DnaJ heat shock protein family member B9 (DNAJB9)

DnaJ heat shock protein family member B9 (DNAJB9), also known as ERdj4, is a co-chaperone protein of the Hsp40/DnaJ family localized primarily in the endoplasmic reticulum (ER)[5][2]. DNAJB9 acts as a type 2 DnaJ protein that regulates the activity of Hsp70 chaperones (specifically BiP/GRP78) via its J-domain, facilitating protein folding, quality control, and ER-associated degradation of misfolded proteins[2][4][5]. DNAJB9 is upregulated during ER stress and various cellular stimuli and provides a protective role against apoptosis by repressing pro-apoptotic activity of p53 and supporting cell survival under genotoxic or unfolding stress[3][2]. It also tightly controls processes such as epithelial-mesenchymal transition, B-cell maturation, and immunoglobulin switching[2]. DNAJB9 is expressed in most tissues, particularly those with high secretory activity, and is notably a highly specific diagnostic marker for fibrillary glomerulonephritis, where its abnormal extracellular deposition characterizes the disease[1][2]. Research indicates involvement in the pathogenesis of diabetes, certain amyloid diseases (including Alzheimer’s), and possibly cancer, but currently there are no clinically approved drugs targeting DNAJB9 directly[5][2][3].

Other names

DnaJ homolog subfamily B member 9ER-resident protein ERdj4ERdj4Mdg-1Microvascular endothelial differentiation gene 1 proteinMDG1Mdj7Endoplasmic reticulum DNA J domain-containing protein 4MST049MSTP049

Not applicable (no established targeted drugs). As a biological mechanism: Co-chaperone activity modulates Hsp70 (BiP) ATPase activity, affects unfolded protein response and protein degradation[5][2].