Modulation of bombesin-induced phosphatidylinositol hydrolysis in a small-cell lung-cancer cell line.
Bombesin is an amphibian tetradecapeptide whose mammalian homologue, gastrin-releasing peptide (GRP), is produced by many small-cell lung-cancer (SCLC) cells, and which can function in an autocrine growth-promoting manner in SCLC. Studies reported here show that [Tyr4]bombesin and its congeners increase inositol 1,4,5-trisphosphate within seconds in NCI-H345, a SCLC cell line that constitutively produces GRP. After 30 min in the presence of 0.01 M-Li+ and [Tyr4]bombesin, there is marked accumulation of inositol monophosphates and inositol tetrakisphosphate. Pretreatment with phorbol 12-myristate 13-acetate (PMA) for 20 min inhibited the ability of [Tyr4]bombesin to induce phosphatidylinositol (PtdIns) turnover and to increase intracellular free Ca2+ ([Ca2+]i). Pretreatment with PMA for 48 h attenuated the ability of subsequently added PMA to decrease the response to [Tyr4]bombesin. Pretreatment with pertussis toxin (PT; 1 microgram/ml for 18-24 h) decreased by less than 30% [Tyr4]bombesin-induced increases in [Ca2+]i and PtdIns metabolites. However, interpretation of this result is complicated by the inability of PT to ADP-ribosylate completely its substrates in intact NCI-H345 cells. In contrast, pretreatment with cholera toxin (1 microgram/ml for 18-24 h) lowered basal [Ca2+]i and basal inositol phosphate concentrations, attenuated the response of NCI-H345 to subsequently added [Tyr4]bombesin, and was not mimicked by treatments that increase cellular cyclic AMP. These data demonstrate the activation of phospholipase C in SCLC by bombesin congeners. In addition, the results suggest a regulatory role for protein kinase C, a cholera-toxin substrate, and perhaps a pertussis-toxin substrate in the response of SCLC to bombesin.
Trepel
J B
JB
National Cancer Institute--Navy Medical Oncology Branch, Bethesda, MD 20814.
Moyer
J D
JD
Heikkila
R
R
Sausville
E A
EA
D000244:Adenosine Diphosphate / Q000378:metabolism; D000818:Animals; D001839:Bombesin / Q000494:pharmacology*; D018288:Carcinoma, Small Cell / Q000378:metabolism*; D002460:Cell Line; D002772:Cholera Toxin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D007295:Inositol Phosphates / Q000302:isolation & purification; D008175:Lung Neoplasms / Q000378:metabolism*; D037342:Pertussis Toxin; D010703:Phorbol Esters / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism*; D013329:Structure-Activity Relationship; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D007295:Inositol Phosphates; D010703:Phorbol Esters; D010716:Phosphatidylinositols; D010566:Virulence Factors, Bordetella; D000244:Adenosine Diphosphate; D002772:Cholera Toxin; D037342:Pertussis Toxin; D001839:Bombesin