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A correlation of bombesin-responsiveness with myc-family gene expression in small cell lung carcinoma cell lines
E A Sausville1, J D Moyer, R Heikkila
1National Cancer Institute-Navy Medical Oncology Branch, Bethesda, Maryland 20814.
Abstract:
Bombesin is a 14 amino acid peptide originally isolated from amphibian skin; its mammalian homolog is gastrin-releasing peptide (GRP). GRP is found in a high proportion of human small cell lung cancer (SCLC) cell lines. [Tyr4]bombesin caused an increase in intracellular Ca2+ ([Ca2+]i) in 5/11 SCLC cell lines tested. Bombesin action was not inhibited by agents known to alter the plasma membrane potential, nor did replacement of external Na+ with choline affect the bombesin-induced signal. [Tyr4]bombesin did not itself affect the membrane potential. Chelation of external Ca2+ reduced but did not prevent the bombesin-evoked increase in [Ca2+]i. This suggested that in SCLC, bombesin congeners not only promote an influx of extracellular Ca2+ but also release Ca2+ from intracellular stores. [Tyr4]bombesin increased levels of inositol 1,4,5-trisphosphate within seconds of addition to SCLC cell cultures and enhanced the accumulation of inositol 1-phosphate and inositol 4-phosphate in the presence of Li+. The SCLC cell lines responsive to bombesin constitutively expressed L-myc and did not express c-myc or N-myc. In contrast, SCLC cells non-responsive to bombesin had prominent constitutive expression of c-myc or N-myc with or without L-myc expression. Responding cell lines also had constitutive expression of the preproGRP gene, while non-responding cell lines showed no evidence of GRP gene expression. These data support the concept that SCLC which constitutively express the GRP gene and L-myc but not c-myc or N-myc can be stimulated in an autocrine fashion by GRP or its congeners to increase [Ca2+]i by a pathway involving phosphatidylinositol turnover.
Insights
Gastrin-releasing peptide (GRP) and bombesin stimulate intracellular calcium ([Ca2+]i) increases in small cell lung cancer (SCLC) cells. This response involves both extracellular calcium influx and intracellular calcium release, mediated by phosphatidylinositol turnover and linked to specific gene expression patterns.
Area of Science:
- Molecular Biology
- Cellular Signaling
- Oncology
Background:
- Bombesin, a peptide hormone, has a mammalian homolog, gastrin-releasing peptide (GRP).
- GRP is frequently detected in human small cell lung cancer (SCLC) cell lines.
- The role of GRP and bombesin signaling in SCLC pathogenesis is under investigation.
Purpose of the Study:
- To investigate the effects of bombesin and its analogs on intracellular calcium levels in SCLC cells.
- To elucidate the signaling pathways involved in bombesin-induced calcium responses in SCLC.
- To correlate bombesin responsiveness with the expression of specific oncogenes (myc family) and the GRP gene.
Main Methods:
- Treatment of SCLC cell lines with [Tyr4]bombesin.
- Measurement of intracellular calcium ([Ca2+]i) using calcium indicators.
- Assessment of plasma membrane potential and extracellular ion concentrations.
- Analysis of inositol phosphate levels following bombesin stimulation.
- Detection of L-myc, c-myc, N-myc, and preproGRP gene expression via molecular techniques.
Main Results:
- [Tyr4]bombesin increased [Ca2+]i in a subset of SCLC cell lines, indicating differential responsiveness.
- The bombesin-induced calcium increase involved both extracellular calcium influx and intracellular calcium release.
- Bombesin stimulation led to rapid increases in inositol 1,4,5-trisphosphate and enhanced inositol phosphate accumulation.
- Responsive SCLC cells constitutively expressed L-myc and the preproGRP gene, but not c-myc or N-myc.
- Non-responsive SCLC cells showed prominent c-myc or N-myc expression and lacked GRP gene expression.
Conclusions:
- Bombesin signaling in SCLC involves a complex calcium mobilization mechanism dependent on phosphatidylinositol turnover.
- Autocrine stimulation by GRP may play a role in SCLC growth, particularly in tumors expressing GRP and L-myc.
- Specific oncogene expression profiles (L-myc vs. c-myc/N-myc) distinguish bombesin-responsive SCLC, suggesting distinct molecular subtypes.
