Polymeric black tea polyphenols modulate the localization and activity of 12-O-tetradecanoylphorbol-13-acetate-mediated kinases in mouse skin: Mechanisms of their anti-tumor-promoting action

Polymeric black tea polyphenols (PBPs) have been shown to possess anti-tumor-promoting effects in two-stage skin carcinogenesis. However, their mechanisms of action are not fully elucidated. In this study, mechanisms of PBP-mediated antipromoting effects were investigated in a mouse model employing the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). Compared to controls, a single topical application of TPA to mouse skin increased the translocation of protein kinase C (PKC) from cytosol to membrane. Pretreatment with PBPs 1-3 decreased TPA-induced translocation of PKC isozymes (α, β, η, γ, ε) from cytosol to membrane, whereas PBPs 4 and 5 were less effective. The levels of PKCs δ and ζ in cytosol/membrane were similar in all the treatment groups. Complementary confocal microscopic evaluation showed a decrease in TPA-induced PKCα fluorescence in PBP-3-pretreated membranes, whereas pretreatment with PBP-5 did not show a similar decrease. Based on the experiments with specific enzyme inhibitors and phosphospecific antibodies, both PBP-3 and PBP-5 were observed to decrease TPA-induced level and/or activity of phosphatidylinositol 3-kinase (PI3K) and AKT1 (pS473). An additional ability of PBP-3 to inhibit site-specific phosphorylation of PKCα at all three positions responsible for its activation [PKCα (pT497), PKC PAN (βII pS660), PKCα/βII (pT638/641)] and AKT1 at the Thr308 position, along with a decrease in TPA-induced PDK1 protein level, correlated with the inhibition of translocation of PKC, which may impart relatively stronger chemoprotective activity to PBP-3 than to PBP-5. Altogether, PBP-mediated decrease in TPA-induced PKC phosphorylation correlated well with decreased TPA-induced NF-κB phosphorylation and downstream target proteins associated with proliferation, apoptosis, and inflammation in mouse skin. Results suggest that the antipromoting effects of PBPs are due to modulation of TPA-induced PI3K-mediated signal transduction.     

Kinetic and phylogenetic analysis of plant polyamine uptake transporters

The rice gene POLYAMINE UPTAKE TRANSPORTER1 (PUT1) was originally identified based on its homology to the polyamine uptake transporters LmPOT1 and TcPAT12 in Leishmania major and Trypanosoma cruzi, respectively. Here we show that five additional transporters from rice and Arabidopsis that cluster in the same clade as PUT1 all function as high affinity spermidine uptake transporters. Yeast expression assays of these genes confirmed that uptake of spermidine was minimally affected by 166 fold or greater concentrations of amino acids. Characterized polyamine transporters from both Arabidopsis thaliana and Oryza sativa along with the two polyamine transporters from L. major and T. cruzi were aligned and used to generate a hidden Markov model. This model was used to identify significant matches to proteins in other angiosperms, bryophytes, chlorophyta, discicristates, excavates, stramenopiles and amoebozoa. No significant matches were identified in fungal or metazoan genomes. Phylogenic analysis showed that some sequences from the haptophyte, Emiliania huxleyi, as well as sequences from oomycetes and diatoms clustered closer to sequences from plant genomes than from a homologous sequence in the red algal genome Galdieria sulphuraria, consistent with the hypothesis that these polyamine transporters were acquired by horizontal transfer from green algae. Leishmania and Trypansosoma formed a separate cluster with genes from other Discicristates and two Entamoeba species. We surmise that the genes in Entamoeba species were acquired by phagotrophy of Discicristates. In summary, phylogenetic and functional analysis has identified two clades of genes that are predictive of polyamine transport activity.     

