We have performed several lines of experiments to examine the interactions between the endocrine and immune systems particularly by focusing on viral infection, including that by the human immunodeficiency syndrome type-1 (HIV-1), cytomegalovirus (CMV) or Newcastle disease (NDV) virus. Viruses are known as potent activators and modulators of the host immune and endocrine systems, influencing hormonal actions in host tissues, such as leukocytes, adipose tissue and skeletal muscles. These effects may further contribute to viral expansion and pathogenesis. Indeed, we demonstrated that HIV-1 accessory protein Vpr enhances GR transcriptional activity, whereas it suppresses PPAR-gamma and -delta activity, playing a potentially important role in the development of the characteristic AIDS-associated lipodystrophy and insulin-resistance syndrome. This viral protein can be found in sera of the AIDS patients and changes activity of the cells uninfected by the HIV-1 virus, such as hepatocytes and adipocytes, by penetrating their cell membrane. In this fiscal year, we published one manuscript demonstrating impact of Vpr on intermediary metabolism by employing transgenic mice specifically expressing Vpr in adipose tissue and liver, and those implanted with the Alzt pump, which releases a synthetic Vpr peptide into circulation. We found that both mice demonstrated accelerated whole-body lipolysis, hyperglycemia and hypertriglyceridemia. In the liver, they developed severe steatosis with blunted expression of the PPAR-responsive genes and increased expression of GR target genes. Similar to human HIV-infected patients, Vpr circulated in the serum of Vpr-transgenic mice. Vpr blocked differentiation in preadipocytes through cell cycle arrest, whereas in mature adipocytes, it increased lipolysis with reciprocally altered binding of PPARgamma and GR to their recognition DNA sequences in respective target gene promoters. These results thus indicate that Vpr regulates activities of these nuclear receptors in vivo, and most likely, contributes to the development of AIDS-associated lipodystrophy and insulin-resistance syndrome in AIDS patients. In dendritic cells (DCs), which play a central role in the recognition and presentation of viral antigens, infection of CMV or NDV, and perhaps HIV-1, causes dramatic changes in the expression of a group of nuclear hormone receptors, including the glucocorticoid and estrogen receptors, as well as of several transcriptional co-regulators, including p300 and p160-type histone acetyltransferase coactivators, possibly altering secretion/production of interferons and other cytokines by these cells. Since NOR1, one member of NR4A group nuclear receptors, was the most highly regulated NR upon viral infection in DCs, we obtained NOR1 knockout mice from Dr. Conneely, the Baylor Collage of Medicine, and have examined impact of pathogen infection to the action of DCs purified from NOR1 knockout mice. DCs from these mice showed a significant defect in the response of interleukin (IL)-12 to viral infection compared to those from wild type mice, while NOR-1 stimulated the IL-12 p40 promoter activity through its DNA response elements in reporter assays. NOR-1 knockout mice demonstrated significant reduction of IL-12 production against infection of Toxoplasma gondii, a protozoa against which IL-12 acts as an essential component for host defense. We are currently examining details of molecular regulation of NOR-1 on IL-12 production both in cellular and animal systems. In the same line of experiments, we found that CMV and NDV stimulated IL-10 expression in DCs, and glucocorticoids further potentiated such virus-induced expression of this cytokine. Since IL-10 inhibits synthesis of pro-inflammatory cytokines and has ability to suppress antigen presentation by DCs and monocytes, synergistic activation of IL-10 by glucocorticoids may explain why exposure to stress and subsequent activation of the HPA axis increases susceptibility to viral infection, and possibly, subsequent development of viral-associated disorders, such as asthma, atherosclerosis and cancers. We found that viral infection activated the extracellular signal-regulated kinase (ERK), a member of the mitogen-activated protein kinase family, which in turn phosphorylated the human GR at serine located at amino acid position 211 and enhanced the transcriptional activity of GR on the IL-10 promoter.
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