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Nicotinic Acetylcholine Receptors of Muscle and Neuronal (α 7 ) Types Coexpressed in a Small Cell Lung Carcinoma
Author(s) -
Sciamanna Michele A.,
Griesmann Guy E.,
Williams Carol L.,
Len Vanda A.
Publication year - 1997
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1997.69062302.x
Subject(s) - acetylcholine receptor , nicotinic agonist , acetylcholine , muscarinic acetylcholine receptor , receptor , neuroscience , biology , small cell lung carcinoma , lung , endocrinology , medicine , small cell carcinoma , biochemistry
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 125 I‐labeled α‐bungarotoxin ( 125 I‐α‐BTx), cosediment with 9S nAChR pentamers, and bind to a monoclonal antibody (MAb 35) specific for muscle‐type (α 1 subunit) α‐BTx receptors. The agonist carbamylcholine (carbachol) stimulates influx of 22 Na + in SCC‐37 cells; this is inhibited by α‐BTx and by d ‐tubocurarine. Long‐term cultured SCC‐37 cells have functional and ligand‐binding evidence for surface coexpression of both α 1 and neuronal‐type (α 7 subunit) α‐BTx receptors. A subclone of SCC‐37, designated SCC‐A9, expresses only the neuronal‐type (α 7 subunit) α‐BTx receptors on its surface. Carbachol does not stimulate 22 Na + influx in SCC‐A9 cells, but cytisine initiates a sustained influx of Ca 2+ . Activation of this response is inhibited by α‐BTx and by the α 7 ‐selective antagonist methyllycaconitine. Addition of Co 2+ abrogates the sustained elevation of intracellular free Ca 2+ concentration, implying that the cytisine‐stimulated influx of Ca 2+ is sustained by secondary opening of voltage‐sensitive channels in the plasma membrane. Surface receptors for 125 I‐α‐BTx are blocked by methyllycaconitine and d ‐tubocurarine. Solubilized α‐BTx receptors from plasma membranes of SCC‐A9 cells cosediment with 10S neuronal nAChR pentamers and bind to an α 7 ‐specific monoclonal antibody (MAb P27) but not to the muscle nAChR‐reactive MAb 35. However, MAb P27 and MAb 35 both bind to α‐BTx receptors solubilized from the cytoplasmic compartments of SCC‐A9 and the parental SCC‐37 line. Reverse transcription‐PCR analysis revealed RNA transcripts for α 7 and α 1 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 Ca 2+ 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.