Increased degradation of newly synthesized interferon-gamma (IFN-gamma) in anti CD3-stimulated lymphocytes treated with glycoprotein processing inhibitors.

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-gamma (IFN-gamma) 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-gamma but enhanced the degradation of newly synthesized IFN-gamma in anti CD3-stimulated lymphocytes. Furthermore, since the stability of N-glycosylated 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-gamma with calnexin and calreticulin was investigated. It was found that IFN-gamma formed complexes with calnexin and calreticulin in anti CD3-stimulated lymphocytes. Total binding of IFN-gamma 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-gamma 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-gamma from already formed calreticulin complexes, which prevents the binding of newly synthesized IFN-gamma to calreticulin and results in the enhancement of IFN-gamma degradation.