The subapical compartment and its role in intracellular trafficking and cell polarity

In polarized epithelial cells and hepatocytes, apical and basolateral plasm a membrane surfaces are maintained, each displaying a distinct molecular co mposition. In recent years, it has become apparent that a subapical compart ment, referred to as SAC, plays a prominent if not crucial role in the doma in-specific sorting and targeting of proteins and lipids that are in dynami c transit between these plasma membrane domains. Although the molecular ide ntity of the traffic-regulating devices is still obscure, the organization of SAC in distinct subcompartments and/or subdomains may well be instrument al to such functions. In this review, we will focus on the potential subcom partmentalization of the SAC in terms of regulation of membrane traffic, on how SAC relates to the endosomal system, and on how this compartment may o perate in the context of other intracellular sorting organelles such as the Golgi complex, in generating and maintaining cell polarity. J. Cell. Physi ol. 184:151-160, 2000. (C) 2000 Wiley-Liss, Inc.