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Kim, Hyung-Ryong,Lee, Geum-Hwa,Ha, Ki-Chan,Ahn, Taeho,Moon, Ji-Yong,Lee, Bong-Jin,Cho, Ssang-Goo,Kim, Sanguk,Seo, Young-Rok,Shin, Yong-Joo,Chae, Soo-Wan,Reed, John C.,Chae, Han-Jung American Society for Biochemistry and Molecular Bi 2008 The Journal of biological chemistry Vol.283 No.23
<P>In this study, Bax inhibitor-1 (BI-1) overexpression reduces the ER pool of Ca(2+) released by thapsigargin. Cells overexpressing BI-1 also showed lower intracellular Ca(2+) release induced by the Ca(2+) ionophore ionomycin as well as agonists of ryanodine receptors and inositol trisphosphate receptors. In contrast, cells expressing carboxyl-terminal deleted BI-1 (CDelta-BI-1 cells) displayed normal intracellular Ca(2+) mobilization. Basal Ca(2+) release rates from the ER were higher in BI-1-overexpressing cells than in control or CDelta-BI-1 cells. We determined that the carboxyl-terminal cytosolic region of BI-1 contains a lysine-rich motif (EKDKKKEKK) resembling the pH-sensing domains of ion channels. Acidic conditions triggered more extensive Ca(2+) release from ER microsomes from BI-1-overexpressing cells and BI-1-reconstituted liposomes. Acidic conditions also induced BI-1 protein oligomerization. Interestingly subjecting BI-1-overexpressing cells to acidic conditions induced more Bax recruitment to mitochondria, more cytochrome c release from mitochondria, and more cell death. These findings suggest that BI-1 increases Ca(2+) leak rates from the ER through a mechanism that is dependent on pH and on the carboxyl-terminal cytosolic region of the BI-1 protein. The findings also reveal a cell death-promoting phenotype for BI-1 that is manifested under low pH conditions.</P>
Leucyl-tRNA synthetase-dependent and -independent activation of a group I intron.
Boniecki, Michal T,Rho, Seung Bae,Tukalo, Mikhail,Hsu, Jennifer L,Romero, Eliana P,Martinis, Susan A American Society for Biochemistry and Molecular Bi 2009 The Journal of biological chemistry Vol.284 No.39
<P>Leucyl-tRNA synthetase (LeuRS) is an essential RNA splicing factor for yeast mitochondrial introns. Intracellular experiments have suggested that it works in collaboration with a maturase that is encoded within the bI4 intron. RNA deletion mutants of the large bI4 intron were constructed to identify a competently folded intron for biochemical analysis. The minimized bI4 intron was active in RNA splicing and contrasts with previous proposals that the canonical core of the bI4 intron is deficient for catalysis. The activity of the minimized bI4 intron was enhanced in vitro by the presence of the bI4 maturase or LeuRS.</P>
Kim, Yoonju,Ha, Chang Man,Chang, Sunghoe American Society for Biochemistry and Molecular Bi 2013 The Journal of biological chemistry Vol.288 No.41
<P>SNX26, a brain-enriched RhoGAP, plays a key role in dendritic arborization during early neuronal development in the neocortex. In mature neurons, it is localized to dendritic spines, but little is known about its role in later stages of development. Our results show that SNX26 interacts with PSD-95 in dendritic spines of cultured hippocampal neurons, and as a GTPase-activating protein for Cdc42, it decreased the F-actin content in COS-7 cells and in dendritic spines of neurons. Overexpression of SNX26 resulted in a GTPase-activating protein activity-dependent decrease in total protrusions and spine density together with dramatic inhibition of filopodia-to-spine transformations. Such effects of SNX26 were largely rescued by a constitutively active mutant of Cdc42. Consistently, an shRNA-mediated knockdown of SNX26 significantly increased total protrusions and spine density, resulting in an increase in thin or stubby type spines at the expense of the mushroom spine type. Moreover, endogenous expression of SNX26 was shown to be bi-directionally modulated by neuronal activity. Therefore, we propose that in addition to its key role in neuronal development, SNX26 also has a role in the activity-dependent structural change of dendritic spines in mature neurons.</P>
Cyclin-dependent Kinase 5 (Cdk5) Regulates the Function of CLOCK Protein by Direct Phosphorylation
Kwak, Yongdo,Jeong, Jaehoon,Lee, Saebom,Park, Young-Un,Lee, Seol-Ae,Han, Dong-Hee,Kim, Joung-Hun,Ohshima, Toshio,Mikoshiba, Katsuhiko,Suh, Yoo-Hun,Cho, Sehyung,Park, Sang Ki American Society for Biochemistry and Molecular Bi 2013 The Journal of biological chemistry Vol.288 No.52
<P>Circadian rhythm is a biological rhythm governing physiology and behavior with a period of ∼24 h. At the molecular level, circadian output is controlled by a molecular clock composed of positive and negative feedback loops in transcriptional and post-translational processes. CLOCK is a transcription factor known as a central component of the molecular clock feedback loops generating circadian oscillation. Although CLOCK is known to undergo multiple post-translational modifications, the knowledge of their entities remains limited. Cyclin-dependent kinase 5 (Cdk5) is a proline-directed serine-threonine kinase that is involved in various neuronal processes. Here, we report that Cdk5 is a novel regulator of CLOCK protein. Cdk5 phosphorylates CLOCK at the Thr-451 and Thr-461 residues in association with transcriptional activation of CLOCK. The Cdk5-dependent regulation of CLOCK function is mediated by alterations of its stability and subcellular distribution. These results suggest that Cdk5 is a novel regulatory component of the core molecular clock machinery.</P>
