Browsing by Subject "Protein degradation"

Now showing 1 - 6 of 6
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    Degradation of Group V Secretory Phospholipase A2 in Lung Endothelium is Mediated by Autophagy
    (Elsevier, 2020-05) Meliton, Lucille N.; Zhu, Xiangdong; Brown, Mary; Epshtein, Yulia; Kawasaki, Takeshi; Letsiou, Eleftheria; Dudek, Steven M.; Medicine, School of Medicine
    Group V secretory phospholipase A2 (gVPLA2) is a potent inflammatory mediator in mammalian tissues that hydrolyzes phospholipids and initiates eicosanoid biosynthesis. Previous work has demonstrated that multiple inflammatory stimuli induce its expression and secretion in several cell types, including the lung endothelium. However, little is known about the mechanism(s) by which gVPLA2 inflammatory signaling is subsequently downregulated. Therefore, in this study we characterized potential clearance mechanisms for gVPLA2 in lung endothelial cells (EC). We observed that exogenous gVPLA2 is taken up rapidly by nutrient-starved human pulmonary artery EC (HPAEC) in vitro, and its cellular expression subsequently is reduced over several hours. In parallel experiments performed in pulmonary vascular EC isolated from mice genetically deficient in gVPLA2, the degradation of exogenously applied gVPLA2 occurs in a qualitatively similar fashion. This degradation is significantly attenuated in EC treated with ammonium chloride or chloroquine, which are lysosomal inhibitors that block autophagic flux. In contrast, the proteasomal inhibitor MG132 fails to prevent the clearance of gVPLA2. Both immunofluorescence microscopy and proximity ligation assay demonstrate the co-localization of LC3 and gVPLA2 during this process, indicating the association of gVPLA2 with autophagosomes. Nutrient starvation, a known inducer of autophagy, is sufficient to stimulate gVPLA2 degradation. These results suggest that a lysosome-mediated autophagy pathway contributes to gVPLA2 clearance from lung EC. These novel observations advance our understanding of the mechanism by which this key inflammatory enzyme is downregulated in the lung vasculature.
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    Effects of Slide Storage on Detection of Molecular Markers by IHC and FISH in Endometrial Cancer Tissues From a Clinical Trial: An NRG Oncology/GOG Pilot Study
    (Wolters Kluwer, 2022) Grushko, Tatyana A.; Filiaci, Virginia L.; Montag, Anthony G.; Apushkin, Marsha; Gomez, Maria J.; Monovich, Laura; Ramirez, Nilsa C.; Schwab, Carlton; Kesterson, Joshua P.; Seward, Shelly M.; Method, Michael W.; Olopade, Olufunmilayo I.; Fleming, Gini F.; Birrer, Michael J.; Medicine, School of Medicine
    We performed a pilot study in anticipation of using long-aged precut formalin fixed paraffin embedded (FFPE) tissue sections stored in real-world conditions for translational biomarker studies of TOP2A, Ki67, and HER2 in endometrial cancer. FFPE tissue blocks or unstained slides or both from GOG-0177 were collected centrally (1999-2000) and stored at room temperature. During 2004-2011 specimens were stored at 4°C. Matched pairs of stored slides and freshly cut slides from stored blocks were analyzed for TOP2A (KiS1), Ki67 (MIB1) and HER2 (Herceptest™) proteins. To assess DNA stability (HER2 PathVision), FISH was repeated on stored slides from 21 cases previously shown to be HER2-amplified. IHC staining intensity and extent, mean FISH copies/cell, and copy number ratios were compared using the kappa statistic for concordance or signed rank test for differences in old cut versus new cut slides. IHC results reflected some protein degradation in stored slides. The proportion of cells with TOP2A staining was lower on average by 12% in older sections (p=.03). The proportion of Ki67 positive cells was lower in stored slides by an average of 10% (p<.01). Too few cases in the IHC cohort were FISH positive for any conclusions. HER2 amplification by FISH was unaffected by slide storage. We conclude that use of aged stored slides for proliferation markers TOP2A and Ki67 is feasible but may modestly underestimate true values in endometrial cancer. Pilot studies for particular storage conditions/durations/antigens to be used in translational studies are warranted.
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    Expression and localization of RGS9-2/G 5/R7BP complex in vivo is set by dynamic control of its constitutive degradation by cellular cysteine proteases
    (Society for Neuroscience, 2007-12-19) Anderson, Garret R.; Lujan, Rafael; Semenov, Arthur; Pravetoni, Marco; Posokhova, Ekaterina N.; Song, Joseph H.; Uversky, Vladimir; Chen, Ching-Kang; Wickman, Kevin; Martemyanov, Kirill A.; Biochemistry and Molecular Biology, School of Medicine
    A member of regulator of G-protein signaling family, RGS9-2, is an essential modulator of signaling through neuronal dopamine and opioid G-protein-coupled receptors. Recent findings indicate that the abundance of RGS9-2 determines sensitivity of signaling in the locomotor and reward systems in the striatum. In this study we report the mechanism that sets the concentration of RGS9-2 in vivo, thus controlling G-protein signaling sensitivity in the region. We found that RGS9-2 possesses specific degradation determinants which target it for constitutive destruction by lysosomal cysteine proteases. Shielding of these determinants by the binding partner R7 binding-protein (R7BP) controls RGS9-2 expression at the posttranslational level. In addition, binding to R7BP in neurons targets RGS9-2 to the specific intracellular compartment, the postsynaptic density. Implementation of this mechanism throughout ontogenetic development ensures expression of RGS9-2/type 5 G-protein beta subunit/R7BP complexes at postsynaptic sites in unison with increased signaling demands at mature synapses.
