Weisz O A, Machamer C E, Hubbard A L
Department of Cell Biology and Anatomy, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
J Biol Chem. 1992 Nov 5;267(31):22282-8.
Madin-Darby canine kidney (MDCK) cells deliver endogenous apical and basolateral proteins directly to the appropriate domains. We are investigating the molecular signals on a model plasma membrane hydrolase, dipeptidylpeptidase IV (DPPIV). Most newly synthesized rat liver DPPIV is delivered directly to the apical surface of transfected MDCK cells; however, about 20% is delivered first to the basolateral surface and reaches the apical surface via transcytosis (Casanova, J. E., Mishumi, Y., Ikehara, Y., Hubbard, A. L., and Mostov, K. E. (1991) J. Biol. Chem. 266, 24428-24432). A soluble form of DPPIV (solDPPIV) containing only the lumenal domain of the protein was efficiently transported and secreted by stably transfected MDCK cells. If this domain contains apical sorting information, we would expect 80% of the soluble protein to be secreted apically. Surprisingly, 95% of the secreted solDPPIV was found in the apical medium. The high efficiency of apical secretion suggested that the transmembrane domain and cytoplasmic tail of DPPIV might contain competing basolateral targeting information. To test this hypothesis, we investigated the trafficking of a chimera in which the cytoplasmic tail and transmembrane domains of DPPIV were joined to lysozyme, an exogenous protein which should not contain sorting information. This protein was delivered predominantly to the basolateral surface. Our results suggest that the lumenal domain of DPPIV carries dominant apical sorting information while the transmembrane domain and cytoplasmic tail of the molecule contains competing basolateral sorting information.
犬肾Madin-Darby细胞（MDCK）可将内源性顶端和基底外侧蛋白直接递送至相应区域。我们正在研究一种模型质膜水解酶——二肽基肽酶IV（DPPIV）上的分子信号。大多数新合成的大鼠肝脏DPPIV直接被递送至转染的MDCK细胞的顶端表面；然而，约20%首先被递送至基底外侧表面，并通过转胞吞作用到达顶端表面（Casanova, J. E., Mishumi, Y., Ikehara, Y., Hubbard, A. L., and Mostov, K. E. (1991) J. Biol. Chem. 266, 24428 - 24432）。一种仅包含该蛋白腔结构域的可溶性形式的DPPIV（solDPPIV），可被稳定转染的MDCK细胞有效转运和分泌。如果该结构域包含顶端分选信息，我们预期80%的可溶性蛋白会从顶端分泌。令人惊讶的是，95%分泌的solDPPIV存在于顶端培养基中。顶端分泌的高效率表明DPPIV的跨膜结构域和细胞质尾部可能包含竞争性的基底外侧靶向信息。为了验证这一假设，我们研究了一种嵌合体的运输情况，其中DPPIV的细胞质尾部和跨膜结构域与溶菌酶相连，溶菌酶是一种外源性蛋白，不应包含分选信息。该蛋白主要被递送至基底外侧表面。我们的结果表明，DPPIV的腔结构域携带显性的顶端分选信息，而该分子的跨膜结构域和细胞质尾部包含竞争性的基底外侧分选信息。
