Hea-Jin Jung

University of California, Los Angeles, Los Angeles, California, United States

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Publications (20)112.74 Total impact

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    ABSTRACT: B-type lamins (lamins B1 and B2) have been considered to be essential for many crucial functions in the cell nucleus (e.g., DNA replication, mitotic spindle formation). However, this view has been challenged by the observation that an absence of both B-type lamins in keratinocytes had no effect on cell proliferation or the development of skin and hair. The latter findings raised the possibility that the functions of B-type lamins might be subserved by lamins A and C. To explore that idea, we created mice lacking all nuclear lamins in keratinocytes. Those mice developed ichthyosis and a skin barrier defect, which led to death from dehydration within a few days after birth. Microscopy of nuclear lamin-deficient skin revealed hyperkeratosis and a disordered stratum corneum with an accumulation of neutral lipid droplets; however, BrdU incorporation into keratinocytes was normal. Skin grafting experiments confirmed the stratum corneum abnormalities and normal BrdU uptake. Interestingly, the absence of nuclear lamins in keratinocytes resulted in an interspersion of nuclear/endoplasmic reticulum membranes with the chromatin. Thus, a key function of the nuclear lamina is to serve as a "fence" and prevent the incursion of cytoplasmic organelles into the nuclear chromatin.
    Molecular and cellular biology. 10/2014;
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    ABSTRACT: Lamins B1 and B2 have a high degree of sequence similarity and are widely expressed from the earliest stages of development. Studies of Lmnb1 and Lmnb2 knockout mice revealed that both of the B-type lamins are crucial for neuronal migration in the developing brain. These observations naturally posed the question of whether the two B-type lamins might play redundant functions in the development of the brain. To explore that issue, Lee and coworkers generated "reciprocal knock-in mice" (knock-in mice that produce lamin B1 from the Lmnb2 locus and knock-in mice that produce lamin B2 from the Lmnb1 locus). Both lines of knock-in mice manifested neurodevelopmental abnormalities similar to those in conventional knockout mice, indicating that lamins B1 and B2 have unique functions and that increased production of one B-type lamin cannot compensate for the loss of the other.
    Nucleus (Austin, Texas) 06/2014; 5(4).
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    ABSTRACT: Lamins B1 and B2 (B-type lamins) have very similar sequences and are expressed ubiquitously. Also, both Lmnb1- and Lmnb2-deficient mice die shortly after birth with neuronal layering abnormalities in the cerebral cortex, a consequence of defective neuronal migration. The similarities in amino acid sequences, expression patterns, and knockout phenotypes raise the question of whether the two proteins have redundant functions. To investigate this topic, we generated "reciprocal knock-in mice"-mice that make lamin B2 from the Lmnb1 locus (Lmnb1B2/B2) and mice that make lamin B1 from the Lmnb2 locus (Lmnb2B1/B1). Lmnb1B2/B2 mice produced increased amounts of lamin B2 but no lamin B1; they died shortly after birth with neuronal layering abnormalities in the cerebral cortex. However, the defects in Lmnb1B2/B2 mice were less severe than those in Lmnb1 knockout mice, indicating that increased amounts of lamin B2 partially ameliorate the abnormalities associated with lamin B1 deficiency. Similarly, increased amounts of lamin B1 in Lmnb2B1/B1 mice did not prevent the neurodevelopmental defects elicited by lamin B2 deficiency. We conclude that lamin B1 and lamin B2 have unique roles in the developing brain and that increased production of one B-type lamin does not fully complement the loss of the other.
