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Feng Chu

Publications and source records attributed to Feng Chu.

10 recordsLinked to original sources
PubMed2006

Protein kinase Calpha and epsilon small-molecule targeted therapeutics: a new roadmap to two Holy Grails in drug discovery?

Protein kinase (PK)Calpha and epsilon are rational targets for cancer therapy. However, targeted experimental therapeutics that inhibit PKCalpha or epsilon are unavailable. The authors established recently that covalent modification of an active-site cysteine in human PKCepsilon, Cys452, by small molecules, for example 2-mercaptoethanolamine, is necessary and sufficient to render PKCepsilon kinase-dead. Cys452 is conserved in only eleven human protein kinase genes, including PKCalpha. Therefore, the design of small molecules that bind PKC active sites with an electrophile substituent positioned proximal to the Cys452 side chain may lead to targeted therapeutics that selectively inhibit PKCepsilon, PKCalpha or other PKC isozymes.

Antineoplastic Agents↗
PubMed2005

Identification of an inactivating cysteine switch in protein kinase Cepsilon, a rational target for the design of protein kinase Cepsilon-inhibitory cancer therapeutics.

Critical roles played by some protein kinases in neoplastic transformation and progression provide a rationale for developing selective, small-molecule kinase inhibitors as antineoplastic drugs. Protein kinase Cepsilon (PKCepsilon) is a rational target for cancer therapy, because it is oncogenic and prometastatic in transgenic mouse models. PKCepsilon is activated by sn-1,2-diacylglycerol (DAG). Attempts to develop selective PKCepsilon inhibitors that block activation by DAG or compete with ATP have not yet met with success, suggesting a need for new strategies. We previously reported that cystamine and a metabolic cystine precursor inactivate PKCepsilon in cells in a thiol-reversible manner. In this report, we first determined that PKCepsilon became resistant to inactivation by disulfides when Cys452 was replaced with alanine by site-specific mutagenesis of human PKCepsilon or a constitutively active PKCepsilon mutant. These results showed that the disulfides inactivated PKCepsilon by thiol-disulfide exchange, either upon Cys452 S-thiolation or by rearrangement to an intra-protein disulfide. Mass spectrometric analysis of peptide digests of cystamine-inactivated, carbamidomethylated PKCepsilon detected a peptide S-cysteaminylated at Cys452, indicating that Cys452 S-cysteaminylation is a stable modification. Furthermore, PKCepsilon inactivation by N-ethylmaleimide was Cys452 dependent, providing corroborative evidence that PKCepsilon inhibitors can be designed by targeting Cys452 with small molecules that stably modify the residue. Cys452 is an active site residue that is conserved in only 11 human protein kinase genes. Therefore, the PKCepsilon-inactivating Cys452 switch is a rational target for the design of antineoplastic drugs that selectively inhibit PKCepsilon.

Amino Acid Sequence↗
PubMed2005

Post-translational disulfide modifications in cell signaling--role of inter-protein, intra-protein, S-glutathionyl, and S-cysteaminyl disulfide modifications in signal transmission.

Cell signaling entails a host of post-translational modifications of effector-proteins. These modifications control signal transmission by regulating the activity, localization or half-life of the effector-protein. Prominent oxidative modifications induced by cell-signaling reactive oxygen species (ROS) are cysteinyl modifications such as S-nitrosylation, sulfenic acid and disulfide formation. Disulfides protect protein sulfhydryls against oxidative destruction and simultaneously influence cell signaling by engaging redox-regulatory sulfhydryls in effector-proteins. The types of disulfides implicated in signaling span (1) protein S-glutathionylation, e.g. as a novel mode of Ras activation through S-glutathionylation at Cys-118 in response to a hydrogen-peroxide burst, (2) intra-protein disulfides, e.g. in the regulation of the stability of the protein phosphatase Cdc25C by hydrogen-peroxide, (3) inter-protein disulfides, e.g. in the hydrogen peroxide-mediated inactivation of receptor protein-tyrosine phosphatase alpha (RPTPalpha) by dimerization and (4) protein S-cysteaminylation by cystamine. Cystamine is a byproduct of pantetheinase-catalyzed pantothenic acid recycling from pantetheine for biosynthesis of Coenzyme A (CoA), a ubiquitous and metabolically indispensable cofactor. Cystamine inactivates protein kinase C-epsilon (PKCepsilon), gamma-glutamylcysteine synthetase and tissue transglutaminase by S-cysteaminylation-triggered mechanisms. The importance of protein S-cysteaminylation in signal transmission in vivo is evident from the ability of cystamine administration to rescue the intestinal inflammatory-response deficit of pantetheinase knockout mice. These mice lack the predominant epithelial pantetheinase isoform and have sharply reduced levels of cystamine/cysteamine in epithelial tissues. In addition, intraperitoneal administration of cystamine significantly delays neurodegenerative pathogenesis in a Huntington's disease mouse model. Thus, cystamine may serve as a prototype for the development of novel therapeutics that target effector-proteins regulated by S-cysteaminylation.

