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

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.

Enhanced expression in spleen macrophages of the mouse homolog to the human putative tumor suppressor gene ZFM1.

We have characterized the cDNA of MZFM, the mouse homolog to the novel human putative tumor suppressor gene ZFM1. The total length of the cDNA is 2,637 nucleotides with an open reading frame for a protein of 548 amino acids containing 4.7% methionine and 17.2% proline. The predicted molecular mass of 59 kD fits the 62-kD band experimentally determined by NaDodSO4-PAGE from in vitro translation products of in vitro-transcribed MZFM cDNA. The MZFM cDNA best matches to that ZFM1-isoform without the so-called 0.25-kb E-domain and to the L49345 cDNA recently identified in a human leukemia cell line. Northern analysis reveals expression of MZFM only in spleen macrophages. Reverse transcription polymerase chain reaction (RT-PCR) in combination with Southern analysis also detects a low basal expression in splenic T cells and B cells, as well as in other tissues such as heart, kidney, brain, liver, testis, bone marrow, adrenal gland, lymph nodes, pancreas, and thymus. In splenic macrophages, MZFM mRNA is alternatively spliced yielding a 3.6-kb transcript with E-domain, a 3.0-kb transcript without E-domain, and a 2.7-kb transcript with E-domain. The predicted MZFM protein contains diverse functional domains, i.e., a nuclear localization signal, a metal binding motif, a glutamine/proline stretch, proline-clusters, a CGA-motif, and a QUA1-KH-QUA2 region, thus indicating multiple functions of MZFM. Presumably, MZFM is a new member of those proteins combining features of signal transduction and RNA activation (STAR-proteins). The different MZFM-isoforms may be part of a macrophage-inherent program of transduction of environmental signals into different activational states of macrophages.

Genomic organization of mouse gene zfp162.

We report the cloning and characterization of the alternatively spliced mouse gene zfp162, formerly termed mzfm, the homolog of the human ZFM1 gene encoding the splicing factor SF1 and a putative signal transduction and activation of RNA (STAR) protein. The zfp162 gene is about 14 kb long and consists of 14 exons and 13 introns. Comparison of zfp162 with the genomic sequences of ZFM1/SF1 revealed that the exon-intron structure and exon sequences are well conserved between the genes, whereas the introns differ in length and sequence composition. Using fluorescent in situ hybridization, the zfp162 gene was assigned to chromosome 19, region B. Screening of a genomic library integrated in lambda DASH II resulted in the identification of the 5'-flanking region of zfp162. Sequence analysis of this region showed that zfp162 is a TATA-less gene containing an initiator control element and two CCAAT boxes. The promoter exhibits the following motifs: AP-2, CRE, Ets, GRE, HNF5, MRE, SP-1, TRE, TCF1, and PU.1. The core promoter, from position -331 to -157, contains the motifs CRE, SP-1, MRE, and AP-2, as determined in transfected CHO-K1 cells and IC-21 cells by reporter gene assay using a secreted form of human placental alkaline phosphatase. The occurrence of PU.1/GRE supports the view that the zfp162 gene encodes a protein involved not only in nuclear RNA metabolism, as the human ZFM1/SF1, but also in as yet unknown macrophage-inherent functions.

Functional testosterone receptors in plasma membranes of T cells.

T cells are considered to be unresponsive to testosterone due to the absence of androgen receptors (AR). Here, we demonstrate the testosterone responsiveness of murine splenic T cells in vitro as well as the presence of unconventional cell surface receptors for testosterone and classical intracellular AR. Binding sites for testosterone on the surface of both CD4(+) and CD8(+) subsets of T cells are directly revealed with the impeded ligand testosterone-BSA-FITC by confocal laser scanning microscopy (CLSM) and flow cytometry, respectively. Binding of the plasma membrane impermeable testosterone-BSA conjugate induces a rapid rise (<5 s) in [Ca2+]i of Fura-2-loaded T cells. This rise reflects influx of extracellular Ca2+ through non-voltage-gated and Ni2+-blockable Ca2+ channels of the plasma membrane. The testosterone-BSA-induced Ca2+ import is not affected by cyproterone, a blocker of the AR. In addition, AR are not detectable on the surface of intact T cells when using anti-AR antibodies directed against the amino and carboxy terminus of the AR, although T cells contain AR, as revealed by reverse transcription-polymerase chain reactions and Western blotting. AR can be visualized with the anti-AR antibodies in the cytoplasm of permeabilized T cells by using CLSM, though AR are not detectable in cytosol fractions when using the charcoal binding assay with 3H-R1881 as ligand. Cytoplasmic AR do not translocate to the nucleus of T cells in the presence of testosterone, in contrast to cytoplasmic AR in human cancer LNCaP cells. These findings suggest that the classical AR present in splenic T cells are not active in the genomic pathway. By contrast, the cell surface receptors for testosterone are in a functionally active state, enabling T cells a nongenomic response to testosterone.