Winning Abstracts from the 2006 National Medical Student Poster Competition: The Role of EB1 and Adenomatous Polyposis Coli in Microtubule Dynamics and Organization.
Ryan K. Louie, Stanford University School of Medicine, 2007
End-Binding Protein 1 (EB1) is a member of a class of proteins which bind to the plus-ends of growing microtubules. A binding partner of EB1 is the tumor suppressor protein adenomatous polyposis coli (APC), which is mutated in familial and sporadic colorectal cancers. In addition to being a key component in the Wnt signal transduction pathway controlling cell differentiation and proliferation, APC also plays a role in microtubule organization and cell migration. We focus on EB1 and APC to track their dynamic properties in context of the cytoskeletal architecture.
In this study, we use live cell video microscopy to investigate the structural cytoskeletal roles of EB1 and APC by examining protein motion behavior in Madin-Darby canine kidney epithelial cells. Dual-color fluorescence imaging is used to simultaneously visualize both proteins, with APC tagged with green fluorescent protein and EB1 tagged with a tandem-dimeric red fluorescent protein.
We demonstrate that EB1 comets at the plus-ends of growing microtubules show preferential movement towards regions of the cell with cortical APC clusters at the tips of membrane extensions. EB1 displays tracking behavior, with EB1 comets following one after another along the same path. In contrast, for regions of the cell with no APC clusters, EB1 motion is less directed and less organized. There are two distinct pools of APC - “cluster” APC and “interior” APC. While cluster APC is less motile and shows no accumulation of EB1 in that region, interior APC in the forward direction can be matched together with EB1 comets and travel at the velocity of microtubule plus-end directed growth.
APC protein may serve a cytoskeletal role by organizing and directing the travel patterns of growing microtubules tipped with EB1 protein. Together, these data help to understand the dynamic properties of EB1 and APC during physiological processes such as cell membrane extension and cell migration.
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