Isolation and sequence of a mouse brain cDNA coding for protein kinase C-gamma isozyme

Solid-phase synthesis, mass spectrometric analysis of the zinc-folding, and phorbol ester-binding studies of the 116-mer peptide containing the tandem cysteine-rich C1 domains of protein kinase C gamma

Tumor-promoting phorbol esters activate protein kinase C (PKC) isozymes by binding to the zinc-finger like cysteine-rich domains in the N-terminal regulatory region. Our recent studies have revealed that only PKCgamma has two high affinity phorbol ester-binding domains, providing a structural blueprint for the rational design of PKCgamma-selective modulators for the treatment of neuropathic pain. To extend this approach, the 116-mer peptide containing the double cysteine-rich motifs of PKCgamma (gamma-C1A-C1B) has been synthesized for the first time using an Fmoc-solid phase strategy with a stepwise chain elongation. This peptide was purified by the reversed phase HPLC to give satisfactory mass data (MALDI-TOF-MS and ESI-TOF-MS). The peptide was successfully folded by zinc treatment and the folded peptide was analyzed intact under neutral conditions by ESI-TOF-MS. The multiple charge mass envelopes shifted to those of the lower mass charge state by addition of 4 molar equiv. ZnCl2, suggesting that gamma-C1A-C1B preserves some higher order structure by the zinc folding. Moreover, the mass spectrum of the zinc-folded peptide in the presence of EDTA clearly showed that gamma-C1A-C1B coordinates exactly four atoms of zinc. This zinc stoichiometry is identical to that of native PKCgamma. Scatchard analysis of the zinc-folded peptide revealed two binding sites of distinctly different affinities (Kd=6.0 +/- 1.5 and 47.0 +/- 6.6 nM) comparable to those reported by Quest and Bell for the GST fusion protein of gamma-C1A-C1B prepared by DNA recombination. These results indicate that gamma-C1A-C1B serves as an effective surrogate for native PKCgamma for the study of the structural characteristics of the binding recognition event and the design, discovery, and development of new PKCgamma-selective modulators.

Protein kinase C isoforms play differential roles in the regulation of adipocyte differentiation

In this study we first established, by immunoblotting with specific antibodies, the temporal changes in cellular levels of protein kinase C (PKC) isoforms during differentiation of 3T3-F442A pre-adipocytes. Both pre-adipocyte and adipocyte 3T3-F442A cells were found to express PKC-alpha, -gamma, -delta, -epsilon, -zeta and -mu. However we were unable to detect PKC-beta, -eta or -theta. The same PKC isoform expression profile was found in rat adipocytes. The alpha, delta and gamma isoforms displayed similar temporal patterns of expression during differentiation of 3T3-F442A cells; all increased rapidly, peaking at day 2 of differentiation. Subsequently, the expression of these isoforms decreased, resulting in lower levels in fully differentiated adipocytes than in pre-adipocytes. The expression of PKC-epsilon increased steadily during differentiation, resulting in markedly elevated levels in adipocytes. Although expression of PKC-mu increased during differentiation, this was attributable to prolonged confluence rather than to the differentiation process itself. No change was observed in PKC-zeta levels during adipocyte development. Anti-sense oligodeoxynucleotides (ODNs) were used to deplete selectively the individual PKC subtypes. Each of the ODNs used effectively depleted the specific isoforms to undetectable levels and did not affect expression of the other PKC subtypes. This approach indicated that pre-adipocyte differentiation is not dependent upon PKC-zeta but that PKC-alpha,-delta and -mu each exert an inhibitory influence upon differentiation. Use of anti-sense ODNs to deplete PKC-epsilon and -gamma revealed that pre-adipocyte differentiation is dependent upon each of these isoforms. However, PKC-gamma, but not PKC-epsilon, appeared to be necessary for the clonal expansion of differentiating cells, suggesting that PKC-epsilon is required at a later phase in the differentiation process, when its expression is elevated, for the attainment and maintenance of the adipocyte phenotype.

