Expression and regulation of interferon γ-inducible proteasomal subunits LMP7 and LMP10 in the bovine corpus luteum

The proteasome is a large, polymeric protease complex responsible for intracellular protein degradation and generation of peptides that bind to class I major histocompatibility complex (MHC) molecules. Interferon γ (INFγ) induces expression of alternative proteasomal subunits that affect intracellular protein degradation, thereby changing the types of peptides that bind to class I MHC molecules. These alterations in class I MHC peptides can influence whether cells and tissues are tolerated by the immune system. Expression of two INFγ-inducible proteasomal subunits, LMP7 and LMP10, in bovine luteal tissue was examined in this study. Northern analysis revealed the presence of mRNA encoding LMP7 and LMP10 in luteal tissue. Steady-state amounts of LMP7 mRNA did not change during the estrous cycle, but LMP10 mRNA was low in early corpus luteum (CL) and elevated in midcycle and late CL. Tumor necrosis factor α alone and in the presence of LH and/or prostaglandin F_2α elevated steady-state amounts of LMP10 mRNA but did not affect LMP7 mRNA in cultured luteal cells. Immunohistochemistry revealed the presence of LMP10 primarily in small luteal cells. Numbers of LMP10-positive cells were lower in early CL than in midcycle and late CL. The finding that INFγ-inducible proteasomal subunits are expressed in luteal tissue when the CL is fully functional was unexpected and suggests that proteasomes in luteal cells may generate peptides capable of stimulating a class I MHC-dependent inflammatory response.