Anti-TMUB1 monoclonal antibody, clone FQS25177

Misfolded proteins in the endoplasmic reticulum (ER) are degraded by ER-associated degradation (ERAD). Although ERAD components involved in degradation of luminal substrates are well characterized, much less is known about quality control of membrane proteins. Here, we analyzed the degradation pathways of two short-lived ER membrane model proteins in mammalian cells. Using a CRISPR-Cas9 genome-wide library screen, we identified an ERAD branch required for quality control of a subset of membrane proteins. Using biochemical and mass spectrometry approaches, we showed that this ERAD branch is defined by an ER membrane complex consisting of the ubiquitin ligase RNF185, the ubiquitin-like domain containing proteins TMUB1/2 and TMEM259/Membralin, a poorly characterized protein. This complex cooperates with cytosolic ubiquitin ligase UBE3C and p97 ATPase in degrading their membrane substrates. Our data reveal that ERAD branches have remarkable specificity for their membrane substrates, suggesting that multiple, perhaps combinatorial, determinants are involved in substrate selection.

Transmembrane and ubiquitin-like domain containing 1 (Tmub1) protein has a negative effect on liver regeneration; however, the mechanisms of Tmub1 expression regulation are currently unknown. CCAAT/enhancer-binding protein beta (C/EBP beta) is a key transcription factor associated with interleukin-6 (IL-6) in liver regeneration. The present study aimed to investigate the involvement of C/EBP beta in the IL-6-induced upregulation of Tmub1. A series of Tmub1 luciferase reporter vectors were constructed to detect the effects of IL-6 on the transcriptional activity of Tmub1. Small interfering RNA and overexpression vectors were employed to either inhibit or enhance the expression of C/EBP beta, respectively, to determine the effect of C/EBP beta on Tmub1 expression in liver cells. Additionally, chromatin immunoprecipitation experiments were performed to determine whether C/EBP beta bound to the Tmub1 gene, and the sequences associated with the regulation of Tmub1 expression by C/EBP beta were subsequently determined. Several potential binding sites of C/EBP beta were identified in the 5'-upstream region of the Tmub1 gene. C/EBP beta expression was positively correlated with Tmub1 gene expression in rat liver cells. Furthermore, it Was demonstrated that C/EBP beta bound to 5'-upstream sequences of the Tmub1 gene to enhance the promoter activity. The present study demonstrated that C/EBP beta is a key transcription factor, which can positively regulate the expression of Tmub1 during liver cell proliferation through a possible association with IL-6.