Heat Shock Protein gp96 as an Immune Chaperone of Inflammation and Cancer


Austin J Clin Immunol. 2014;1(3): 1014.

Heat Shock Protein gp96 as an Immune Chaperone of Inflammation and Cancer

Bei Liu*

Department of Microbiology & Immunology, Medical University of South Carolina, USA

*Corresponding author: Bei Liu, Department of Microbiology & Immunology, Hollings Cancer Center, Medical University of South Carolina, 86 Jonathan Lucas Street, Charleston, SC 29425, USA

Received: March 25, 2014; Accepted: April 10, 2014; Published: April 14, 2014

Heat shock protein gp96 [1], also known as grp94 [2], endoplasmin [3], ERp99 [4],and HSP90b1 [5]; is an endoplasmic reticulum (ER) paralogue of heat shock protein 90 (HSP90). However, the structure and function of gp96 are distinctfrom other cytosolic HSP90. gp96 is induced by the accumulation of misfolded proteins in the cells [6]; it binds to and hydrolizes ATP [7]. gp96 is the most abundant and a ubiquitous glycoprotein in the ER lumen. Accumulating evidence including work from my own laboratory reveals that gp96 serves as a unique and an important chaperone for inflammation and cancer. The key evidence is summarized in this editorial.

Gp96 as a molecular chaperone for Toll-like receptors (TLRs) was first discovered in 2001. This study showed that a murine pre-Bcell line (70Z/3)that was rendered deficient of gp96 is unresponsive to ligands for TLR2 and TLR4 [8]. Using classic gene knockout strategies, subsequent studies conclusively demonstrated that gp96 is an obligate master chaperone for folding most of TLRs (except TLR3), integrins, platelet glycoprotein Ib-IX-V complex, and the Wnt co-receptor low-density lipoprotein receptor-related protein 6(LRP6) [9-15].

TLRs are germline-encoded pattern recognition receptors (PRR) that function in recognizing pathogen-associated molecular patterns (PAMP) such as lipopolysaccharide (LPS), dsRNA, unmethylatedCpG DNA and flagellin for initiation of the innate immunity and subsequent activation of the adaptive immunity [16,17].Yang et al found that gp96-deficient macrophages fail to respond to ligands for both surface and intracellular TLRs except TLR3. In the absence of gp96, TLRs fail to translocate to the cell surface or endosome, and are retained in the ER. Furthermore, macrophage-specific gp96-deficient miceare highly susceptible to the acute infection by Listeria monocytogenes (LM), indicating the functions of macrophagesin the clearance of this organismare regulated by TLR signaling [9]. More recently, Morales et al showed that macrophage-specific gp96-deficient miceare more resistant to chemical-inducedcolitis.Macrophage-specific gp96-deficient mice have significantly less inflammation in the colon and lower percentages of Th17 and Th1 cells in coloniclamina propriacompared with wild type littermates. Intriguingly, by using a standard colon cancer model induced byazoxymethane (AOM) and DSS, they found that macrophage-specific gp96-deficient mice developed fewer and smaller tumors, indicating that deletion of gp96 in macrophages renders miceresistant against colitis-associated colon cancer [18]. This study demonstrates the critical role of gp96 and its clientele (such as TLRs) on myeloid cells in conferring intestinal inflammation, inducing genetic instability in the colonic epithelium, and promoting inflammation-associated colon tumorigenesis.

