Characterization of GIV‐GRP78 Interaction During Endoplasmic Reticulum Stress

Abstract

Endoplasmic Reticulum (ER) stress occurs when misfolded proteins accumulate in the ER. Cells facing ER stress initially attempt to restore cellular homeostasis, but if the stress becomes chronic and homeostasis is not achieved within a reasonable timeframe, cells initiate programmed cell death. Cancer cells are able to withstand and survive ER stress better than regular cells. Overexpression of the chaperone Glucose Regulated Protein 78 kDa (GRP78) is one of the key factors that promote cancer cell survival during ER stress. Although it is an ER resident protein, recent studies have shown that when overexpressed, GRP78 can translocate to other cellular locations including the cell surface from where it can activate cytoprotective signals; however, the mechanism by which it does so remains elusive. Our laboratory has recently identified Gα‐Interacting Vesicle associated protein (GIV) ‐ a known enhancer of the pro‐survival Akt signaling ‐ as a novel binding partner of GRP78. We hypothesize that this interaction may be the missing link in understanding the mechanism by which cell surface GRP78 increases cell viability. Because GIV and GRP78 are normally localized in different cellular compartments, we characterized the spatiotemporal dynamics of this interaction by analyzing the sub‐cellular localization of these proteins in HeLa cells treated with Tunicamycin (an ER stress inducer) through differential centrifugation and immunofluorescence microscopy. Our results showed that GIV is present in both membrane and cytosolic fractions during normal as well as ER stress conditions. GRP78, on the other hand, is in the membrane fraction under normal cellular conditions but appears in the cytosolic fraction upon ER stress. GIV and GRP78 co‐localized in a perinuclear region as well as at the cell surface of the ER stressed cells. Finally, we also mapped the interaction between GIV and GRP78 to the carboxyl terminus domains on both proteins by performing pull‐down assays. Taken together, this work has characterized GIV‐GRP78 interaction in the face of ER stress. Our current and future goals include studying the role of this novel interaction in mediating cell survival during chronic ER stress.Support or Funding InformationThis project is supported by the NIH‐NIGMS grant # SC2GM121246 (DB). JN is supported by the NIH MARC program award number: T34GM008074.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.