Abstract
GRP94 is an ATP-dependent chaperone able to regulate pro-oncogenic signaling pathways. Previous studies have shown a critical role of GRP94 in brain metastasis (BrM) pathogenesis and progression. In this work, an untargeted lipidomic analysis revealed that some lipid species were altered in GRP94-deficient cells, specially GM2 and GM3 gangliosides. The catalytic pathway of GM2 is affected by the low enzymatic activity of β-Hexosaminidase (HexA), responsible for the hydrolysis of GM2 to GM3. Moreover, a deficiency of the GM2-activator protein (GM2-AP), the cofactor of HexA, is observed without alteration of gene expression, indicating a post-transcriptional alteration of GM2-AP in the GRP94-ablated cells. One plausible explanation of these observations is that GM2-AP is a client of GRP94, resulting in defective GM2 catabolic processing and lysosomal accumulation of GM2 in GRP94-ablated cells. Overall, given the role of gangliosides in cell surface dynamics and signaling, their imbalance might be linked to modifications of cell behaviour acquired in BrM progression. This work indicates that GM2-AP could be an important factor in ganglioside balance maintenance. These findings highlight the relevance of GM3 and GM2 gangliosides in BrM and reveal GM2-AP as a promising diagnosis and therapeutic target in BrM research.
Highlights
The endoplasmic reticulum (ER) has emerged as a major site of cellular homeostasis by harbouring a refined network of molecular chaperones, which acts as a quality control mechanism for homeostatic synthesis, folding and glycosylation of nascent proteins, either secreted from the cell or transported to the plasma membrane[1]
When partial least squares-discriminant analysis (PLS-DA) was applied to see if cells with different GRP94 expression level could be correctly discriminated in the positive mode, shGRP94-2 (Fig. 2C) and shGRP94-8 (Fig. 2D) samples were differentiated from non-silenced ones using two latent variables, explaining 62.2% and 67.5% of the variance, and Mathew’s Correlation Coefficient (MCC) values of 1 and 0.83, respectively
We show that GM2 ganglioside levels are increased in BRV5CA1 GRP94-ablated cells whereas GM3 decreases, which drastically change the ratio of GM3/GM2 in cells; second, levels of β-Hexosaminidase (HexA) activity, responsible for the synthesis of GM3 from GM2, are decreased in GRP94-ablated cells, and third, we describe that a post-transcriptional alteration of GM2-activator protein (GM2-AP), the cofactor that interacts with HexA, is responsible for the lower HexA activity observed in BRV5CA1 GRP94-ablated cells
Summary
The endoplasmic reticulum (ER) has emerged as a major site of cellular homeostasis by harbouring a refined network of molecular chaperones, which acts as a quality control mechanism for homeostatic synthesis, folding and glycosylation of nascent proteins, either secreted from the cell or transported to the plasma membrane[1]. When the efficiency of secretory protein folding is threatened, unfolded/misfolded proteins are improperly glycosylated These proteins are accumulated and the cell goes through ER stress (ERS) which elicits a homeostatic unfolded protein response (UPR). Among ER chaperons, glucose-regulated proteins (GRP) are characterized by increasing their expression under deregulation of ER-homeostasis induced through hypoxia, nutrient limitation, redox glycolytic reactions, stressful conditions in the calcium metabolism and UPR4,5. The ability of cancer cells to handle ERS conditions lies in their intrinsic capacity to adapt for cell survival, or alternatively, to initiate an apoptosis or senescence program through ER-associated machinery[1,13] In this scene, overexpression of GRP94 induces metabolic stress resistance associated with cellular transformation and increased tumorigenicity in a variety of cancer cell lines[14,15,16]. The glucose levels in the brain interstitial space are lower than in blood[21,22]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
