Cardiac intracellular calcium release channels: role in heart failure.
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Animals↗
Biomedical subjects
A R Marks
Publications and source records attributed to A R Marks.
PKA phosphorylation dissociates FKBP12.6 from the calcium release channel (ryanodine receptor): defective regulation in failing hearts.
The ryanodine receptor (RyR)/calcium release channel on the sarcoplasmic reticulum (SR) is the major source of calcium (Ca2+) required for cardiac muscle excitation-contraction (EC) coupling. The channel is a tetramer comprised of four type 2 RyR polypeptides (RyR2) and four FK506 binding proteins (FKBP12.6). We show that protein kinase A (PKA) phosphorylation of RyR2 dissociates FKBP12.6 and regulates the channel open probability (Po). Using cosedimentation and coimmunoprecipitation we have defined a macromolecular complex comprised of RyR2, FKBP12.6, PKA, the protein phosphatases PP1 and PP2A, and an anchoring protein, mAKAP. In failing human hearts, RyR2 is PKA hyperphosphorylated, resulting in defective channel function due to increased sensitivity to Ca2+-induced activation.
Animals↗
Calcineurin is downstream of the inositol 1,4,5-trisphosphate receptor in the apoptotic and cell growth pathways.
The inositol 1,4,5-trisphosphate receptor (IP(3)R) is a calcium (Ca(2+)) release channel found on the endoplasmic reticulum of virtually all types of cells. Human T lymphocytes (Jurkat) that are made deficient in IP(3)R do not generate Ca(2+) signals in response to T cell receptor stimulation, fail to translocate the nuclear factor for activated T cells to the nucleus, and are remarkably resistant to induction of apoptosis with CD95 (Fas), dexamethasone, gamma irradiation, and T cell receptor stimulation using anti-CD3 antibody. Expression of constitutively active calcineurin A in IP(3)R-deficient T cells restored nuclear factor for activated T cells translocation to the nucleus and dephosphorylation of Bad and rendered the cells sensitive to apoptotic inducers. Induction of apoptosis required both active calcineurin A (DeltaCnA) and activation-dependent colocalization of CnA with its substrate. Thus, the Ca(2+)-dependent phosphatase calcineurin (CnA) is downstream of the IP(3)R in both the cell growth and apoptotic signaling pathways.
Apoptosis↗
Intracellular calcium release channel expression during embryogenesis.
The release of intracellular calcium (Ca2+) via either inositol 1,4, 5-trisphosphate receptors (IP3R) or ryanodine receptors (RyR) activates a wide variety of signaling pathways in virtually every type of cell. In the present study we demonstrate that at early stages of development IP3R mRNA and functional IP3-gated Ca2+ release channels are widely expressed in virtually all tissues in murine embryos. As organogenesis proceeds, more specialized RyR channels are expressed in many cell types and the triggering mechanisms for intracellular Ca2+ release become more diverse to include IP3-dependent and voltage-dependent and Ca2+-induced Ca2+ release. As development proceeds virtually all cell types continue to express IP3R channels but in excitable cells including skeletal and cardiac muscles the major Ca2+ release channels are RyRs. This developmental switch from predominantly IP3-mediated to both IP3-mediated and IP3-independent pathways for intracellular Ca2+ release is consistent with data showing that IP3R plays an important regulatory role in cellular proliferation and apoptosis, whereas RyR is required for other cellular functions including muscle contraction.
Animals↗
Cell cycle progression and proliferation despite 4BP-1 dephosphorylation.
