Antisense oligonucleotides targeted against protein kinase c alpha inhibit proliferation of cultured avian myoblasts

Inositol 1,4,5-trisphosphate (IP3)-dependent Ca2+ signaling mediates delayed myogenesis in Duchenne muscular dystrophy fetal muscle

Duchenne muscular dystrophy (DMD) is a progressive neuromuscular disorder characterized by muscle wasting and premature death. The defective gene is dystrophin, a structural protein, absence of which causes membrane fragility and myofiber necrosis. Several lines of evidence showed that in adult DMD patients dystrophin is involved in signaling pathways that regulate calcium homeostasis and differentiation programs. However, secondary aspects of the disease, such as inflammation and fibrosis development, might represent a bias in the analysis. Because fetal muscle is not influenced by gravity and does not suffer from mechanical load and/or inflammation, we investigated 12-week-old fetal DMD skeletal muscles, highlighting for the first time early alterations in signaling pathways mediated by the absence of dystrophin itself. We found that PLC/IP3/IP3R/Ryr1/Ca2+ signaling is widely active in fetal DMD skeletal muscles and, through the calcium-dependent PKCα protein, exerts a fundamental regulatory role in delaying myogenesis and in myofiber commitment. These data provide new insights into the origin of DMD pathology during muscle development.

Protein kinase Cδ promotes proliferation and induces malignant transformation in skeletal muscle

In this paper, we investigated the isoform-specific roles of certain protein kinase C (PKC) isoforms in the regulation of skeletal muscle growth. Here, we provide the first intriguing functional evidence that nPKCδ (originally described as an inhibitor of proliferation in various cells types) is a key player in promoting both in vitro and in vivo skeletal muscle growth. Recombinant overexpression of a constitutively active nPKCδ in C2C12 myoblast increased proliferation and inhibited differentiation. Conversely, overexpression of kinase-negative mutant of nPKCδ (DN-nPKCδ) markedly inhibited cell growth. Moreover, overexpression of nPKCδ also stimulated in vivo tumour growth and induced malignant transformation in immunodeficient (SCID) mice whereas that of DN-nPKCδ suppressed tumour formation. The role of nPKCδ in the formation of rhabdomyosarcoma was also investigated where recombinant overexpression of nPKCδ in human rhabdomyosarcoma RD cells also increased cell proliferation and enhanced tumour formation in mouse xenografts. The other isoforms investigated (PKCα, β, ε) exerted only minor (mostly growth-inhibitory) effects in skeletal muscle cells. Collectively, our data introduce nPKCδ as a novel growth-promoting molecule in skeletal muscles and invite further trials to exploit its therapeutic potential in the treatment of skeletal muscle malignancies.

Inhibition of δ-opioid receptors induces brain glioma cell apoptosis through the mitochondrial and protein kinase C pathways

Brain glioma is a malignant tumor with a high incidence rate and poor prognosis that has become a focus of studies of central nervous system diseases. Previous studies have suggested that δ-opioid receptors may affect the proliferation and apoptosis of numerous types of tumor cells. However, to date, their precise mechanism(s) of action have not been elucidated. The present study aimed to investigate the effects of inhibiting δ-opioid receptors in brain glioma cell proliferation and apoptosis and their relevant molecular mechanisms. Various doses of naltrindole were supplied to treat brain glioma cells using the MTT method to assess the proliferation index. Flow cytometry was used to investigate the changes in cell apoptosis and mitochondrial membrane potential. The expression levels of Bax, Bcl-2, Bcl-xL, cytochrome c, caspase-9, caspase-3 and protein kinase C (PKC) were measured using western blotting. Naltrindole was observed to inhibit brain glioma cell proliferation and promote apoptosis in a dose- and time-dependent manner. Furthermore, the addition of naltrindole lead to changes in the brain glioma cell membrane potential and regulated Bax translocation to the mitochondrial membrane, consequently promoting the release of cytochrome c into the cytoplasm, followed by the activation of caspase-9 and -3, which caused cell apoptosis. In addition, naltrindole was able to regulate the expression levels of the cellular internal phosphorylated PKC proteins, which are closely associated with the inhibition of cell proliferation. In conclusion, the inhibition of δ-opioid receptors may inhibit brain glioma cell proliferation and lead to apoptosis, which is closely associated with the mitochondrial and PKC pathways.

