HIV-1 NL4-3, but not IIIB, inhibits JAK3/STAT5 activation in CD4(+) T cells

HIV-1 infection leads to T cell dysfunction and apoptosis in vivo and in vitro. The shared common gamma chain of IL-2R and its associated Janus kinase, JAK3, are indispensable for normal T cell function and survival. We have reported that CD4 ligation with HIV gp120 inhibits T cell receptor-induced activation and expression of JAK3. We have also shown that while some strains of HIV-1, such as NL4-3, induce apoptosis of infected CD4(+) T cells, other strains, such as HIV-1 IIIB, do not. Interestingly, we show here that infection of CD4(+) T cells with HIV-1 NL4-3, but not IIIB, inhibited activation and expression of JAK3. NL4-3-infected T cells were unable to upregulate JAK3 expression following stimulation through TCR/CD3. In addition, NL4-3, but not IIIB, inhibited tyrosine phosphorylation and expression of STAT5, a downstream target of JAK3. These data suggest a correlation between apoptosis of HIV-1-infected T cells and inhibition of the JAK3/STAT5 activation pathway.

Cutting edge: JAK3 activation and rescue of T cells from HIV gp120-induced unresponsiveness

In early HIV disease, immunodeficiency is characterized by the inability of CD4+ T cells to produce a critical cytokine, IL-2, and to express the receptor for IL-2 (IL-2R) in response to antigenic or mitogenic stimulation. The shared common gamma-chain (gamma(c)) of IL-2R and its associated Janus kinase, JAK3, are indispensable for normal T cell function. Here, we show that the inhibition of IL-2R expression and proliferation induced by ligation of CD4 by HIV envelope glycoprotein, gp120, is correlated with inhibition of expression and activation of JAK3. Stimulation through the gamma(c)-related cytokine receptors restores JAK3 expression and activation and rescues CD4-mediated T cell unresponsiveness. Collectively, these data argue that inhibition of JAK3 expression and activation may, in part, explain the T cell dysfunction seen in early HIV disease. In addition, rescue from gp120-mediated T cell unresponsiveness by activation of JAK3 suggests a novel therapeutic approach for enhancing immune function in HIV disease.

Proteolytic cleavage of alpha-actinin by calpain in T cells stimulated with anti-CD3 monoclonal antibody

Stimulation of the TCR/CD3 complex on T cells initiates rearrangement of the actin cytoskeleton. The results presented show that a temporal increase in the appearance of filamentous actin begins immediately after stimulation of T cells with immobilized anti-CD3 mAb. The formation of filamentous actin in these stimulated cells reaches a steady state within 30 min after anti-CD3 mAb stimulation. At this time, pseudopod formation is observed and becomes progressively more evident over the next several hours. Experiments were done to investigate the role of the actin cytoskeletal associated proteins, alpha-actinin, vinculin, and talin, in the assembly of the actin cytoskeleton in anti-CD3 mAb-stimulated T cells. Using immunofluorescence, these three proteins are detected throughout the cytosol in resting T cells. However, after anti-CD3 mAb stimulation of the T cells, these proteins move to one pole of the cell. Electrophoresis followed by immunoblotting of T cell lysates prepared from resting as well as anti-CD3 mAb-stimulated cells revealed that alpha-actinin, but not vinculin or talin, was modified as a consequence of cell activation. Results show that alpha-actinin exists as a 105-kDa subunit in resting T cells, but that anti-CD3 mAb stimulation of T cells leads to the appearance of an 80-kDa lower molecular form of alpha-actinin. Experiments show that this occurs as a consequence of the 105-kDa subunit being proteolytically cleaved by calpain.

