The protein kinase inhibitor, staurosporine, inhibits L-type Ca2+ current in rabbit atrial myocytes

Staurosporine enhances ATRA-induced granulocytic differentiation in human leukemia U937 cells via the MEK/ERK signaling pathway

Although all-trans retinoic acid (ATRA) is regarded as a prominent example of differentiation therapy, it is not effective for the treatment of other subtypes of acute myeloid leukemia (AML) beyond acute promyelocytic leukemia (APL). Therefore, new strategies need to be explored to extend the efficacy of ATRA-based therapy to non-APL AML patients. In the present study, staurosporine, a protein kinase C (PKC) pan-inhibitor, exhibited synergism with ATRA to promote granulocytic differentiation in poorly ATRA-sensitive U937 cells but not in ATRA unresponsive K562 and Kasumi cells. Staurosporine or the combined treatment did not affect PKC activity in U937 cells. Moreover, other selective PKC inhibitors, UCN-01, Go6976 or rottlerin failed to enhance ATRA‑induced granulocytic differentiation in U937 cells. Therefore, staurosporine-enhanced ATRA-induced granulocytic differentiation in U937 cells may be independent of PKC. Staurosporine activated mitogen‑activated protein kinase kinase (MEK) and extracellular signal‑regulated kinase (ERK). Meanwhile, staurosporine also enhanced ATRA-promoted upregulation of the protein level of CCAAT/enhancer‑binding protein β (C/EBPβ) and C/EBPε in U937 cells. Furthermore, blockade of MEK activation suppressed staurosporine‑enhanced differentiation as well as the elevated protein level of C/EBPs. Taken together, we concluded that staurosporine enhanced ATRA‑induced granulocytic differentiation in U937 cells via MEK/ERK-mediated modulation of the protein level of C/EBPs.

Dual response of the KATP channels to staurosporine: a novel role of SUR2B, SUR1 and Kir6.2 subunits in the regulation of the atrophy in different skeletal muscle phenotypes

We investigated on the role of the genes encoding for the ATP-sensitive K(+)-channel (KATP) subunits (SUR1-2A/B, Kir6.2) in the atrophy induced "in vitro" by staurosporine (STS) in different skeletal muscle phenotypes of mouse. Patch-clamp and gene expression experiments showed that the expression/activity of the sarcolemma KATP channel subunits was higher in the fast-twitch than in the slow-twitch fibers. After 1 to 3h of incubation time, the STS (2.14×10(-6)M) treatment enhanced the expression/activity of the SUR2B, SUR1 and Kir6.2 subunit genes, but not SUR2A, in the slow-twitch muscle fibers, induced the caspase-3-9, Atrogin-1 and Murf-1 gene expression without affecting protein content. After 3 to 6h, the STS-related atrophy markedly down-regulated the SUR2B, SUR1 and Kir6.2 genes reducing the KATP currents and reduced the protein content/muscle weight ratio of the slow-twitch muscle by -36.4±6% (p<0.05). After 6 to 24h, no additional changes of the SUR1-2B and Kir6.2 gene expression and muscle protein were observed. In the fast-twitch muscles, STS mildly affected the atrophic genes and protein content, but potentiated the KATP currents down-regulating the Bnip-3 gene. Diazoxide (250-500×10(-6)M), a SUR1-2B/Kir6.2 channel opener, prevented the protein loss induced by STS in the slow-twitch muscle after 6h showing an EC50 of 1.35×10(-7)M and Emax of 75%, down-regulated the caspase-9 gene and enhanced the KATP currents. The enhanced expression/activity of the SUR2B, SUR1 and Kir6.2 genes are cytoprotective against STS-induced atrophy in the slow-twitch muscle; their reduced expression/activity is associated with proteolysis and atrophy in skeletal muscle.

Possible involvement of calcium channels and plasma membrane receptors on Staurosporine-induced neurite outgrowth