Role of VDR in 1α,25-dihydroxyvitamin D3-dependent non-genomic activation of MAPKs, Src and Akt in skeletal muscle cells

1α,25-dihydroxyvitamin D3 [1,25D] is recognized as a steroid hormone that rapidly elicits intracellular signals in various tissues. In skeletal myoblasts, we have previously demonstrated that one of the 1,25D-induced non-genomic effects is the upstream stimulation of MAPKs through Src activation. In this work, the data obtained suggest that the classical receptor of vitamin D (VDR) participates in non-transcriptional actions of 1,25D. We significantly reduced VDR expression by infection of C2C12 murine myoblasts with lentiviral particles containing the pLKO.1 plasmid with information to express a shRNA against mouse VDR. In these cells (C2C12-shVDR), Western blot analyses show that 1,25D-induced p38 MAPK activation and Src tyr416 phosphorylation were abolished. In addition, 1,25D-dependent activity of ERK1/2 was diminished in cells lacking VDR but to a lesser extent (∼-60%). Phosphorylation of Akt by 1,25D, recently demonstrated in C2C12 cells, in the present work also appeared to be partially dependent on VDR expression (∼50% in C2C12-shVDR cells). Our results indicate that VDR is involved in 1,25D-induced rapid events related to survival/proliferation responses in skeletal muscle cells, providing relevant information on the mechanism of initiation of the non-genomic hormone signal. The participation of a VDR-independent non-genomic mechanism of action should also be taken into consideration. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

1α,25(OH)2D3-dependent modulation of Akt in proliferating and differentiating C2C12 skeletal muscle cells

We previously reported that 1α,25-dihydroxy-vitamin D(3) [1α,25(OH)(2)D(3)] induces non-transcriptional rapid responses through activation of Src and MAPKs in the skeletal muscle cell line C2C12. In the present study we investigated the modulation of Akt by the secosteroid hormone in C2C12 cells at proliferative stage (myoblasts) and at early differentiation stage. In proliferating cells, 1α,25(OH)(2)D(3) activates Akt by phosphorylation in Ser473 in a time-dependent manner (5-60 min). When these cells were pretreated with methyl-beta-cyclodextrin to disrupt caveolae microdomains, hormone-induced activation of Akt was suppressed. Similar results were obtained by siRNA silencing of caveolin-1 expression, further indicating that hormone effects on cell membrane caveolae are required for downstream signaling. PI3K and p38 MAPK, but not ERK1/2, participate in 1α,25(OH)(2)D(3) activation of Akt in myoblasts. The involvement of p38 MAPK in Akt phosphorylation by the hormone probably occurs through MAPK-activated protein kinase 2 (MK2), which is activated by the steroid. In addition, the participation of Src in Akt phosphorylation by 1α,25(OH)(2)D(3) was demonstrated using the inhibitor PP2 and antisense oligodeoxynucleotides that suppress Src expression. We also observed that PI3K participates in hormone-induced proliferation. During the early phase of C2C12 cell differentiation 1α,25(OH)(2)D(3) also increases Akt phosphorylation and activates Src. Of relevance, Src and PI3K are involved in Akt activation and in MHC and myogenin increased expression by 1α,25(OH)(2)D(3). Altogether, these data suggest that 1α,25(OH)(2)D(3) upregulates Akt through Src, PI(3)K, and p38 MAPK to stimulate myogenesis in C2C12 cells.

