Human breast cancer cell line MDA-MB-231 expresses endogenous A2B adenosine receptors mediating a Ca2+ signal

1 Two human breast cancer cell lines, MCF-7 and MDA-MB-231, were screened for the presence of functionally significant adenosine receptor subtypes. 2 MCF-7 cells did not contain adenosine receptors as judged by the lack of an effect of nonselective agonists on adenylyl cyclase activity or intracellular Ca(2+) levels. MDA-MB-231 cells showed both a stimulation of adenylyl cyclase and a PLC-dependent increase in intracellular Ca(2+) in response to nonselective adenosine receptor agonists. 3 Both adenosine-mediated responses in MDA-MB-231 cells were observed with the nonselective agonists 5'-N-ethylcarboxamidoadenosine (NECA) and 2-(3-hydroxy-3-phenyl)propyn-1-yladenosine-5'-N-ethyluronamide (PHPNECA), but no responses were observed with agonists selective for A(1), A(2A) or A(3) adenosine receptors. The Ca(2+) signal was antagonized by 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) and the nonselective antagonist 9-ethyl-8-furyladenine (ANR 152), but not by A(2A) or A(3) selective compounds. 4 In radioligand binding with [2-(3)H](4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol) ([(3)H]ZM 241385), a specific binding site with a K(D) value of 87 nM and a B(max) value of 1600 fmol mg(-1) membrane protein was identified in membranes from MDA-MB-231 cells. 5 The pharmacological characteristics provide evidence for the expression of an A(2B) adenosine receptor in MDA-MB-231 cells, which not only mediates a stimulation of adenylyl cyclase but also couples to a PLC-dependent Ca(2+) signal, most likely via G(q/11). The A(2B) receptor in such cancer cells may serve as a target to control cell growth and proliferation. 6 The selective expression of high levels of endogenous A(2B) receptors coupled to two signaling pathways make MDA-MB-231 cells a suitable model for this human adenosine receptor subtype.