CCKA and CCKB 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 hormonal family characterized by an identical carboxy-terminal amino acid sequence, a domain critical for receptor binding. The addition of gastrin to small cell lung cancer (SCLC) cells causes a rapid and transient increase in the intracellular concentration of calcium ([Ca2+]i). Furthermore, gastrin acts as a direct growth factor through CCKB/gastrin receptors. We report here that the expression of the mRNA coding for CCKB/gastrin receptors correlates with the responsiveness of SCLC cells to gastrin in terms of Ca2+ mobilization and stimulation of clonal growth in semisolid medium. The GLC19 SCLC cell line had no detectable expression of CCKB/gastrin receptor mRNA. Accordingly, gastrin (1-100 nM) did not cause any measurable increase in [Ca2+]i. In contrast, the addition of cholecystokinin residues 26-33 (CCK-8) caused a rapid and transient increase in [Ca2+]i in this cell line. CCK-8 mobilized Ca2+ in a dose-dependent manner in the nanomolar range (half-maximal stimulatory concentration = 12 nM). Furthermore, the selective CCKA antagonist CAM-1481 inhibited the increase in [Ca2+]i induced by CCK-8 (half-maximal inhibitory concentration = 3 nM) in GLC19 but not in H510 cells. The selective CCKB/gastrin antagonist blocked the increase 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 are mediated through CCKA receptors in GLC19 cells and via CCKB/gastrin receptors in H510 cells. CCK-8 markedly stimulated colony formation in GLC19 cells in a dose-dependent manner in the nanomolar range, whereas over the same concentration range, gastrin had no effect on clonal growth. CAM-1481 inhibited the CCK-stimulated colony formation in GLC19 but not in H510 cells. Our results show, for the first time, that CCKA receptors can mediate Ca2+ mobilization and growth in SCLC cells and that SCLC cells express two distinct functional CCK receptor subtypes.
Sethi
T
T
Imperial Cancer Research Fund, London, England.
Herget
T
T
Wu
S V
SV
Walsh
J H
JH
Rozengurt
E
E
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D018288:Carcinoma, Small Cell / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002999:Clone Cells; D017931:DNA Primers; D004285:Dogs; D005755:Gastrins / Q000494:pharmacology*; D015870:Gene Expression; D006801:Humans; D007700:Kinetics; D008175:Lung Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D008969:Molecular Sequence Data; D009115:Muridae; D016133:Polymerase Chain Reaction / Q000379:methods; D012333:RNA, Messenger / Q000096:biosynthesis / Q000378:metabolism*; D012334:RNA, Neoplasm / Q000302:isolation & purification; D051381:Rats; D011949:Receptors, Cholecystokinin / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012844:Sincalide / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D017931:DNA Primers; D005755:Gastrins; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D011949:Receptors, Cholecystokinin; D012844:Sincalide; D001920:Bradykinin; D002118:Calcium