Proliferation and cell cycle progression in response to growth factors require de novo protein synthesis. It has been proposed that binding of the eukaryotic translation initiation factor 4E (eIF-4E) to the inhibitory protein 4BP-1 blocks translation by preventing access of eIF-4G to the 5' cap of the mRNA. The signal for translation initiation is thought to involve phosphorylation of 4BP-1, which causes it to dissociate from eIF-4E and allows eIF-4G to localize to the 5' cap. It has been suggested that the ability of the macrolide antibiotic rapamycin to inhibit 4BP-1 phosphorylation is responsible for the potent antiproliferative property of this drug. We now show that rapamycin-resistant cells exhibited normal proliferation despite dephosphorylation of 4BP-1 that allows it to bind to eIF-4E. Moreover, despite rapamycin-induced dephosphorylation of 4BP-1, eIF-4E-eIF-4G complexes (eIF-4F) were still detected. In contrast, amino acid withdrawal, which caused a similar degree of 4BP-1 dephosphorylation, resulted in dissociation of the eIF-4E-eIF-4G complex. Thus, 4BP-1 dephosphorylation is not equivalent to eIF-4E inactivation and does not explain the antiproliferative property of rapamycin.
Adaptor Proteins, Signal Transducing↗
Ceramide triggers intracellular calcium release via the IP(3) receptor in Xenopus laevis oocytes.
Ceramide, a product of sphingomyelin turnover, is a lipid second messenger that mediates diverse signaling pathways, including those leading to cell cycle arrest and differentiation. The mechanism(s) by which ceramide signals downstream events have not been fully elucidated. Here we show that, in Xenopus laevis oocytes, ceramide-induced maturation is associated with the release of intracellular calcium stores. Ceramide caused a dose-dependent elevation in the second messenger inositol 1,4,5-trisphosphate (IP(3)) via activation of G(q/11)alpha and phospholipase C-betaX. Elevation of IP(3), in turn, activated the IP(3) receptor calcium release channel on the endoplasmic reticulum, resulting in a rise in cytoplasmic calcium. Thus our study demonstrates that cross talk between the ceramide and phosphoinositide signaling pathways modulates intracellular calcium homeostasis.
Animals↗
FKBP12 modulates gating of the ryanodine receptor/calcium release channel.
Excitation-contraction (EC) coupling in muscle requires the activation of intracellular calcium release channels (CRC). Four type 1 ryanodine receptor (RyR1) molecules form each tetrameric CRC. Each RyR1 contains a binding site for the FK506 binding protein (FKBP12), a cis-trans peptidyl-prolyl isomerase that is required for coordinated gating of the four RyR1 subunits comprising the channel. When FKBP12 is bound to RyR1, it stabilizes the four subunits that form each CRC. We propose that binding of one FKBP12 to each RyR1 lowers the energy of twisted-amide peptidyl-prolyl bonds and stabilizes RyR1 in a conformation that permits coordinated gating of the four RyR1 subunits.
Animals↗
Coupled gating between individual skeletal muscle Ca2+ release channels (ryanodine receptors)
Excitation-contraction coupling in skeletal muscle requires the release of intracellular calcium ions (Ca2+) through ryanodine receptor (RyR1) channels in the sarcoplasmic reticulum. Half of the RyR1 channels are activated by voltage-dependent Ca2+ channels in the plasma membrane. In planar lipid bilayers, RyR1 channels exhibited simultaneous openings and closings, termed "coupled gating." Addition of the channel accessory protein FKBP12 induced coupled gating, and removal of FKBP12 uncoupled channels. Coupled gating provides a mechanism by which RyR1 channels that are not associated with voltage-dependent Ca2+ channels can be regulated.
Animals↗
Intact temporal memory in amnesic patients.
Current theories propose that amnesia is caused by an inability to encode the temporal properties of recent events and/or to associate information across time. The present investigation tested this postulation by manipulating the recency effect which is theorized to be caused by the encoding of temporal information. The continual-distractor paradigm was used to vary the temporal properties of recently presented lists. Amnesics' recall responded normally to the temporal manipulations in lists ranging from 18-54 s. In contrast, overall recall was impaired compared to normals in all conditions and across all positions, including the final position. These findings dissociate memory for temporal information from overall levels of recall. They suggest that the amnesic patient's memory deficit is not caused by an inability to encode temporally associated information.
Aged↗
Effect of 2-CDA on thrombocytopenia in myelofibrosis.
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Cladribine↗
Temporal distinctiveness and modality.
