neuroendocrine cells. They can act as neurotransmitters, paracrine or endocrine hormones but also as growth factors, which shows that the demarcation line between hormones, cytokines, neuroendocrine effectors and growth factors is becoming increasingly blurred. Bombesin is a “sole mitogen” for Swiss 3T3 cells, which means that bombesin can initiate all the necessary events for cell division on its own (Rozengurt E, Sinnett-Smith J 1990). This is quite surprising since bombesin signals through a G-protein linked receptor, whereas all other sole mitogens for Swiss 3T3 cells (PDGF, FGF) signal through a tyrosine kinase containing receptor (Rozengurt E, Sinnett-Smith J 1990). We therefore set out to investigate whether bombesin could stimulate any of the protein kinases in Swiss 3T3 cells, that are known to be activated in the signaling pathways initiated by tyrosine kinase containing receptors.