Animals↗
PubMed2005

Applications of support vector machines to cancer classification with microarray data.

Microarray gene expression data usually have a large number of dimensions, e.g., over ten thousand genes, and a small number of samples, e.g., a few tens of patients. In this paper, we use the support vector machine (SVM) for cancer classification with microarray data. Dimensionality reduction methods, such as principal components analysis (PCA), class-separability measure, Fisher ratio, and t-test, are used for gene selection. A voting scheme is then employed to do multi-group classification by k(k - 1) binary SVMs. We are able to obtain the same classification accuracy but with much fewer features compared to other published results.

Algorithms↗
PubMed2004

[A study on detecting specific antibodies of hemorrhagic fever with renal syndrome and treatment with integrated traditional Chinese and western medicine].

OBJECTIVE: To explore a simple speedy specific and sensitive method to detect specific IgM (sIgM) and IgG (sIgG) antibodies of hemorrhagic fever with renal syndrome (HFRS),and to study the therapeutic effects of integrated traditional Chinese and western medicine on HFRS. METHODS: The serum of 559 patients with HFRS were tested with colloidal gold immuno-dot assay (CGIDA) for sIgM and sIgG antibodies and compared with enzyme linked immunosorbent assay (ELISA) or indirect fluorescent antibody test (IFAT). One hundred and one patients with HFRS were randomized into treatment group (n=50),treated with Kuhuang Injection, Shenmai Injection and Huangqi Liquid) and control group (n=51),treated with Ribarvirin and Ganlixin Injection). RESULTS: The positive rate of sIgM detected with CGIDA was 70.8% and the positive rate of sIgG detected with CGIDA was 87.5%. The days for fever decline, symptoms alleviation and sign relief between the treatment group and control group were similar (P>0.05). The days for recovery of kidney function in the control group was less than that in the treatment group (P<0.01). The rate of crossing shock stage in the treatment group was higher than that of the control group (P<0.01). CONCLUSION: CGIDA was more simple, speedy, specific and sensitive than ELISA or IFAT in detecting the sIgM or sIgG antibodies in serum of patients with HFRS. Although the sensitivity of CGIDA was lower than that of ELISA the CGIDA had no false positive reaction the sensitivity of CGIDA was higher than that of IFAT on detecting IgG. The effect of the treatment group was similar to that of the control group. But the crossing shock stage rate in the treatment group was higher than that of the control group while the control group was better than the treatment group in recovering the kidney function.

Adolescent↗
PubMed2003

Cellular protein kinase C isozyme regulation by exogenously delivered physiological disulfides--implications of oxidative protein kinase C regulation to cancer prevention.

We reported previously that cystine produces regulatory responses in purified, recombinant human protein kinase C-delta (PKCdelta) and PKCepsilon via S-thiolation-triggered mechanisms that are consistent with a cancer preventive effect, i.e. stimulation of the pro-apoptotic, tumor-suppressive isozyme PKCdelta and inactivation of the growth-stimulatory, oncogenic isozyme PKCepsilon, at S-cysteinylation stoichiometries that correspond to modification of a single redox-regulatory cysteine (Cys) switch in each isozyme. In this report, we show that the oxidative regulatory responses of purified PKCdelta and PKCepsilon to cystine are recapitulated in disulfide-treated cells. We report that treatment of COS7-PKCepsilon transfectants with the cystine precursor cystine dimethyl ester (CDME) produced concentration- and time-dependent PKCepsilon inactivation that was associated with oxidative PKCepsilon modification manifested as attenuated band intensity in PKCepsilon immunoblot analyses, and that both PKCepsilon inactivation and modification were reversed by dithiothreitol (DTT) as well as by thioredoxin. We also show that CDME induced biphasic PKCdelta regulation in COS7-PKCdelta transfectants, with DTT-irreversible PKCdelta stimulation at low and DTT-reversible PKCdelta inactivation at high CDME concentrations. The degrees of PKCdelta versus PKCepsilon inactivation by CDME treatment of COS7-PKC transfectants indicate substantial resistance of PKCdelta to inactivation. The PKCdelta stimulatory response in COS7-PKCdelta cells was triggered only by the disulfide agent and not by its reduced thiol counterpart, providing evidence for an oxidative mechanism. Also paralleling the oxidative stimulation of purified PKCdelta by cystine, the stimulation of PKCdelta elicited by CDME treatment of cells involved a stable structural change, which was evident from the stability of the stimulated form of PKCdelta to immunoprecipitation. Demonstration of oxidative regulation of cellular PKCdelta and PKCepsilon by disulfides in this report provides evidence that redox-regulatory sites in PKCdelta and PKCepsilon may offer novel targets for development of cancer preventive or therapeutic agents that selectively inactivate PKCepsilon or stimulate PKCdelta.

