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Biomedical subjects

Cam Patterson

Publications and source records attributed to Cam Patterson.

At least 37 records · Page 2Linked to original sources
PubMed2005

Reduced Apaf-1 levels in cardiomyocytes engage strict regulation of apoptosis by endogenous XIAP.

Overexpression studies have identified X-linked inhibitor of apoptosis protein (XIAP) as a potent inhibitor of caspases. However, the exact function of endogenous XIAP in regulating mammalian apoptosis is less clear. Endogenous XIAP strictly regulates cytochrome c-dependent caspase activation in sympathetic neurons but not in many mitotic cells. We report that postmitotic cardiomyocytes, unlike fibroblasts, are remarkably resistant to cytosolic microinjection of cytochrome c. The cardiomyocyte resistance to cytochrome c is mediated by endogenous XIAP, as XIAP-deficient cardiomyocytes die rapidly with cytosolic cytochrome c alone. Importantly, we found that cardiomyocytes, like neurons, have markedly reduced Apaf-1 levels and that this decrease in Apaf-1 is directly linked to the tight regulation of caspase activation by XIAP. These data identify an important function of XIAP in cardiomyocytes and point to a striking similarity in the regulation of apoptosis in postmitotic cells.

Animals↗
PubMed2005

Regulation of the cytoplasmic quality control protein degradation pathway by BAG2.

The cytoplasm is protected against the perils of protein misfolding by two mechanisms: molecular chaperones (which facilitate proper folding) and the ubiquitin-proteasome system, which regulates degradation of misfolded proteins. CHIP (carboxyl terminus of Hsp70-interacting protein) is an Hsp70-associated ubiquitin ligase that participates in this process by ubiquitylating misfolded proteins associated with cytoplasmic chaperones. Mechanisms that regulate the activity of CHIP are, at present, poorly understood. Using a proteomics approach, we have identified BAG2, a previously uncharacterized BAG domain-containing protein, as a common component of CHIP holocomplexes in vivo. Binding assays indicate that BAG2 associates with CHIP as part of a ternary complex with Hsc70, and BAG2 colocalizes with CHIP under both quiescent conditions and after heat shock. In vitro and in vivo ubiquitylation assays indicate that BAG2 is an efficient and specific inhibitor of CHIP-dependent ubiquitin ligase activity. This activity is due, in part, to inhibition of interactions between CHIP and its cognate ubiquitin-conjugating enzyme, UbcH5a, which may in turn be facilitated by ATP-dependent remodeling of the BAG2-Hsc70-CHIP heterocomplex. The association of BAG2 with CHIP provides a cochaperone-dependent regulatory mechanism for preventing unregulated ubiquitylation of misfolded proteins by CHIP.

Adenosine Triphosphate↗
PubMed2005

Mechanisms of endothelial differentiation in embryonic vasculogenesis.

The formation of new blood vessels in the adult organism not only contributes to the progression of diseases such as cancer and diabetic retinopathy but also can be promoted in therapeutic approaches to various ischemic pathologies. Because many of the signals important to blood vessel development during embryogenesis are recapitulated during adult blood vessel formation, much work has been performed to better-understand the molecular control of endothelial differentiation in the developing embryo. In this review, we describe the current understanding of where endothelial differentiation from pluripotent progenitor cells occurs during development, how this process is controlled at the molecular level, and what model systems can be used to investigate the earliest steps of blood vessel formation.

Animals↗
PubMed2005

The co-chaperone carboxyl terminus of Hsp70-interacting protein (CHIP) mediates alpha-synuclein degradation decisions between proteasomal and lysosomal pathways.

Alpha-synuclein is a major component of Lewy bodies, the pathological hallmark of Parkinson disease, dementia with Lewy bodies, and related disorders. Misfolding and aggregation of alpha-synuclein is thought to be a critical cofactor in the pathogenesis of certain neurodegenerative diseases. In the current study, we investigate the role of the carboxyl terminus of Hsp70-interacting protein (CHIP) in alpha-synuclein aggregation. We demonstrate that CHIP is a component of Lewy bodies in the human brain, where it colocalizes with alpha-synuclein and Hsp70. In a cell culture model, endogenous CHIP colocalizes with alpha-synuclein and Hsp70 in intracellular inclusions, and overexpression of CHIP inhibits alpha-synuclein inclusion formation and reduces alpha-synuclein protein levels. We demonstrate that CHIP can mediate alpha-synuclein degradation by two discrete mechanisms that can be dissected using deletion mutants; the tetratricopeptide repeat domain is critical for proteasomal degradation, whereas the U-box domain is sufficient to direct alpha-synuclein toward the lysosomal degradation pathway. Furthermore, alpha-synuclein, synphilin-1, and Hsp70 all coimmunoprecipitate with CHIP, raising the possibility of a direct alpha-synuclein-CHIP interaction. The fact that the tetratricopeptide repeat domain is required for the effects of CHIP on alpha-synuclein inclusion morphology, number of inclusions, and proteasomal degradation as well as the direct interaction of CHIP with Hsp70 implicates a cooperation of CHIP and Hsp70 in these processes. Taken together, these data suggest that CHIP acts a molecular switch between proteasomal and lysosomal degradation pathways.