Proteolytic cleavage of alpha-actinin by calpain in T cells stimulated with anti-CD3 monoclonal antibody

Stimulation of the TCR/CD3 complex on T cells initiates rearrangement of the actin cytoskeleton. The results presented show that a temporal increase in the appearance of filamentous actin begins immediately after stimulation of T cells with immobilized anti-CD3 mAb. The formation of filamentous actin in these stimulated cells reaches a steady state within 30 min after anti-CD3 mAb stimulation. At this time, pseudopod formation is observed and becomes progressively more evident over the next several hours. Experiments were done to investigate the role of the actin cytoskeletal associated proteins, alpha-actinin, vinculin, and talin, in the assembly of the actin cytoskeleton in anti-CD3 mAb-stimulated T cells. Using immunofluorescence, these three proteins are detected throughout the cytosol in resting T cells. However, after anti-CD3 mAb stimulation of the T cells, these proteins move to one pole of the cell. Electrophoresis followed by immunoblotting of T cell lysates prepared from resting as well as anti-CD3 mAb-stimulated cells revealed that alpha-actinin, but not vinculin or talin, was modified as a consequence of cell activation. Results show that alpha-actinin exists as a 105-kDa subunit in resting T cells, but that anti-CD3 mAb stimulation of T cells leads to the appearance of an 80-kDa lower molecular form of alpha-actinin. Experiments show that this occurs as a consequence of the 105-kDa subunit being proteolytically cleaved by calpain.

cAMP accumulation in T-cells inhibits anti-CD3 monoclonal antibody-induced actin polymerization

The results presented in this report offer a novel explanation for how stimulation of the beta-adrenergic receptor (beta AR) inhibits the ability of T cells to proliferate after interaction with immobilized anti-CD3 monoclonal antibody (mAb). Accordingly, T cells binding to immobilized anti-CD3 mAb but not anti-CD4 mAb undergo time-dependent F-actin assembly with concomitant formation of pseudopodia. This process is completely inhibited in the presence of isoproterenol (ISO) indicating that stimulation of the beta AR on T cells interferes with the biochemical processes responsible for the assembly of actin. To confirm these observations, we quantitated the formation of F-actin in T cells stimulated with immobilized anti-CD3 mAb in the presence of cAMP elevating agents. The results show that stimulation of the beta AR on T-cells, as well as the addition of forskolin or dibutyryl cAMP, abrogates the formation of F-actin.

Prognostic significance of proliferation associated nucleolar antigen P120 in human breast carcinoma

Nucleolar antigen P120 is detected in rapidly proliferating cells but not in normal resting cells or in many benign and slowly growing malignant tumors. The objective of the study was to determine whether the expression of P120 in breast cancer correlated with histopathological or biological properties associated with prognosis. In this retrospective study, 120 primary breast tumors were analyzed for P120; 114 of these tumors were also stained for the erbB-2 protein. Immunopositive staining was correlated with patient survival, nodal status, estrogen receptor levels, and number of mitoses. Sixty-nine % (83 of 120) of the tumors were positive for P120; 25% (28 of 114) stained positively for erbB-2. Of the 28 erbB-2 positive tumors 26 were also positive for the P120 protein. Forty-six % (55 of 120) of the specimens were from patients who later died from recurrent breast cancer; P120 was detected in 89% (49 of 55) of these specimens. In 52% of the survivors the P120 protein was also expressed. P120 negative tumors were highly correlative with survival (P = 0.0001); 84% (32 of 37) of patients with P120 negative tumors survived more than 7 years without evidence of recurrent disease. Multivariate analysis showed that the worst prognosis was for patients who had tumor positive nodes and expressed P120 (P = 0.0001); death occurred in 73% (30 of 41) of these patients. For the node negative patients who did not express P120, 5-year survival was 90% (19 of 21 patients); 5-year survival for the node negative patients who expressed P120 was significantly less (67%; 28 of 42 patients). Patients with P120 negative tumors had a good prognosis, irrespective of their nodal status. In this group, survival of node negative patients was 86% (18 of 21) and for those with positive nodes survival was 82% (13 of 16). A poor prognosis was found for patients with intense erbB-2 stained tumors (5 of 7 patients died). Weak staining of erbB-2 tumors (21 specimens) was not correlated with patient survival. Compared to P120 negative tumors, P120 positive tumors had greater numbers of mitoses (9.06 versus 6.65) and an almost 2-fold increase in the occurrence of positive nodes (one of every 4.67 versus one of every 8.81). The number of P120 positive tumors was greater in estrogen receptor positive tumors (75%) than in estrogen negative tumors (54%).(ABSTRACT TRUNCATED AT 250 WORDS)