Induction of immunoproteasomes in porcine kidney (PK)-15 cells by interferon-γ and tumor necrosis factor-α

Immunoproteasome (i-proteasome) has both immune and non-immune functions and plays important roles in controlling infections and combating illnesses. Our previous studies suggest that interferon (IFN)-gamma induces the expression of three immune-specific catalytic subunits of the 20S proteasome that can replace their constitutive homologues to form the i-proteasome in immune cells, such as porcine alveolar macrophages (AMs) in vitro. However, i-proteasome levels and their modulation in non-immune cells such as the epithelial cells in pigs remain unknown. Here, we investigated the expression of i-proteasomes in non-immune cells (porcine kidney (PK)-15 cells) to determine i-proteasome modulation upon stimulation of PK-15 cells with IFN-gamma and tumor necrosis factor (TNF)-alpha in vitro. The expression of i-proteasome subunits in PK-15 cells were regulated by IFN-gamma and TNF-alpha. Remarkably, we found that the combination treatment of IFN-gamma and TNF-alpha increased the expression of i-proteasome subunits LMP2, LMP7, and MECL-1 in PK-15 cells at transcriptional levels, but may decrease their expression at translational level, compared to their expression levels induced by individual cytokine treatments. These results provide critical insight into i-proteasome modulation in porcine non-immune cells, contribute further to our understanding of i-proteasome function in tissue pathogenesis and the development of antiviral adaptive immune responses against intracellular infections.