Proteasome subunit beta type-6 (PSMB6) and Proteasome subunit beta type-9 (PSMB9) (PSMB6 and PSMB9)

The 20S proteasome beta 1 (Proteasome subunit beta type-6, PSMB6) and beta 1i (Proteasome subunit beta type-9, PSMB9) subunits are the catalytic components of the 20S core particle responsible for caspase-like proteolytic activity, which involves the cleavage of peptide bonds after acidic amino acid residues (NIH, 2023; ResearchGate, 2024). PSMB6 is a constitutive subunit expressed in most tissues, while PSMB9 is an inducible subunit (also known as LMP2) that replaces PSMB6 in the immunoproteasome during inflammatory responses or upon stimulation by cytokines like interferon-gamma (Wikipedia, 2024; NIH, 2014). These subunits are essential for maintaining cellular protein homeostasis by degrading misfolded or damaged proteins and play a specialized role in the immune system by generating peptides for MHC class I antigen presentation (NIH, 2007; ResearchGate, 2011). In oncology, particularly in hematologic malignancies like multiple myeloma, these subunits are targeted by drugs such as bortezomib and carfilzomib to disrupt protein degradation, leading to the accumulation of toxic proteins, endoplasmic reticulum stress, and subsequent apoptosis (Patsnap, 2024; NIH, 2020). Additionally, selective inhibition of the immunoproteasome subunit PSMB9 is being investigated as a therapeutic strategy for autoimmune and inflammatory diseases to modulate immune cell function while minimizing the systemic side effects associated with broad proteasome inhibition (Patsnap, 2024).

Other names

20S proteasome beta 1 and beta 1i subunitsPSMB6PSMB9LMP2DeltaLMPYYRING12Proteasome subunit beta type-6Proteasome subunit beta type-9

Inhibition of the caspase-like proteolytic activity of the 20S proteasome and immunoproteasome, leading to the accumulation of ubiquitinated proteins, induction of endoplasmic reticulum stress, and activation of pro-apoptotic pathways. In the context of the immunoproteasome, inhibition of the beta 1i subunit also modulates MHC class I antigen processing and reduces the production of pro-inflammatory cytokines.