CCK(A) AND CCK(B) RECEPTORS ARE EXPRESSED IN SMALL-CELL LUNG-CANCER LINES AND MEDIATE CA2+ MOBILIZATION AND CLONAL GROWTH

Gastrin, cholecystokinin (CCK), and CCK-related peptides comprise a ho rmonal family characterized by an identical carboxy-terminal amino aci d sequence, a domain critical for receptor binding. The addition of ga strin to small cell lung cancer (SCLC) cells causes a rapid and transi ent increase in the intracellular concentration of calcium ([Ca2+]i). Furthermore, gastrin acts as a direct growth factor through CCK(B)/gas trin receptors. We report here that the expression of the mRNA coding for CCK(B)/gastrin receptors correlates with the responsiveness of SCL C cells to gastrin in terms of Ca2+ mobilization and stimulation of cl onal growth in semisolid medium. The GLC19 SCLC cell line had no detec table expression of CCK(B)/gastrin receptor mRNA. Accordingly, gastrin (1-100 nM) did not cause any measurable increase in [Ca2+]i. In contr ast, the addition of cholecystokinin residues 26-33 (CCK-8) caused a r apid and transient increase in [Ca2+], in this cell line. CCK-8 mobili zed Ca2+ in a dose-dependent manner in the nanomolar range (half-maxim al stimulatory concentration = 12 nM). Furthermore, the selective CCK( A) antagonist CAM-1481 inhibited the increase in [Ca2+]i induced by CC K-8 (half-maximal inhibitory concentration = 3 nM) in GLC19 but not in H510 cells. The selective CCK(B)/gastrin antagonist blocked the incre ase in [Ca2+]i induced by CCK-8 (half-maximal inhibitory concentration = 80 pM) in H510 but not in GLC19 cells. Thus, the effects of CCK-8 a re mediated through CCK(A) receptors in GLC19 cells and via CCK(B)/gas trin receptors in H510 cells. CCK-8 markedly stimulated colony formati on in GLC19 cells in a dose-dependent manner in the nanomolar range, w hereas over the same concentration range, gastrin had no effect on clo nal growth. CAM-1481 inhibited the CCK-stimulated colony formation in GLC19 but not in H510 cells. Our results show, for the first time, tha t CCK(A) receptors can mediate Ca2+ mobilization and growth in SCLC ce lls and that SCLC cells express two distinct functional CCK receptor s ubtypes.