    Molecular biology of the cell 03/2014; · 5.98 Impact Factor
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    ABSTRACT: Lamins A and C (products of the LMNA gene) are found in roughly equal amounts in peripheral tissues, but the brain produces mainly lamin C and little lamin A. In HeLa cells and fibroblasts, the expression of prelamin A (the precursor to lamin A) can be reduced by miR-9, but the relevance of those cell culture studies to lamin A regulation in the brain was unclear. To address this issue, we created two new Lmna knock-in alleles, one (Lmna(PLAO-5NT)) with a 5-bp mutation in a predicted miR-9 binding site in prelamin A's 3' UTR, and a second (Lmna(PLAO-UTR)) in which prelamin A's 3' UTR was replaced with lamin C's 3' UTR. Neither allele had significant effects on lamin A levels in peripheral tissues; however, both substantially increased prelamin A transcript levels and lamin A protein levels in the cerebral cortex and the cerebellum. The increase in lamin A expression in the brain was more pronounced with the Lmna(PLAO-UTR) allele than with the Lmna(PLAO-5NT) allele. With both alleles, the increased expression of prelamin A transcripts and lamin A protein was greater in the cerebral cortex than in the cerebellum. Our studies demonstrate the in vivo importance of prelamin A's 3' UTR and its miR-9 binding site in regulating lamin A expression in the brain. The reduced expression of prelamin A in the brain likely explains why children with Hutchinson-Gilford progeria syndrome (a progeroid syndrome caused by a mutant form of prelamin A) are spared from neurodegenerative disease.The abstract has been published online on the ASCB website (2013) for the ASCB annual meeting. Abstract No. 1622. http://www.miracd.com/Verify/ASCB2013/submission/temp/rad838C6.pdf.
    Human Molecular Genetics 11/2013; · 7.69 Impact Factor
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    ABSTRACT: The role of protein farnesylation in lamin A biogenesis and the pathogenesis of progeria has been studied in considerable detail, but the importance of farnesylation for the B-type lamins, lamin B1 and lamin B2, has received little attention. Lamins B1 and B2 are expressed in nearly every cell type from the earliest stages of development, and they have been implicated in a variety of functions within the cell nucleus. To assess the importance of protein farnesylation for B-type lamins, we created knock-in mice expressing nonfarnesylated versions of lamin B1 and lamin B2. Mice expressing nonfarnesylated lamin B2 developed normally and were free of disease. In contrast, mice expressing nonfarnesylated lamin B1 died soon after birth, with severe neurodevelopmental defects and striking nuclear abnormalities in neurons. The nuclear lamina in migrating neurons was pulled away from the chromatin so that the chromatin was left "naked" (free from the nuclear lamina). Thus, farnesylation of lamin B1-but not lamin B2-is crucial for brain development and for retaining chromatin within the bounds of the nuclear lamina during neuronal migration.
    Proceedings of the National Academy of Sciences 05/2013; · 9.81 Impact Factor
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    ABSTRACT: A clinical trial of a protein farnesyltransferase inhibitor (lonafarnib) for the treatment of Hutchinson-Gilford progeria syndrome (HGPS) was recently completed. Here, we discuss the mutation that causes HGPS, the rationale for inhibiting protein farnesyltransferase, the potential limitations of this therapeutic approach, and new potential strategies for treating the disease.
    Science translational medicine 02/2013; 5(171):171ps3. · 10.76 Impact Factor
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    ABSTRACT: The nuclear lamina is an intermediate filament meshwork composed largely of four nuclear lamins - lamins A and C (A-type lamins) and lamins B1 and B2 (B-type lamins). Located immediately adjacent to the inner nuclear membrane, the nuclear lamina provides a structural scaffolding for the cell nucleus. It also interacts with both nuclear membrane proteins and the chromatin and is thought to participate in many important functions within the cell nucleus. Defects in A-type lamins cause cardiomyopathy, muscular dystrophy, peripheral neuropathy, lipodystrophy, and progeroid disorders. In contrast, the only bona fide link between the B-type lamins and human disease is a rare demyelinating disease of the central nervous system - adult-onset autosomal-dominant leukoencephalopathy, caused by a duplication of the gene for lamin B1. However, this leukoencephalopathy is not the only association between the brain and B-type nuclear lamins. Studies of conventional and tissue-specific knockout mice have demonstrated that B-type lamins play essential roles in neuronal migration in the developing brain and in neuronal survival. The importance of A-type lamin expression in the brain is unclear, but it is intriguing that the adult brain preferentially expresses lamin C rather than lamin A, very likely due to microRNA-mediated removal of prelamin A transcripts. Here, we review recent studies on nuclear lamins, focusing on the function and regulation of the nuclear lamins in the central nervous system.
