GOLGI RETARDATION IN MADIN-DARBY CANINE KIDNEY AND CHINESE-HAMSTER OVARY CELLS OF A TRANSMEMBRANE CHIMERA OF 2 SURFACE-PROTEINS

Dipeptidyl peptidase IV (DDD) is a type II plasma membrane protein. Re placement of its transmembrane domain with that of another surface pro tein, aminopeptidase N, resulted in accumulation in the Golgi apparatu s of Madin-Darby canine kidney cells and a delayed Golgi to surface tr ansport in Chinese hamster ovary (CHO) cells. The compartment of retar dation was identified as post medial-Golgi, most likely to be the tran s-Golgi/trans Golgi network (TGN). Compared to native DDD, the rate of endoplasmic reticulum to Golgi transport for the chimera was largely unchanged in both cell types. On the other hand, Golgi to surface tran sport was delayed by more than 2 h in CHO cells and essentially undete ctable up to 22 h of chase in Madin-Darby canine kidney cells. The dec rease in the rate of Golgi to surface transport in CHO cells resulted in a significant accumulation of the fusion protein in the trans-Golgi /TGN. This phenomena is very unlikely to be due to any drastic conform ational changes, as neither the enzyme activity nor the dimerization o f the constructed molecule was affected. The findings of this study in dicate that the transmembrane domain, in the context of its flanking s equences, is important for efficient Golgi to cell surface transport.