AJP - Cell Physiology, Vol 260, C691-C700, Copyright © 1991 by the American Physiological Society

Disruption of microtubules alters polarity of basement membrane proteoglycan secretion in epithelial cells

¹ Renal Unit, Departments of Medicine and Pathology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114

Basement membrane proteins such as the heparan sulfate proteoglycan (HSPG) are secreted in a polarized fashion from the basolateral membrane of epithelial cells. We have used the microtubule-disrupting drug colchicine to study the role of the microtubule network in directing constitutive secretion to the basolateral membrane of LLC-PK₁ renal epithelial cells. Microtubule depolymerization induced by colchicine resulted in fragmentation and redistribution of fluorescently labeled trans-Golgi membranes. Increased immunofluorescent staining of HSPG was associated with these dispersed Golgi cisternae. The biosynthetic processing of HSPG was not significantly altered by the loss of microtubules or by the dispersal of the Golgi elements. The most striking effect of microtubule disruption was the loss of polarity of HSPG secretion. Immunoprecipitation studies showed that HSPG was secreted from both apical and basolateral surfaces of LLC-PK₁ cells treated with colchicine, and a similar result was found for the delivery of laminin, another basement membrane protein. In contrast, there was no change in the distribution of an integral basolateral membrane protein, Na⁺-K⁺-ATPase, following colchicine treatment. Our results provide the first demonstration that microtubules are involved in the constitutive trafficking of basolateral secretory proteins. These data also suggest that there may be an inherent difference in the targeting or delivery of membrane and secretory proteins to the basolateral cell surface.

Submitted on July 10, 1990
Accepted on November 12, 1990