Motoi Ohba

Induction of differentiation in normal human keratinocytes by adenovirus-mediated introduction of the eta and delta isoforms of protein kinase C.

ABSTRACT Protein kinase C (PKC) plays a crucial role(s) in regulation of growth and differentiation of cells. In the present study, we examined possible roles of the α, δ, η, and ζ isoforms of PKC in squamous differentiation by overexpressing these genes in normal human keratinocytes. Because of the difficulty of introducing foreign genes into keratinocytes, we used an adenovirus vector system, Ax, which allows expression of these genes at a high level in almost all the cells infected for at least 72 h. Increased kinase activity was demonstrated in the cells overexpressing the α, δ, and η isoforms. Overexpression of the η isoform inhibited the growth of keratinocytes of humans and mice in a dose (multiplicity of infection [MOI])-dependent manner, leading to G1 arrest. The η-overexpressing cells became enlarged and flattened, showing squamous cell phenotypes. Expression and activity of transglutaminase 1, a key enzyme of squamous cell differentiation, were induced in the η-overexpressing cells in dose (MOI)- and time-dependent manners. The inhibition of growth and the induction of transglutaminase 1 activity were found only in the cells that express the η isoform endogenously, i.e., in human and mouse keratinocytes but not in human and mouse fibroblasts or COS1 cells. A dominant-negative η isoform counteracted the induction of transglutaminase 1 by differentiation inducers such as a phorbol ester, 1α,25-dihydroxyvitamin D3, and a high concentration of Ca2+. Among the isoforms examined, the δ isoform also inhibited the growth of keratinocytes and induced transglutaminase 1, but the α and ζ isoforms did not. These findings indicate that the η and δ isoforms of PKC are involved crucially in squamous cell differentiation.

Protein kinase Cδ amplifies ceramide formation via mitochondrial signaling in prostate cancer cells

We studied the role of protein kinase C isoform PKCδ in ceramide (Cer) formation, as well as in the mitochondrial apoptosis pathway induced by anticancer drugs in prostate cancer (PC) cells. Etoposide and paclitaxel induced Cer formation and apoptosis in PKCδ-positive LNCaP and DU145 cells but not in PKCδ-negative LN-TPA or PC-3 cells. In contrast, these drugs induced mitotic cell cycle arrest in all PC cell lines. Treatment with Rottlerin, a specific PKCδ inhibitor, significantly inhibited drug-induced Cer formation and apoptosis in LNCaP cells, as did overexpression of dominant negative–type PKCδ. Overexpression of wild-type PKCδ had an opposite effect in PC-3 cells. Notably, etoposide induced biphasic Cer formation in LNCaP cells. The early and transient Cer increase resulted from de novo Cer synthesis, while the late and sustained Cer accumulation was derived from sphingomyelin hydrolysis by neutral sphingomyelinase (nSMase). Cer, in turn, induced mitochondrial translocation of PKCδ and stimulated the activity of this kinase, promoting cytochrome c release and caspase-9 activation. Furthermore, the specific caspase-9 inhibitor LEHD-fmk significantly inhibited etoposide-induced nSMase activation, Cer accumulation, and PKCδ mitochondrial translocation. These results indicate that PKCδ plays a crucial role in activating anticancer drug–induced apoptosis signaling by amplifying the Cer-mediated mitochondrial amplification loop.

Distinct Mechanisms of Receptor and Nonreceptor Tyrosine Kinase Activation by Reactive Oxygen Species in Vascular Smooth Muscle Cells: Role of Metalloprotease and Protein Kinase C-δ