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    F-box protein-32 down-regulates small-conductance calcium-activated potassium channel 2 in diabetic mouse atria
    (Elsevier, 2019-03-15) Ling, Tian-You; Yi, Fu; Lu, Tong; Wang, Xiao-Li; Sun, Xiaojing; Willis, Monte S.; Wu, Li-Qun; Shen, Win-Kuang; Adelman, John P.; Lee, Hon-Chi; Pathology and Laboratory Medicine, School of Medicine
    Diabetes mellitus (DM) is an independent risk factor for atrial fibrillation, but the underlying ionic mechanism for this association remains unclear. We recently reported that expression of the small-conductance calcium-activated potassium channel 2 (SK2, encoded by KCCN2) in atria from diabetic mice is significantly down-regulated, resulting in reduced SK currents in atrial myocytes from these mice. We also reported that the level of SK2 mRNA expression is not reduced in DM atria but that the ubiquitin-proteasome system (UPS), a major mechanism of intracellular protein degradation, is activated in vascular smooth muscle cells in DM. This suggests a possible role of the UPS in reduced SK currents. To test this possibility, we examined the role of the UPS in atrial SK2 down-regulation in DM. We found that a muscle-specific E3 ligase, F-box protein 32 (FBXO-32, also called atrogin-1), was significantly up-regulated in diabetic mouse atria. Enhanced FBXO-32 expression in atrial cells significantly reduced SK2 protein expression, and siRNA-mediated FBXO-32 knockdown increased SK2 protein expression. Furthermore, co-transfection of SK2 with FBXO-32 complementary DNA in HEK293 cells significantly reduced SK2 expression, whereas co-transfection with atrogin-1ΔF complementary DNA (a nonfunctional FBXO-32 variant in which the F-box domain is deleted) did not have any effects on SK2. These results indicate that FBXO-32 contributes to SK2 down-regulation and that the F-box domain is essential for FBXO-32 function. In conclusion, DM-induced SK2 channel down-regulation appears to be due to an FBXO-32-dependent increase in UPS-mediated SK2 protein degradation.
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    Increased AMP deaminase activity decreases ATP content and slows protein degradation in cultured skeletal muscle
    (Elsevier, 2020-07) Davis, Patrick R.; Miller, Spencer G.; Verhoeven, Nicolas A.; Morgan, Joshua S.; Tulis, David A.; Witczak, Carol A.; Brault, Jeffrey J.; Anatomy and Cell Biology, School of Medicine
    Background: Protein degradation is an energy-dependent process, requiring ATP at multiple steps. However, reports conflict as to the relationship between intracellular energetics and the rate of proteasome-mediated protein degradation. Methods: To determine whether the concentration of the adenine nucleotide pool (ATP + ADP + AMP) affects protein degradation in muscle cells, we overexpressed an AMP degrading enzyme, AMP deaminase 3 (AMPD3), via adenovirus in C2C12 myotubes. Results: Overexpression of AMPD3 resulted in a dose- and time-dependent reduction of total adenine nucleotides (ATP, ADP and AMP) without increasing the ADP/ATP or AMP/ATP ratios. In agreement, the reduction of total adenine nucleotide concentration did not result in increased Thr172 phosphorylation of AMP-activated protein kinase (AMPK), a common indicator of intracellular energetic state. Furthermore, LC3 protein accumulation and ULK1 (Ser 555) phosphorylation were not induced. However, overall protein degradation and ubiquitin-dependent proteolysis were slowed by overexpression of AMPD3, despite unchanged content of several proteasome subunit proteins and proteasome activity in vitro under standard conditions. Conclusions: Altogether, these findings indicate that a physiologically relevant decrease in ATP content, without a concomitant increase in ADP or AMP, is sufficient to decrease the rate of protein degradation and activity of the ubiquitin-proteasome system in muscle cells. This suggests that adenine nucleotide degrading enzymes, such as AMPD3, may be a viable target to control muscle protein degradation and perhaps muscle mass.
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    Regulation of Organic Anion Transporting Polypeptides (OATP) 1B1- and OATP1B3-Mediated Transport: An Updated Review in the Context of OATP-Mediated Drug-Drug Interactions
    (MDPI, 2018-03-14) Alam, Khondoker; Crowe, Alexandra; Wang, Xueying; Zhang, Pengyue; Ding, Kai; Li, Lang; Yue, Wei; Medical and Molecular Genetics, School of Medicine
    Organic anion transporting polypeptides (OATP) 1B1 and OATP1B3 are important hepatic transporters that mediate the uptake of many clinically important drugs, including statins from the blood into the liver. Reduced transport function of OATP1B1 and OATP1B3 can lead to clinically relevant drug-drug interactions (DDIs). Considering the importance of OATP1B1 and OATP1B3 in hepatic drug disposition, substantial efforts have been given on evaluating OATP1B1/1B3-mediated DDIs in order to avoid unwanted adverse effects of drugs that are OATP substrates due to their altered pharmacokinetics. Growing evidences suggest that the transport function of OATP1B1 and OATP1B3 can be regulated at various levels such as genetic variation, transcriptional and post-translational regulation. The present review summarizes the up to date information on the regulation of OATP1B1 and OATP1B3 transport function at different levels with a focus on potential impact on OATP-mediated DDIs.