Erythroid cell differentiation is characterized by nuclear matrix localization and phosphorylation of protein kinases C (PKC) alpha, delta, and zeta

Induction of GD3/α1-adrenergic receptor/transglutaminase 2-mediated erythroid differentiation in chronic myelogenous leukemic K562 cells

The disialic acid-containing glycosphingolipid GD3 recruited membrane transglutaminase 2 (TG2) as a signaling molecule for erythroid differentiation in human chronic myelogenous leukemia (CML) K562 cells. The α1-adrenergic receptor (α1-AR)/TG2-mediated signaling pathway regulated GD3 functions, including gene expression and production, to differentiate CML K562 cells into erythroid lineage cells. Epinephrine, an AR agonist, increased membrane recruitment as well as GTP-photoaffinity of TG2, inducing GD3 synthase gene expression. Epinephrine activated PI3K/Akt signaling and GTPase downstream of TG2 activated Akt. The coupling of TG2 and GD3 production was specifically suppressed by prazosin (α1-AR antagonist), but not by propranolol (β-AR antagonist) or rauwolscine (α2-AR antagonist), indicating α1-AR specificity. Small interfering RNA (siRNA) experiment results indicated that the α1-AR/TG2-mediated signaling pathway activated PKCs α and δ to induce GD3 synthase gene expression. Transcription factors CREB, AP-1, and NF-κB regulated GD3 synthase gene expression during α1-AR-induced differentiation in CML K562 cells. In addition, GD3 synthase gene expression was upregulated in TG2-transfected cells via α1-AR with expression of erythroid lineage markers and benzidine-positive staining. α1-AR/TG2 signaling pathway-directed GD3 production is a crucial step in erythroid differentiation of K562 cells and GD3 interacts with α1-AR/TG2, inducing GD3/α1-AR/TG2-mediated erythroid differentiation. These results suggest that GD3, which acts as a membrane mediator of erythroid differentiation in CML cells, provides a therapeutic avenue for leukemia treatment.

Human thrombopoiesis depends on Protein kinase Cδ/protein kinase Cε functional couple

A deeper understanding of the molecular events driving megakaryocytopoiesis and thrombopoiesis is essential to regulate in vitro and in vivo platelet production for clinical applications. We previously documented the crucial role of PKCε in the regulation of human and mouse megakaryocyte maturation and platelet release. However, since several data show that different PKC isoforms fulfill complementary functions, we targeted PKCε and PKCδ, which show functional and phenotypical reciprocity, at the same time as boosting platelet production in vitro. Results show that PKCδ, contrary to PKCε, is persistently expressed during megakaryocytic differentiation, and a forced PKCδ down-modulation impairs megakaryocyte maturation and platelet production. PKCδ and PKCε work as a functional couple with opposite roles on thrombopoiesis, and the modulation of their balance strongly impacts platelet production. Indeed, we show an imbalance of PKCδ/PKCε ratio both in primary myelofibrosis and essential thrombocythemia, featured by impaired megakaryocyte differentiation and increased platelet production, respectively. Finally, we demonstrate that concurrent molecular targeting of both PKCδ and PKCε represents a strategy for in vitro platelet factories.

IL-6 Activates PI3K and PKCζ Signaling and Determines Cardiac Differentiation in Rat Embryonic H9c2 Cells

INTRODUCTION

IL-6 influences several biological processes, including cardiac stem cell and cardiomyocyte physiology. Although JAK-STAT3 activation is the defining feature of IL-6 signaling, signaling molecules such as PI3K, PKCs, and ERK1/2 are also activated and elicit different responses. Moreover, most studies on the specific role of these signaling molecules focus on the adult heart, and few studies are available on the biological effects evoked by IL-6 in embryonic cardiomyocytes.

AIM

The aim of this study was to clarify the biological response of embryonic heart derived cells to IL-6 by analyzing the morphological modifications and the signaling cascades evoked by the cytokine in H9c2 cells.

RESULTS

IL-6 stimulation determined the terminal differentiation of H9c2 cells, as evidenced by the increased expression of cardiac transcription factors (NKX2.5 and GATA4), structural proteins (α-myosin heavy chain and cardiac Troponin T) and the gap junction protein Connexin 43. This process was mediated by the rapid modulation of PI3K, Akt, PTEN, and PKCζ phosphorylation levels. PI3K recruitment was an upstream event in the signaling cascade and when PI3K was inhibited, IL-6 failed to modify PKCζ, PTEN, and Akt phosphorylation. Blocking PKCζ activity affected only PTEN and Akt. Finally, the overexpression of a constitutively active form of PKCζ in H9c2 cells largely mimicked the morphological and molecular effects evoked by IL-6.

CONCLUSIONS

This study demonstrated that IL-6 induces the cardiac differentiation of H9c2 embryonic cells though a signaling cascade that involves PI3K, PTEN, and PKCζ activities.

Aberrant expression of nuclear matrix proteins during HMBA-induced differentiation of gastric cancer cells

AIM: To investigate the aberrant expression of nuclear matrix proteins in human gastric cancer cells before and after hexamethylene bisacetamide (HMBA) treatment.