    Molecular Neurobiology 10/2012; · 5.47 Impact Factor
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    ABSTRACT: Protein farnesyltransferase (FTase) inhibitors, generally called "FTIs," block the farnesylation of prelamin A, inhibiting the biogenesis of mature lamin A and leading to an accumulation of prelamin A within cells. A recent report found that a GGTI, an inhibitor of protein geranylgeranyltransferase-I (GGTase-I), caused an exaggerated accumulation of prelamin A in the presence of low amounts of an FTI. This finding was interpreted as indicating that prelamin A can be alternately prenylated by GGTase-I and that inhibiting both protein prenyltransferases leads to more prelamin A accumulation than blocking FTase alone. Here, we tested an alternative hypothesis-GGTIs are not specific for GGTase-I, and they lead to prelamin A accumulation by inhibiting ZMPSTE24 (a zinc metalloprotease that converts farnesyl-prelamin A to mature lamin A). In our studies, commonly used GGTIs caused prelamin A accumulation in human fibroblasts, but the prelamin A in GGTI-treated cells exhibited a more rapid electrophoretic mobility than prelamin A from FTI-treated cells. The latter finding suggested that the prelamin A in GGTI-treated cells might be farnesylated (which would be consistent with the notion that GGTIs inhibit ZMPSTE24). Indeed, metabolic labeling studies revealed that the prelamin A in GGTI-treated fibroblasts is farnesylated. Moreover, biochemical assays of ZMPSTE24 activity showed that ZMPSTE24 is potently inhibited by a GGTI. Our studies show that GGTIs inhibit ZMPSTE24, leading to an accumulation of farnesyl-prelamin A. Thus, caution is required when interpreting the effects of GGTIs on prelamin A processing.
    The Journal of Lipid Research 03/2012; 53(6):1176-82. · 4.39 Impact Factor
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    ABSTRACT: The nuclear lamina is composed mainly of lamins A and C (A-type lamins) and lamins B1 and B2 (B-type lamins). Dogma has held that lamins B1 and B2 play unique and essential roles in the nucleus of every eukaryotic cell. Recent studies have raised doubts about that view but have uncovered crucial roles for lamins B1 and B2 in neuronal migration during the development of the brain. The relevance of lamins A and C in the brain remains unclear, but it is intriguing that prelamin A expression in the brain is low and is regulated by miR-9, a brain-specific microRNA.
    Journal of Biological Chemistry 03/2012; 287(20):16103-10. · 4.65 Impact Factor
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    ABSTRACT: Lamins A and C, alternatively spliced products of the LMNA gene, are key components of the nuclear lamina. The two isoforms are found in similar amounts in most tissues, but we observed an unexpected pattern of expression in the brain. Western blot and immunohistochemistry studies showed that lamin C is abundant in the mouse brain, whereas lamin A and its precursor prelamin A are restricted to endothelial cells and meningeal cells and are absent in neurons and glia. Prelamin A transcript levels were low in the brain, but this finding could not be explained by alternative splicing. In lamin A-only knockin mice, where alternative splicing is absent and all the output of the gene is channeled into prelamin A transcripts, large amounts of lamin A were found in peripheral tissues, but there was very little lamin A in the brain. Also, in knockin mice expressing exclusively progerin (a toxic form of prelamin A found in Hutchinson-Gilford progeria syndrome), the levels of progerin in the brain were extremely low. Further studies showed that prelamin A expression, but not lamin C expression, is down-regulated by a brain-specific microRNA, miR-9. Expression of miR-9 in cultured cells reduced lamin A expression, and this effect was abolished when the miR-9-binding site in the prelamin A 3' UTR was mutated. The down-regulation of prelamin A expression in the brain could explain why mouse models of Hutchinson-Gilford progeria syndrome are free of central nervous system pathology.