Activation of MAPKs by 1alpha,25(OH)2-Vitamin D3 and 17beta-estradiol in skeletal muscle cells leads to phosphorylation of Elk-1 and CREB transcription factors

The mitogen activated protein kinases (MAPKs) have been classified into at least six subfamilies, among which ERK1/2, JNK1/2 and p38 MAPK are the most extensively studied. The steroid hormones 1alpha,25-dihydroxy-Vitamin D(3) and 17beta-estradiol promote biological responses through activation of MAPK cascades in various cell types. We previously reported that 1alpha,25(OH)(2)D(3) rapidly (within 1 min) activates p38 MAPK in C2C12 skeletal muscle cells. In this work, using the same muscle cell line, we demonstrate that 1alpha,25(OH)(2)D(3) or 17beta-estradiol phosphorylate and activate ERK1/2 and p38 MAPK after longer treatment intervals, maximal effects seen at 90 and 30 min (ERK1/2) and at 60 and 15 min (p38 MAPK) for these hormones, respectively. Hormone-dependent ERK and p38 activation was abolished by MAPK specific inhibitors U0126 and SB203580. 1alpha,25(OH)(2)D(3) and 17beta-estradiol also induced the phosphorylation of CREB and Elk-1 transcription factors in an ERK1/2-dependent manner. Simultaneous addition of both hormones potentiated CREB phosphorylation. 1alpha,25(OH)(2)D(3)- and 17beta-estradiol-induced c-fos expression, which was mediated by p38 phosphorylation. The action of 17beta-estradiol on c-fos levels was also dependent on ERK1/2. These results suggest that MAPK signalling pathways play an important role in regulating early gene expression through CREB and Elk-1 activation in skeletal muscle cells.

MAP kinases p38 and JNK are activated by the steroid hormone 1alpha,25(OH)2-vitamin D3 in the C2C12 muscle cell line

In chick skeletal muscle cell primary cultures, we previously demonstrated that 1alpha,25(OH)2-vitamin D3 [1alpha,25(OH)2D3], the hormonally active form of vitamin D, increases the phosphorylation and activity of the extracellular signal-regulated mitogen-activated protein (MAP) kinase isoforms ERK1 and ERK2, their subsequent translocation to the nucleus and involvement in DNA synthesis stimulation. In this study, we show that other members of the MAP kinase superfamily are also activated by the hormone. Using the muscle cell line C2C12 we found that 1alpha,25(OH)2D3 within 1 min phosphorylates and increases the activity of p38 MAPK. The immediately upstream mitogen-activated protein kinase kinases 3/6 (MKK3/MKK6) were also phosphorylated by the hormone suggesting their participation in p38 activation. 1Alpha,25(OH)2D3 was able to dephosphorylate/activate the ubiquitous cytosolic tyrosine kinase c-Src in C2C12 cells and studies with specific inhibitors imply that Src participates in hormone induced-p38 activation. Of relevance, 1alpha,25(OH)2D3 induced in the C2C12 line the stimulation of mitogen-activated protein kinase activating protein kinase 2 (MAPKAP-kinase 2) and subsequent phosphorylation of heat shock protein 27 (HSP27) in a p38 kinase activation-dependent manner. Treatment with the p38 inhibitor, SB203580, blocked p38 phosphorylation caused by the hormone and inhibited the phosphorylation of its downstrean substrates. 1Alpha,25(OH)2D3 also promotes the phosphorylation of c-jun N-terminal protein kinases (JNK 1/2), the response is fast (0.5-1 min) and maximal phosphorylation of the enzyme is observed at physiological doses of 1alpha,25(OH)2D3 (1 nM). The relative contribution of ERK-1/2, p38, and JNK-1/2 and their interrelationships in hormonal regulation of muscle cell proliferation and differentiation remain to be established.