Historically, one of the most well-known clients of gp96 is the immunoglobulin (Ig) heavy chain [19] and several studies have suggested the roles of gp96 in B cell function. For example, gp96 is induced more than 10 fold during B cell activation [4]; it has been shown to participate in the assembly of B cell receptor (BCR) complexes through its association with Iga molecules [20]. To answer the direct roles of gp96 in B cell biology in vivo, Liu and Li generated a B cell specific gp96 deficient mouse [10]. They found that B cells are unable to proliferate in response to multiple TLR ligands and are defective in the expression/function of selective integrins. In this study, they also demonstrated that gp96 null conventional B cells do not accumulate efficiently in the lymph nodes and innate-like B cells (B1 cells and marginal zone B cells) fail to compartmentize properly which is most likely due to selective integrin defect. Moreover, both proliferation and Ig production by the gp96 null B cells are attenuated even though a robust proximal BCR signaling was preserved. Despite these multiple defects, B cell selective gp96-deficient mice are able to mount robust antibody response against both T cell-dependent and T cell-independent antigen, indicating gp96 plays more selective roles in the function of B cells in vivo by chaperoning a limited set of client proteins in B cell biology.

Gp96 is a key downstream chaperone in the ER to mediate unfolded protein response (UPR) [21]. UPR is an evolutionally conserved mechanism to maintain protein quality control in the secretory pathway. Although under the steady state conditions, gp96 is not required for B cell activation, germinal center formation, plasma cell differentiation, and class-switching or affinity maturation [10]. It is unclear if gp96 is required for plasma cell biology and for the development of multiple myeloma (MM) during chronic ER stress conditions. MM is an incurable plasma cell neoplasm whose pathogenesis is closely linked to dys regulated unfolded protein response (UPR) in the endoplasmic reticulum (ER). Constitutive activation of UPR in mice causes myeloma, as demonstrated by transgenic expression of a master UPR transcription factor XBP1s (XBP1s Tg mice) [22]. To address this question, Hua et al generated a mouse model with over-expression of XBP1s and deletion of gp96 in B cell compartment simultaneously; it was found that the persistence of plasma cells as well as the development of myeloma is critically dependent on gp96 [15].Furthermore, a recent study by Liu et al. demonstrated that gp96 is a chaperone for Wnt co-receptor LRP6 and Wnt signaling is decreased in the absence of gp96 [13]. gp96 knock down causes severe compromise in MM cell growth which can be significantly rescued by GSK3β inhibitors. In the absence of gp96, MM cells undergo mitotic catastrophe and apoptosis which correlated with decreased expression of surviv in a Wnt target molecule. This study indicates that myeloma is uniquely dependent on gp96 for survival, which is mediated in part by a LRP6-Wnt-survivin pathway. This finding suggests that gp96 is a novel therapeutic target for multiple myeloma.

Currently, the number of identified protein substrates that are dependent on gp96 for folding is still limited. Further identification of more gp96 client proteins and understanding the functional implications of gp96-client network in inflammation and cancer may catalyze the development of novel gp96-targeted therapeutics for these conditions.