Cell Line, Tumor↗
PubMed2005

Differential activation of mitogenic signaling pathways in aortic smooth muscle cells deficient in superoxide dismutase isoforms.

OBJECTIVE: Reactive oxygen species (ROS) integrate cellular signaling pathways involved in aortic smooth muscle cell (SMC) proliferation and migration associated with atherosclerosis. However, the effect of subcellular localization of ROS on SMC mitogenic signaling is not yet fully understood. METHODS AND RESULTS: We used superoxide dismutase (SOD)-deficient mouse aortic SMCs to address the role of subcellular ROS localization on SMC phenotype and mitogenic signaling. Compared with wild-type, a 54% decrease in total SOD activity (almost equal to 50% decrease in SOD1 protein levels) and a 42% reduction in SOD2 activity (approximately equal to 50% decrease in SOD2 protein levels) were observed in SOD1+/- and SOD2+/- SMCs, respectively. Consistent with this, basal and thrombin-induced superoxide levels increased in these SMCs. SOD1+/- and SOD2+/- SMCs exhibit increased basal proliferation and enhanced [3H]-thymidine and [3H]-leucine incorporation in basal and thrombin-stimulated conditions. Our results indicate preferential activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 mitogen-activated protein kinases in SOD1+/- and janus kinase/signal transducer and activator of transcriptase (JAK/STAT) pathway in SOD2+/- SMCs. Pharmacological inhibitors of ERK1/2 p38 and JAK2 confirm the SOD genotype-dependent SMC proliferation. CONCLUSIONS: Our results suggest that SOD1 and SOD2 regulate SMC quiescence by suppressing divergent mitogenic signaling pathways, and dysregulation of these enzymes under pathophysiological conditions may lead to SMC hyperplasia and hypertrophy.

Animals↗
PubMed2005

Adenosine produces nitric oxide and prevents mitochondrial oxidant damage in rat cardiomyocytes.

OBJECTIVE: To examine if adenosine prevents oxidant-induced mitochondrial dysfunction by producing nitric oxide (NO) in cardiomyocytes. METHODS AND RESULTS: Adenosine significantly enhanced the fluorescence of DAF-FM, a dye specific for NO, implying that adenosine induces synthesis of NO. Adenosine-induced NO production was blocked by both the nonspecific NOS inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME) and N(5)-(1-Iminoethyl)-l-ornithine dihydrochloride (l-NIO), an inhibitor of endothelial NOS (eNOS), but not by N(6)-(1-Iminoethyl)-l-lysine hydrochloride (l-NIL), an inhibitor of inducible NOS (iNOS), indicating that adenosine activates eNOS. Adenosine also enhances eNOS phosphorylation and its activity. The adenosine A(2) receptor antagonist 8-(3-chlorostyryl)caffeine but not the A(1) antagonist 8-cyclopentyl-1,3-dipropylxanthine prevented the increase in NO production. CGS21680, an adenosine A(2) receptor agonist, markedly increased NO, further supporting the involvement of A(2) receptors. Adenosine-induced NO production was blocked by 4-Amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo(3,4-d)pyrimidine (PP2), a selective Src tyrosine kinase inhibitor, suggesting that Src tyrosine kinase is crucial for adenosine-induced NO production. Adenosine-induced NO production was partially reversed by both wortmannin and Akt inhibitor indicating an involvement of PI3-kinase/Akt. Pretreatment of cells with adenosine prevented H(2)O(2)-induced depolarization of mitochondrial membrane potential (DeltaPsi(m)). The protective effect was blocked by l-NAME and l-NIO but not by l-NIL, indicating that eNOS plays a role in the action of adenosine. The protective effect of adenosine was further suppressed by KT5823, a specific inhibitor of protein kinase G (PKG), indicating the PKG may serve as a downstream target of adenosine. CONCLUSION: Adenosine protects mitochondria from oxidant damage through a pathway involving A(2) receptors, eNOS, NO, PI3-kinase/Akt, and Src tyrosine kinase.