Staurosporine as a protein kinases inhibitor induced cell death or neurite outgrowth in PC12 cells. We investigated the involvement of calcium channel and plasma membrane receptors on staurosporine inducing neurite outgrowth in PC12 cells. PC12 cells were preincubated with NMDA receptor inhibitors (1.8 mM ketamine and 1µM MK801, treatment 1) or L-Type Calcium channels (100 μM nifedipine and 100 µM flavoxate hydrochloride, treatment 2) or calcium-calmoduline kinasses (10 μM trifluoprazine, treatment 3) and nifedipine, MK801, flavoxate hydrochloride and ketamine (treatment4) or without pretreatments (control). Then, the cells were cultured in RPMI culture medium containing 214nM staurosporine for induction of neurite outgrowth. The percentage of Cell cytotoxicity and apoptotic index was assessed. Total neurite length (TNL) and fraction of cell differentiation were assessed. After 24h, the percentage of cell cytotoxicity were increased in treatments 1, 2 and 4 compared with control (p<0.05). After 6h, apoptotic index was similar between all treatments. After 12h, apoptotic index were increased in treatment 4 compared with control (p<0.05). After 24h, apoptotic index were increased in treatments 1, 2 and 4 compared with control (p<0.05). TNL were decreased in treatments 1, 2 and 4 compared with control in different times of assessment (6, 12 and 24 h) (p<0.05). The fraction of cell differentiation were decreased in treatments 1, 2 and 4 compared with control (p<0.05). It can be concluded that the possible involvement of L-type calcium channel and the N-methyl D-aspartate receptor on staurosporine-induced neurite outgrowth process in PC12 cells.

Neurotoxic injury pathways in differentiated mouse motor neuron-neuroblastoma hybrid (NSC-34D) cells in vitro--limited effect of riluzole on thapsigargin, but not staurosporine, hydrogen peroxide and homocysteine neurotoxicity

The neuroblastoma-spinal motor neuron fusion cell line, NSC-34, in its differentiated form, NSC-34D, permits examining the effects of riluzole, a proven treatment for amyotrophic lateral sclerosis (ALS) on cell death induction by staurosporine (STS), thapsigargin (Thaps), hydrogen peroxide (H(2)O(2)) and homocysteine (HCy). These neurotoxins, applied exogenously, have mechanisms of action related to the various proposed molecular pathogenetic pathways in ALS and are differentiated from endogenous cell death that is associated with cytoplasmic aggregate formation in motor neurons. Nuclear morphology, caspase-3/7 activation and high content imaging were used to assess toxicity of these neurotoxins with and without co-treatment with riluzole, a benzothiazole compound with multiple pharmacological actions. STS was the most potent neurotoxin at killing NSC-34D cells with a toxic concentration at which 50% of maximal cell death is achieved (TC(50)=0.01μM), followed by Thaps (TC(50)=0.9μM) and H(2)O(2) (TC(50)=15μM) with HCy requiring higher concentrations to kill at the same level (TC(50)=2200μM). Riluzole provided neurorescue with a 20% absolute reduction (47.6% relative reduction) in apoptotic cell death against Thaps-induced NSC-34D cell (p≤0.05), but had no effect on STS-, H(2)O(2)- and HCy-induced NSC-34D cell death. This effect of riluzole on Thaps induction of cell death was independent of caspase-3/7 activation. Riluzole mitigated a toxin that can cause intracellular calcium dysregulation associated with endoplasmic reticulum (ER) stress but not toxins associated with other cell death mechanisms.

Activation of L-type Ca2+ channels by protein kinase C is reduced in smooth muscle-specific Na+/Ca2+ exchanger knockout mice

L-type voltage-gated Ca(2+) channels (LVGCs) are functionally downregulated in arterial smooth muscle (SM) cells (ASMCs) of mice with SM-specific knockout of Na(+)/Ca(2+) exchanger type-1 (NCX1(SM-/-)) (32). Here, using activators and inhibitors of protein kinase C (PKC), we explore the regulation of these channels by a PKC-dependent mechanism. In both wild-type (WT) and NCX1(SM-/-) myocytes, the PKC activator phorbol 12,13-dibutyrate (PDBu) increases LVGC conductance, decreases channel closing rate, and shifts the voltage dependence of channel opening to more negative potentials. Three different PKC inhibitors, bisindolylmaleimide, Ro-31-8220, and PKC 19-31, all decrease LVGC currents in WT myocytes and prevent the PDBu-induced increase in LVGC current. Dialysis of WT ASMCs with activated PKC increases LVGC current and decreases channel closing rate. These results demonstrate that PKC activates LVGCs in ASMCs. The phosphatase inhibitor calyculin A increases LVGC conductance by over 50%, indicating that the level of LVGC activation is a balance between phosphatase and PKC activities. PDBu causes a larger increase in LVGC conductance and a larger shift in voltage dependence in NCX1(SM-/-) myocytes than in WT myocytes. The inhibition of PKC with PKC 19-31 decreased LVGC conductance by 65% in WT myocytes but by only 37% in NCX1(SM-/-) myocytes. These results suggest that LVGCs are in a state of low PKC-induced phosphorylation in NCX1(SM-/-) myocytes. We conclude that in NCX1(SM-/-) myocytes, reduced Ca(2+) entry via NCX1 lowers cytosolic [Ca(2+)], thereby reducing PKC activation that lowers LVGC activation.