Cooperative inhibitory effects of antisense oligonucleotide of cell adhesion molecules and cimetidine on cancer cell adhesion

AIM: To explore the cooperative effects of antisense oligonucleotide (ASON) of cell adhesion molecules and cimetidine on the expression of E-selectin and ICAM-1 in endothelial cells and their adhesion to tumor cells.

METHODS: After treatment of endothelial cells with ASON and/or cimetidine and induction with TNF-α, the protein and mRNA changes of E-selectin and ICAM-1 in endothelial cells were examined by flow cytometry and RT-PCR, respectively. The adhesion rates of endothelial cells to tumor cells were measured by cell adhesion experiment.

RESULTS: In comparison with TNF-α inducing group, lipo-ASON and lipo-ASON/cimetidine could significantly decrease the protein and mRNA levels of E-selectin and ICAM-1 in endothelial cells, and lipo-ASON/cimetidine had most significant inhibitory effect on E-selectin expression (from 36.37 ± 1.56% to 14.23 ± 1.07%, P < 0.001). Meanwhile, cimetidine alone could inhibit the expression of E-selectin (36.37 ± 1.56% vs 27.2 ± 1.31%, P < 0.001), but not ICAM-1 (69.34 ± 2.50% vs 68.07 ± 2.10%, P > 0.05)and the two kinds of mRNA, either. Compared with TNF-α inducing group, the rate of adhesion was markedly decreased in lipo-E-selectin ASON and lipo-E-selectin ASON/cimetidine treated groups(P < 0.05), and lipo-E-selectin ASON/cimetidine worked better than lipo-E-selectin ASON alone except for HepG2/ECV304 group (P < 0.05). However, the decrease of adhesion was not significant in lipo-ICAM-1 ASON and lipo-ICAM-1 ASON/cimetidine treated groups except for HepG2/ECV304 group (P > 0.05).

CONCLUSION: These data demonstrate that ASON in combination with cimetidine in vitro can significantly reduce the adhesion between endothelial cells and hepatic or colorectal cancer cells, which is stronger than ASON or cimetidine alone. This study provides some useful proofs for gene therapy of antiadhesion.

Suppression of protein kinase Calpha triggers apoptosis through down-regulation of Bcl-xL in a rat hepatic epithelial cell line

Inactivation of protein kinase C (PKC)alpha plays an important role in modulating hepatic failure and/or apoptosis during sepsis. To determine whether and how PKCalpha inactivation mediates the apoptosis, PKCalpha was suppressed by antisense treatment or transiently transfection in Clone-9 rat hepatic epithelial cell line. Apoptosis was evaluated by cell survival rate, poly-adenyl ribonuclease polymerase (PARP) cleavage, and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-digoxigenin nick end labeling stain. The expressions of PKCalpha and Bcl-xL were quantified by Western blot analysis after antisense treatment. In the transfection studies, cells were co-transfected with green fluorescent protein cDNA as a transfection marker. The expressions of PKCalpha and Bcl-xL were detected by immunohistochemical staining with second antibody conjugated with Texas red. Apoptosis was evaluated by tetramethyl-rhodamine labeling of DNA strand breaks and immunostaining of 85-kDa fragment of PARP. The results showed that cytosolic and membrane-associated PKCalpha were decreased by 54.5% and 41.4%, respectively, after PKCalpha antisense treatment. The apoptotic incidence and percentage of PARP cleavage were significantly increased, whereas protein expression of Bcl-xL was decreased after PKCalpha-antisense treatment. In the transfection studies, the results showed that most of the cells expressing green fluorescent protein revealed less PKCalpha and Bcl-xL protein contents and more in situ PARP cleavage and DNA strand breaks. These findings indicated that decrease of PKCalpha declines the Bcl-xL content and leads to the vulnerability of apoptosis in hepatic epithelial cells. Taken together, our data provide evidence that suppression of PKCalpha plays a critical role in triggering caspase-dependent apoptosis, which may act through modulating the Bcl-xL expression.

