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

The 20S proteasome beta-1 subunit (PSMB6) and the immunoproteasome beta-1i subunit (PSMB9/LMP2) are the catalytic components responsible for the caspase-like activity within the proteasome complex. While PSMB6 is a constitutive component of the 20S core in most cells, PSMB9 is an inducible subunit primarily expressed in hematopoietic cells or upregulated in response to inflammatory stimuli such as interferon-gamma [1.2.1, 1.3.1]. These subunits are essential for maintaining cellular protein homeostasis by degrading misfolded or regulatory proteins and are critical for the generation of peptide fragments for MHC class I antigen presentation, thereby regulating immune surveillance and inflammatory signaling [1.2.3, 1.4.2]. Therapeutically, these subunits are targeted in the treatment of hematologic malignancies and autoimmune disorders. Non-selective proteasome inhibitors like bortezomib inhibit these subunits alongside the chymotrypsin-like beta-5 subunits to induce apoptosis in cancer cells, particularly in multiple myeloma [1.5.2, 1.5.4]. In contrast, selective immunoproteasome inhibitors like zetomipzomib (KZR-616) specifically target PSMB9 and PSMB8 to modulate immune cell function and reduce the production of pro-inflammatory cytokines without the broad toxicity associated with constitutive proteasome inhibition [1.1.1, 1.1.3].

Other names

20S proteasome beta-1 subunitImmunoproteasome beta-1i subunitLMP2Low molecular mass protein 2Caspase-like subunitPost-glutamyl peptide hydrolyzing subunitPSMB6iRING12Delta subunitY subunit

Inhibition of the caspase-like (post-glutamyl peptide hydrolyzing) proteolytic activity of the 20S proteasome and immunoproteasome, leading to the accumulation of polyubiquitinated proteins, induction of the unfolded protein response (UPR), and endoplasmic reticulum (ER) stress, which ultimately triggers apoptosis in malignant cells and modulates pro-inflammatory cytokine production in immune cells [1.1.1, 1.2.3, 1.5.4].