alytesin and Carcinoma--Small-Cell

The production and postsecretory stability of gastrin-releasing peptide (GRP) and the C-terminal part of the GRP precursor were studied in small cell lung cancer cell lines using RIAs developed against these two parts of the precursor. In three otherwise different cell lines (NIC-H345, NIC-H69, and NIC-H510), similar chromatographic patterns of mainly GRP-(18-27) and some GRP-(14-27) along with large fragments of the C-terminal counterpart of the precursor were found to be stored in the cells. In tissue culture medium, gel filtration chromatography indicated that postsecretory limited proteolysis of the GRP precursor fragments occurred. The amount of accumulated immunoreactivity varied among the three cell lines and between the two parts of the precursor. In medium in which only low amounts of GRP immunoreactivity accumulated, the radiolabeled GRP was degraded rapidly. When incubated with plasma, GRP-(14-27) disappeared within a few hours, whereas the C-terminal precursor fragments were stable. It is concluded that the postsecretory stability of peptides excised from the GRP precursor in small cell lung cancer cells varies under tissue culture conditions, but epitopes in the C-terminal part of the precursor are more stable in plasma than the small GRP peptides and, thus, may serve as a better indicator than GRP itself for expression of the GRP precursor in cancer cells.

Topics: Amino Acid Sequence; Biomarkers, Tumor; Bombesin; Carcinoma, Small Cell; Cell Line; Chromatography, Gel; Chromatography, High Pressure Liquid; Chromosome Mapping; Gastrin-Releasing Peptide; Gene Expression; Humans; Immunoradiometric Assay; In Vitro Techniques; Lung Neoplasms; Molecular Sequence Data; Peptide Fragments; Peptides; Sequence Homology, Nucleic Acid; Substance P

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.

Topics: Amino Acid Sequence; Bombesin; Calcium; Carcinoma, Small Cell; Cell Line; Dose-Response Relationship, Drug; Gastrin-Releasing Peptide; Humans; Kinetics; Lung Neoplasms; Oligopeptides; Peptides; Pyrrolidonecarboxylic Acid; Structure-Activity Relationship