Biomedical subjects

Ke Zu

Publications and source records attributed to Ke Zu.

5 recordsLinked to original sources

PubMed2006

Neural network-based analysis of thiol proteomics data in identifying potential selenium targets.

Generation of a monomethylated selenium metabolite is critical for the anticancer activity of selenium. Because of its strong nucleophilicity, the metabolite can react directly with protein thiols to cause redox modification. Here, we report a neural network-based analysis to identify potential selenium targets. A reactive thiol specific reagent, BIAM, was used to monitor thiol proteome changes on 2D gel. We constructed a dynamic model and evaluated the relative importance of proteins mediating the cellular responses to selenium. Information from this study will provide new clues to unravel mechanisms of anticancer action of selenium. High impact selenium targets could also serve as biomarkers to gauge the efficacy of selenium chemoprevention.

Antineoplastic Agents↗

PubMed2006

Delineating the mechanism by which selenium deactivates Akt in prostate cancer cells.

The up-regulation of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway is prevalent in many cancers. This phenomenon makes PI3K and Akt fruitful targets for cancer therapy and/or prevention because they are mediators of cell survival signaling. Although the suppression of phospho-Akt by selenium has been reported previously, little information is available on whether selenium modulates primarily the PI3K-phosphoinositide-dependent kinase 1 (PDK1) side of Akt phosphorylation or the phosphatase side of Akt dephosphorylation. The present study was aimed at addressing these questions in PC-3 prostate cancer cells which are phosphatase and tensin homologue-null. Our results showed that selenium decreased Akt phosphorylation at Thr308 (by PDK1) and Ser473 (by an unidentified kinase); the Thr308 site was more sensitive to selenium inhibition than the Ser473 site. The protein levels of PI3K and phospho-PDK1 were not affected by selenium. However, the activity of PI3K was reduced by 30% in selenium-treated cells, thus discouraging the recruitment of PDK1 and Akt to the membrane due to low phosphatidylinositol-3,4,5-trisphosphate formation by PI3K. Consistent with the above interpretation, the membrane localization of PDK1 and Akt was significantly diminished as shown by Western blotting. In the presence of a calcium chelator or a specific inhibitor of calcineurin (a calcium-dependent phosphatase), the suppressive effect of selenium on phospho-Akt(Ser473) was greatly reduced. The finding suggests that selenium-mediated dephosphorylation of Akt via calcineurin is likely to be an additional mechanism in regulating the status of phospho-Akt.

3-Phosphoinositide-Dependent Protein Kinases↗

PubMed2005

Up-regulation of c-Jun-NH2-kinase pathway contributes to the induction of mitochondria-mediated apoptosis by alpha-tocopheryl succinate in human prostate cancer cells.

Previously, alpha-tocopheryl succinate (alpha-TOS) has been reported to induce caspase-mediated apoptosis in PC-3 human prostate cancer cells. Caspase-9 was among several initiator caspases activated by alpha-TOS, suggesting a potential contribution of the intrinsic apoptotic pathway in mediating the response to alpha-TOS. Gene expression microarray was carried out as a screen to identify novel signaling molecules modulated by alpha-TOS, with a special focus on those known to play a role in mitochondria-mediated apoptosis. We discovered that Ask1, GADD45beta, and Sek1, three key components of the stress-activated mitogen-activated protein kinase pathway, are novel targets of alpha-TOS. Western blot analysis showed increased levels of phospho-Sek1 and phospho-c-Jun-NH2-kinase (JNK) in addition to total Ask1, GADD45beta, and Sek1. alpha-TOS also altered JNK-specific phosphorylation of Bcl-2 and Bim in a manner consistent with enhanced mitochondrial translocation of Bax and Bim. Because the expression level of most Bcl-2 family members remained unchanged, the posttranslational modification of Bcl-2 and Bim by JNK is likely to be a driving force in alpha-TOS activation of the intrinsic apoptotic pathway. Based on our findings, we propose a working model to capture the salient features of the apoptotic signaling circuitry of alpha-TOS.

