RAC3 more than a nuclear receptor coactivator: a key inhibitor of senescence that is downregulated in aging.

Receptor-associated coactivator 3 (RAC3) is a nuclear receptor coactivator usually overexpressed in tumors that exerts oncogenic functions in the cytoplasm and the nucleus. Although as part of its oncogenic actions it was previously identified as an inhibitor of apoptosis and autophagy, its expression is required in order to preserve the pluripotency and embryonic stem cell self-renewal. In this work we investigated its role in cellular senescence. We found that RAC3 overexpression in the nontumoral HEK293 cells inhibits the premature senescence induced by hydrogen peroxide or rapamycin. The mechanism involves not only the inhibition of autophagy early induced by these stimuli in the pathway to senescence, but also the increase in levels and nuclear localization of both the cell cycle suppressors p53/p21 and the longevity promoters FOXO1A, FOXO3A and SIRT1. Furthermore, we found that RAC3 overexpression is required in order to maintain the telomerase activity. In tumoral HeLa cells its activity was inhibited by depletion of RAC3 inducing replicative senescence. Moreover, we demonstrated that in vivo, levels of RAC3 are downregulated in the liver from aged as compared with young rats, whereas the levels of p21 are increased, correlating with the expected senescent cell contents in aged tissues. A similar downregulation of RAC3 was observed in the premature and replicative senescence of human fetal WI-38 cells and premature senescence of hepatocyte HepG2 cell line. Taken together, all these results demonstrate that RAC3 is an inhibitor of senescence whose downregulation in aged individuals could be probably a tumor suppressor mechanism, avoiding the clonal expansion of risky old cells having damaged DNA.

Two immunomodulators, curcumin and sulfasalazine, enhance IDV antiretroviral activity in HIV-1 persistently infected cells.

Since the appearance of resistance to antiretroviral treatment is unavoidable, the host cell's transcription factor NF-kappaB is a novel HIV target. The goal of this study was to characterize the effect of two immunomodulators, curcumin (Cur) and sulfasalazine (Sul), with a protease inhibitor, indinavir (IDV), on HIV-1 persistently infected CD4+ T-cells. Viral p24 antigen production, viral infectivity (tested on MAGI cells) and viral relative infectivity (viral infectivity/p24) were analysed. When used alone, both immunomodulators were able to reduce viral infectivity. When in combination, both 10 microM IDV plus 10 microM Cur and 10 microM IDV plus 250 microM Sul showed a significant reduction in viral infectivity and viral relative infectivity when compared to the reduction produced by IDV alone. Thus, the use of immunomodulators with IDV could help to reduce HIV-1 production in persistently infected cells.

Viral reactivation and pseudotype production in an in vitro superinfection system with two different strains of HIV-1.

Viral production and variability of HIV-1 is normally high in vivo causing the necessary conditions for cellular superinfection. In order to evaluate the superinfection dynamics in vitro, H9HTLVIIIB cell line was superinfected with HIVMN. Superinfected cells showed nearly 50% cell mortality at day 1 post-superinfection (ps), which increased significantly up to day 4 ps. Superinfecting genome was detectable until day 10 ps. The superinfecting strain was found in the supernatant only on day 1 ps, but was recovered up to day 4 ps by coculture with non-infected cells. The existing strain (HIVHXB2) was recovered throughout the studied period. Pseudotype formation by the HIVHXB2 genome and envelope proteins of the superinfecting strain (HIVMN) was observed from day 1 to 6 ps. Viral production was increased by 1.7 LOG in superinfected cells from day 1 ps. Both viral production increase and pseudotype formation could be relevant for HIV pathogenesis in vivo.

Oxytocin and prostaglandins F2alpha and E2 do not enhance HIV antigen production in vitro.

Oxytocin and prostaglandins (PGs) are hormones involved in labor and are used clinically for its induction. In this study the effect of oxytocin, PGF(2alpha), and PGE(2) on Humour immunodeficiency virus-1 production in acutely and persistently infected cells was measured. No significant effect on p24 antigen production was found with oxytocin or PGs, except for a transient decrease in persistently infected cells treated with 1 micro M PGF(2alpha). These results showed that oxytocin and PGs could be used clinically for labor induction without any direct enhancement in viral production. Besides, the results with PGF(2alpha) at the highest concentration studied may indicate a pharmacological effect.