METHODS: Proteomics analysis of differential nuclear matrix proteins was performed by two dimensional electrophoresis polyacrylamide gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The expression levels of three nuclear matrix proteins were further confirmed by Western blotting and their locations in nuclear matrix filament were observed by quantum dots-based immunofluorescence.

RESULTS: Proteomics analysis showed that 43 protein spots were significantly changed due to HMBA treatment. Fifteen proteins were identified in the HMBA-induced differentiation of gastric tumor cells. Eight proteins spots were down-regulated while seven were up-regulated. Among these proteins, prohibitin, nucleophosmin and hnRNP A2/B1 were significantly decreased in HMBA-treated human gastric cancer cells, and their locations in nuclear matrix were altered by HMBA. Our results proved the alteration of specific nuclear matrix proteins during the differentiation of human gastric cancer cells. And the aberrant expressions of nuclear matrix proteins were of significance in revealing the regulatory mechanism of tumor cell proliferation and differentiation.

CONCLUSION: The aberrant expressions and intracellular redistributions of nuclear matrix proteins before and after HMBA treatment indicated that nuclear matrix proteins play a pivotal role in the differentiation of gastric cancer cells.

Protein kinase C zeta mediates cigarette smoke/aldehyde- and lipopolysaccharide-induced lung inflammation and histone modifications

Atypical protein kinase C (PKC) zeta is an important regulator of inflammation through activation of the nuclear factor-kappaB (NF-kappaB) pathway. Chromatin remodeling on pro-inflammatory genes plays a pivotal role in cigarette smoke (CS)- and lipopolysaccharide (LPS)-induced abnormal lung inflammation. However, the signaling mechanism whereby chromatin remodeling occurs in CS- and LPS-induced lung inflammation is not known. We hypothesized that PKCzeta is an important regulator of chromatin remodeling, and down-regulation of PKCzeta ameliorates lung inflammation by CS and LPS exposures. We determined the role and molecular mechanism of PKCzeta in abnormal lung inflammatory response to CS and LPS exposures in PKCzeta-deficient (PKCzeta(-/-)) and wild-type mice. Lung inflammatory response was decreased in PKCzeta(-/-) mice compared with WT mice exposed to CS and LPS. Moreover, inhibition of PKCzeta by a specific pharmacological PKCzeta inhibitor attenuated CS extract-, reactive aldehydes (present in CS)-, and LPS-mediated pro-inflammatory mediator release from macrophages. The mechanism underlying these findings is associated with decreased RelA/p65 phosphorylation (Ser(311)) and translocation of the RelA/p65 subunit of NF-kappaB into the nucleus. Furthermore, CS/reactive aldehydes and LPS exposures led to activation and translocation of PKCzeta into the nucleus where it forms a complex with CREB-binding protein (CBP) and acetylated RelA/p65 causing histone phosphorylation and acetylation on promoters of pro-inflammatory genes. Taken together, these data suggest that PKCzeta plays an important role in CS/aldehyde- and LPS-induced lung inflammation through acetylation of RelA/p65 and histone modifications via CBP. These data provide new insights into the molecular mechanisms underlying the pathogenesis of chronic inflammatory lung diseases.

Expression and Phosphorylation of Protein Kinase C Isoforms in Aβ1–42 Activated T Lymphocytes from Alzheimer's Disease

The protein kinase C (PKC) family of enzymes is a regulator of transmembrane signal transduction. There is evidence demonstrating altered activity of some PKC isoforms (PKC-α, PKC-δ and PKC-ζ) in the neurons of brains of Alzheimer's Disease (AD) sufferers, but little is known about their involvement in the intracellular machinery of amyloid β protein-reactive T lymphocytes in AD. By applying a modified “split-well culture system” for Aβ1–42 reactivity, we carried out flow cytometry analysis and biochemical investigations on the possible involvement of PKC-α, PKC-δ and PKC-ζ in the signalling system activated in Aβ-reactive T cells purified from peripheral blood mononucleate cells (PBMC) from healthy subjects and patients with AD. Flow cytometry analysis of Aβ1–42 activated T lymphocytes in the majority of AD patients highlighted a distinct cellular cluster highly expressing phospho-PKC-δ (P-PKC-δ), while most full-blown AD patients highly expressed two distinct P-PKC-δ and phospho-PKC-ζ (P-PKC-ζ) bright sub-populations. The same investigation performed in freshly purified peripheral T lymphocytes, did not highlight any subpopulation, suggesting that the detection of P-PKC-δ and P-PKC-ζ bright subpopulations is specifically linked to Aβ1–42 activated T lymphocytes. The data presented here, therefore, suggest possible novel hallmarks to discriminate between healthy elderly subjects and beginning or full-blown Alzheimer's Disease patients.