Mechanisms of transition from normal to reentrant electrical activity in a model of rabbit atrial tissue: interaction of tissue heterogeneity and anisotropy

Experimental evidence suggests that regional differences in action potential (AP) morphology can provide a substrate for initiation and maintenance of reentrant arrhythmias in the right atrium (RA), but the relationships between the complex electrophysiological and anatomical organization of the RA and the genesis of reentry are unclear. In this study, a biophysically detailed three-dimensional computer model of the right atrial tissue was constructed to study the role of tissue heterogeneity and anisotropy in arrhythmogenesis. The model of Lindblad et al. for a rabbit atrial cell was modified to incorporate experimental data on regional differences in several ionic currents (primarily, I(Na), I(CaL), I(K1), I(to), and I(sus)) between the crista terminalis and pectinate muscle cells. The modified model was validated by its ability to reproduce the AP properties measured experimentally. The anatomical model of the rabbit RA (including tissue geometry and fiber orientation) was based on a recent histological reconstruction. Simulations with the resultant electrophysiologically and anatomically detailed three-dimensional model show that complex organization of the RA tissue causes breakdown of regular AP conduction patterns at high pacing rates (>11.75 Hz): as the AP in the crista terminalis cells is longer, and electrotonic coupling transverse to fibers of the crista terminalis is weak, high-frequency pacing at the border between the crista terminalis and pectinate muscles results in a unidirectional conduction block toward the crista terminalis and generation of reentry. Contributions of the tissue heterogeneity and anisotropy to reentry initiation mechanisms are quantified by measuring action potential duration (APD) gradients at the border between the crista terminalis and pectinate muscles: the APD gradients are high in areas where both heterogeneity and anisotropy are high, such that intrinsic APD differences are not diminished by electrotonic interactions. Thus, our detailed computer model reconstructs complex electrical activity in the RA, and provides new insights into the mechanisms of transition from focal atrial tachycardia into reentry.

PKC-Independent Stimulation of Cardiac Na/Ca Exchanger by Staurosporine

[Ca(2+)](i) transients by reverse mode of cardiac Na(+)/Ca(2+) exchanger (NCX1) were recorded in fura-2 loaded BHK cells with stable expression of NCX1. Repeated stimulation of reverse NCX1 produced a long-lasting decrease of Ca(2+) transients ('rundown'). Rundown of NCX1 was independent of membrane PIP(2) depletion. Although the activation of protein kinase C (PKC) was observed during the Ca(2+) transients, neither a selective PKC inhibitor (calphostin C) nor a PKC activator (PMA) changed the degrees of rundown. By comparison, a non-specific PKC inhibitor, staurosporine (STS), reversed rundown in a dose-dependent and reversible manner. The action of STS was unaffected by pretreatment of the cells with calphostin C, PMA, or forskolin. Taken together, the results suggest that the stimulation of reverse NCX1 by STS is independent of PKC and/or PKA inhibition.

mGlu4 potentiation of K(2P)2.1 is dependant on C-terminal dephosphorylation

Two-pore domain potassium (K(2P)) channels are proposed to underlie the background or leak current found in many excitable cells. Extensive studies have been performed investigating the inhibition of K(2P)2.1 by Galpha(q)- and Galpha(s)-coupled G-protein-coupled receptors (GPCRs), whereas in the present study we investigate the mechanisms underlying Galpha(i)/Galpha(o)-coupled GPCR increases in K(2P)2.1 activity. Activation of mGlu4 increases K(2P)2.1 activity, with pharmacological inhibition of protein kinases and phosphatases revealing the involvement of PKA whereas PKC, PKG or protein phosphatases play no role. Mutational analysis of potential C-terminal phosphorylation sites indicates S333 to control approximately 70%, with S300 controlling approximately 30% of the increase in K(2P)2.1 activity following mGlu4 activation. These data reveal that activation of mGlu4 leads to an increase in K(2P)2.1 activity through a reduction in C-terminal phosphorylation, which represents a novel mechanism by which group III mGlu receptors may regulate cell excitability and synaptic activity.

