epidermal-growth-factor and 1-3-dipropyl-8-cyclopentylxanthine

This report concerns the study of homologous and heterologous regulation of cell surface A1 adenosine receptors (A1R) in a pituitary-derived cell line. This has been possible by the use of the recently developed anti-A1R antibodies in immunocytochemical assays. Functional desensitization and internalization of A1R in GH4 cells occurred after treatment with agonist but also with antagonist. Epidermal growth factor (EGF) treatment led to the up-regulation of cell surface A1R in GH4 cells. Confocal analysis evidenced an EGF-induced increase of A1R present in intracellular clathrin-coated vesicles. The up-regulation was blocked by actinomycin D thus suggesting the involvement of protein synthesis in the effect induced by the growth factor. These results constitute the first example of adenosine receptor regulation by EGF and one of the few examples of antagonist-induced desensitization and internalization among G-protein-coupled receptors.

Topics: Adenosine; Animals; Calcium; Cell Division; Cell Line; Dactinomycin; Epidermal Growth Factor; Flow Cytometry; Immunohistochemistry; Pituitary Gland; Protein Synthesis Inhibitors; Purinergic P1 Receptor Agonists; Purinergic P1 Receptor Antagonists; Rats; Receptors, Purinergic P1; Up-Regulation; Xanthines

The activation of A1 and A2 adenosine receptors was shown to modulate DNA synthesis. In A431 cells, low concentrations of adenosine (approximately 10 microM) inhibited while higher concentrations (approximately 100 microM) stimulated [14C]thymidine incorporation. Epidermal growth factor (EGF) (10 ng/ml) could partially alleviate the inhibitory effects and further enhance the stimulatory effects of adenosine. Treatment of the cells with adenosine analogues (R-PIA and NECA) and antagonists (theophylline and DPCPX), which are selective for either the A1 (inhibitory) or A2 (stimulatory) receptors, indicated the involvement of these two receptors in the biphasic response to adenosine.

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Carcinoma, Squamous Cell; DNA, Neoplasm; Epidermal Growth Factor; Humans; Phenylisopropyladenosine; Purinergic P1 Receptor Antagonists; Receptors, Purinergic P1; Theophylline; Tumor Cells, Cultured; Xanthines