Nicotinic acetylcholine receptors of muscle and neuronal (alpha7) types coexpressed in a small cell lung carcinoma.
SCC-37 is a small cell lung carcinoma line that aberrantly expresses muscle-type nicotinic acetylcholine receptors (nAChRs). It was established from a patient with a paraneoplastic autoimmune neuromuscular disorder, myasthenia gravis. When grown as a xenograft tumor, SCC-37 cells express plasma membrane receptors that bind 1251-labeled alpha-bungarotoxin (125I-alpha-BTx), cosediment with 9S nAChR pentamers, and bind to a monoclonal antibody (MAb 35) specific for muscle-type (alpha1 subunit) alpha-BTx receptors. The agonist carbamylcholine (carbachol) stimulates influx of 22Na+ in SCC-37 cells; this is inhibited by alpha-BTx and by d-tubocurarine. Long-term cultured SCC-37 cells have functional and ligand-binding evidence for surface coexpression of both alpha1 and neuronal-type (alpha7 subunit) alpha-BTx receptors. A subclone of SCC-37, designated SCC-A9, expresses only the neuronal-type (alpha7 subunit) alpha-BTx receptors on its surface. Carbachol does not stimulate 22Na+ influx in SCC-A9 cells, but cytisine initiates a sustained influx of Ca2+. Activation of this response is inhibited by alpha-BTx and by the alpha7-selective antagonist methyllycaconitine. Addition of Co2+ abrogates the sustained elevation of intracellular free Ca2+ concentration, implying that the cytisine-stimulated influx of Ca2+ is sustained by secondary opening of voltage-sensitive channels in the plasma membrane. Surface receptors for 125I-alpha-BTx are blocked by methyllycaconitine and d-tubocurarine. Solubilized alpha-BTx receptors from plasma membranes of SCC-A9 cells cosediment with 10S neuronal nAChR pentamers and bind to an alpha7-specific monoclonal antibody (MAb P27) but not to the muscle nAChR-reactive MAb 35. However, MAb P27 and MAb 35 both bind to alpha-BTx receptors solubilized from the cytoplasmic compartments of SCC-A9 and the parental SCC-37 line. Reverse transcription-PCR analysis revealed RNA transcripts for alpha7 and alpha1 subunits in both SCC-A9 and SCC-37 cells. The nAChRs that are expressed in these novel human cell lines can regulate cation fluxes directly as well as indirectly by synergizing with the activity of voltage-sensitive Ca2+ channels. These activities may influence the secretion of autocrine growth factors and the transcription of growth regulatory genes and thus be pertinent to the growth and metastasis of malignant neuroendocrine neoplasms.
Sciamanna
M A
MA
Department of Immunology, Mayo Clinic, Rochester, Minnesota 55905, U.S.A.
Griesmann
G E
GE
Williams
C L
CL
Lennon
V A
VA
D000941:Antigens / Q000276:immunology; D002038:Bungarotoxins / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D018288:Carcinoma, Small Cell / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002499:Centrifugation, Density Gradient; D006801:Humans; D008175:Lung Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D009132:Muscles / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D018722:Nicotinic Agonists / Q000494:pharmacology; D016133:Polymerase Chain Reaction; D012334:RNA, Neoplasm / Q000032:analysis; D011956:Receptors, Cell Surface / Q000276:immunology / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured / Q000187:drug effects
D000941:Antigens; D002038:Bungarotoxins; D018722:Nicotinic Agonists; D012334:RNA, Neoplasm; D011956:Receptors, Cell Surface; D011978:Receptors, Nicotinic; D012964:Sodium; D002118:Calcium