Sara Dovrat

Role of Protein Kinase C δ in Reactivation of Kaposi's Sarcoma-Associated Herpesvirus

ABSTRACT TPA (12-O-tetradecanoylphorbol-13-acetate), a well-known activator of protein kinase C (PKC), can experimentally induce reactivation of Kaposis sarcoma-associated herpesvirus (KSHV) in certain latently infected cells. We selectively blocked the activity of PKC isoforms by using GF 109203X or rottlerin and demonstrated that this inhibition largely decreased lytic KSHV reactivation by TPA. Translocation of the PKCδ isoform was evident shortly after TPA stimulation. Overexpression of the dominant-negative PKCδ mutant supported an essential role for the PKCδ isoform in virus reactivation, yet overexpression of PKCδ alone was not sufficient to induce lytic reactivation of KSHV, suggesting that additional signaling molecules participate in this pathway.

Inhibition of Inflammatory Cytokine Secretion by Plant-Derived Compounds Inuviscolide and Tomentosin: The Role of NFκB and STAT1~!2010-02-10~!2010-06-28~!2010-08-12~!

The plant Inula viscosa has been shown to possess many important medicinal benefits, including anti-inflammatory, anti-oxidant, anti-bacterial, and anti-fungal activities, but the plant metabolites that mediate these effects and their mechanism of action are poorly understood. In a previous study, we demonstrated a reduced expression of the p65 subunit of nuclear factor kappa B (NFB) in melanoma cells treated with the purified sesquiterpene lactone compounds, Inuviscolide (Inv) and Tomentosin (Tom), extracted from Inula viscosa leaves. In this study, we tested the in- vitro effect of these purified compounds on the secretion of pro-inflammatory cytokines from human peripheral blood mononuclear cells (PBMCs) upon stimulation with lipopolysaccharide (LPS) or phorbol myristate acetate (PMA). Their possible mechanism of action was also studied. The results showed that both agents caused decreased production of IL-2, IL-1� , IFN� , and slightly increased secretion of TNF� , whereas secretion of IL-6 was not affected. The elevated levels of TNFdid not appear to affect the viability of human PBMCs. Western blot analysis revealed a reduction in the protein level of both the transcription factor component p65/RelA of nuclear factor-� B (NF B) and the signal transducer and activator of transcription 1 (STAT1) through proteosomal degradation. However, no change was observed in the expression level of the nuclear factor-� B component, p50 (NF B), or the signal transducer and activator of transcription 3 (STAT3). Taken together, our results indicate the possible future use of these agents as an anti-inflammatory treatment in cases where overstimulation of cytokine secretion is the basis for the pathological symptoms.

Unique natural antioxidants (NAOs) and derived purified components inhibit cell cycle progression by downregulation of ppRb and E2F in human PC3 prostate cancer cells.

Prostate cancer (PCA) is the leading cause of cancer mortality among older men in Western countries. Epidemiological studies have shown correlation between a lower risk of PCA and a higher consumption of antioxidants. However, the mechanism by which antioxidants exert their effects is still unknown. In the present study, we explored the signaling mechanism through which unique natural antioxidant derived from spinach extract (NAO) exerts their beneficial effects in the chemoprevention of PCA using human PC3 cells. Probing into the effect of NAO and its derived polyphenols on cell‐cycle G1 arrest, we found that they cause cell‐cycle prolongation. NAO and its two derived purified components exhibited a significant increase in the level of p21cip1 expression after 36 h of starvation, followed by 18 h of treatment with NAO in the presence of serum. In addition, under similar conditions, the expressed level of Cyclin A and CDK‐2 in the PC3 cells was significantly reduced after treatment with NAO or its purified components. Immunoblot analysis demonstrated a significant increase in the hypophosphorylated form of pRb and a decrease in ppRb. NAO and its purified derived components were found to downregulate the protein expression of another member of the pRb family, p107, as well as that of E2F‐1. These results suggest that NAO‐induced G1 delay and cell cycle prolongation are caused by downregulation of the protein expression of ppRb and E2F in the human PCA cell line PC3.