Inhibition of PKCalpha induces a PKCdelta-dependent apoptotic program in salivary epithelial cells

We have used expression of a kinase dead mutant of PKCalpha (PKCalphaKD) to explore the role of this isoform in salivary epithelial cell apoptosis. Expression of PKCalphaKD by adenovirus-mediated transduction results in a dose-dependent induction of apoptosis in salivary epithelial cells as measured by the accumulation of sub-G1 DNA, activation of caspase-3, and cleavage of PKCdelta and PKCzeta, known caspase substrates. Induction of apoptosis is accompanied by nine-fold activation of c-Jun-N-terminal kinase, and an approximately two to three-fold increase in activated mitogen-activated protein kinase (MAPK) as well as total MAPK protein. Previous studies from our laboratory have shown that PKCdelta activity is essential for the apoptotic response of salivary epithelial cells to a variety of cell toxins. To explore the contribution of PKCdelta to PKCalphaKD-induced apoptosis, salivary epithelial cells were cotransduced with PKCalphaKD and PKCdeltaKD expression vectors. Inhibition of endogenous PKCdelta blocked the ability of PKCalphaKD to induce apoptosis as indicated by cell morphology, DNA fragmentation, and caspase-3 activation, indicating that PKCdelta activity is required for the apoptotic program induced under conditions where PKCalpha is inhibited. These findings indicate that PKCalpha functions as a survival factor in salivary epithelial cells, while PKCdelta functions to regulate entry into the apoptotic pathway.

Polyol pathway and protein kinase C activity of rat Schwannoma cells

BACKGROUND

Polyol pathway hyperactivity-induced decreases in protein kinase C (PKC) activities have been proposed as a pathogenic mechanism of diabetic neuropathy. Increased PKC activities have recently been invoked in the pathogenesis of other diabetic complications, especially retinopathy, nephropathy, and macroangiopathy. However, it remains unclear whether PKC activities in neural cells such as Schwann cells are increased, decreased, or unchanged. This study investigated the effects of high glucose and increased polyol pathway activity on neural cell growth and PKC activities.

METHODS

Rat Schwannoma cells were cultured in 5.5 or 20 mM glucose in the presence or absence of an aldose reductase inhibitor, epalrestat (1 microM) for 14 days. Proliferation activities, PKC activities, and the protein expression of PKC isoforms were measured.

RESULTS

Proliferation and PKC activities under the 20 mM glucose condition were significantly decreased compared to those under the 5.5 mM glucose condition and were prevented by epalrestat. Among PKC isoforms, the protein expression of PKC-alpha under the 20 mM glucose condition was significantly reduced compared to that under the 5.5 mM glucose condition. Epalrestat significantly inhibited the decreased expression of PKC-alpha protein. There were no significant changes in the protein expression of PKC-beta.

CONCLUSIONS

These results suggest that PKC, especially PKC-alpha activity, is decreased in Schwann cells exposed to high glucose and that this deficit is mediated through polyol pathway hyperactivity.

Activation of RAF-1 through Ras and protein kinase Calpha mediates 1alpha,25(OH)2-vitamin D3 regulation of the mitogen-activated protein kinase pathway in muscle cells

