Neuropeptides like galanin produced and released by small cell lung cancer (SCLC) cells are considered principal mitogens in these tumors. We identi®ed the galanin receptor type 2 (GALR2) as the only galanin receptor expressed in H69 and H510 cells. Photoa nity labeling of G proteins in H69 cell membranes revealed that GALR2 activates G proteins of three subfamilies: G q , G i , and G 12 . In H69 cells, galanin-induced Ca 2+ mobilization was pertussis toxin-insensitive. While phorbol ester-induced extracellular signal-regulated kinase (ERK) activation required protein kinase C (PKC) activity, preincubation of H69 cells with the PKCinhibitor GF109203X had no e ect on galanin-dependent ERK activity. A rise of the intracellular calcium concentration was necessary and su cient to mediate galanin-induced ERK activation. In support of G i coupling, stimulation of GALR2 expressed in HEK293 cells inhibited isoproterenol-induced cAMP accumulation and raised cAMP levels in COS-7 cells when coexpressed with a chimeric Ga S -Ga i protein. In H69 cells, galanin activated the monomeric GTPase RhoA and induced stress ®ber formation in Swiss 3T3 cells expressing GALR2. Thus, we provide the ®rst direct evidence that in SCLC the mitogenic neuropeptide galanin, interacting with GALR2, simultaneously activates multiple classes of G proteins and signals through the G q phospholipase C/calcium sequence and a G 12 /Rho pathway. Oncogene (2000) 19, 4199 ± 4209.