Expression of Immunoproteasome Subunit LMP7 in Breast Cancer and Its Association with Immune-Related Markers.

Purpose In the presence of interferon, proteasome subunits are replaced by their inducible counter-parts 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-elF2a [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.