We have previously shown that stimulation of proliferation of avian embryonic muscle cells (myoblasts) by 1alpha,25(OH)(2)-vitamin D(3) (1alpha,25(OH)(2)D(3)) is mediated by activation of the mitogen-activated protein kinase (MAPK; ERK1/2). To understand how 1alpha,25(OH)(2)D(3) up-regulates the MAPK cascade, we have investigated whether the hormone acts upstream through stimulation of Raf-1 and the signaling mechanism by which this effect might take place. Treatment of chick myoblasts with 1alpha,25(OH)(2)D(3) (1 nm) caused a fast increase of Raf-1 serine phosphorylation (1- and 3-fold over basal at 1 and 2 min, respectively), indicating activation of Raf-1 by the hormone. These effects were abolished by preincubation of cells with a specific Ras inhibitor peptide that involves Ras in 1alpha,25(OH)(2)D(3) stimulation of Raf-1. 1alpha,25(OH)(2)D(3) rapidly induced tyrosine de-phosphorylation of Ras-GTPase-activating protein, suggesting that inhibition of Ras-GTP hydrolysis is part of the mechanism by which 1alpha,25(OH)(2)D(3) activates Ras in myoblasts. The protein kinase C (PKC) inhibitors calphostin C, bisindolylmaleimide I, and Ro 318220 blocked 1alpha,25(OH)(2)D(3)-induced Raf-1 serine phosphorylation, revealing that hormone stimulation of Raf-1 also involves PKC. In addition, transfection of muscle cells with an antisense oligodeoxynucleotide against PKCalpha mRNA suppressed serine phosphorylation by 1alpha,25(OH)(2)D(3). The increase in MAPK activity and tyrosine phosphorylation caused by 1alpha,25(OH)(2)D(3) could be abolished by Ras inhibitor peptide, compound PD 98059, which prevents the activation of MEK by Raf-1, or incubation of cell lysates before 1alpha,25(OH)(2)D(3) exposure with an anti-Raf-1 antibody. In conclusion, these results demonstrate for the first time in a 1alpha,25(OH)(2)D(3) target cell that activation of Raf-1 via Ras and PKCalpha-dependent serine phosphorylation plays a central role in hormone stimulation of the MAPK-signaling pathway leading to muscle cell proliferation.

PKC-regulated myogenesis is associated with increased tyrosine phosphorylation of FAK, Cas, and paxillin, formation of Cas-CRK complex, and JNK activation

Previous reports suggest that PKC plays an important role in regulating myogenesis. However, the regulatory signaling pathways are not fully understood. We examined the effects of PKC downregulation on signaling events during skeletal muscle differentiation. We found that downregulation of PKC results in increased myogenesis in C2C12 cells as measured by creatine kinase activity and myogenin expression. We showed that, during differentiation, downregulation of PKC expression results in increased tyrosine phosphorylation of FAK, Cas, and paxillin, concomitant with enhanced Cas-CrkII complex formation, which leads to activation of JNK2. But in proliferated muscle cells, PKC inhibition results in FAK and Cas tyrosine dephosphorylation. Further, disruption of actin cytoskeleton by cytochalasin D prevents the activation of FAK and Cas as well as the formation of Cas-CrkII complex stimulated by PKC downregulation during muscle cell differentiation. Finally, we observed that PKC downregulation increases the tyrosine phosphorylation of focal adhesion associated proteins. Based on the above data, we propose that PKC downregulation results in enhanced tyrosine phosphorylation of FAK, Cas, and paxillin, thus promoting the establishment of Cas-CrkII complex, leading to activation of JNK and that these interactions are dependent upon the integrity of actin cytoskeleton during muscle cell differentiation. Data presented here significantly contribute to elucidating the regulatory role of PKC in myogenesis possibly through integrin signaling pathway.

Non-genomic stimulation of tyrosine phosphorylation cascades by 1,25(OH)(2)D(3) by VDR-dependent and -independent mechanisms in muscle cells

