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Principal Investigator: Chris Glembotski
Organization: UNIVERSITY OF ARIZONA
Fiscal Year: 2024
Award: $602,693
Funding agency: National Heart Lung and Blood Institute
PROJECT SUMMARY
Increases in protein synthesis during pathological cardiac hypertrophy places demands on protein-folding
machinery to avert the accumulation of toxic misfolded proteins. Associated with the endoplasmic reticulum
(ER), where many important proteins are synthesized in cardiac myocytes, is a system that recognizes and
degrades misfolded proteins, i.e. ER associated (protein) degradation, or ERAD. We discovered a different,
non-canonical role for ERAD as a regulator of the levels of the growth-promoting kinase, serum glucocorticoid
kinase 1 (SGK1). SGK1 is a cytosolic kinase involved in growth of other cell types, such as cancer cells.
Interestingly, SGK1 can traffic to the ER where it is ubiquitylated by ERAD machinery and subsequently
degraded by cytosolic proteasomes; however, this unique regulatory mechanism has not been studied in the
heart. Our preliminary evidence shows that non-canonical ERAD could regulate SGK1 levels in the heart and,
thereby regulating cardiac growth under pathological conditions. We also found that an SGK1-binding protein,
called glucocorticoid-inducible leucine zipper protein (GILZ), can bind to and protect SGK1 from non-canonical
ERAD-mediated degradation, which we believe increases SGK1-mediated growth of the heart during pressure
overload. Accordingly, our hypothesis is that SGK1 is a major inducer of pressure overload-induced cardiac
pathology. During pressure overload, SGK1 levels, and thus, SGK1-mediated cardiac hypertrophy and
subsequent pathology, are increased by GILZ-dependent diversion of SGK1 away from the ER, which decreases
SGK1 degradation by non-canonical ERAD. Ectopic expression of an SGK1 peptide disrupts the GILZ-SGK1
interaction, increases SGK1 degradation, thus decreasing SGK1-mediated cardiac hypertrophy and subsequent
pathology. This hypothesis will be examined in mice subjected to pressure overload-induced cardiac pathology
in our specific aims, which are to 1-couple cardiac-specific SGK1 deletion with AAV9 encoding SGK1-WT
(active; ER-targeted), SGK1-KD (kinase-dead ER-targeted) or SGK1-∆60 (active; not ER-targeted) to examine
the effect of SGK1 and ERAD on overload-induced cardiac pathology, 2-combine AAV9-SGK1-WT or AAV9-
SGK1-∆60 with AAV9-mediated GILZ overexpression or knockdown to determine whether GILZ diverts SGK1-
WT from the ER and protects it from ERAD in the heart, 3-evaluate the potential therapeutic, antihypertrophic
effects of a novel SGK1 peptide that interrupts GILZ-SGK1 binding, and increases non-canonical ERAD-
mediated SGK1 degradation. These studies are significant because they will reveal previously unappreciated
roles for SGK1, GILZ and ERAD in pathologic cardiac hypertrophy. We will use an innovative molecular strategy
to mechanistically dissect roles for GILZ and non-canonical ERAD as regulators of SGK1 signaling and cardiac
pathology. Peptide-based disruption of the SGK1-GILZ interaction could be a highly specific method for inhibiting
the maladaptive pathological effects of SGK1 in the heart by selective degradation of SGK1.
Terms: <20S Catalytic Proteasome><20S Core Proteasome><20S Proteasome><20S Proteosome><Address><Aldosterone><Amino Acids><Binding><Binding Proteins><Blood Plasma><Blood Serum><Calcium><Cancer Cell Growth><Cardiac><Cardiac Diseases><Cardiac Disorders><Cardiac Muscle Cells><Cardiac Myocytes><Cardiocyte><Cardiovascular Diseases><Catalytic Core><Catalytic Domain><Catalytic Region><Catalytic Site><Catalytic Subunit><Cell Communication and Signaling><Cell Signaling><Cessation of life><Common Rat Strains><Data><Death><E3 Ligase><E3 Ubiquitin Ligase><ER stress><Ectopic Expression><Endoplasmic Reticulum><Ensure><Epithelial Cells><Ergastoplasm><Generalized Growth><Glucocorticoids><Growth><Heart><Heart Diseases><Heart Hypertrophy><Heart Muscle Cells><Heart failure><Heart myocyte><Human><Hypertrophy><Interruption><Intracellular Communication and Signaling><Intraventricular Pressure><Kidney><Kidney Urinary System><Kinases><Knowledge><Left><Leucine Zippers><Ligand Binding Protein><Ligand Binding Protein Gene><Link><Macropain><Macroxyproteinase><Malignant Cell><Mediating><Membrane><Methods><Mice><Mice Mammals><Modern Man><Molecular><Molecular Interaction><Multicatalytic Proteinase><Murine><Mus><Muscle Cells><Myocytes><Neonatal><Pathologic><Pathology><Peptides><Phosphotransferase Gene><Phosphotransferases><Physiologic intraventricular pressure><Plasma><Plasma Serum><Prosome><Proteasome><Proteasome Endopeptidase Complex><Protein Binding><Protein Biosynthesis><Protein Overexpression><Protein Secretion><Proteins><Proteome><Proteosome><Rat><Rats Mammals><Rattus><Receptor Protein><Reticuloendothelial System, Serum, Plasma><Ribosomal Peptide Biosynthesis><Ribosomal Protein Biosynthesis><Ribosomal Protein Synthesis><Role><SGK1 protein><Serum><Serum Proteins><Serum-glucocorticoid-regulated kinase 1><Sgk protein><Side><Signal Transduction><Signal Transduction Systems><Signaling><Site><Study of serum><System><Therapeutic><Tissue Growth><Transphosphorylases><Ubiquitin Protein Ligase><Ubiquitin-Protein Ligase Complexes><Ubiquitin-Protein Ligase E3><Ventricular><Ventricular Pressure><aberrant folded protein><aberrant folded proteins><abnormal folded protein><abnormal folded proteins><absorption><aminoacid><biological signal transduction><bound protein><cancer cell><cardiac failure><cardiac function><cardiac hypertrophy><cardiomyocyte><cardiovascular disorder><cell type><endoplasmic reticulum stress><function of the heart><heart disorder><heart function><innovate><innovation><innovative><knock-down><knockdown><membrane structure><misfolded protein><misfolded proteins><mortality><multicatalytic endopeptidase complex><novel><ontogeny><overexpress><overexpression><pressure><protein folding><protein homeostasis><protein synthesis><proteostasis><proteotoxic protein><proteotoxin><receptor><renal><renal epithelium><response><serum and glucocorticoid-regulated kinase><social role><ubiquitin-protein ligase>