Adenosine↗
PubMed2005

CHIP, a cochaperone/ubiquitin ligase that regulates protein quality control, is required for maximal cardioprotection after myocardial infarction in mice.

Limitation of damage after ischemia and reperfusion injury to the myocardium remains an elusive clinical goal. Previous studies have suggested that molecular chaperones, which include members of the heat shock protein (Hsp) family, may have cardioprotective effects, although the protective role of endogenous chaperones has not been well documented. CHIP (carboxyl terminus of Hsp70-interacting protein) is a cochaperone/ubiquitin ligase that integrates the response to stress at multiple levels. We tested the response of CHIP(-/-) mice to in vivo ischemia and reperfusion injury induced by left anterior descending coronary artery ligation. Compared with wild-type littermates, CHIP(-/-) mice had decreased survival and increased incidence of arrhythmias during reperfusion. The size of myocardial infarction, as assessed by the ratio of infarct area to area at risk, was 50% greater in CHIP(-/-) mice. Increased infarct size was accompanied by impaired upregulation of the chaperone Hsp70 after ischemia-reperfusion injury. In situ analysis also indicated that hearts of CHIP(-/-) mice were more prone to develop apoptosis in cardiomyocytes and especially endothelial cells of intramural vessels. Previous studies have found that CHIP plays a central role in maintaining protein quality control and coordinating the response to stress. The present data indicate that these functions of CHIP provide a critical cardioprotective effect in the setting of ischemia-reperfusion injury due in part to increased apoptosis in cardiac cells. Quality control mechanisms therefore may be underappreciated clinical targets for maximizing myocardial protection after injury.

Adaptor Proteins, Signal Transducing↗
PubMed2005

Bone morphogenetic proteins and vascular differentiation: BMPing up vasculogenesis.

Vasculogenesis is an important mechanism of blood vessel formation not only in embryos but also in adults. It may contribute to reparative effects of progenitor cell therapy in ischemic diseases such as myocardial infarction. Signaling pathways involved in embryonic development, including the BMP pathway, are reactivated in adult vasculogenesis. As a consequence knowledge about embryonic signaling events will help to understand blood vessel formation in the adult. The role of BMPs in embryonic development has been studied extensively in the past decades but only recently their role in vasculogenesis has been recognized. Gain and loss of function models indicate that BMPs stimulate vasculogenesis in the embryo as well as in the adult. Additionally, BMPs interact with other pathways involved in blood vessel formation, such asVEGF signaling. Studying novel molecules such as BMPER that modulate BMP activity and that are expressed in vascular cells will help to understand vasculogenetic signaling and may open up new therapeutic avenues in vascular disease.

Animals↗
PubMed2005

C-terminus of heat shock protein 70-interacting protein facilitates degradation of apoptosis signal-regulating kinase 1 and inhibits apoptosis signal-regulating kinase 1-dependent apoptosis.

Apoptosis signal-regulating kinase 1 (ASK1) is a mitogen-activated protein kinase kinase kinase (MAPKKK) that is regulated under conditions of cellular stress. ASK1 phosphorylates c-Jun N-terminal kinase (JNK) and elicits an apoptotic response. ASK1 activity is regulated at multiple levels, 1 of which is through inhibition by cytosolic chaperones of the heat shock protein (Hsp) 70 family. Among the proteins that determine Hsp70 function, CHIP (C-terminus of Hsp70-interacting protein) is a cochaperone and ubiquitin ligase that interacts with Hsp70 through an amino-terminal tetratricopeptide repeat (TPR) domain. Prominent among the cellular functions mediated by CHIP is protection against physiologic stress. Because ASK1 is known to contain a TPR-acceptor site, we examined the role of CHIP in regulating ASK1 function. CHIP interacted with ASK1 in a TPR-dependent fashion and induced ubiquitylation and proteasome-dependent degradation of ASK1. Targeting of ASK1 by CHIP inhibited JNK activation in response to oxidative challenge and reduced ASK1-dependent apoptosis, whereas short interfering RNA (siRNA)-dependent depletion of CHIP enhanced JNK activation. Consistent with its ability to reduce cytoplasmic ASK1 levels, CHIP triggered the translocation of ASK1 partner protein death-associated protein (Daxx) into the nucleus, where it is known to activate an antiapoptotic response. These results indicate that CHIP regulates ASK1 activity by inducing its ubiquitylation and degradation, which, together with its effects on Daxx localization, provides a mechanism for the antiapoptotic effects of CHIP observed in the face of cellular and physiologic stress.