It has been proposed that auditory stimuli are more temporally discriminable in memory than visual stimuli. Studies using the continual-distractor paradigm have provided both supporting and contradictory evidence for this hypothesis. The conflicting reports differed, however, in the modality of the interleaved distractor tasks. The present experiments manipulated both word and distractor-task modality. Results showed that aurally presented word lists were more sensitive to temporal schedules of presentation when the distractor task was auditory than when it was visual. The same effect was not consistently found for visually presented word lists. Such an interaction may help explain the previously reported disparate findings and suggests that the auditory modality, in the presence of silent distraction, can reduce participants' use of temporal-distinctiveness information at retrieval.
Acoustic Stimulation↗
T cells deficient in inositol 1,4,5-trisphosphate receptor are resistant to apoptosis.
The type 1 inositol 1,4,5-trisphosphate receptor (IP3R1) calcium release channel is present on the endoplasmic reticulum of most cell types. T lymphocytes which have been made deficient in IP3R1 lack detectable IP3-induced intracellular calcium release and exhibit defective signaling via the T-cell receptor (TCR) (T. Jayaraman, E. Ondriasova, K. Ondrias, D. Harnick, and A. R. Marks, Proc. Natl. Acad. Sci. USA 92:6007-6011, 1995). We now show that IP3R1-deficient T cells are resistant to apoptosis induced by dexamethasone, TCR stimulation, ionizing radiation, and Fas. Resistance to TCR-mediated apoptosis in IP3R1-deficient cells is reversed by pharmacologically raising cytoplasmic calcium levels. TCR-mediated apoptosis can be induced in calcium-free media, indicating that extracellular calcium influx is not required. These findings suggest that intracellular calcium release via the IP3R1 is a critical mediator of apoptosis.
Apoptosis↗
Intracellular calcium-release channels: regulators of cell life and death.
Intracellular Ca2+-release channels on the sarcoplasmic reticulum of striated muscle [ryanodine receptors (RyRs)] and on the endoplasmic reticulum of almost all types of cells [inositol 1,4,5-trisphosphate receptors (IP3Rs)] comprise a unique family of molecules that are structurally and functionally distinct from all other known ion channels. These channels play crucial roles in Ca2+-mediated signaling that triggers excitation-contraction coupling, T-lymphocyte activation, fertilization, and many other cellular functions. Three forms of RyR have been identified: RyR1, expressed predominantly in skeletal muscle; RyR2, expressed predominantly in cardiac muscle; and RyR3, expressed in specialized muscles and nonmuscle tissues including the brain. RyR channels are tetramers composed of four subunits each with a molecular mass of approximately 560,000 Da. The tetrameric structures of RyR1 and RyR2 are stabilized by a channel-associated protein known as the FK506 binding protein (FKBP). FKBP is the cytosolic receptor for the immunosuppressant drugs FK506 and rapamycin that inhibit the prolyl isomerase activity of FKBP and can dissociate FKBP from RyRs. Rapamycin and FK506 increase the sensitivity of RyRs to agonists such as caffeine and could be a cause of cardiac dysfunction associated with high-dose immunosuppressant therapy by promoting leakage of Ca2+ from the sarcoplasmic reticulum. The role of prolyl isomerase activity of FKBP in regulating RyR function remains uncertain, and several models have been proposed that could explain how the channel is modulated by its association with FKBP. Three forms of IP3Rs (types 1, 2 and 3) have been characterized by cDNA cloning. Most cells have at least one form of IP3R, and many express all three types. Like RyRs, the IP3R channels are tetramers composed of four subunits (approximately 300,000 Da each). IP3R1 function is regulated by at least two major cellular signaling pathways: the second messenger IP3 activates the channel, and phosphorylation by nonreceptor protein tyrosine kinases (e.g., Fyn) increase its open probability. During end-stage human heart failure, RyR2 mRNA and protein are downregulated, whereas IP3R1 is upregulated, suggesting that altered Ca2+-release channel levels may contribute to defects in Ca2+ homeostasis. Cells that are deficient in IP3R1 exhibit defective T cell-receptor signaling and thus cannot be activated by T cell-receptor stimulation. IP3R1-deficient cells are also resistant to induced apoptosis. Thus RyRs and IP3Rs play critical roles in fundamental and diverse signaling phenomena that include excitation-contraction coupling, T-cell activation, and programmed cell death.