Animals↗
PubMed2003

PKC isozyme S-cysteinylation by cystine stimulates the pro-apoptotic isozyme PKC delta and inactivates the oncogenic isozyme PKC epsilon.

Protein kinase C (PKC) is a family of ten isozymes that play distinct and in some cases opposing roles in cell growth and survival. We recently reported that diamide, a diazene carbonyl derivative which oxidizes thiols to disulfides through addition/displacement reactions at the diazene bond, induces potent GSH-dependent inactivation of several PKC isozymes, including the oncogenic isozyme PKC epsilon, via S-glutathiolation. PKC delta, a pro-apoptotic isozyme, was distinguished by its resistance to inactivation. In this report, we show that PKC-regulatory S-thiolation modifications produced by physiological disulfides elicit opposing effects on PKC delta and PKC epsilon activity. We report that PKC delta is stimulated 2.0-2.5 fold by GSSG, (Cys-Gly)(2) and cystine, under conditions where PKC gamma and PKC epsilon are fully inactivated by cystine, and PKC alpha activity is affected marginally or not at all by the disulfides. Focusing on cystine, we show that DTT quenches cystine-induced PKC delta stimulation and PKC gamma and PKC epsilon inactivation, indicative of oxidative regulation. By analyzing DTT-reversible isozyme radiolabeling by [(35)S]cystine, we demonstrate that PKC gamma, PKC delta and PKC epsilon are each [(35)S] S-cysteinylated in association with the concentration-dependent regulation of isozyme activity by cystine. The restricted reactivity of cystine, together with the effects of DTT and thioredoxin on cystine-induced PKC isozyme regulation reported here, indicate that the cystine-induced PKC-regulatory effects entail isozyme S-cysteinylation. We recently hypothesized that antagonism of tumor promotion/progression by small cellular thiols may involve PKC regulation via oxidant-induced S-thiolation reactions with PKC isozymes. The findings of cystine-induced PKC isozyme regulation by S-cysteinylation reported here offer correlative support to the hypothetical model. Thus, PKC delta, a potent antagonist of DMBA-TPA-induced tumor promotion/progression in mouse skin, is stimulated by S-cysteinylation, PKC epsilon, an important mediator of the tumor promotion/progression response, is inactivated by S-cysteinylation, and PKC alpha, which is not influential in DMBA-TPA-induced tumor promotion/progression, is not regulated by cystine. Furthermore, PKC gamma has oncogenic activity, and S-cysteinylation inactivated PKC gamma and PKC epsilon similarly. These findings provide evidence that S-cysteinyl acceptor-sites in PKC isozymes may offer attractive targets for development of novel cancer preventive agents.

Apoptosis↗
PubMedDate not supplied

PKC sulfhydryl targeting by disulfiram produces divergent isozymic regulatory responses that accord with the cancer preventive activity of the thiuram disulfide.

The protein kinase C (PKC) isozyme family plays key roles in cell growth regulation and influences neoplastic disease development and progression. For example, PKCepsilon is oncogenic, and PKCdelta tumor-suppressive. PKC isozymes are characterized by distinct activation mechanisms entailing phosphatidylserine-dependent cofactor binding to the regulatory domain. Evidence is now emerging that redox signaling offers another platform of PKC regulation. We have established that PKC isozymes are regulated by S-thiolation, a posttranslational modification entailing disulfide linkage of low-molecular-weight species to select protein sulfhydryls. Our recent studies demonstrate that physiologically occurring disulfides with cysteinyl constituents, e.g., cystine, regulate cellular PKC isozymes by S-thiolation-triggered mechanisms. This report shows that PKC isozymes are also molecular targets of a chemically distinct class of disulfides. Disulfiram is a thiuram disulfide with potent cancer preventive activity in in vivo models of chemical carcinogenesis. Our results indicate that PKC Sthiolation by disulfiram induces differential regulatory effects on PKC isozymes that correlate with the cancer preventive activity of the drug. The implication of these findings is that PKC-regulatory effects of thiuram disulfides may offer a useful pharmacological guide for development of disulfiram analogues with superior cancer preventive activity.

Animals↗