Parallel regulation of PKC-alpha and PKC-delta characterizes the occurrence of erythroid differentiation from human primary hematopoietic progenitors

OBJECTIVE

Erythroid differentiation is a process characterized by modulation of different proteins including phosphoinositide-related enzymes such as protein kinase C (PKC) isoforms. Because in different cell lines PKC-alpha and PKC-delta have been reported to be involved in the mechanisms controlling proliferation and differentiation, the aim of this study was to examine the relative involvement of these PKC isoforms in the development of CD235a+ erythroid cells from human healthy hematopoietic progenitors.

MATERIALS AND METHODS

Erythroid differentiation from human primary hematopoietic progenitor cells was achieved by adopting the human erythroblasts mass amplification culture. Expression and activity of PKC isoforms and their relationship with proliferation and differentiation were investigated by morphologic analysis, reverse-transcriptase polymerase chain reaction, Western blotting, multiparametric flow cytometry, and transfection experiments.

RESULTS

PKC-alpha was found expressed and phosphorylated in cells undergoing both proliferation and differentiation, although PKC-delta, largely expressed and activated during proliferation, was evidently downregulated during differentiation. Overexpression of PKC-delta-CAT scarcely influenced the development of glycophorin-A (CD235a)+ erythroid cells from hematopoietic progenitors, although overexpression of PKC-alpha-CAT strongly induced the development of CD235a+ erythroid cells. On the other hand, in PKC-alpha-CAT-transfected cells, pharmacologic inhibition of PKC-delta further increased the number of CD235a+ cells, although inhibition of PKC-alpha resulted in an evident impairment of the development of CD235a+ erythroid cells.

CONCLUSIONS

Our results indicate that the suppression or at least a strong downregulation of PKC-delta, concomitant to PKC-alpha expression and activity, might be a cofactor to be further investigated and might be involved in the events regulating erythropoietin-induced erythroid differentiation from human primary hematopoietic progenitor cells.

The expression of phosphatidic acid phosphatase 2a, which hydrolyzes lipids to generate diacylglycerol, is regulated by p73, a member of the p53 family

p73, a p53-related gene, is essential for a development of animals, while p53 is important for tumor formation. And little is known about the target genes specifically regulated by p73. Identifying the specific targets of p73 is important to understand the physiological roles of p73. To identify the genes specifically regulated by p73, we conducted serial analysis of gene expression to quantitatively evaluate messenger RNA populations. We found that the gene for phosphatidic acid phosphatase 2a (PAP2a), an enzyme that hydrolyzes lipids to generate diacylglycerol, was specifically upregulated by ectopic production of p73beta. The promoter region of this gene contains an element that is functionally responsive to p73beta. And the quantity of PAP2a protein was upregulated by ectopic production of p73beta. These results suggest that the expression of PAP2a is directly regulated by p73.

The effects of time delays in a phosphorylation-dephosphorylation pathway

Complex signaling cascades involve many interlocked positive and negative feedback loops which have inherent delays. Modeling these complex cascades often requires a large number of variables and parameters. Delay differential equation models have been helpful in describing inherent time lags and also in reducing the number of governing equations. However the consequences of model reduction via delay differential equations have not been fully explored. In this paper we systematically examine the effect of delays in a complex network of phosphorylation-dephosphorylation cycles (described by Gonze and Goldbeter, J. Theor. Biol., 210, (2001) 167-186), which commonly occur in many biochemical pathways. By introducing delays in the positive and negative regulatory interactions, we show that a delay differential model can indeed reduce the number of cycles actually required to describe the phosphorylation-dephosphorylation pathway. In addition, we find some of the unique properties of the network and a quantitative measure of the minimum number of delay variables required to model the network. These results can be extended for modeling complex signalling cascades.

Nuclear protein kinase C-delta: a possible check-point of cell cycle progression

Protein kinase Cs (PKCs) belong to a serine/threonine kinase family, ubiquitously expressed and claimed to be involved in physiological processes including apoptosis, cell growth and differentiation. The question of the subcellular localization and activity of PKCs remains to be clarified. Here we report that nuclear PKC-delta cooperates to regulate the S-G2/M phase transition of cell cycle, apparently being associated to chromosome condensation and alignment on the metaphase plate.

Nuclear protein kinase C

Protein kinase C (PKC) isozymes constitute a family of ubiquitous phosphotransferases which act as key transducers in many agonist-induced signaling cascades. To date, at least 11 different PKC isotypes have been identified and are believed to play distinct regulatory roles. PKC isoforms are physiologically activated by a number of lipid cofactors. PKC is thought to reside in the cytoplasm in an inactive conformation and to translocate to the plasma membrane or cytoplasmic organelles upon cell activation by different stimuli. However, a sizable body of evidence collected over the last 20 years has shown PKC to be capable of translocating to the nucleus. Furthermore, PKC isoforms are resident within the nucleus. Studies from independent laboratories have to led to the identification of quite a few nuclear proteins which are PKC substrates and to the characterization of nuclear PKC-binding proteins which may be critical for finely tuning PKC function in this cell microenvironment. Several lines of evidence suggest that nuclear PKC isozymes are involved in the regulation of biological processes as important as cell proliferation and differentiation, gene expression, neoplastic transformation, and apoptosis. In this review, we shall highlight the most intriguing and updated findings about the functions of nuclear PKC isozymes.