Chronic low dose exposure to hydrogen peroxide changes sensitivity of V79 cells to different damaging agents

Chinese hamster V79 cells were repeatedly exposed to a low dose of hydrogen peroxide (H2O2) over several weeks and then exposed to H2O2, cisplatin or ultraviolet (UV) light. Cell killing was examined by colony formation, following these treatments. It was seen that cells conditioned by multiple low doses of H2O2 showed resistance to killing in case of H2O2 and cisplatin but the sensitivity to UV light was same as the control cells. Apoptosis was also determined in these cells after the same treatments. UV light failed to induce apoptosis in both conditioned and in control cells, but in case of cells treated with H2O2 and with cisplatin, there was less apoptosis in the conditioned cells compared to the control cells. From our observation we can say that the enhanced survival of cells after treatment with H2O2 or cisplatin could be due to inhibition of apoptosis.     

The inadequate smear: does it matter?

The objective of this study was to quantify the incidence of underlying cervical intraepithelial neoplasia (CIN) among women referred for colposcopy with three consecutive inadequate smears. The design was a retrospective cohort study analysing data from a regional colposcopy database at Cervical Screening Wales. Women who were referred to all the colposcopy clinics in Wales with three consecutive inadequate smears, the third inadequate smear being taken between 1 April 2001 and 31 March 2002 constituted the study population. The results of the fourth smear taken at the colposcopy clinic after three consecutive inadequate smears, the worst biopsy results from any of the subsequent colposcopies and the relationship between the result of the fourth smear taken at colposcopy clinic and any histology result were the main outcome measures. The accuracy of the colposcopic opinion was also examined. Of the 433 women identified as having been referred because of three consecutive inadequate smears, 302 were linked to either a subsequent smear and/or a biopsy result. An adequate smear result was available for 85% of these women when the smear was taken in the colposcopy clinic; 77% were reported as negative and 8% were abnormal. Of the 347 women seen in the colposcopy clinic, high-grade CIN was seen in 3% and low-grade lesion in 8%. The sensitivity and specificity of the fourth inadequate smear test in predicting underlying CIN were 15% and 84% respectively, with a positive predictive value of 8%. The sensitivity and specificity of colposcopy in predicting histological CIN among patients with three inadequate smears was 70% and 49%, respectively, and the positive predictive value was 44%. This study raises the question as to whether three consecutive inadequate smears should be considered as an indication for colposcopy, or merely for a further smear to be taken in circumstances where there is a greater likelihood getting an adequate result.     

Structural insights into loss of function of a pore forming toxin and its role in pneumococcal adaptation to an intracellular lifestyle

The opportunistic pathogen Streptococcus pneumoniae has dual lifestyles: one of an asymptomatic colonizer in the human nasopharynx and the other of a deadly pathogen invading sterile host compartments. The latter triggers an overwhelming inflammatory response, partly driven via pore forming activity of the cholesterol dependent cytolysin (CDC), pneumolysin. Although pneumolysin-induced inflammation drives person-to-person transmission from nasopharynx, the primary reservoir for pneumococcus, it also contributes to high mortality rates, creating a bottleneck that hampers widespread bacterial dissemination, thus acting as a double-edged sword. Serotype 1 ST306, a widespread pneumococcal clone, harbours a non-hemolytic variant of pneumolysin (Ply-NH). Performing crystal structure analysis of Ply-NH, we identified Y150H and T172I as key substitutions responsible for loss of its pore forming activity. We uncovered a novel inter-molecular cation-π interaction, governing formation of the transmembrane β-hairpins (TMH) in the pore state of Ply, which can be extended to other CDCs. H150 in Ply-NH disrupts this interaction, while I172 provides structural rigidity to domain-3, through hydrophobic interactions, inhibiting TMH formation. Loss of pore forming activity enabled improved cellular invasion and autophagy evasion, promoting an atypical intracellular lifestyle for pneumococcus, a finding that was corroborated in in vivo infection models. Attenuation of inflammatory responses and tissue damage promoted tolerance of Ply-NH-expressing pneumococcus in the lower respiratory tract. Adoption of this altered lifestyle may be necessary for ST306 due to its limited nasopharyngeal carriage, with Ply-NH, aided partly by loss of its pore forming ability, facilitating a benign association of SPN in an alternative, intracellular host niche.