Increased Degradation of Newly Synthesized Interferon-γ (IFN-γ) in Anti CD3-Stimulated Lymphocytes Treated with Glycoprotein Processing Inhibitors

Abstract

As described previously (Kosuge T., Toyoshima S., Biol. Pharm. Bull., 23, 1-5 (2000)), inhibitors of the glycoprotein processing enzymes, glucosidase I and II, induce decreased secretion of interferon-γ (IFN-γ) into culture supernatants of anti CD3-stimulated lymphocytes, and in the present study the mechanism has been investigated in further detail.The processing inhibitors did not affect intracellular levels of IFN-γ but enhanced the degradation of newly synthesized IFN-γ-in anti CD3-stimulated lymphocytes. Furthermore, since the stability of N-glycosylatd proteins is known to be regulated by lectin family chaperones, such as calnexin, a type I transmembrane protein located in the endoplasmic reticulum (ER), and calreticulin, a soluble protein in the ER lumen, the effect of the processing inhibitors on the interaction of IFN-γ with calnexin and calreticulin was investigated. It was found that IFN-γ formed complexes with calnexin and calreticulin in anti CD3-stimulated lymphocytes. Total binding of IFN-γ to calnexin was not affected but that to calreticulin was increased in anti CD3-stimulated lymphocytes treated with the processing inhibitors. However, binding of newly synthesized IFN-γ to calreticulin was decreased in the lymphocytes under the same conditions as above. These results suggest that these glycoprotein processing inhibitors block the release of IFN-γ from already formed calreticulin complexes, which prevents the binding of newly synthesized IFN-γ to calreticulin and results in the enhancement of IFN-γ degradation.