New perspectives on PKCtheta, a member of the novel subfamily of protein kinase C

Members of the protein kinase C (PKC) family of serine/threonine protein kinases have been implicated in numerous cellular responses in a large variety of cell types. Expression patterns of individual members and differences in their cofactor requirements and potential substrate specificity suggest that each isoenzyme may be involved in specific regulatory processes. The PKCtheta isoenzyme exhibits a relatively restricted expression pattern with high protein levels found predominantly in hematopoietic cells and skeletal muscle. PKCtheta was found to be expressed in T, but not B lymphocytes, and to colocalize with the T-cell antigen receptor (TCR) at the site of contact between the antigen-responding T cell and the antigen-presenting cell (APC). Colocalization of PKCtheta with the TCR was selective for this isoenzyme and occurred only upon antigen-mediated responses leading to T-cell activation and proliferation. PKCtheta was found to be involved in the regulation of transcriptional activation of early-activation genes, predominantly AP-1, and its cellular distribution and activation were found to be regulated by the 14-3-3 protein. Other findings indicated that PKCtheta can associate with the HIV negative factor (Nef) protein, suggesting that altered regulation of PKCtheta by Nef may contribute to the T-cell impairments that are characteristic of infection by HIV. PKCtheta is expressed at relatively high levels in skeletal muscle, where it is suggested to play a role in signal transduction in both the developing and mature neuromuscular junction. In addition, PKCtheta appears to be involved in the insulin-mediated response of intact skeletal muscle, as well as in experimentally induced insulin resistance of skeletal muscle. Further studies suggest that PKCtheta is expressed in endothelial cells and is involved in multiple processes essential for angiogenesis and wound healing, including the regulation of cell cycle progression, formation and maintenance of actin cytoskeleton, and formation of capillary tubes. Here, we review recent progress in the study of PKCtheta and discuss its potential role in various cellular responses.

Growth hormone and phorbol esters require specific protein kinase C isoforms to activate mitogen-activated protein kinases in 3T3-F442A cells

Previous studies have shown that the activation of p44 and p42 mitogen-activated protein (MAP) kinases (ERK1 and ERK2) by growth hormone (GH) and phorbol esters, but not by epidermal growth factor, in 3T3-F442A preadipocytes is dependent on protein kinase C (PKC). In the present study two approaches have been taken to determine the PKC isoform dependence of MAP kinase activation in these cells. By immunoblotting with specific antibodies, the cells were found to express PKC-alpha, -gamma,-delta, -epsilon and -zeta. Treatment of cells with 500 nM PMA for 3 h led to the complete depletion of PKC-delta and the partial depletion of PKC-alpha but did not significantly affect the expression of the other PKC isoforms. In parallel, such treatment severely attenuated the ability of GH to activate MAP kinase. The degree of this attenuation was not increased by more prolonged PMA pretreatment, indicating that PKC-delta and perhaps PKC-alpha are important for MAP kinase activation by GH. These experiments further revealed that additional PKC isoforms were required for the full activation of MAP kinases by acute treatment with PMA. A second approach involved the use of anti-sense oligodeoxynucleotides (ODNs) to deplete the individual PKC isoforms selectively. Each of the ODNs used effectively depleted the relevant isoform to undetectable levels and did not affect the expression of the other PKC isoforms. Pretreatment of cells with PKC-delta anti-sense ODN, but not with anti-sense ODN to the other phorbol ester-sensitive isoforms, severely attenuated the activation of MAP kinases by GH. PKC-delta anti-sense ODN also blocked (by approx. 50%) the activation of MAP kinases by PMA. Furthermore a combination of PKC-delta and -epsilon anti-sense ODNs completely blocked the effect of PMA on MAP kinases. Collectively, these results indicate that the novel PKC-delta and -epsilon isoforms can couple to the MAP kinase pathway in 3T3-F442A cells but that the activation of MAP kinases by GH specifically involves PKC-delta.