Studies with different cell types have shown that modulation of various of the fast as well as long-term responses to 1,25(OH)(2)D(3) depends on the activation of tyrosine kinase pathways. Recent investigations of our laboratory have demonstrated that 1,25(OH)(2)D(3) rapidly stimulates in muscle cells tyrosine phosphorylation of PLC-gamma and the growth-related proteins MAPK and c-myc. We have now obtained evidence using antisense technology indicating that VDR-dependent activation of Src mediates the fast stimulation of tyrosine phosphorylation of c-myc elicited by the hormone. This non-genomic action of 1,25(OH)(2)D(3) requires tyrosine phosphorylation of the VDR. Immunoprecipitation under native conditions coupled to Western blot analysis revealed 1,25(OH)(2)D(3)-dependent formation of complexes between Src and the VDR and c-myc. However, the activation of MAPK by the hormone was only partially mediated by the VDR and required in addition increased PKC and intracellular Ca(2+). Following its phosphorylation, MAPK translocates into the nucleus where it regulates c-myc transcription. Altogether these results indicate that tyrosine phosphorylation plays a role in the stimulation of muscle cell growth by 1,25(OH)(2)D(3). Data were also obtained involving tyrosine kinases and the VDR in hormone regulation of the Ca(2+) messenger system by mediating the stimulation of store-operated calcium (SOC; TRP) channels. Congruent with this action, 1,25(OH)(2)D(3) induces a rapid translocation of the VDR to the plasma cell membrane which can be blocked by tyrosine kinase inhibitors. Of mechanistic relevance, an association between the VDR and TRP proteins with the participation of the scaffold protein INAD was shown.

Nongenomic action of 1 alpha,25(OH)(2)-vitamin D3. Activation of muscle cell PLC gamma through the tyrosine kinase c-Src and PtdIns 3-kinase

We have previously demonstrated that the steroid hormone 1 alpha,25(OH)(2)-vitamin D(3)[1 alpha,25(OH)(2)D(3)] stimulates the production of inositol trisphosphate (InsP(3)), the breakdown product of phosphatidylinositol 4,5-biphosphate (PtdInsP(2)) by phospholipase C (PtdIns-PLC), and activates the cytosolic tyrosine kinase c-Src in skeletal muscle cells. In the present study we examined whether 1 alpha,25(OH)(2)D(3) induces the phosphorylation and membrane translocation of PLC gamma and the mechanism involved in this isozyme activation. We found that the steroid hormone triggers a significant phosphorylation on tyrosine residues of PLC gamma and induces a rapid increase in membrane-associated PLC gamma immunoreactivity with a time course that correlates with that of phosphorylation in muscle cells. Genistein, a tyrosine kinase inhibitor, blocked the phosphorylation of PLC gamma. Inhibition of 1 alpha,25(OH)(2)D(3)-induced c-Src activity by its specific inhibitor PP1 or muscle cell transfection with an antisense oligodeoxynucleotide directed against c-Src mRNA, prevented hormone stimulation of PLC gamma tyrosine phosphorylation. The isozyme phosphorylation is also blocked by both wortmannin and LY294002, two structurally different inhibitors of phosphatidyl inositol 3-kinase (PtdIns3K), the enzyme that produces PtdInsP(3) known to activate PLC gamma isozymes specifically by interacting with their SH2 and pleckstrin homology domains. The hormone also increases the physical association of c-Src and PtdIns3K with PLC gamma and induces a c-Src-dependent tyrosine phosphorylation of the p85 regulatory subunit of PtdIns3K. The time course of hormone-dependent PLC gamma phosphorylation closely correlates with the time course of its redistribution to the membrane, suggesting that phosphorylation and redistribution to the membrane of PLC gamma are two interdependent events. 1 alpha,25(OH)(2)D(3)-induced membrane translocation of PLC gamma was prevented to a great extent by c-Src and PtdIns3K inhibitors, PP1 and LY294002. Taken together, the present data indicates that the cytosolic tyrosine kinase c-Src and PtdIns 3-kinase play indispensable roles in 1 alpha,25(OH)(2)D(3) signal transduction cascades leading to PLC gamma activation.

