GRPR and neoplasm: Experiments using different types of normal and tumor cells from humans and rodents have provided consistent evidence that the GRPR is directly coupled to the Gq type of G protein, and GRPR activation leads to an increase in cellular [Ca2+] and stimulation of the phospholipase C (PLC)/protein kinase C (PKC) and extracellular signal-regulated protein kinase (ERK)/mitogen-activated protein kinase (MAPK) pathways (Hellmich et al., 1999; Chen and Kroog, 2004; Stangelberger et al., 2005).