Our long-term goal is to understand the mechanisms by which epithelial cells develop structural and functional asymmetry. This process is critical to the normal function of epithelial tissues and loss of epithelial polarity is associated with a variety of human pathologies including cancers, cystic diseases, secretory and absorptive disorders and cardiovascular disease. An evolutionarily conserved event in cell polarization involves cortical capture and selective stabilization of MTs. In stabilizing a subset of MTs selectively, cells develop an axis of morphological asymmetry along which local signals are transduced and on which MT motor proteins carry diverse cargoes to and from specific domains inside and on the surface of cells. While it is known that signaling from specific cortical sites triggers the local MT reorganization necessary for polarization, the molecules and regulatory mechanisms orchestrating these processes have not been elucidated fully. Recently, we obtained evidence implicating a member of the kinesin family of MT motors in polarization of epithelial cells. Interestingly, this kinesin localizes to MT plus-ends and to the cell cortex where it interacts with well- characterized MT plus-end associated proteins and cortical membrane-cytoskeletal scaffolding proteins. This suggests that the kinesin is involved in cortical capture and stabilization of MTs. Based on analogy with polarization mechanisms in single-cell organisms, we hypothesize that this kinesin acts as a selective transporter of factors regulating MT stabilization and cell polarity in epithelia. However, the relevant cargoes transported by this motor that could promote MT stabilization and cell polarity are still unknown. We will test our hypothesis by identifying epithelial cargoes of KIF17 and testing whether they too regulate epithelial polarization. In addition, we will characterize the mechanism by which this kinesin and its cargoes regulate cell polarity. Another important process in epithelial polarization involves the selective and targeted transport of membrane and secreted proteins to different regions of the cell surface. However, little is known about how cellular cargoes select appropriate motor(s) to get them to the correct destination and how motors identify appropriate routes to these destinations. We showed recently the existence of polarization-dependent, "kinesin-switching" by an apical membrane protein cargo being transported from the Golgi to the plasma membrane. This leads us to hypothesize that kinesin interactions with specific cargoes are regulated during epithelial polarization. This kinesin-cargo switch likely facilitates development of functional membrane asymmetry in response to MT reorganization. To test this idea we will identify proteins that regulate the binding of kinesin to vesicles containing the apical membrane protein p75. We will then characterize how kinesin- vesicle interactions are regulated during epithelial polarization. Understanding the role of kinesins in epithelial polarization may provide critical new information about how this process is controlled and could lead to identification of novel therapeutic targets in treating diseases of epithelial origin.
Polarized epithelial cells play a key role in maintaining internal homeostasis by acting as a barrier between the outside environment and internal organs. Our long-term goal is to understand, at molecular and mechanistic levels, how epithelial cells develop structural and functional asymmetry, a process critical to the normal function of tissues comprised of these cells. Indeed, loss of epithelial polarity is associated with a variety of human pathologies including cancers of diverse tissue origin, cystic diseases and mal-absorption and secretory disorders in several organ systems. Elucidation of molecular events driving polarization is important, not only for understanding normal development, but also because the details of this process will enable us to develop therapeutic intervention strategies targeting diseases associated with loss of epithelial polarity.
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