Anticarcinogenic Agents↗

PubMed2003

Synergy between selenium and vitamin E in apoptosis induction is associated with activation of distinctive initiator caspases in human prostate cancer cells.

The ongoing Selenium and Vitamin E Chemoprevention Trial is designed to evaluate the efficacy of these two agents, either individually or in combination, in reducing the incidence of prostate cancer in healthy men over 55 years of age. Little information, however, is available on the potential synergy between vitamin E and selenium in chemoprevention. The present study was aimed at addressing this gap of knowledge with the use of the androgen-unresponsive, p53-null, PC-3 human prostate cancer cell line. The growth-inhibitory activity of vitamin E appeared to be dependent on the chemical form. In our hands, D-alpha-tocopheryl succinate (VES) was much more potent than either DL-alpha-tocopherol or D-alpha-tocopheryl acetate. Combining VES with methylseleninic acid (MSA), a selenium metabolite, produced a synergistic effect on cell growth suppression. The synergy was accounted for primarily by an augmented apoptotic response. Poly(ADP-ribose) polymerase cleavage and activation of specific caspases were confirmed by Western blot analysis. The caspases that were commonly modulated by either VES or MSA included initiator caspases-8 and -10, as well as executioner caspases-3, -6, and -7. In contrast, caspase-9 was activated only by VES, whereas caspases-1 and -12 were activated only by MSA. Based on the above information, it is proposed that the mitochondrial pathway and the endoplasmic reticulum stress/cytokine signaling pathway might be involved in apoptosis induction by VES and MSA, respectively. These two pathways may act in a cooperative manner to switch on the full force of the apoptotic machinery when cells are treated with both VES and MSA.

Anticarcinogenic Agents↗

PubMedDate not supplied

Cellular and molecular effects of alpha-tocopheryloxybutyrate: lessons for the design of vitamin E analog for cancer prevention.

alpha-Tocopherol and its synthetic derivative, a-tocopheryl succinate (alpha-TS), are known to inhibit proliferation of cancer cells. alpha-TS is considered a more desirable anticancer agent because of the ability to induce apoptosis. It has been established previously that the whole intact alpha-TS molecule is necessary for its pro-apoptotic activity. For this reason, alpha-TS is not suitable for oral use because the ester bond linking succinate to tocopherol is subject to hydrolysis by intestinal esterases. One approach to overcome this problem is to replace the ester bond with an ether bond, since the latter is resistant to esterase-mediated hydrolysis. alpha-Tocopheryloxybutyrate (alpha-TOB) is the ether analog of alpha-TS. In this study, we compared the potency of alpha-TS and alpha-TOB using a panel of bioassays: cell growth, TUNEL labelling for apoptosis, PARP cleavage, caspase-3 and caspase-9 activation, as well as Akt and JNK phosphorylation. The experiments were carried out in two human prostate cancer cell lines: LNCaP and PC-3. Our results showed that alpha-TOB was capable of inhibiting cell growth and inducing apoptosis, although alpha-TOB was less active than alpha-TS on an equimolar basis. In general, it took twice as much alpha-TOB as alpha-TS to achieve the same response. Nonetheless, these two compounds shared the same mechanism of targeting the Akt and JNK signaling pathways, and activating the intrinsic cell death mediators of caspase-9 and caspase-3. Cellular analysis of alpha-TS and alpha-TOB showed that alpha-TOB was taken up as efficiently as alpha-TS (if not more so), suggesting that the lower activity of alpha-TOB is an inherent property of the molecule and not due to impaired uptake. Additional evidence is provided to show that beta-TS may act at the membrane level to interfere with Akt phosphorylation, although the exact nature of this disruption remains unclear. The future design of new anticancer tocopherol analogs should incorporate the ether linkage of the side chain for esterase resistance as well as other structural modifications for enhanced blocking of membrane signaling.

Anticarcinogenic Agents↗