Intracellular leucine-rich alpha-2-glycoprotein-1 competes with Apaf-1 for binding cytochrome c in protecting MCF-7 breast cancer cells from apoptosis.

Leucine-rich alpha-2-glycoprotein-1 (LRG1) has been shown to compete with apoptosis activating factor-1 (Apaf-1) for binding cytochrome c (Cyt c) and could play a role in inhibition of apoptosis. Employing MCF-7 breast cancer cells, we report that intracellular LRG1 does protect against apoptosis. Thus, cells transfected with the lrg1 gene and expressing higher levels of LRG1 were more resistant to hydrogen peroxide-induced apoptosis than parental cells, while cells in which LRG mRNA was knocked down by short hairpin (sh) RNA-induced degradation were more sensitive. The amount of Cyt c co-immunoprecipitated with Apaf-1 from the cytosol of apoptotic cells was inversely related to the level of LRG1 expression. In lrg1-transfected cells partially-glycosylated LRG1 was found in the cytosol and there was an increase in cytosolic Cyt c in live lrg1-transfected cells relative to parental cells. However, apoptosis was not spontaneously induced because Cyt c was bound to LRG1 and not to Apaf-1. Cyt c was the only detectable protein co-immunoprecipitated with LRG1. Following hydrogen peroxide treatment degradation of LRG1 allowed for induction of apoptosis. We propose that intracellular LRG1 raises the threshold of cytoplasmic Cyt c required to induce apoptosis and, thus, prevents onset of the intrinsic pathway in cells where Cyt c release from mitochondria does not result from committed apoptotic signaling. This mechanism of survival afforded by LRG1 is likely to be distinct from its extracellular survival function that has been reported by several research groups.

Persistence of Kaposi sarcoma-associated herpesvirus (KSHV)-infected cells in KSHV/HIV-1-coinfected subjects without KSHV-associated diseases.

Inguinal lymph nodes from 24 human immunodeficiency virus (HIV) type 1-infected subjects without Kaposi sarcoma-associated herpesvirus (KSHV)-associated diseases were examined for KSHV infection. KSHV-infected cells were detected at a very low frequency in the lymph nodes of 7 subjects (median frequency, 2 infected cells/10(7) lymph node cells). Latent, but not lytic, KSHV gene expression was detected and KSHV-infected cells were located in B cell-rich areas of lymph node follicles. These findings provide evidence that, in the absence of KSHV-associated diseases, latent infection of lymph node cells provides a mechanism for the persistence of KSHV in KSHV/HIV-1-coinfected persons.

Lymphatic dysfunction in transgenic mice expressing KSHV k-cyclin under the control of the VEGFR-3 promoter.

Kaposi sarcoma-associated herpesvirus (KSHV) infects endothelial cells within KS tumors, and these cells express the KSHV latent-cycle gene k-cyclin (kCYC) as well as vascular endothelial growth factor receptor 3 (VEGFR-3), a marker for lymphatic endothelium. To further understand KSHV-mediated pathogenesis, we generated transgenic mice expressing kCYC under the control of the VEGFR-3 promoter. kCYC mRNA and functional protein expression within tissue correlated with VEGFR-3 expression and were most abundantly detected within lung tissue. Clinically, most transgenic mice died within 6 months of age secondary to progressive accumulation of chylous pleural fluid. In skin, edema was detected by magnetic resonance imaging and mice demonstrated persistent erythema of the ears following trauma. Histologically, erythematous skin showed extravasation of erythrocytes and accumulation of erythrocytes within lymphatic lumens. In addition, lymphatic drainage of injected contrast dyes was markedly impaired in transgenic mice. Karyomegaly, a feature observed in kCYC-expressing cells in vitro, was detected in many tissues, and selectively occurred within lymphatic endothelial cells expressing kCYC mRNA by in situ hybridization. In summary, kCYC expression within VEGFR-3+ cells of mice causes marked impairment of lymphatic function. kCYC may contribute to the development of certain clinical and histologic features of KS, including localized edema and retention of extravasated erythrocytes within KS tumors.

A pilot study of cidofovir in patients with kaposi sarcoma.

A clinical trial was conducted to test the activity of cidofovir (CDV), a drug with in vitro activity against Kaposi sarcoma (KS)-associated herpesvirus (KSHV), in KS. Five patients with human immunodeficiency virus-associated KS (4 receiving antiretroviral therapy) and 2 patients with classical KS were administered CDV (5 mg/kg/dose) weekly for 2 weeks and then every other week. All 7 patients had progression of their KS at a median of 8.1 weeks (range, 5-27 weeks). Skin biopsy specimens of KS lesions showed no change in expression of latent or early lytic genes, but, in the 1 assessable patient, there was decreased expression of a late lytic gene. There was no decrease in the virus load of KSHV in peripheral blood mononuclear cells. This study does not provide proof of principle for the treatment of KS with CDV. However, it remains possible that antiherpesvirus therapy can be developed for herpes-induced tumors.