Differential effect of the immunomodulatory hormone somatostatin on replication of human immunodeficiency virus type 1 in CD4+ and CD8+ T lymphocytes

Measles virus modulates human T-cell somatostatin receptors and their coupling to adenylyl cyclase

The possible role of immunomodulatory peptide somatostatin (SRIF) in measles virus (MV)-induced immunopathology was addressed by analysis of SRIF receptors and their coupling to adenylyl cyclase in mitogen-stimulated Jurkat T cells and human peripheral blood mononuclear cells (PBMC). SRIF-specific receptors were assayed in semipurified membrane preparations by using SRIF14 containing iodinated tyrosine at the first position in the amino acid chain ([125I]Tyr1) as a radioligand. A determination of receptor number by saturation of radioligand binding at equilibrium showed that in Jurkat cells, MV infection led to a dramatic decrease in the total receptor number. The virus-associated disappearance of one (Ki2 = 12 +/- 4 nM [mean +/- standard error of the mean [SEM]]; n = 4) of two somatostatin binding sites identified in control Jurkat cells (Ki1 = 78 +/- 3 pM and Ki2 = 12 +/- 4 nM [mean +/- SEM]; n = 4) was also observed. Almost identical results were obtained for phytohemagglutinin-activated human PBMC. In the absence of MV infection, two somatostatin binding sites were present (Ki1 = 111 +/- 31 pM and Ki2 = 17 +/- 2 nM [mean +/- SEM]; n = 2), whereas in MV-infected cells, only the high-affinity (Ki1 = 48 +/- 15 pM [mean +/- SEM]; n = 2) binding site remained. In addition, MV infection reinforced the inhibitory effects of SRIF on adenylyl cyclase activity, since maximal inhibition at 1 microM peptide was 11% +/- 4% in control cells versus 25% +/- 3% (P < 0.05) in infected Jurkat cells. Moreover, MV infection severely impaired the capacity of adenylyl cyclase to be activated directly (by forskolin) or indirectly (via Gs protein-coupled vasoactive intestinal peptide receptor). An assessment of [methyl-3H]thymidine incorporation showed that SRIF increased proliferative responses to mitogens only in control cells, not in MV-infected cells. Altogether, our data emphasize that MV-associated alteration of SRIF transduction appears to be related to the loss of SRIF-dependent increase of mitogen-induced proliferation.

Endocrine implications of human immunodeficiency virus infection

Endocrine abnormalities occur frequently in HIV-infected patients. Although the majority of endocrine disorders reflect chronic infection, stress, and malnutrition, some disorders are characteristic of HIV infection or AIDS and deserve particular clinical attention. Identification of HIV patients at risk of frank endocrine disorders, rapid and correct diagnosis, and appropriate management are essential steps to minimize morbidity and mortality. Finally, increasing evidence from in vitro studies suggests that various hormones may influence HIV replication as well as the course of HIV disease and associated disorders. Future studies on the molecular mechanisms of hormones on HIV action and clinical studies on the effects of hormones as adjunctives to established forms of therapy may stimulate development of novel therapeutic strategies that will benefit HIV-infected patients.

Expression of the somatostatin gene in human astrocytoma cell lines

Somatostatin (somatotropin release-inhibiting hormone; SRIH) has been demonstrated in neurons of the central nervous system (CNS) as well as in endocrine cells of the pancreas and gastrointestinal tract and can suppress various immune functions including lymphocyte proliferation, immunoglobulin synthesis, and cytokine production. Since astrocytes possess antigen-presenting activity and can secrete a wide array of immunoregulatory and inflammatory cytokines, we studied SRIH gene expression in both astrocyte cell lines and mitogen-stimulated peripheral blood mononuclear leukocytes from healthy donors. We now report by means of a complementary DNA-based reverse transcription PCR that differential levels of SRIH mRNA were expressed in 9 of 11 human astrocytoma cell lines tested but were undetectable in activated peripheral blood mononuclear leukocytes as well as in a variety of human lymphocyte and monocyte cell lines. The synthesis and secretion of SRIH protein by astrocytoma cells that expressed SRIH transcripts were confirmed by specific radioimmunoassay of cell culture fluids. These findings support the notion that SRIH gene expression occurs in human astrocytoma cells but not in mature lymphoid cells of the immune system.