Retardation of a surface protein chimera at the cis Golgi

Abstract

Dipeptidyl peptidase IV (D4) and the α subunit of human chorionic gonadotrophin (αhcg) are plasma membrane and secretory proteins, respectively. In the course of studies to understand mechanisms involved in transport along the exocytotic pathway, the ectoplasmic domain of D4 was replaced by the mature polypeptide of αhcg, resulting in the membrane anchored chimera, D4αhcg. Surprisingly, when transfected into Chinese hamster ovary (CHO) and Madin-Darby canine kidney (MDCK) cells, strong perinuclear Golgi staining was predominant, in addition to the expected surface staining. By following the biogenesis and transport of the molecule, it was established that newly synthesized D4αhdg is eventually transported to the cell surface but only after a significant retardation in the Golgi apparatus. The compartment of retardation was identified as the early or cis Golgi, before the medial Golgi, where resistance to endoglycosidase (endo) H is conferred. As a result of the transport retardation of the chimera, we were able to document the appearance of an endo D sensitive intermediate, which is usually too transient to be apparent in normal cells. The retardation of this chimera in the cis Golgi complements our previous report in which the D4 molecule with its transmembrane domain replaced by that of aminopeptidase N resulted in retardation in the trans Golgi/trans Golgi network in MDCK and CHO cells [Low, S. H., Tang, B. L., Wong, S. H., & Hong, W. (1994) J. Biol. Chem. 269, 1985-1994). Together, these reports indicate that transport along the exocytic pathway may not be simply by default but requires some sort of signal, the disruption of which results in inefficient intra-Golgi and/or Golgi to surface transport. © 1995 American Chemical Society.