    Proceedings of the National Academy of Sciences 02/2012; 109(7):E423-31. · 9.81 Impact Factor
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    ABSTRACT: Neuronal migration is essential for the development of the mammalian brain. Here, we document severe defects in neuronal migration and reduced numbers of neurons in lamin B1-deficient mice. Lamin B1 deficiency resulted in striking abnormalities in the nuclear shape of cortical neurons; many neurons contained a solitary nuclear bleb and exhibited an asymmetric distribution of lamin B2. In contrast, lamin B2 deficiency led to increased numbers of neurons with elongated nuclei. We used conditional alleles for Lmnb1 and Lmnb2 to create forebrain-specific knockout mice. The forebrain-specific Lmnb1- and Lmnb2-knockout models had a small forebrain with disorganized layering of neurons and nuclear shape abnormalities, similar to abnormalities identified in the conventional knockout mice. A more severe phenotype, complete atrophy of the cortex, was observed in forebrain-specific Lmnb1/Lmnb2 double-knockout mice. This study demonstrates that both lamin B1 and lamin B2 are essential for brain development, with lamin B1 being required for the integrity of the nuclear lamina, and lamin B2 being important for resistance to nuclear elongation in neurons.
    Molecular biology of the cell 12/2011; 22(23):4683-93. · 5.98 Impact Factor
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    ABSTRACT: It has been assumed, based largely on morphologic evidence, that human pluripotent stem cells (hPSCs) contain underdeveloped, bioenergetically inactive mitochondria. In contrast, differentiated cells harbour a branched mitochondrial network with oxidative phosphorylation as the main energy source. A role for mitochondria in hPSC bioenergetics and in cell differentiation therefore remains uncertain. Here, we show that hPSCs have functional respiratory complexes that are able to consume O(2) at maximal capacity. Despite this, ATP generation in hPSCs is mainly by glycolysis and ATP is consumed by the F(1)F(0) ATP synthase to partially maintain hPSC mitochondrial membrane potential and cell viability. Uncoupling protein 2 (UCP2) plays a regulating role in hPSC energy metabolism by preventing mitochondrial glucose oxidation and facilitating glycolysis via a substrate shunting mechanism. With early differentiation, hPSC proliferation slows, energy metabolism decreases, and UCP2 is repressed, resulting in decreased glycolysis and maintained or increased mitochondrial glucose oxidation. Ectopic UCP2 expression perturbs this metabolic transition and impairs hPSC differentiation. Overall, hPSCs contain active mitochondria and require UCP2 repression for full differentiation potential.
    The EMBO Journal 11/2011; 30(24):4860-73. · 9.82 Impact Factor
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    ABSTRACT: The B-type lamins are widely assumed to be essential for mammalian cells. In part, this assumption is based on a highly cited study that found that RNAi-mediated knockdown of lamin B1 or lamin B2 in HeLa cells arrested cell growth and led to apoptosis. Studies indicating that B-type lamins play roles in DNA replication, the formation of the mitotic spindle, chromatin organization and regulation of gene expression have fueled the notion that B-type lamins must be essential. But surprisingly, this idea had never been tested with genetic approaches. Earlier this year, a research group from UCLA reported the development of genetically modified mice that lack expression of both Lmnb1 and Lmnb2 in skin keratinocytes (a cell type that proliferates rapidly and participates in complex developmental programs). They reasoned that if lamins B1 and B2 were truly essential, then keratinocyte-specific lamin B1/lamin B2 knockout mice would exhibit severe pathology. Contrary to expectations, the skin and hair of lamin B1/lamin B2-deficient mice were quite normal, indicating that the B-type lamins are dispensable in some cell types. The same UCLA research group has gone on to show that lamin B1 and lamin B2 are critical for neuronal migration in the developing brain and for neuronal survival. The absence of either lamin B1 or lamin B2, or the absence of both B-type lamins, results in severe neurodevelopmental abnormalities.
    Nucleus (Austin, Texas) 11/2011; 2(6):562-9.
