Testosterone Signaling through Internalizable Surface Receptors in Androgen Receptor-free Macrophages

Abstract

Testosterone acts on cells through intracellular transcription-regulating androgen receptors (ARs). Here, we show that mouse IC-21 macrophages lack the classical AR yet exhibit specific nongenomic responses to testosterone. These manifest themselves as testosterone-induced rapid increase in intracellular free [Ca(2+)], which is due to release of Ca(2+) from intracellular Ca(2+) stores. This Ca(2+) mobilization is also inducible by plasma membrane-impermeable testosterone-BSA. It is not affected by the AR blockers cyproterone and flutamide, whereas it is completely inhibited by the phospholipase C inhibitor U-73122 and pertussis toxin. Binding sites for testosterone are detectable on the surface of intact IC-21 cells, which become selectively internalized independent on caveolae and clathrin-coated vesicles upon agonist stimulation. Internalization is dependent on temperature, ATP, cytoskeletal elements, phospholipase C, and G-proteins. Collectively, our data provide evidence for the existence of G-protein-coupled, agonist-sequestrable receptors for testosterone in plasma membranes, which initiate a transcription-independent signaling pathway of testosterone.

Membrane androgen receptor activation in prostate and breast tumor cells: Molecular signaling and clinical impact

“…Three classes of mAR ligands have been reported to date and include natural androgen steroids such as testosterone and DHT (8,9,19,22), albumin conjugated steroids (8,9,19,22) and the less well characterized class of flavonol compounds comprising catechin, epicatechin, and their oligomers (47). Although current clinical practice precludes use of testosterone for the treatment of prostate tumors because of its tumor promoting action via the iAR pathway, albumin conjugated androgens are reasonably expected to initiate only mAR-dependent effects in cells.…”

“…Most recently, membrane androgen receptors transmitting rapid androgen signals have been characterized biochemically in several cell types including macrophages and T cells (8,19), LNCaP (9), T47D (15), MCF7 (20), DU145 (21), C6 (22), PC12 (23), or VSMC cells (24). Signals emanating from this receptor result in increased intracellular [Ca 21 ] and inositol 1,4,5-triphosphate formation, cannot be blocked by anti-androgens (9,25) and are sensitive to pertussis toxin inhibition indicating that mAR may actually be a GPCR (14)(15)(16).…”

Shape bistability of a membrane neck: A toggle switch to control vesicle content release

“…One of the most intriguing findings is the pore ''flicker,'' fluctuations of the pore conductance between high and low level (17,(19)(20)(21). IC-21 cells, capable of endocytosis and phagocytosis (22,23), can form relatively large endocytic granules, close in size to the smallest end-ring in the BLM system. On IC-21 cells, a small (several micrometers in diameter) patch of the plasma membrane of an individual cell was electrically isolated inside a micropipette (Fig.…”

Androgen decreases osteoprotegerin expression in prostate cancer cells

“…Steroids can induce a response in cells lacking classical steroid receptors, such as mouse T lymphocytes and the murine macrophage/ monocyte cell lines RAW 264.7 and IC-21, through a mode of action that may involve binding at the plasma membrane. [29][30][31][32][33][34] In both LNCaP-FGC and PC-3 ARÀ cell lines, testosterone has been shown to have actions at the plasma membrane that are independent of the intracellular AR. [33][34][35][36] Furthermore, we analyzed 5 kb of the promoter sequence directly upstream of the OPG coding sequence using several transcription factor binding site software algorithms (MatchTM, P-Match, TFBIND and Alibaba 2.1), none of which revealed a putative AR binding site.…”