The dichotomous role of immunoproteasome in cancer: Friend or foe?

Immunoproteasome is a variant of proteasome with structural differences in 20S subunits optimizing them for the production of antigenic peptides with higher binding affinity to major histocompatibility complex (MHC)-I molecules. Apart from this primary function in antigen presentation, immunoproteasome is also responsible for the degradation of proteins, both unfolded proteins for the maintenance of protein homeostasis and tumor suppressor proteins contributing to tumor progression. The altered expression of immunoproteasome is frequently observed in cancers; however, its expression levels and effects vary among different cancer types exhibiting antagonistic roles in tumor development. This review focuses on the dichotomous role of immunoproteasome in different cancer types, as well as summarizes the current progression in immunoproteasome activators and inhibitors. Specifically targeting immunoproteasome may be a beneficial therapeutic intervention in cancer treatment and understanding the role of immunoproteasome in cancers will provide a significant therapeutic insight for the prevention and treatment of cancers.

Proteasoma, subtipos y sus implicaciones en la tolerancia central / The proteasome: subtypes and involvement in central tolerance

El proteasoma es un complejo proteico grande, el cual se encuentra fundamentalmente en todas las células eucariotas ya que juega un rol muy importante en los procesos celulares, tales como: la diferenciación celular, la progresión del ciclo celular, el desarrollo y la apoptosis celular. Existen varios tipos de proteasomas como el constitutivo, los intermedios, el inmunoproteasoma y el timoproteasoma, los cuales están presenten en las células del cuerpo en dependencia de la estructura y función de ellas. Sin embargo, se encuentran en las células del sistema inmune donde no solo juegan un papel muy importante en el procesamiento antigénico para la respuesta inmune, sino en los mecanismos de tolerancia central durante el proceso de ontogenia de los linfocitos T en el timo. Así, las células epiteliales tímicas corticales son células presentadoras de antígenos, las cuales presentan características intrínsecas únicas al presentar el timoproteasoma, la catepsina L y la proteasa serin específica del timo. Además, se ha observado una alta tasa de macroautofagia en comparación a las otras células del cuerpo, por lo que serán esenciales en la obtención de un repertorio de linfocitos T CD4+ y CD8+ que tendrán la capacidad de discriminar lo propio y lo no propio. Por lo que se debería considerar que la tolerancia central no está únicamente definida por el mecanismo de selección negativa, sino que a su vez la selección positiva juega un papel muy importante en la definición del repertorio de clones de linfocitos T no autorreactivos. El objetivo es discutir acerca del proteasoma, los tipos de proteasomas y sus implicaciones en la tolerancia central de los linfocitos T(AU)

The proteasome is a large protein complex mainly located in all eukaryote cells, where it plays a very important role in cellular processes like differentiation, cycle progression, development and apoptosis. There are several types of proteasomes: constitutive, intermediate, immunoproteasome and thymoproteasome, which are present in cells depending on their structure and functions. However, they are found in cells of the immune system, where they play a very important role not only in antigenic processes related to the immune response, but also in central tolerance mechanisms during T lymphocyte ontogeny in the thymus. Thymic cortical epithelial cells are therefore antigen-presenting cells with unique intrinsic characteristics, since they contain thymoproteasome, cathepsin L, and thymus-specific serine protease. Additionally, a high rate of macroautophagy has been observed in comparison with bibr cells of the body. They are thus essential to obtain a repertoire of CD4+ and CD8+ T lymphocytes capable of distinguishing the body's own elements from alien structures. Therefore, central tolerance should not be viewed as only defined by the negative selection mechanism, since positive selection also plays a very important role in defining the repertoire of non-autoreactive T lymphocyte clones. The purpose of the study was to discuss the proteasome, the types of proteasomes and their involvement in T lymphocyte central tolerance(AU)

Expression of Immunoproteasome Subunit LMP7 in Breast Cancer and Its Association with Immune-Related Markers / Journal of the Korean Cancer Association, 대한암학회지

PURPOSE: In the presence of interferon, proteasome subunits are replaced by their inducible counterparts to form an immunoproteasome (IP) plays a key role in generation of antigenic peptides presented by MHC class I molecules, leading to elicitation of a T cell‒mediated immune response. Although the roles of IP in other cancers, and inflammatory diseases have been extensively studied, its significance in breast cancer is unclear. MATERIALS AND METHODS: We investigated the expression of LMP7, an IP subunit, and its relationship with immune system components in two breast cancer cohorts. RESULTS: In 668 consecutive breast cancer cohort, 40% of tumors showed high level of LMP7 expression, and tumors with high expression of LMP7 had more tumor-infiltrating lymphocytes (TILs) in each subtype of breast cancer. In another cohort of 681 triple-negative breast cancer patients cohort, the expression of LMP7 in tumor cells was significantly correlated with the amount of TILs and the expression of interferon-associated molecules (MxA [p < 0.001] and PKR [p < 0.001]), endoplasmic reticulum stress-associated molecules (PERK [p=0.012], p-eIF2a [p=0.001], and XBP1 [p < 0.001]), and damage-associated molecular patterns (HMGN1 [p < 0.001] and HMGB1 [p < 0.001]). Patients with higher LMP7 expression had better disease-free survival outcomes than those with no or low expression in the positive lymph node metastasis group (p=0.041). CONCLUSION: Close association between the TIL levels and LMP7 expression in breast cancer indicates that better antigen presentation through greater LMP7 expression might be associated with more TILs.

Expression Pattern of Immunoproteasome Subunits in Human Thymus

The expression pattern of immunoproteasomes in human thymus has not been analyzed but may have important consequences during thymic selection. Here we examined the expression patterns of immunoproteasome subunits in fetal and adult thymic tissues by immunohistochemistry and found that all three subunits are expressed in both cortical and medullary stromal cells. These data suggest that thymic selection in human can be affected by peptide repertoires generated by immunoproteasomes.