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    ABSTRACT: Lmna yields two major protein products in somatic cells, lamin C and prelamin A. Mature lamin A is produced from prelamin A by four posttranslational processing steps-farnesylation of a carboxyl-terminal cysteine, release of the last three amino acids of the protein, methylation of the farnesylcysteine, and the endoproteolytic release of the carboxyl-terminal 15 amino acids of the protein (including the farnesylcysteine methyl ester). Although the posttranslational processing of prelamin A has been conserved in vertebrate evolution, its physiologic significance remains unclear. Here we review recent studies in which we investigated prelamin A processing with Lmna knock-in mice that produce exclusively prelamin A (Lmna(PLAO)), mature lamin A (Lmna(LAO)) or nonfarnesylated prelamin A (Lmna(nPLAO)). We found that the synthesis of lamin C is dispensable in laboratory mice, that the direct production of mature lamin A (completely bypassing all prelamin A processing) causes no discernable pathology in mice, and that exclusive production of nonfarnesylated prelamin A leads to cardiomyopathy.
    Nucleus (Austin, Texas) 01/2011; 2(1):4-9.
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    ABSTRACT: Lamin A, a key component of the nuclear lamina, is generated from prelamin A by four post-translational processing steps: farnesylation, endoproteolytic release of the last three amino acids of the protein, methylation of the C-terminal farnesylcysteine, and finally, endoproteolytic release of the last 15 amino acids of the protein (including the farnesylcysteine methyl ester). The last cleavage step, mediated by ZMPSTE24, releases mature lamin A. This processing scheme has been conserved through vertebrate evolution and is widely assumed to be crucial for targeting lamin A to the nuclear envelope. However, its physiologic importance has never been tested. To address this issue, we created mice with a "mature lamin A-only" allele (Lmna(LAO)), which contains a stop codon immediately after the last codon of mature lamin A. Thus, Lmna(LAO/LAO) mice synthesize mature lamin A directly, bypassing prelamin A synthesis and processing. The levels of mature lamin A in Lmna(LAO/LAO) mice were indistinguishable from those in "prelamin A-only" mice (Lmna(PLAO/PLAO)), where all of the lamin A is produced from prelamin A. Lmna(LAO/LAO) exhibited normal body weights and had no detectable disease phenotypes. A higher frequency of nuclear blebs was observed in Lmna(LAO/LAO) embryonic fibroblasts; however, the mature lamin A in the tissues of Lmna(LAO/LAO) mice was positioned normally at the nuclear rim. We conclude that prelamin A processing is dispensable in mice and that direct synthesis of mature lamin A has little if any effect on the targeting of lamin A to the nuclear rim in mouse tissues.
    Journal of Biological Chemistry 05/2010; 285(27):20818-26. · 4.65 Impact Factor
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    ABSTRACT: Orai1 and STIM1 are critical components of Ca(2+) release-activated Ca(2+) (CRAC) channels that mediate store-operated Ca(2+) entry (SOCE) in immune cells. Although it is known that Orai1 and STIM1 co-cluster and physically interact to mediate SOCE, the cytoplasmic machinery modulating these functions remains poorly understood. We sought to find modulators of Orai1 and STIM1 using affinity protein purification and identified a novel EF-hand protein, CRACR2A (also called CRAC regulator 2A, EFCAB4B or FLJ33805). We show that CRACR2A interacts directly with Orai1 and STIM1, forming a ternary complex that dissociates at elevated Ca(2+) concentrations. Studies using knockdown mediated by small interfering RNA (siRNA) and mutagenesis show that CRACR2A is important for clustering of Orai1 and STIM1 upon store depletion. Expression of an EF-hand mutant of CRACR2A enhanced STIM1 clustering, elevated cytoplasmic Ca(2+) and induced cell death, suggesting its active interaction with CRAC channels. These observations implicate CRACR2A, a novel Ca(2+) binding protein that is highly expressed in T cells and conserved in vertebrates, as a key regulator of CRAC channel-mediated SOCE.