Animals↗
PubMed2005

Cystic fibrosis transmembrane conductance regulator as a model substrate to study endoplasmic reticulum protein quality control in mammalian cells.

Components of the ubiquitin-proteasome system function on the surface of the endoplasmic reticulum (ER) to select misfolded proteins for degradation. Herein we describe methods that allow for the study of the pathway for proteasomal degradation of the cystic fibrosis transmembrane conductance regulator (CFTR). The experimental system described employs transiently transfected HEK-293 cells and is utilized to monitor the biogenesis of CFTR by Western blot and pulse-chase analysis.

Cell Line↗
PubMed2004

A foldable CFTR{Delta}F508 biogenic intermediate accumulates upon inhibition of the Hsc70-CHIP E3 ubiquitin ligase.

CFTRDeltaF508 exhibits a correctable protein-folding defect that leads to its misfolding and premature degradation, which is the cause of cystic fibrosis (CF). Herein we report on the characterization of the CFTRDeltaF508 biogenic intermediate that is selected for proteasomal degradation and identification of cellular components that polyubiquitinate CFTRDeltaF508. Nonubiquitinated CFTRDeltaF508 accumulates in a kinetically trapped, but folding competent conformation, that is maintained in a soluble state by cytosolic Hsc70. Ubiquitination of Hsc70-bound CFTRDeltaF508 requires CHIP, a U box containing cytosolic cochaperone. CHIP is demonstrated to function as a scaffold that nucleates the formation of a multisubunit E3 ubiquitin ligase whose reconstituted activity toward CFTR is dependent upon Hdj2, Hsc70, and the E2 UbcH5a. Inactivation of the Hsc70-CHIP E3 leads CFTRDeltaF508 to accumulate in a nonaggregated state, which upon lowering of cell growth temperatures, can fold and reach the cell surface. Inhibition of CFTRDeltaF508 ubiquitination can increase its cell surface expression and may provide an approach to treat CF.

Animals↗
PubMed2004

Muscle-specific RING finger 1 is a bona fide ubiquitin ligase that degrades cardiac troponin I.

Muscle-specific RING finger protein 1 (MuRF1) is a sarcomere-associated protein that is restricted to cardiac and skeletal muscle. In skeletal muscle, MuRF1 is up-regulated by conditions that provoke atrophy, but its function in the heart is not known. The presence of a RING finger in MuRF1 raises the possibility that it is a component of the ubiquitin-proteasome system of protein degradation. We performed a yeast two-hybrid screen to search for interaction partners of MuRF1 in the heart that might be targets of its putative ubiquitin ligase activity. This screen identified troponin I as a MuRF1 partner protein. MuRF1 and troponin I were found to associate both in vitro and in vivo in cultured cardiomyocytes. MuRF1 reduced steady-state troponin I levels when coexpressed in COS-7 cells and increased degradation of endogenous troponin I protein in cardiomyocytes. The degradation of troponin I in cardiomyocytes was associated with the accumulation of ubiquitylated intermediates of troponin I and was proteasome-dependent. In vitro, MuRF1 functioned as a ubiquitin ligase to catalyze ubiquitylation of troponin I through a RING finger-dependent mechanism. In isolated cardiomyocytes, MuRF1 reduced indices of contractility. In cardiomyocytes, these processes may determine the balance between hypertrophic and antihypertrophic signals and the regulation of myocyte contractile responses in the setting of heart failure.

Animals↗
PubMed2004

Muscle ring finger protein-1 inhibits PKC{epsilon} activation and prevents cardiomyocyte hypertrophy.

Much effort has focused on characterizing the signal transduction cascades that are associated with cardiac hypertrophy. In spite of this, we still know little about the mechanisms that inhibit hypertrophic growth. We define a novel anti-hypertrophic signaling pathway regulated by muscle ring finger protein-1 (MURF1) that inhibits the agonist-stimulated PKC-mediated signaling response in neonatal rat ventricular myocytes. MURF1 interacts with receptor for activated protein kinase C (RACK1) and colocalizes with RACK1 after activation with phenylephrine or PMA. Coincident with this agonist-stimulated interaction, MURF1 blocks PKCepsilon translocation to focal adhesions, which is a critical event in the hypertrophic signaling cascade. MURF1 inhibits focal adhesion formation, and the activity of downstream effector ERK1/2 is also inhibited in the presence of MURF1. MURF1 inhibits phenylephrine-induced (but not IGF-1-induced) increases in cell size. These findings establish that MURF1 is a key regulator of the PKC-dependent hypertrophic response and can blunt cardiomyocyte hypertrophy, which may have important implications in the pathophysiology of clinical cardiac hypertrophy.

