LMP2 immunoproteasome promotes lymphocyte survival by degrading apoptotic BH3-only proteins

Immunohistochemical Identification and Assessment of the Location of Immunoproteasome Subunits LMP2 and LMP7 in Acquired Cholesteatoma

Cholesteatoma, accompanied by chronic inflammatory response, is characterized by invasive growth and osteolytic activity. As specific proteasome isoforms, the immunoproteasomes serve as an important modulator of inflammatory responses. The aim of the present study was to determine the biological activity of cholesteatoma through the analysis of the expression and localization of immunoproteasome subunits of low molecule weight protein (LMP) 2 and LMP7. Cholesteatoma specimens were obtained from 15 adults who underwent ear surgery due to acquired attic cholesteatoma. Normal skin specimens were taken from retro-auricular skin incisions from the same patients. The specimens were stained with anti-LMP7 antibody, using immunohistochemistry techniques based on the binding of biotinylated secondary antibody with the enzyme-labeled streptavidin and the Envision FLEX system. In all specimens of cholesteatoma, the immunohistochemical reaction with the antibody against the LMP2 was positive, in both the cytoplasm of the cholesteatoma matrix and the perimatrix. A negative reaction with anti-LMP2 was observed in the cytoplasm and nuclei of control skin cells. A positive nuclear and cytoplasmic immunohistochemical reaction with anti-LMP7 has been demonstrated in numerous cells, in both the matrix and perimatrix of cholesteatoma. We present evidence of the presence of expressions of LMP2 and LMP7 within cholesteatoma tissue. Our results might bring new information concerning immunoproteasome-dependent pathophysiologic mechanisms in cholesteatoma.

Intratumoral administration of the Toll-like receptor 7/8 agonist 3M-052 enhances interferon-driven tumor immunogenicity and suppresses metastatic spread in preclinical triple-negative breast cancer

Objectives

Loss of tumor‐inherent type I interferon (IFN) signalling has been closely linked to accelerated metastatic progression via decreased immunogenicity and antitumor immunity. Previous studies in murine models of triple‐negative breast cancer (TNBC) demonstrate that systemic IFN inducers are effective antimetastatic agents, via sustained antitumor CD8⁺ T‐cell responses. Repeated systemic dosing with recombinant IFNs or IFN inducers is associated with significant toxicities; hence, the use of alternate intratumoral agents is an active area of investigation. It is critical to investigate the impact of intratumoral agents on subsequent metastatic spread to predict clinical impact.

Methods

In this study, the local and systemic impact of the intratumoral Toll‐like receptor (TLR) 7/8 agonist 3M‐052 alone or in combination with anti‐PD1 was evaluated in metastatic TNBC models. The IFN‐α receptor (IFNAR1) blocking antibody, MAR1‐5A3, along with immune‐deficient mice and ex vivo assays are utilised to examine the key targets of this agent that are critical for an antimetastatic response.

Results

Single intratumoral administration of 3M‐052 reduced mammary tumor growth, induced a T‐cell‐inflamed tumor microenvironment (TME) and reduced metastatic spread to lung. Metastasis suppression was reliant on IFN signalling and an antitumor immune response, in contrast to primary tumor growth inhibition, which was retained in NSG and CD8⁺ T‐cell‐depleted mice. 3M‐052 action was demonstrated via dendritic cell activation and production of type I IFN and other pro‐inflammatory cytokines to initiate a T‐cell‐inflamed TME and promote tumor cell antigen presentation.

Conclusion

This work supports neoadjuvant TLR agonist‐based immunotherapeutics as realistic options for immune activation in the TME and long‐term metastatic protection in TNBC.

Immunoproteasome Inhibition Selectively Kills Human CD14+ Monocytes and as a Result Dampens IL-23 Secretion

MECL-1 (β2i), LMP2 (β1i), and LMP7 (β5i) are the proteolytically active subunits of the immunoproteasome (IP), a special type of proteasome mainly expressed in hematopoietic cells. Targeting the IP in autoimmune diseases proved to be therapeutically effective in preclinical mouse models. In endotoxin-stimulated human PBMCs, IP inhibition reduces the secretion of several proinflammatory cytokines, with the suppression of IL-23 being the most prominent. In this study, we investigated why the production of IL-23, a key mediator of inflammation in autoimmunity, is blocked when the IP is inhibited in LPS-stimulated human PBMCs. CD14⁺ monocytes could be identified as the main producers of IL-23 in LPS-stimulated PBMCs. We found that IP inhibition with the irreversible LMP7/LMP2 inhibitor ONX 0914 induced apoptosis in CD14⁺ monocytes, whereas CD4⁺, CD3⁺, CD19⁺, and CD56⁺ cells remained unaffected. A high expression of IPs renders monocytes susceptible to IP inhibition, leading to an accumulation of polyubiquitylated proteins and the induction of the unfolded protein response. Similar to IP inhibition, inducers of the unfolded protein response selectively kill CD14⁺ monocytes in human PBMCs. The blockage of the translation in CD14⁺ monocytes protects these cells from ONX 0914-induced cell death, indicating that the IP is required to maintain protein turnover in monocytes. Taken together, our data reveal why IP inhibition is particularly effective in the suppression of IL-23-driven autoimmunity.