ABSTRACT Reactive oxygen species (ROS) are implicated in cardiovascular diseases. ROS, such as H2O2, act as second messengers to activate diverse signaling pathways. Although H2O2 activates several tyrosine kinases, including the epidermal growth factor (EGF) receptor, JAK2, and PYK2, in vascular smooth muscle cells (VSMCs), the intracellular mechanism by which ROS activate these tyrosine kinases remains unclear. Here, we identified two distinct signaling pathways required for receptor and nonreceptor tyrosine kinase activation by H2O2 involving a metalloprotease-dependent generation of heparin-binding EGF-like growth factor (HB-EGF) and protein kinase C (PKC)-δ activation, respectively. H2O2-induced EGF receptor tyrosine phosphorylation was inhibited by a metalloprotease inhibitor, whereas the inhibitor had no effect on H2O2-induced JAK2 tyrosine phosphorylation. HB-EGF neutralizing antibody inhibited H2O2-induced EGF receptor phosphorylation. In COS-7 cells expressing an HB-EGF construct tagged with alkaline phosphatase, H2O2 stimulates HB-EGF production through metalloprotease activation. By contrast, dominant negative PKC-δ transfection inhibited H2O2-induced JAK2 phosphorylation but not EGF receptor phosphorylation. Dominant negative PYK2 inhibited H2O2-induced JAK2 activation but not EGF receptor activation, whereas dominant negative PKC-δ inhibited PYK2 activation by H2O2. These data demonstrate the presence of distinct tyrosine kinase activation pathways (PKC-δ/PYK2/JAK2 and metalloprotease/HB-EGF/EGF receptor) utilized by H2O2 in VSMCs, thus providing unique therapeutic targets for cardiovascular diseases.

Activation of Protein Kinase Cζ Induces Serine Phosphorylation of VAMP2 in the GLUT4 Compartment and Increases Glucose Transport in Skeletal Muscle

ABSTRACT Insulin stimulates glucose uptake into skeletal muscle tissue mainly through the translocation of glucose transporter 4 (GLUT4) to the plasma membrane. The precise mechanism involved in this process is presently unknown. In the cascade of events leading to insulin-induced glucose transport, insulin activates specific protein kinase C (PKC) isoforms. In this study we investigated the roles of PKCζ in insulin-stimulated glucose uptake and GLUT4 translocation in primary cultures of rat skeletal muscle. We found that insulin initially caused PKCζ to associate specifically with the GLUT4 compartments and that PKCζ together with the GLUT4 compartments were then translocated to the plasma membrane as a complex. PKCζ and GLUT4 recycled independently of one another. To further establish the importance of PKCζ in glucose transport, we used adenovirus constructs containing wild-type or kinase-inactive, dominant-negative PKCζ (DNPKCζ) cDNA to overexpress this isoform in skeletal muscle myotube cultures. We found that overexpression of PKCζ was associated with a marked increase in the activity of this isoform. The overexpressed, active PKCζ coprecipitated with the GLUT4 compartments. Moreover, overexpression of PKCζ caused GLUT4 translocation to the plasma membrane and increased glucose uptake in the absence of insulin. Finally, either insulin or overexpression of PKCζ induced serine phosphorylation of the GLUT4-compartment-associated vesicle-associated membrane protein 2. Furthermore, DNPKCζ disrupted the GLUT4 compartment integrity and abrogated insulin-induced GLUT4 translocation and glucose uptake. These results demonstrate that PKCζ regulates insulin-stimulated GLUT4 translocation and glucose transport through the unique colocalization of this isoform with the GLUT4 compartments.

PKCα mediates TGFβ-induced growth inhibition of human keratinocytes via phosphorylation of S100C/A11

Growth regulation of epithelial cells is of major concern because most human cancers arise from them. We demonstrated previously a novel signal pathway involving S100C/A11 for high Ca2+-induced growth inhibition of normal human keratinocytes (Sakaguchi, M., M. Miyazaki, M. Takaishi, Y. Sakaguchi, E. Makino, N. Kataoka, H. Yamada, M. Namba, and N.H. Huh. 2003. J. Cell Biol. 163:825–835). This paper addresses a question whether transforming growth factor β (TGFβ) shares the pathway with high Ca2+. On exposure of the cells to TGFβ1, S100C/A11 was phosphorylated, bound to nucleolin, and transferred to the nucleus, resulting in induction of p21WAF1/CIP1 and p15INK4B through activation of Sp1. Protein kinase C α (PKCα) was shown to phosphorylate 10Thr of S100C/A11, which is a critical event for the signal transduction. The TGFβ1-induced growth inhibition was almost completely mitigated when PKCα activity was blocked or when S100C/A11 was functionally sequestered. These results indicate that, in addition to the well-characterized Smad-mediated pathway, the PKCα–S100C/A11-mediated pathway is involved in and essential for the growth inhibition of normal human keratinocytes cells by TGFβ1.