    Nature Cell Biology 04/2010; 12(5):436-46. · 20.76 Impact Factor
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    ABSTRACT: Store-operated Ca2+ entry (SOCE) due to activation of Ca2+ release-activated Ca2+ (CRAC) channels leads to sustained elevation of cytoplasmic Ca2+ and activation of lymphocytes. CRAC channels consisting of four pore-forming Orai1 subunits are activated by STIM1, an endoplasmic reticulum Ca2+ sensor that senses intracellular store depletion and migrates to plasma membrane proximal regions to mediate SOCE. One of the fundamental properties of CRAC channels is their Ca2+-dependent fast inactivation. To identify the domains of Orai1 involved in fast inactivation, we have mutated residues in the Orai1 intracellular loop linking transmembrane segment II to III. Mutation of four residues, V151SNV154, at the center of the loop (MutA) abrogated fast inactivation, leading to increased SOCE as well as higher CRAC currents. Point mutation analysis identified five key amino acids, N153VHNL157, that increased SOCE in Orai1 null murine embryonic fibroblasts. Expression or direct application of a peptide comprising the entire intracellular loop or the sequence N153VHNL157 blocked CRAC currents from both wild type (WT) and MutA Orai1. A peptide incorporating the MutA mutations had no blocking effect. Concatenated Orai1 constructs with four MutA monomers exhibited high CRAC currents lacking fast inactivation. Reintroduction of a single WT monomer (MutA-MutA-MutA-WT) was sufficient to fully restore fast inactivation, suggesting that only a single intracellular loop can block the channel. These data suggest that the intracellular loop of Orai1 acts as an inactivation particle, which is stabilized in the ion permeation pathway by the N153VHNL157 residues. These results along with recent reports support a model in which the N terminus and the selectivity filter of Orai1 as well as STIM1 act in concert to regulate the movement of the intracellular loop and evoke fast inactivation.
    Journal of Biological Chemistry 02/2010; 285(7):5066-5075. · 4.65 Impact Factor
  • Biophysical Journal 12/2009; 98:540. · 3.67 Impact Factor
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    ABSTRACT: Store-operated Ca(2+) entry (SOCE) due to activation of Ca(2+) release-activated Ca(2+) (CRAC) channels leads to sustained elevation of cytoplasmic Ca(2+) and activation of lymphocytes. CRAC channels consisting of four pore-forming Orai1 subunits are activated by STIM1, an endoplasmic reticulum Ca(2+) sensor that senses intracellular store depletion and migrates to plasma membrane proximal regions to mediate SOCE. One of the fundamental properties of CRAC channels is their Ca(2+)-dependent fast inactivation. To identify the domains of Orai1 involved in fast inactivation, we have mutated residues in the Orai1 intracellular loop linking transmembrane segment II to III. Mutation of four residues, V(151)SNV(154), at the center of the loop (MutA) abrogated fast inactivation, leading to increased SOCE as well as higher CRAC currents. Point mutation analysis identified five key amino acids, N(153)VHNL(157), that increased SOCE in Orai1 null murine embryonic fibroblasts. Expression or direct application of a peptide comprising the entire intracellular loop or the sequence N(153)VHNL(157) blocked CRAC currents from both wild type (WT) and MutA Orai1. A peptide incorporating the MutA mutations had no blocking effect. Concatenated Orai1 constructs with four MutA monomers exhibited high CRAC currents lacking fast inactivation. Reintroduction of a single WT monomer (MutA-MutA-MutA-WT) was sufficient to fully restore fast inactivation, suggesting that only a single intracellular loop can block the channel. These data suggest that the intracellular loop of Orai1 acts as an inactivation particle, which is stabilized in the ion permeation pathway by the N(153)VHNL(157) residues. These results along with recent reports support a model in which the N terminus and the selectivity filter of Orai1 as well as STIM1 act in concert to regulate the movement of the intracellular loop and evoke fast inactivation.
    Journal of Biological Chemistry 12/2009; 285(7):5066-75. · 4.65 Impact Factor