The mitochondrial Ca2+-activated K+ channel activator, NS 1619 inhibits L-type Ca2+ channels in rat ventricular myocytes

We examined the effects of the mitochondrial Ca(2+)-activated K(+) (mitoBK(Ca)) channel activator NS 1619 on L-type Ca(2+) channels in rat ventricular myocytes. NS 1619 inhibited the Ca(2+) current in a dose-dependent manner. NS 1619 shifted the activation curve to more positive potentials, but did not have a significant effect on the inactivation curve. Pretreatment with inhibitors of membrane BK(Ca) channel, mitoBK(Ca) channel, protein kinase C, protein kinase A, and protein kinase G had little effect on the Ca(2+) current and did not alter the inhibitory effect of NS 1619 significantly. The application of additional NS 1619 in the presence of isoproterenol, a selective beta-adrenoreceptor agonist, reduced the Ca(2+) current to approximately the same level as a single application of NS 1619. In conclusion, our results suggest that NS 1619 inhibits the Ca(2+) current independent of the mitoBK(Ca) channel and protein kinases. Since NS 1619 is widely used to study mitoBK(Ca) channel function, it is essential to verify these unexpected effects of NS 1619 before experimental data can be interpreted accurately.

(±)3,4-Methylenedioxyamphetamine elicits action potential bursts in a central snail neuron

The effects of (+/-)3,4-methylenedioxyamphetamine (MDA) were studied in an identifiable RP4 neuron of the African snail, Achatina fulica Ferussac, using the two-electrode voltage-clamp method. The RP4 neuron generated spontaneous action potentials. Extracellular or intracellular application of MDA elicited action potential bursts of the central RP4 neuron. The action potential bursts elicited by MDA were not blocked when neurons were immersed in high-Mg2+ solution, Ca2+-free solution, nor after continuous perfusion with atropine, d-tubocurarine, propranolol, prazosin, haloperidol, sulpiride or methiothepin. Notably, the induction of action potential bursts was blocked by pretreatment with protein kinase C (PKC) inhibitors, chelerythrine and Ro 31-8220, but not by protein kinase A (PKA) inhibitors, KT-5720 and H89, nor by the phospholipase C (PLC) inhibitor, U73122. PKC activators, i.e., phorbol 12,13-dibutyrate (PDBu) and 1-oleoyl-2-acety-sn-glycerol (OAG; a membrane-permeant DAG analog), facilitate the induction of action potential bursts elicited by MDA. Voltage-clamp studies revealed that MDA decreased the delayed rectifying K+ current (I(KD)) of the RP4 neuron. Further, although Ro 31-8220 did not affect the I(KD), Ro 31-8220 decreased the inhibitory effect of MDA on the I(KD). These results suggest that the generation of action potential bursts elicited by MDA was not due to (1) the synaptic effects of neurotransmitters, (2) the cholinergic, adrenergic, dopaminergic or serotoninergic receptors of the excitable membrane. Instead, the MDA-elicited action potential bursts are closely related to PKC activity and the inhibitory effects on the I(KD).

Ionic involvement and kinase activity on the mechanism of nongenomic action of thyroid hormones on 45Ca2+ uptake in cerebral cortex from young rats

Thyroid hormones (TH) play important roles in brain development. Although most of the nongenomic actions of TH are known to be calcium-dependent, the effects of 3,5,3'-triiodo-L-thyronine (T(3)) or thyroxine (T(4)) on calcium influx in cerebral cortex of rats are not clear. In this study we investigate some mechanisms involved in the effect of T(3) and T(4) on Ca(2+) uptake in slices of cerebral cortex from 10-day-old male rats. Results indicated 10(-6)M T(3) or 10(-7)M T(4) was able to increase (45)Ca(2+) uptake after 30s of hormone exposure. The involvement of L- and T-type voltage-dependent Ca(2+) channels (VDCC) on the effect of TH on (45)Ca(2+) uptake was evidenced by using nifedipine and flunarizine, L- and T-type channel blockers, respectively. Otherwise, chloride currents were not involved in the hormone actions, as demonstrated by using 9-anthracene carboxylic acid, a Cl(-)-channel blocker. In addition, results demonstrated a PKC-dependent mechanism for both T(3) and T(4), as evidenced by stearoylcarnitine chloride, a specific PKC inhibitor. Furthermore, we verified that the T(3) action was also mediated by PKA activity, as demonstrated coincubating T(3) and KT 5720 (PKA inhibitor), and reinforced by using theophylline, a phosphodiesterase inhibitor. In contrast, concerning the effect of T(4), results suggest a partial involvement of PKA activity, and demonstrated that high cAMP levels were not able to support the effect of T(4), suggesting the participation of G inhibitory protein-coupled receptor in the action of this hormone on (45)Ca(2+) uptake. In conclusion, our results evidence a nongenomic action of TH promoting Ca(2+) influx by ionic channels involving mechanisms dependent on kinase activities. It is possible that the modulation of Ca(2+) channels by kinase activities represent an important membrane action of TH signaling mechanism in the central nervous system during development.

