To examine the biochemical basis for
growth factor-induced responses in human
lung cancer cells, we used the
quin2 technique to study the effect of the amphibian
peptide bombesin and its congeners including mammalian
gastrin-releasing peptide (GRP) on the intracellular free
calcium level [Ca2+]i in
small cell lung cancer cell lines. In five of eleven cell lines tested, Tyr4-bombesin or GRP elicited a rapid and transient increase in [Ca2+]i. The response was seen with as little as 1 nM
ligand, was not affected by membrane depolarization, and derived in part from internal
calcium stores. Desensitization to a second addition of active
bombesin congeners occurs subsequent to initial addition of Tyr4-bombesin. Structure-activity analysis showed the carboxyl-terminal octapeptide was the active portion of the
peptide. Analogs in which the carboxyl terminus was oxidized or deamidated were inactive.
Ranatensin,
litorin,
alytesin, and GRP, but not
physalaemin, were as active as Tyr4-bombesin. A
monoclonal antibody to the carboxyl terminus of
bombesin selectively blocked the increased [Ca2+]i elicited by Tyr4-bombesin. These studies suggest that
bombesin congeners can act on some
small cell lung cancer cell lines by a pathway utilizing increased [Ca2+]i.