Testosterone signaling through internalizable surface receptors in androgen receptor-free macrophages

Testosterone acts on cells through intracellular transcription-regulating a ndrogen receptors (ARs). Here, we show that mouse IC-21 macrophages lack th e classical AR yet exhibit specific non-genomic responses to testosterone. These manifest themselves as testosterone-induced rapid increase in intrace llular free [Ca2+], which is due to release of Ca2+ from intracellular Ca2 stores. This Ca2+ mobilization is also inducible by plasma membrane-imperm eable testosterone-BSA. It is not affected by the AR blockers cyproterone a nd flutamide, whereas it is completely inhibited by the phospholipase C inh ibitor U-73122 and pertussis toxin. Binding sites for testosterone are dete ctable on the surface of intact IC-21 cells, which become selectively inter nalized independent on caveolae and clathrin-coated vesicles upon agonist s timulation. Internalization is dependent on temperature, ATP, cytoskeletal elements, phospholipase C, and G-proteins. Collectively, our data provide e vidence for the existence of G-protein-coupled, agonist-sequestrable recept ors for testosterone in plasma membranes, which initiate a transcription-in dependent signaling pathway of testosterone.