Glycoprotein (gp) 96 expression: induced during differentiation of intestinal macrophages but impaired in Crohn's disease

Abstract

Background: The glycoprotein (gp) 96 links the adaptive with the innate immune system. It is a chaperone with a binding domain for peptides generated by proteasomal degradation. During cellular stress, peptide loaded gp96 can be released and presented to T cells by antigen presenting cells (APCs). Methods: mRNAs from in vitro differentiated macrophages (iv mac) and normal intestinal macrophages (IMACs) were compared by subtractive hybridisation and Affymetrix GeneChip analysis. Differentiation induced expression of gp96 was investigated in the multicellular spheroid (MCS) model. In vivo gp96 protein expression was detected by double labelling immunohistochemistry of human colon and in the CD4 + CD62L + T cell transfer mouse model. Results: Five of 76 clones obtained by subtractive hybridisation revealed .99% sequence homology to gp96. Affymetrix GeneChip analysis confirmed induction of gp96 in IMACs. Gp96 mRNA was detected in IMACs from normal and intestinal bowel disease mucosa. Induction of gp96 protein was observed after seven days in the MCS model of IMAC differentiation. Immunohistochemistry confirmed the presence of gp96 protein in IMACs in normal mucosa as well as in mucosa from patients with ulcerative colitis and diverticulitis. In mucosa from Crohn's disease (CD) patients, gp96 protein was not detectable. In the CD4

Crohn's Disease: Loss of Tolerance or a Disorder of Autophagy?

“…gp96 is induced during differentiation of normal iMACs but is not detected in iMACs in CD mucosa. As gp96 has been described as having a role in tolerance induction, this may be relevant for loss of tolerance against luminal bacteria found in CD patients [17]. Further, a reduced expression of subunits of the ubiquitin-proteasome system in iMACs of normal mucosa supports the concept of the presence of a nonreactive, anergic macrophage phenotype in the gut under normal conditions.…”

Mucosal macrophages and the regulation of immune responses in the intestine

“…These findings suggest simple transcriptional control may not be the most important mechanism for preventing TLR expression by intestinal m. An alternative factor which could account for lack of TLR expression is failure to express the endoplasmic reticulum (ER)-associated heat shock protein, gp96, that acts as an essential chaperone for folding and shuttling TLR1, 2, 4, 5, 7, and 9 to the cell surface or correct intracellular compartment of m [45,46]. Although gp96 is reported to be absent in murine colonic m, it is expressed in normal human intestinal m, suggesting this is either not the explanation, or that distinct mechanisms may be involved in the two species [47]. Little is known of the role of recycling and degradation in the control of TLR expression, but an E3 ubiquitin-protein ligase, Triad3A, has been shown to regulate the ubiquitination and proteasomal degradation of TLR4 and TLR9 [48].…”

Clients and Oncogenic Roles of Molecular Chaperone gp96/grp94

“…Thus, gp96 may serve as a key molecule in mediating gut mucosal immune tolerance. This theory is supported by the fact that gp96 is induced during differentiation of normal intestinal macrophages, but not detected in intestinal macrophages in the gut mucosa of CD patients [134]. As gp96 may have a role in tolerance induction, this observation suggests that downregulation of gp96 is responsible for the loss of tolerance against luminal bacteria found in CD patients [134, 135].…”