| Heat shock protein gp96 is an Endoplasmic Reticulum (ER) resident chaperone protein of hsp90 family. To understand the biological function of gp96 in vivo, we have generated a conditional gp96 knockout mouse in which gp96 was specifically deleted in macrophages, but not in other cell types (including dendritic cells). The macrophages from gp96-null mice were examined for their innate immune function in response to a variety of Toll-like Receptor (TLR) ligands. We found that gp96 null macrophages have abrogated function to multiple TLRs, including TLR2, 4, 5, 7 and 9, which prompted us to propose that gp96 is an indispensable chaperone for multiple TLRs. We focused on TLR9, an intracellular TLR, as an example to elucidate the defect in TLR pathway as a consequence of gp96 loss. Consistent with the role of gp96 as a molecular chaperone, we found that TLR9 protein was not stable in the absence of gp96. Given that this is a macrophage-selective pan-TLR deficient mouse model, we determined the contribution of macrophages to immune response against microbial components in vivo. It was found that these mice were resistant to endotoxin induced septic shock, but were hypersensitive to Listeria monocytogenes, suggesting that macrophages are the major cytokine mediators in these scenarios. To our surprise, we found that gp96 null cells were able to mount a response to dsRNA in a TLR3 dependent fashion, indicating that TLR3 utilizes different ER chaperone machinery. We further provided evidence that gp96 is required for the folding of the extracellular domain of TLR4 and 9, but not that of TLR3. Taken together, my thesis work provided strong evidence that gp96 is specifically required for the expression and function of multiple TLRs, that includes both TLRs at cell surface and intracellular TLRs. |