Protein kinase Calpha is required for endothelin-1-induced proliferation of human myometrial cells

The role of protein kinase C (PKC)-alpha in endothelin-1 (ET-1)-induced proliferation of human myometrial cells was investigated. Inhibition of conventional PKC with Gö 6976 eliminated the proliferative effect of ET-1. Treatment of myometrial cells with an antisense oligonucleotide against PKCalpha efficiently reduced PKCalpha protein expression without effect on other PKC isoforms and resulted in the loss of ET-1-induced cell growth. Immunocytochemistry using an antibody against PKCalpha revealed that there was no PKCalpha immunoreactivity in the nuclei of quiescent nonconfluent untreated cells, whereas it is evenly distributed throughout the cytoplasm. Exposure of myometrial cells to ET-1 for 15 min caused the PKCalpha to shift towards the perinuclear area, and incubation for 60 min caused a shift towards the nucleus. These results reveal that PKCalpha is required for ET-1-induced human myometrial cell growth and suggest that targeting of PKCalpha by antisense nucleotides might be an important approach for the development of anticancer treatments.

The vitamin D receptor mediates rapid changes in muscle protein tyrosine phosphorylation induced by 1,25(OH)(2)D(3)

It has been recently shown that the fast non-genomic responses of 1,25(OH)(2)-vitamin D(3) [1,25(OH)(2)D(3)] in skeletal muscle cells involve tyrosine phosphorylation of MAP kinase (ERK1/2), c-Src kinase and the oncoprotein c-myc. In the present work, blockade of vitamin D receptor (VDR) expression (> or =80%) by preincubation of chick embryonic muscle cells with three different antisense oligonucleotides against the VDR mRNA (AS-VDR ODNs) significantly reduced (-94%) 1,25(OH)(2)D(3) stimulation of c-myc tyrosine phosphorylation and inhibited c-Src tyrosine dephosphorylation implying lack of c-Src activation by the hormone. Coimmunoprecipitation experiments revealed that 1,25(OH)(2)D(3) induces the formation of complexes between c-Src and c-myc, in agreement with the above results and previous studies showing hormone-dependent association between c-Src and tyrosine phosphorylated VDR and c-Src mediated c-myc tyrosine phosphorylation. MAPK tyrosine phosphorylation by 1,25(OH)(2)D(3) was affected to a lesser extent (-35%) by transfection with AS-VDR ODNs implying that both VDR-dependent and VDR-independent signalling mediate hormone stimulation of MAPK. These are the first results providing direct evidence on the participation of the VDR in non-genomic 1,25(OH)(2)D(3) signal transduction. Activation of tyrosine phosphorylation cascades through this mechanism may contribute to hormone regulation of muscle growth.

The tyrosine kinase c-Src is required for 1,25(OH)2-vitamin D3 signalling to the nucleus in muscle cells

We have recently shown that the hormonal form of vitamin D3, 1,25(OH)2-vitamin D3 (1,25(OH)2D3), stimulates the enzymatic activity of the non-receptor protein tyrosine kinase c-Src in skeletal muscle cells. In this study we show that intracellular and extracellular Ca2+ chelation with BAPTA and EGTA, respectively, blocked hormone stimulation of c-Src activity/dephosphorylation, indicating that the calcium messenger system is an upstream activator of c-Src. Tyrosine phosphorylation and stimulation of the growth-related mitogen-activated protein kinase (MAPK) by 1,25(OH)2D3 was shown to be dependent on activation of c-Src, since pretreatment with the c-Src specific inhibitor PP1 or muscle cell transfection with an antisense oligodeoxynucleotide directed against c-Src mRNA markedly reduced hormone stimulation of MAPK phosphorylation. Evidence was obtained indicating that MAPK is then translocated to the cell nucleus in active phosphorylated form and induces the expression of c-myc oncoprotein, as the MAPK kinase (MEK) inhibitor PD98059 abolished stimulation of c-myc synthesis by 1,25(OH)2D3. In addition, the hormone rapidly stimulated tyrosine phosphorylation of c-myc. In cells pretreated with PP1 (4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo-D3,4-pyrimidine), the 1,25(OH)2D3-induced increase in tyrosine phosphorylation of c-myc was suppressed. Taken together, these results demonstrate that 1,25(OH)2D3 stimulates proliferation-associated signalling pathways in skeletal muscle cells and implicate c-Src kinase as mediator of this response.