  1. Srivastava PK, DeLeo AB, Old LJ. Tumor rejection antigens of chemically induced sarcomas of inbred mice. Proc Natl Acad Sci USA. 1986; 83: 3407-3411.
  2. Lee AS, Delegeane A, Scharff D. Highly conserved glucose-regulated protein in hamster and chicken cells: preliminary characterization of its cDNA clone. Proc Natl Acad Sci USA. 1981; 78: 4922-4925.
  3. Koch G, Smith M, Macer D, Webster P, Mortara R. Endoplasmic reticulum contains a common, abundant calcium-binding glycoprotein, endoplasmin. J Cell Sci. 1986; 86; 217-232.
  4. Lewis MJ, Mazzarella RA, Green M. Structure and assembly of the endoplasmic reticulum. The synthesis of three major endoplasmic reticulum proteins during lipopolysaccharide-induced differentiation of murine lymphocytes. J Biol Chem. 1985; 260: 3050-3057.
  5. Chen B, Piel WH, Gui L, Bruford E, Monteiro A. The HSP90 family of genes in the human genome: insights into their divergence and evolution. Genomics. 2005; 86: 627-637.
  6. Kozutsumi Y, Segal M, Normington K, Gething MJ, Sambrook J. The presence of malfolded proteins in the endoplasmic reticulum signals the induction of glucose-regulated proteins. Nature. 1988; 332: 462-464.
  7. Li Z, Srivastava PK. Tumor rejection antigen gp96/grp94 is an ATPase: implications for protein folding and antigen presentation. Embo J. 1993;12: 3143-3151.
  8. Randow F, Seed B. Endoplasmic reticulum chaperone gp96 is required for innate immunity but not cell viability. Nat Cell Biol. 2001; 3: 891-896.
  9. Yang Y, Liu B, Dai J, Srivastava PK, Zammit DJ, Lefrancois L, et al. Heat shock protein gp96 is a master haperone for toll-like receptors and is important in the innate function of macrophages. Immunity. 2007; 26: 215-226.
  10. Liu B, Li Z. Endoplasmic reticulum HSP90b1 (gp96, grp94) optimizes B-cell function via chaperoning integrin and TLR but not immunoglobulin. Blood. 2008; 112: 1223-1230.
  11. Liu B, Yang Y, Qiu Z, Staron M, Hong F, Li Y, et al. Folding of Toll-like receptors by the HSP90 paralogue gp96 requires a substrate-specific cochaperone. Nature communications. 2010; 1: 79.
  12. Staron M, Yang Y, Liu B, Li J, Shen Y, Zuniga-Pflucker, et al. gp96, an endoplasmic reticulum master chaperone for integrins and Toll-like receptors, selectively regulates early T and B lymphopoiesis. Blood. 2010; 115: 2380-2390.
  13. Liu B, Staron M, Hong F, Wu BX, Sun S, Morales C, et al. Essential roles of grp94 in gut homeostasis via chaperoning canonical Wnt pathway. Proceedings of the National Academy of Sciences of the United States of America. 2013; 110: 6877-6882.
  14. Staron M, Wu S, Hong F, Stojanovic A, Du X, Bona R, et al. Heat-shock protein gp96/grp94 is an essential chaperone for the platelet glycoprotein Ib-IX-V complex. Blood. 2011; 117: 7136-7144.
  15. Hua Y, White-Gilbertson S, Kellner J, Rachidi S, Usmani SZ, Chiosis G, et al. Molecular chaperone gp96 is a novel therapeutic target of multiple myeloma. Clin Cancer Res. 2013; 19: 6242-6251.
  16. Medzhitov R. Toll-like receptors and innate immunity. Nat Rev Immunol. 2001; 1: 135-145.
  17. Iwasaki A, Medzhitov R. Toll-like receptor control of the adaptive immune responses. Nat Immunol. 2004; 5: 987-995.
  18. Morales C, Rachidi S, Hong F, Sun S, Ouyang X, Wallace C, et al. Immune chaperone gp96 drives the contributions of macrophages to inflammatory colon tumorigenesis. Cancer Res. 2014; 74: 446-459.
  19. Melnick J, Dul JL, Argon Y. Sequential interaction of the chaperones BiP and GRP94 with immunoglobulin chains in the endoplasmic reticulum. Nature. 1994; 370: 373-375.
  20. Foy SP, Matsuuchi L. Association of B lymphocyte antigen receptor polypeptides with multiple chaperone proteins. Immunol Lett. 2001; 78: 149-160.
  21. Yang Y, Li Z. Roles of heat shock protein gp96 in the ER quality control: redundant or unique function? Mol Cells 2005; 20: 173-182.
  22. Carrasco DR, Sukhdeo K, Protopopova M, Sinha R, Enos M, Carrasco DE, et al. The differentiation and stress response factor XBP-1 drives multiple myeloma pathogenesis. Cancer Cell. 2007; 11: 349-360.

Download PDF

Citation: Albert MJ. Heat Shock Protein gp96 as an Immune Chaperone of Inflammation and Cancer. Austin J Clin Immunol. 2014;1(3): 1014. ISSN : 2381-9138

Journal Scope
Online First
Current Issue
Editorial Board
Instruction for Authors
Submit Your Article
Contact Us