Biomedical subjects

Angus C Nairn

Publications and source records attributed to Angus C Nairn.

76 records · Page 5Linked to original sources

PubMed2002

A novel cAMP-stimulated pathway in protein phosphatase 2A activation.

Elevated cAMP in NRK-52E and L6 cells causes a marked reduction in the phosphorylation of numerous phosphoproteins, as detected initially with phosphoserine-specific antibodies. Here, we show that elevation of cAMP in NRK cells by forskolin/3-isobutyl-1-methylxanthine (IBMX) treatment decreased phosphorylation of substrates for different protein kinases, pointing to a common protein phosphatase as a target for cAMP-dependent regulation. Forskolin/IBMX treatment completely dephosphorylated a selective protein phosphatase 2A (PP2A) substrate, elongation factor-2 (EF-2), at its Ca(2+) calmodulin-dependent kinase site, and decreased phosphorylation of substrates for cyclin-dependent kinases, including retinoblastoma (Rb) protein. As reported before, forskolin/IBMX also decreased phosphorylation of a protein kinase C substrate, the Na,K-ATPase. The cAMP-stimulated dephosphorylation was blocked by the protein phosphatases 1 (PP1) and PP2A inhibitor okadaic acid at concentrations selective for PP2A but was not blocked by tautomycin at concentrations selective for PP1. The data implicate PP2A as a cAMP-activated phosphatase. Contrary to expectation, we found evidence that cAMP-dependent activation of PP2A did not depend on protein kinase A (PKA). Pretreatment of cells with the PKA inhibitor H89 abolished PKA activity measured in cell extracts and significantly decreased cAMP-activated phosphorylation of a known PKA substrate, ARPP-19, in cells, but failed to block the cAMP-stimulated dephosphorylation of EF-2, Rb, and other proteins. This novel pathway of PP2A activation, acting on the time scale of minutes, represents yet another example of a cAMP-mediated, PKA-independent signaling mechanism. Because PP2A is active toward a variety of endogenous substrates, cAMP-stimulated dephosphorylation may have complicated the interpretation of many prior studies.

Animals↗

PubMed2002

TNF-alpha impairs heart and skeletal muscle protein synthesis by altering translation initiation.

This study examined potential mechanisms contributing to the inhibition of protein synthesis in skeletal muscle and heart after administration of tumor necrosis factor (TNF)-alpha. Rats had vascular catheters implanted, and TNF-alpha was infused continuously for 24 h. TNF-alpha decreased in vivo-determined rates of global protein synthesis in gastrocnemius (39%) and heart (25%). The TNF-alpha-induced decrease in protein synthesis in the gastrocnemius involved a reduction in the synthesis of both myofibrillar and sarcoplasmic proteins. To identify potential mechanisms responsible for regulating mRNA translation, we examined several eukaryotic initiation factors (eIFs) and elongation factors (eEFs). TNF-alpha decreased the activity of eIF-2B in muscle (39%) but not in heart. This diminished activity was not caused by a reduction in the content of eIF-2B epsilon or the content and phosphorylation state of eIF-2 alpha. Skeletal muscle and heart from TNF-alpha-treated rats demonstrated 1) an increased binding of the translation repressor 4E-binding protein-1 (4E-BP1) with eIF-4E, 2) a decreased amount of eIF-4E associated with eIF-4G, and 3) a decreased content of the hyperphosphorylated gamma-form of 4E-BP1. In contrast, the infusion of TNF-alpha did not alter the content of eEF-1 alpha or eEF-2, or the phosphorylation state of eEF-2. In summary, these data suggest that TNF-alpha impairs skeletal muscle and heart protein synthesis, at least in part, by decreasing mRNA translational efficiency resulting from an impairment in translation initiation associated with alterations in eIF-4E availability.

Amino Acids↗

PubMed2002

The actin-binding domain of spinophilin is necessary and sufficient for targeting to dendritic spines.

Spinophilin is enriched in dendritic spines, small protrusions of the postsynaptic membrane along the length of the dendrite that contain the majority of excitatory synapses. Spinophilin binds to protein phosphatase 1 with high affinity and targets it to dendritic spines, therefore placing it in proximity to regulate glutamate receptor activity. Spinophilin also binds to and bundles f-actin, the main cytoskeletal constituent of dendritic spines, and may therefore serve to regulate the structure of the synapse. In this study, we sought to determine the structural basis for the targeting of spinophilin to dendritic spines. Our results show that the actin-binding domain of spinophilin is necessary and sufficient for targeting of spinophilin to dendrites and dendritic spines.

Actins↗

PubMed2002

Differential effects of alcohol consumption on eukaryotic elongation factors in heart, skeletal muscle, and liver.

BACKGROUND: Acute and chronic alcohol administration diminishes rates of protein synthesis in a variety of tissues including skeletal muscle, heart, and liver, through a diminished translational efficiency rather than a reduction in the number of ribosomes. METHODS: The purpose of the present study was to examine the effect of chronic alcohol exposure (8, 12, or 16 weeks) on elongation factors (eEF) as a potential mechanism for controlling mRNA translation in psoas, soleus, heart, and liver. The cellular content of eEF1A and eEF2 and the phosphorylation state of eEF2 in each tissue was measured using immunoblot techniques. RESULTS: The protein content of eEF1A was reduced in psoas, heart, and liver (but not soleus) from rats fed a diet containing alcohol for 16 weeks, but not for 8 or 12 weeks, compared with time-matched pair-fed controls. eEF2 content was only reduced in myocardium after feeding rats an alcohol-containing diet for 16 weeks. In other tissues, no change in eEF2 content was observed. The decreases in eEF protein content were not associated with a concomitant reduction in the mRNA abundance for eEF1A or eEF2. The phosphorylation state of eEF2 was not affected by chronic alcohol consumption in the skeletal muscle or heart. In contrast, the level of eEF2 phosphorylation in the liver was reduced after 8, 12, and 16 weeks of feeding rats an alcohol-containing diet. In contrast, acute alcohol intoxication failed to modulate the content of eEF1A or eEF2 in any of the tissues examined. The phosphorylation state of eEF2 was reduced in psoas following acute alcohol intoxication. CONCLUSIONS: A decreased eEF1A protein content could account, in part, for the inhibition of translational efficiency following chronic (16 weeks) alcohol feeding but not the response to acute alcohol intoxication.

Alcohol Drinking↗