Insulin-Induced Akt Activation Is Inhibited by Angiotensin II in the Vasculature Through Protein Kinase C-α

Abstract—Insulin resistance is an important risk factor in the development of cardiovascular diseases such as hypertension and atherosclerosis. However, the specific role of insulin resistance in the etiology of these diseases is poorly understood. Angiotensin (Ang) II is a potent vasculotrophic and vasoconstricting factor. We hypothesize that in vascular smooth muscle cells (VSMCs), Ang II interferes with insulin action by inhibiting Akt, a major signaling molecule implicated in the biological actions of insulin. By immunoblotting with a phospho-specific antibody for Akt, we found that Ang II inhibits insulin-induced Akt phosphorylation in a time- and concentration-dependent manner. The inhibitory effect of Ang II was blocked by a Ang II type 1 receptor antagonist, RNH6270. A protein kinase C (PKC) activator, phorbol 12-myristate 13-acetate, also inhibited insulin-induced Akt phosphorylation. PKC inhibitors, including Go6976 (specific for &agr;- and &bgr;-isoforms), blocked the Ang II– and PMA-induced inhibition of Akt phosphorylation by insulin. Moreover, overexpression of PKC-&agr; but not PKC-&bgr; isoform by adenovirus inhibited insulin-induced Akt phosphorylation. By contrast, an epidermal growth factor receptor inhibitor (AG1478), a p42/44 mitogen-activated protein kinase (MAPK) kinase inhibitor (PD 598,059), and a p38 MAPK inhibitor (SB 203,580) did not block the Ang II–induced inhibition of Akt phosphorylation. From these data, we conclude that Ang II negatively regulates the insulin signal, Akt, in the vasculature specifically through PKC-&agr; activation, providing an alternative molecular mechanism that may explain the association of hyperinsulinemia with cardiovascular diseases.

PKC δ mediates ionizing radiation-induced activation of c-Jun NH2-terminal kinase through MKK7 in human thyroid cells

The thyroid gland is one of the most sensitive organs in ionizing radiation (IR)-induced carcinogenesis. To determine, therefore, the specific cascade of IR-induced signal transduction in human thyroid cells, we investigated the functional role of protein kinase C (PKC), especially its interlocking activation of c-Jun NH2-terminal kinase (JNK) pathway. In the present study, using adenovirus expression vectors for diverse dominant-negative (DN) types of PKC isoforms (α, β2, δ, ε and ζ) expressed in primary cultured human thyroid cells, only DN/PKC δ suppressed IR-induced JNK activation. In addition, Rottlerin, a PKC δ specific inhibitor, inhibited IR-induced JNK activation. IR-induced activation of transcription factor AP-1, downstream target of JNK, was also attenuated by DN/PKC δ. To examine the involvement of upstream kinases of JNK, we performed immune-complex kinase assays of mitogen-activated protein kinase kinase 4 (MKK4) and MKK7. IR activated MKK7 but not MKK4, and this activation was inhibited by Rottlerin. Furthermore, IR-induced JNK activation was suppressed by overexpression of kinase-deficient MKK7. Our results indicate that IR selectively activates the cascade of PKC δ-MKK7-JNK-AP-1 in human thyroid cells, suggesting a not apoptotic but radio-resistant role of PKC δ in human thyroid cells following IR.