Animals↗
Role of inositol 1,4,5-trisphosphate receptors in regulating apoptotic signaling and heart failure.
The inositol 1,4,5-trisphosphate receptor (IP3R) is an endoplasmic reticular calcium release channel found in most cell types. Calcium signaling mediated by IP3Rs regulates a wide variety of physiological processes, including smooth muscle contraction, immune function, and fertility. We have focused on the role of the IP3R in programmed cell death and the regulation of IP3R levels in heart failure, a condition shown to be associated with cardiomyocyte apoptosis. During end-stage human heart failure, we have demonstrated that type 1 IP3R (IP3R1) mRNA and protein levels are up-regulated, in contrast to other cardiac calcium regulatory proteins, such as the type 2 ryanodine receptor (RYR2) and type IIa sarcoplasmic reticulum calcium adenosine triphosphatase (SERCA2), which are down-regulated. These data suggest that altered calcium channel expression may contribute to the defects in calcium homeostasis during heart failure. Furthermore, regulation of the IP3R may have implications for the survival of cardiac myocytes. Data from our laboratory have linked IP3R expression with susceptibility to apoptosis. IP3R-deficient T cells are resistant to apoptosis induced by dexamethasone, T cell receptor stimulation, ionizing radiation, and Fas. These findings suggest that intracellular calcium release via IP3Rs is a critical mediator of apoptosis. Thus the IP3R, which is up-regulated during human heart failure, may play a role in cardiomyocyte apoptosis and therefore in the pathophysiology of heart failure.
Apoptosis↗
Rapamycin inhibits vascular smooth muscle cell migration.
Abnormal vascular smooth muscle cell (SMC) proliferation and migration contribute to the development of restenosis after percutaneous transluminal coronary angioplasty and accelerated arteriopathy after cardiac transplantation. Previously, we reported that the macrolide antibiotic rapamycin, but not the related compound FK506, inhibits both human and rat aortic SMC proliferation in vitro by inhibiting cell cycle-dependent kinases and delaying phosphorylation of retinoblastoma protein (Marx, S.O., T. Jayaraman, L.O. Go, and A.R. Marks. 1995. Circ. Res. 362:801). In the present study the effects of rapamycin on SMC migration were assayed in vitro using a modified Boyden chamber and in vivo using a porcine aortic SMC explant model. Pretreatment with rapamycin (2 ng/ml) for 48 h inhibited PDGF-induced migration (PDGF BB homodimer; 20 ng/ml) in cultured rat and human SMC (n = 10; P < 0.0001), whereas FK506 had no significant effect on migration. Rapamycin administered orally (1 mg/kg per d for 7 d) significantly inhibited porcine aortic SMC migration compared with control (n = 15; P < 0.0001). Thus, in addition to being a potent immunosuppressant and antiproliferative, rapamycin also inhibits SMC migration.
Administration, Oral↗
Wild type and mutant human heart (R)-3-hydroxybutyrate dehydrogenase expressed in insect cells.