Animals↗
PubMed2004

Ubiquitylation of neuronal nitric-oxide synthase by CHIP, a chaperone-dependent E3 ligase.

It is established that neuronal nitric-oxide synthase (nNOS) is ubiquitylated and proteasomally degraded. The proteasomal degradation of nNOS is enhanced by suicide inactivation of nNOS or by the inhibition of hsp90, which is a chaperone found in a native complex with nNOS. In the current study, we have examined whether CHIP, a chaperone-dependent E3 ubiquitin-protein isopeptide ligase that is known to ubiquitylate other hsp90-chaperoned proteins, could act as an ubiquitin ligase for nNOS. We found with the use of HEK293T or COS-7 cells and transient transfection methods that CHIP overexpression causes a decrease in immunodetectable levels of nNOS. The extent of the loss of nNOS is dependent on the amount of CHIP cDNA used for transfection. Lactacystin (10 microM), a selective proteasome inhibitor, attenuates the loss of nNOS in part by causing the nNOS to be found in a detergent-insoluble form. Immunoprecipitation of the nNOS and subsequent Western blotting with an anti-ubiquitin IgG shows an increase in nNOS-ubiquitin conjugates because of CHIP. Moreover, incubation of nNOS with a purified system containing an E1 ubiquitin-activating enzyme, an E2 ubiquitin carrier protein conjugating enzyme (UbcH5a), CHIP, glutathione S-transferase-tagged ubiquitin, and an ATP-generating system leads to the ubiquitylation of nNOS. The addition of purified hsp70 and hsp40 to this in vitro system greatly enhances the amount of nNOS-ubiquitin conjugates, suggesting that CHIP is an E3 ligase for nNOS whose action is facilitated by (and possibly requires) its interaction with nNOS-bound hsp70.

Acetylcysteine↗
PubMed2004

LE-PAS, a novel Arnt-dependent HLH-PAS protein, is expressed in limbic tissues and transactivates the CNS midline enhancer element.

A growing family of helix-loop-helix PAS (HLH-PAS) transcription factors has emerged recently. These proteins form heterodimers and are involved in adaptation to environmental or physiologic stresses as well as in embryonic development. We describe the cloning and characterization of a novel HLH-PAS protein termed LE-PAS (limbic-enriched PAS) in mouse. LE-PAS consists of 802 amino acids and has a predicted molecular mass of 87.4 kDa. In adult mice, it is expressed exclusively in brain. Northern blot and in situ hybridization analysis indicate that LE-PAS is expressed in the limbic system and olfactory bulb. By in vitro overexpression in COS-7, cells we found that LE-PAS is a nuclear protein. Reporter gene analysis indicated that LE-PAS transactivates the CNS midline enhancer (CME) motif but not the xenobiotic response element in an Arnt-dependent fashion and without prior activation of LE-PAS protein. Our observation suggests that LE-PAS shares a similar mode of function with HLH-PAS proteins such as single minded or trachealess indicating that LE-PAS also has constitutive or developmental functions which may be critical for regulating the transcriptional control of limbic patterning and function.

Amino Acid Sequence↗
PubMed2004

An androgen receptor NH2-terminal conserved motif interacts with the COOH terminus of the Hsp70-interacting protein (CHIP).

The NH2-terminal sequence of steroid receptors is highly variable between different receptors and in the same receptor from different species. In this study, a primary sequence homology comparison identified a 14-amino acid NH2-terminal motif of the human androgen receptor (AR) that is common to AR from all species reported, including the lower vertebrates. The evolutionarily conserved motif is unique to AR, with the exception of a partial sequence in the glucocorticoid receptor of higher species. The presence of the conserved motif in AR and the glucocorticoid receptor and its absence in other steroid receptors suggests convergent evolution. The function of the AR NH2-terminal conserved motif was suggested from a yeast two-hybrid screen that identified the COOH terminus of the Hsp70-interacting protein (CHIP) as a binding partner. We found that CHIP functions as a negative regulator of AR transcriptional activity by promoting AR degradation. In support of this, two mutations in the AR NH2-terminal conserved motif previously identified in the transgenic adenocarcinoma of mouse prostate model reduced the interaction between CHIP and AR. Our results suggest that the AR NH2-terminal domain contains an evolutionarily conserved motif that functions to limit AR transcriptional activity. Moreover, we demonstrate that the combination of comparative sequence alignment and yeast two-hybrid screening using short conserved peptides as bait provides an effective strategy to probe the structure-function relationships of steroid receptor NH2-terminal domains and other intrinsically unstructured transcriptional regulatory proteins.

Amino Acid Motifs↗