Functional Characterization of IL-17F as a Selective Neutrophil Attractant in Psoriasis

IL-17F is known to be involved in many inflammatory diseases, but its role in skin diseases has not been fully examined. Because IL-8 is involved in many skin diseases such as psoriasis, we investigated the production of IL-8 in normal human epidermal keratinocytes (NHEKs) stimulated by IL-17F, tumor necrosis factor-alpha (TNF-alpha), IL-17A, and control using real-time PCR and ELISA. The results showed that IL-17F induced production of IL-8 in NHEKs in a time-dependent manner. Interestingly, the amounts of IL-8 stimulated by IL-17F were much higher than those stimulated by TNF-alpha or IL-17A. Next, we confirmed that selective mitogen-activated protein kinase kinase inhibitors significantly inhibited IL-17F-induced IL-8 production. Moreover, mouse skin intradermally injected with IL-17F expressed high level of IL-8 mRNA and induced ERK1/2 phosphorylation. Histological examination of mouse skin that was injected with IL-17F revealed marked neutrophilia in dermis and the infiltration was significantly inhibited by anti-IL-8 antibody. Finally, IL-17F expression in skin biopsy samples from psoriasis patients were examined by western blotting and ELISA. IL-17F was upregulated in lesional psoriatic skin compared with nonlesional skin. These results indicate that IL-17F may be involved in psoriasis via, in part, the activation of ERK1/2 and the induction of IL-8 in keratinocytes.

Lysophosphatidylcholine Activates Adipocyte Glucose Uptake and Lowers Blood Glucose Levels in Murine Models of Diabetes

Glucose homeostasis is maintained by the orchestration of peripheral glucose utilization and hepatic glucose production, mainly by insulin. In this study, we found by utilizing a combined parallel chromatography mass profiling approach that lysophosphatidylcholine (LPC) regulates glucose levels. LPC was found to stimulate glucose uptake in 3T3-L1 adipocytes dose- and time-dependently, and this activity was found to be sensitive to variations in acyl chain lengths and to polar head group types in LPC. Treatment with LPC resulted in a significant increase in the level of GLUT4 at the plasma membranes of 3T3-L1 adipocytes. Moreover, LPC did not affect IRS-1 and AKT2 phosphorylations, and LPC-induced glucose uptake was not influenced by pretreatment with the PI 3-kinase inhibitor LY294002. However, glucose uptake stimulation by LPC was abrogated both by rottlerin (a protein kinase Cδ inhibitor) and by the adenoviral expression of dominant negative protein kinase Cδ. In line with its determined cellular functions, LPC was found to lower blood glucose levels in normal mice. Furthermore, LPC improved blood glucose levels in mouse models of type 1 and 2 diabetes. These results suggest that an understanding of the mode of action of LPC may provide a new perspective of glucose homeostasis.

PKCη associates with cyclin E/cdk2/p21 complex, phosphorylates p21 and inhibits cdk2 kinase in keratinocytes

PKC is activated on the cell membrane by phospholipids, thereby transducing signals to intracellular pathways. We provide here another function of PKC, namely, regulating cell cycle by interaction with the cyclin E/cdk2/p21 complex. Among the 10 isoforms of PKC, PKCη is predominantly expressed in squamous cell epithelia and induces terminal differentiation of keratinocytes. PKCη that is endogenously expressed or overexpressed was found to associate with the cyclin E/cdk2/p21 complex in keratinocytes of mice and humans. Requirement of a possible adaptor protein to the binding was suggested by the reconstitution of PKCη and the cyclin E/cdk2/p21 complex which were prepared from human keratinocytes or Sf9 insect cells. Colocalization of PKCη with cdk2 and cyclin E was observed in the cytoplasm, particularly in the perinuclear region. p21 was phosphorylated in the complex in a PKC-activator dependent manner. Association of PKCη with cdk2 resulted in marked inhibition of cdk2-kinase activity when measured by phosphorylation of Rb. Dominant negative PKCη associated with the cyclin E/cdk2/p21 complex, but caused a little inhibition of cdk2 kinase activity. Among the known regulatory mechanisms of cdk2 activity, dephosphorylation of Thr160 was demonstrated.