(R)-3-Hydroxybutyrate dehydrogenase (BDH) is a lipid-requiring mitochondrial enzyme with a specific requirement of phosphatidylcholine (PC) for function. PC is an allosteric activator that enhances NAD(H) binding to BDH. The enzyme serves as a paradigm to study specific lipid-protein interactions in membranes. Analysis of the primary sequence of BDH, as determined by molecular cloning, predicts that lipid binding and substrate specificity are contributed by the C-terminal third of the protein [Marks, A. R., McIntyre, J. O., Duncan, T. M., Erdjument-Bromage, H., Tempst, P., & Fleischer, S. (1992) J. Biol. Chem. 267, 15459-15463]. The mature form of human heart BDH has now been expressed in catalytically active form in insect cells (Sf9, Spodoptera frugiperda) transfected with BDH-cDNA in baculovirus. Endogenous PC in the insect cells fulfills the lipid requirement for the expressed BDH since enzymatic activity is lost upon digestion with phospholipase A2 and restored selectively by reconstitution with PC vesicles. The K(m)s for NAD+ and (R)-3-hydroxybutyrate (R-HOB) of expressed BDH are similar to those for bovine heart or rat liver BDH in mitochondria. Replacing Cys242 (the only cysteine in the C-terminal domain) with serine by site-directed mutagenesis resulted in a 10-fold increase in K(m) for R-HOB with no change in the K(m) for NAD+, indicating a role for Cys242 in substrate binding. Carboxypeptidase cleavage studies had indicated a requirement of the C-terminal for catalysis and a role in lipid binding [Adami, P., Duncan, T. M., McIntyre, J. O., Carter, C. E., Fu, C., Melin, M., Latruffe, N., & Fleischer, S. (1993) Biochem J. 292, 863-872]. We now show that deletion of twelve C-terminal amino acids to form a truncated BDH mutant results in loss of enzymic function. The expression in Sf 9 cells of the constitutively active full-length mature form of human heart BDH and the first expression and characterization of BDH mutants validate this system for structure-function studies of BDH.
3-Hydroxybutyric Acid↗
Regulation of the inositol 1,4,5-trisphosphate receptor by tyrosine phosphorylation.
Tyrosine kinases indirectly raise intracellular calcium concentration ([Ca2+]i) by activating phospholipases that generate inositol 1,4,5-trisphosphate (IP3). IP3 activates the IP3 receptor (IP3R), an intracellular calcium release channel on the endoplasmic reticulum. T cell receptor stimulation triggered a physical association between the nonreceptor protein tyrosine kinase Fyn and the IP3R, which induced tyrosine phosphorylation of the IP3R. Fyn activated an IP3-gated calcium channel in vitro, and tyrosine phosphorylation of the IP3R during T cell activation was reduced in thymocytes from fyn-/- mice. Thus, activation of the IP3R by tyrosine phosphorylation may play a role in regulating [Ca2+]i.
Animals↗
Regulation of calcium channel expression in neonatal myocytes by catecholamines.
Expression of the dihydropyridine (DHP) receptor (alpha 1 subunit of L-type calcium channel) in heart is regulated by differentiation and innervation and is altered in congestive heart failure. We examined the transmembrane signaling pathways by which norepinephrine regulates DHP receptor expression in cultured neonatal rat ventricular myocytes. Using a 1.3-kb rat cardiac DHP receptor probe, and Northern analysis quantified by laser densitometry, we found that norepinephrine exposure produced a 2.2-fold increase in DHP receptor mRNA levels at 2 h followed by a decline to 50% of control at 4-48 h (P < 0.02). The alpha-adrenergic agonist phenylephrine and a phorbol ester produced a decline in mRNA levels (8-48 h). The beta-adrenergic agonist isoproterenol and 8-bromo-cAMP produced a transient increase in mRNA levels. After 24 h of exposure to isoproterenol, 3H-(+)PN200-110 binding sites increased from 410 +/- 8 to 539 +/- 39 fmol/mg (P < 0.05). The number of functional calcium channels, estimated by whole-cell voltage clamp experiments, was also increased after 24 h of exposure to isoproterenol. Peak current density (recordings performed in absence of isoproterenol) increased from -10.8 +/- 0.8 (n = 23) to -13.9 +/- 1.0 pA/pF (n = 27) (P < 0.01). Other characteristics of the calcium current (voltage for peak current, activation, and inactivation) were unchanged. Exposure for 48 h to phenylephrine produced a significant decline in peak current density (P < 0.01). We conclude that beta -adrenergic transmembrane signaling increases DHP receptor mRNA and number of functional calcium channels and that alpha - adrenergic transmembrane signaling produces a reciprocal effect. Regulation of cardiac calcium channel expression by adrenergic pathways may have physiological and pathophysiological importance.
Adrenergic alpha-Agonists↗