Jeon, Eun Su,Song, Hae Young,Kim, Mi Ra,Moon, Hyun Jung,Bae, Yong Chan,Jung, Jin Sup,Kim, Jae Ho American Society for Biochemistry and Molecular Bi 2006 Journal of lipid research Vol.47 No.3
<P>Sphingosylphosphorylcholine (SPC) has been implicated in a variety of cellular responses, including proliferation and differentiation. In this study, we demonstrate that d-erythro-SPC, but not l-threo-SPC, stereoselectively stimulated the proliferation of human adipose tissue-derived mesenchymal stem cells (hADSCs), with a maximal increase at 5 microM, and increased the intracellular concentration of Ca(2+) ([Ca(2+)](i)) in hADSCs, which do not express known SPC receptors (i.e., OGR1, GPR4, G2A, and GPR12). The SPC-induced proliferation and increase in [Ca(2+)](i) were sensitive to pertussis toxin (PTX) and the phospholipase C (PLC) inhibitor U73122, suggesting that PTX-sensitive G proteins, Gi or Go, and PLC are involved in SPC-induced proliferation. In addition, SPC treatment induced the phosphorylation of c-Jun and extracellular signal-regulated kinase, and SPC-induced proliferation was completely prevented by pretreatment with the c-Jun N-terminal kinase (JNK)-specific inhibitor SP600125 but not with the MEK-specific inhibitor U0126. Furthermore, the SPC-induced proliferation and JNK activation were completely attenuated by overexpression of a dominant negative mutant of JNK2, and the SPC-induced activation of JNK was inhibited by pretreatment with PTX or U73122. Treatment of hADSCs with lysophosphatidic acid (LPA) receptor antagonist, Ki16425, had no impact on the SPC-induced increase in [Ca(2+)](i). However, SPC-induced proliferation was partially, but significantly, attenuated by pretreatment of the cells with Ki16425.These results indicate that SPC stimulates the proliferation of hADSCs through the Gi/Go-PLC-JNK pathway and that LPA receptors may be responsible in part for the SPC-induced proliferation.</P>
Replicative Senescence Induced by Romo1-derived Reactive Oxygen Species
Chung, Young Min,Lee, Seung Baek,Kim, Hyung Jung,Park, Seon Ho,Kim, Jung Jin,Chung, Jin Sil,Yoo, Young Do American Society for Biochemistry and Molecular Bi 2008 The Journal of biological chemistry Vol.283 No.48
<P>Persistent accumulation of DNA damage induced by reactive oxygen species (ROS) is proposed to be a major contributor toward the aging process. Furthermore, an increase in age-associated ROS is strongly correlated with aging in various species, including humans. Here we showed that the enforced expression of the ROS modulator 1 (Romo1) triggered premature senescence by ROS production, and this also contributed toward induction of DNA damage. Romo1-derived ROS was found to originate in the mitochondrial electron transport chain. Romo1 expression gradually increased in proportion to population doublings of IMR-90 human fibroblasts. An increase in ROS production in these cells with high population doubling was blocked by the Romo1 knockdown using Romo1 small interfering RNA. Romo1 knockdown also inhibited the progression of replicative senescence. Based on these results, we suggest that age-related ROS levels increase, and this contributes to replicative senescence, which is directly associated with Romo1 expression.</P>
Cocoa procyanidins suppress transformation by inhibiting mitogen-activated protein kinase kinase.
Kang, Nam Joo,Lee, Ki Won,Lee, Dong Eun,Rogozin, Evgeny A,Bode, Ann M,Lee, Hyong Joo,Dong, Zigang American Society for Biochemistry and Molecular Bi 2008 The Journal of biological chemistry Vol.283 No.30
<P>Cocoa was shown to inhibit chemically induced carcinogenesis in animals and exert antioxidant activity in humans. However, the molecular mechanisms of the chemopreventive potential of cocoa and its active ingredient(s) remain unknown. Here we report that cocoa procyanidins inhibit neoplastic cell transformation by suppressing the kinase activity of mitogen-activated protein kinase kinase (MEK). A cocoa procyanidin fraction (CPF) and procyanidin B2 at 5 mug/ml and 40 mum, respectively, inhibited 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced neoplastic transformation of JB6 P+ mouse epidermal (JB6 P+) cells by 47 and 93%, respectively. The TPA-induced promoter activity and expression of cyclooxygenase-2, which is involved in tumor promotion and inflammation, were dose-dependently inhibited by CPF or procyanidin B2. The activation of activator protein-1 and nuclear factor-kappaB induced by TPA was also attenuated by CPF or procyanidin B2. The TPA-induced phosphorylation of MEK, extracellular signal-regulated kinase, and p90 ribosomal s6 kinase was suppressed by CPF or procyanidin B2. In vitro and ex vivo kinase assay data demonstrated that CPF or procyanidin B2 inhibited the kinase activity of MEK1 and directly bound with MEK1. CPF or procyanidin B2 suppressed JB6 P+ cell transformation induced by epidermal growth factor or H-Ras, both of which are known to be involved in MEK/ERK signal activation. In contrast, theobromine (up to 80 mum) had no effect on TPA-induced transformation, cyclooxygenase-2 expression, the transactivation of activator protein-1 or nuclear factor-kappaB, or MEK. Notably, procyanidin B2 exerted stronger inhibitory effects compared with PD098059 (a well known pharmacological inhibitor of MEK) on MEK1 activity and neoplastic cell transformation.</P>