Functional expression and characterization of the mouse epitope tag-protein kinase C isoforms, alpha, beta I, beta II, gamma, delta and epsilon

The Role of Oxidative Stress and Antioxidants in Diabetic Wound Healing

Foot ulcers are one of the most common and severe complication of diabetes mellitus with significant resultant morbidity and mortality. Multiple factors impair wound healing include skin injury, diabetic neuropathy, ischemia, infection, inadequate glycemic control, poor nutritional status, and severe morbidity. It is currently believed that oxidative stress plays a vital role in diabetic wound healing. An imbalance of free radicals and antioxidants in the body results in overproduction of reactive oxygen species which lead to cell, tissue damage, and delayed wound healing. Therefore, decreasing ROS levels through antioxidative systems may reduce oxidative stress-induced damage to improve healing. In this context, we provide an update on the role of oxidative stress and antioxidants in diabetic wound healing through following four perspectives. We then discuss several therapeutic strategies especially dietary bioactive compounds by targeting oxidative stress to improve wounds healing.

Differentiation-Associated Expression of Conventional Protein Kinase C Isoforms in Primary Cultures of Bone Marrow Cells Induced by M-CSF and G-CSF

The Protein kinase C (PKC) -associated signal pathway plays crucial roles in regulation of cell growth, differentiation and apoptosis. The present study focuses on conventional PKC (cPKC) expression and its regulation in primary cultures of bone marrow cells induced to undergo macrophage/granulocyte differentiation by macrophage colony-stimulating factor (M-CSF) or granular colony-stimulating factor (G-CSF). By performing western blot analysis with pan anti-PKC antibodies, we found that PKC is transiently induced by M-CSF, reaching a maximum level by day 2, and then declines and diminishes by day 9 in primary culture of bone marrow cells. In contrast, the expression of PKC along G-CSF induced granulocytic differentiation of bone marrow stem cells is low and increases gradually. Reverse transcription-PCR (RT-PCR) assay was utilized to investigate the expression of PKC isoforms. PKC-alpha is constitutively expressed in bone marrow cells independently of hematopoietic growth factors in cultures. PKC-gamma mRNA is undetectable. Similarly, the expression of PKC-beta is transiently induced by M-CSF, yet steadily increased by G-CSF, in agreement with results obtained from PKC protein expression. Furthermore, gel-shift assay showed that the activation of NF-kappaB is transiently induced by M-CSF but not by G-CSF. These data suggest that PKC expression is involved in both macrophage and granulocyte differentiation by bone marrow committed stem cells. Yet, NF-kappaB activation is only detected in macrophage and not granulocyte differentiation. Thus, we conclude that the PKC-mediated signaling pathway is distinctly involved in bone-marrow cell differentiation induced by M-CSF and G-CSF.

Protein kinase C involvement in deoxycholate-induced apoptosis in human gastric cells

Bile acids, such as deoxycholic acid (DC), are known to mediate some of their actions by differentially activating various protein kinase C (PKC) isoforms. This study confirms that DC induces apoptosis in gastric epithelial cells through PARP and caspase cascade activation, and examined the role of PKC in DC-induced apoptosis. We found increased activation of PKC in membrane fractions in response to DC that was concentration and time related. The PKC (beta(I)) isoform expression increased with translocation into the cell membrane fraction after DC (300 microM) stimulation. In contrast, PKCepsilon expression markedly decreased in response to DC treatment in a time- and concentration-dependent manner. In addition, this process was regulated by caspases, since the pan-caspase inhibitor z-VAD-fmk and caspase-3-, -6-, and -9-specific inhibitors prevented PKC (beta(I)) and (epsilon epsilon processing induced by DC. Treatment with the caspase-8-specific inhibitor, however, did not affect expression of either PKC isoform. No significant differences in the apoptotic response were observed when PKC (epsilon) overexpressed cells were exposed to DC in the presence of calcium-dependent conventional PKC inhibitors (Gö 6850 or Gö 6976). Our findings demonstrate that PKC is activated in gastric epithelial cells treated with DC with the PKC (beta(I)) and PKC (epsilon) isoforms being particularly involved in this process. The processing of PKC (beta(I) and epsilon) was shown to be closely regulated by caspases; however, modulations in PKC isoform concentrations by themselves have no effect on the apoptotic death of gastric mucosal cells induced by DC.

Construction of a tagging system for subcellular localization of proteins encoded by open reading frames

We have previously characterized a monoclonal antibody (SC1D7) that is directed to maltose-binding protein (MBP) of Escherichia coli and other closely related enteric bacteria. SC1D7 does not cross-react with proteins in eucaryotes and appears to be a highly specific tool in immunochemical analyses. To better map the epitope, we took advantage of an available plasmid, pMAL-c2, that encodes the E. coli MBP-coding sequence and constructed plasmids to express MBP fragments. A construct containing the N-terminal portion of MBP does not react with SC1D7, whereas a second construct expressing glutathione S-transferase fused with the C-terminal half of MBP does react with SC1D7. To precisely define the epitope, random peptides displayed on M13 were used to react with SC1D7. Sequences of reactive peptides were aligned, and a consensus sequence of XDXRIPX was deduced. This sequence matches MBP with an amino acid stretch of KDPRIAA. To consolidate the mapping result, a sequence encoding this epitope was inserted into an expression vector and the resulting recombinant protein did react with SC1D7. Thereafter, this epitope was incorporated into a eucaryotic expression plasmid containing a previously defined hepatitis delta virus epitope for protein tagging. This two-epitope-tagging vector is useful in various molecular analyses. We demonstrate its usage for localization of a bacterial virulence factor in host cells. This vector should be applicable for high-throughput characterization of new open reading frames found in genome sequencing.

The role of DOC-2/DAB2 protein phosphorylation in the inhibition of AP-1 activity. An underlying mechanism of its tumor-suppressive function in prostate cancer

DOC-2/DAB2, a novel phosphoprotein with signal-transducing capability, inhibits human prostatic cancer cells (Tseng, C.-P., Ely, B. D., Li, Y., Pong, R.-C., and Hsieh, J.-T. (1998) Endocrinology 139, 3542-3553). However, its mechanism of action is not understood completely. This study delineates the functional significance of DOC-2/DAB2 protein phosphorylation and demonstrates that in vivo activation of protein kinase C (PKC) by 12-O-tetradecanoylphorbol-13-acetate (TPA) induces DOC-2/DAB2 phosphorylation, including a serine residue at position 24. Mutation of Ser(24) to Ala reduced DOC-2/DAB2 phosphorylation by PKC. Using a synthetic Ser(24) peptide (APS(24)KKEKKKGSEKTD) or recombinant DOC-2/DAB2 as substrates, PKCbetaII, PKCgamma, and PKCdelta (but not casein kinase II) directly phosphorylated Ser(24) in vitro. This indicates that DOC-2/DAB2 is a PKC-specific substrate. Since expression of wild-type DOC-2/DAB2, but not the S24A mutant, inhibited TPA-induced AP-1 activity in prostatic epithelial cells, phosphorylation of Ser(24) appears to play a critical role in modulating TPA-induced AP-1 activity. Taken together, these data suggest that PKC-regulated phosphorylation of DOC-2/DAB2 protein may help its growth inhibitory function.