Abstract
HeLa cells, when exposed to 5 mM sodium butyrate, increased their responsiveness to isoproterenol and their number of beta-receptors. As untreated HeLa cells have a substantial number of receptors but respond poorly to isoproterenol, the effect of butyrate could be due to quantitative or qualitative changes in beta-receptors or other components of the adenylate cyclase system. Receptors were analyzed by membrane/membrane and membrane/cell fusion techniques. HeLa donor membranes, treated to inactivate regulatory and catalytic components of adenylate cyclase, were fused with Fc cells, which lack beta-receptors. Isoproterenol-stimulated adenylate cyclase activity in the fusates was proportional to the number of receptors present. There appeared to be only quantitative but not qualitative differences in beta-receptors from control and butyrate-treated HeLa. Prostaglandin E1 receptors from neuroblastoma cell membranes were similarly coupled to HeLa adenylate cyclase. The hybrid prostaglandin E1-stimulated activity was lower when acceptor membranes were from control HeLa than when they were from butyrate-treated HeLa cells. These results suggested that butyrate was altering the ability of the regulatory component to interact with receptors. HeLa membranes were extracted with sodium cholate and the extracts used to reconstitute effector-stimulated adenylate cyclase activity in S49 cyc- membranes, which lack a functional regulatory component. Whereas extracts from control and butyrate-treated HeLa were equally effective in restoring NaF-stimulated activity in cyc- membranes, extracts from control HeLa were less efficient in reconstituting isoproterenol- and prostaglandin E1-stimulated activities. We conclude that the poor response of control HeLa to beta-agonists is due to a limited activity of the regulatory component but not the receptor. Butyrate induces quantitative changes in the receptor and qualitative changes in the regulatory component that facilitate its ability to couple to receptors but do not alter its ability to interact with the catalytic component of adenylate cyclase.
Highlights
From the $Membrane BiochemistrySection, Developmentaland Metabolic NeurologyBranch and the $Molecular Neurobiology Section, Laboratory of Molecular Biology
Adenylate cyclase in HeLa cells is normally poorly stimulated by catecholamines even though the cells have a substantial number of preceptors and the enzyme is activated by other effectors such as guanine nucleotides, NaF, and cholera toxin [12,13,14,15]
HeLa cells contain a substantial number of B-adrenergic receptors, more than avian myoblasts [27] and human fibroblasts [17]and similar to rat [28]and human [29]astrocytoma cells
Summary
From the $Membrane BiochemistrySection, Developmentaland Metabolic NeurologyBranch and the $Molecular Neurobiology Section, Laboratory of Molecular Biology. HeLa cells, when exposed to mM sodium butyrate, adrenergic receptor, a G/F,’ and a C [1,2,3]. Efficient coupling increased their responsiveness to isoproterenol and between receptor and G/F, on the one hand, and between G/. As untreated HeLa cells have a substantial number of receptors but respond poorly toisoproterenol, the effect of butyrate could be due to quantitative or qualitativechanges in B-receptors or othecromponentsof the adenylate cyclase system. It is unclear as towhether the induction of catecholblastomacell membranes were coupled to aminesensitivity by butyrate is due only to quantitative
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