Mechanisms for gonadotropin-releasing hormone potentiation of growth hormone rebound following norepinephrine inhibition in goldfish pituitary cells

In the goldfish, norepinephrine (NE) inhibits growth hormone (GH) secretion through activation of pituitary alpha(2)-adrenergic receptors. Interestingly, a GH rebound is observed after NE withdrawal, which can be markedly enhanced by prior exposure to gonadotropin-releasing hormone (GnRH). Here we examined the mechanisms responsible for GnRH potentiation of this "postinhibition" GH rebound. In goldfish pituitary cells, alpha(2)-adrenergic stimulation suppressed both basal and GnRH-induced GH mRNA expression, suggesting that a rise in GH synthesis induced by GnRH did not contribute to its potentiating effect. Using a column perifusion approach, GnRH given during NE treatment consistently enhanced the GH rebound following NE withdrawal. This potentiating effect was mimicked by activation of PKC and adenylate cyclase (AC) but not by induction of Ca(2+) entry through voltage-sensitive Ca(2+) channels (VSCC). Furthermore, GnRH-potentiated GH rebound could be alleviated by inactivation of PKC, removal of extracellular Ca(2+), blockade of VSCC, and inhibition of Ca(2+)/calmodulin (CaM)-dependent protein kinase II (CaMKII). Inactivation of AC and PKA, however, was not effective in this regard. These results, as a whole, suggest that GnRH potentiation of GH rebound following NE inhibition is mediated by PKC coupled to Ca(2+) entry through VSCC and subsequent activation of CaMKII. Apparently, the Ca(2+)-dependent cascades are involved in GH secretion during the rebound phase but are not essential for the initiation of GnRH potentiation. Since GnRH has been previously shown to have no effects on cAMP synthesis in goldfish pituitary cells, the involvement of cAMP-dependent mechanisms in GnRH potentiation is rather unlikely.

Stimulation of fibroblast proliferation by neokyotorphin requires Ca2+ influx and activation of PKA, CaMK II and MAPK/ERK

Neokyotorphin [TSKYR, hemoglobin alpha-chain fragment (137-141)] has previously been shown to enhance fibroblast proliferation, its effect depending on cell density and serum level. Here we show the dependence of the effect of neokyotorphin on cell type and its correlation with the effect of protein kinase A (PKA) activator 8-Br-cAMP, but not the PKC activator 4beta-phorbol 12-myristate, 13-acetate (PMA). In L929 fibroblasts, the proliferative effect of neokyotorphin was suppressed by the Ca2+ L-type channel inhibitors verapamil or nifedipine, the intracellular Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester, kinase inhibitors H-89 (PKA), KN-62 (Ca2+/calmodulin-dependent kinase II) and PD98059 (mitogen-activated protein kinase). The proliferative effect of 8-Br-cAMP was also suppressed by KN-62 and PD98059. PKC suppression (downregulation with PMA or inhibition with bisindolylmaleimide XI) did not affect neokyotorphin action. The results obtained point to a cAMP-like action for neokyotorphin.

Slowing of the inactivation of voltage-dependent sodium channels by staurosporine, the protein kinase C inhibitor, in rabbit atrial myocytes

In this study, the effect of staurosporine, a potent protein kinase C (PKC) inhibitor, on Na+ current (I(Na)) was examined by whole-cell patch recording in rabbit atrial myocytes. The most prominent staurosporine effect was a slowing of I(Na) inactivation and 1 microM staurosporine reduced amplitude of I(Na) about 33%. Staurosporine decreased I(Na) at all potentials and slowed the I(Na) inactivation in a dose-dependent manner, with a Kd value of 1.107+/-0.162 microM. Staurosporine did not change the recovery kinetics and show use dependence. However, the activation and the steady-state inactivation curves were shifted toward more negative potentials (-5.5 and -5.1 mV, respectively). Two other PKC inhibitors, GF 109203X (1 microM) and chelerythrine (3 microM), did not show a slowing effect on I(Na) inactivation. In conclusion, our results indicate that the slowing of I(Na) inactivation by staurosporine seems not to be through blockade of PKC rather to act directly on the Na+ channels, and the direct blocking effects of staurosporine on the Na+ channel should be taken into consideration when staurosporine is used in functional studies of ion channel modulation by protein phosphorylation.