Association with endoplasmic reticulum promotes proteasomal degradation of GADD34 protein.

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Stress-induced endogenous and ectopically expressed GADD34 proteins were present both in the cytoplasm and in membranes, with their membrane association showing similar biochemical properties. Deletion of N-terminal sequences in GADD34-GFP proteins highlighted an amphipathic helix, whose hydrophobic surface, specifically valine 25 and leucine 29, mediated endoplasmic reticulum (ER) localization. Substitution of leucines for three arginines on the polar surface indicated that the same helix also mediated the association of GADD34 with mitochondria. Fluorescence protease protection and chemical modification of cysteines substituted in the membrane-binding domain pointed to a monotopic insertion of GADD34 into the outer layer of the ER membrane. Fluorescence recovery after photobleaching showed that ER association retards the mobility of GADD34 in living cells. Both WT GADD34 and the mutant, V25R, effectively scaffolded the α-isoform of protein phosphatase-1 (PP1α) and enabled eIF2α dephosphorylation. However, the largely cytosolic V25R protein displayed a reduced rate of proteasomal degradation, and unlike WT GADD34, whose ectopic expression resulted in a dilated or distended ER, V25R did not modify ER morphology. These studies suggested that the association of with ER modulates intracellular trafficking and proteasomal degradation of GADD34, and in turn, its ability to modify ER morphology.





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Zhou, Wei, Matthew H Brush, Meng S Choy and Shirish Shenolikar (2011). Association with endoplasmic reticulum promotes proteasomal degradation of GADD34 protein. The Journal of biological chemistry, 286(24). pp. 21687–21696. 10.1074/jbc.m110.212787 Retrieved from

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Shirish Shenolikar

Professor Emeritus of Psychiatry and Behavioral Sciences

Protein phosphorylation controls a wide range of physiological processes in mammalian tissues. Phosphorylation state of cellular proteins is controlled by the opposing actions of protein kinases and phosphatases that are regulated by hormones, neurotransmitters, growth factors and other environmental cues. Our research attempts to understand the communication between protein kinases and phosphatases that dictates cellular protein phosphorylation and the cell's response to hormones. Over the last decade, our work has provided critical information about the role of protein phosphatase-1 (PP1) in controlling synaptic function, cell stress, gene expression and growth. We have generated a large repertoire of reagents to decipher PP1's role in signaling pathways in mammalian cells and tissues. Emerging evidence suggests that in many cells, PP1 activity is fine tuned by the protein, inhibitor-1 (I-1). A major focus of our research is to elucidate the role of I-1 in kinase-phosphatase cross-talk and impact of the altered I-1 gene expression seen in several human diseases. Our studies showed that recognition of cellular substrates by PP1 is also directed by its association with a variety of targeting subunits that are themselves also subject to physiological control. Thus, the overall focus of our research is to define the physiological mechanisms that regulate PP1 functions relevant to human health and disease.

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