L. Berrueta et al., THE ADENOMATOUS POLYPOSIS COLI-BINDING PROTEIN EB1 IS ASSOCIATED WITHCYTOPLASMIC AND SPINDLE MICROTUBULES, Proceedings of the National Academy of Sciences of the United Statesof America, 95(18), 1998, pp. 10596-10601
The evolutionarily conserved protein EB1 originally was identified by
its physical association with the carboxyl-terminal portion of the ade
nomatous polyposis coli (APC) tumor suppressor protein, an APC domain
commonly mutated in familial and sporadic forms of colorectal neoplasi
a, The subcellular localization of EB1 in epithelial cells was studied
by using immunofluorescence and biochemical techniques. EB1 colocaliz
ed both to cytoplasmic microtubules in interphase cells and to spindle
microtubules during mitosis, with pronounced centrosome staining. The
cytoskeletal array detected by anti-EB1 antibody was abolished by inc
ubation of the cells with nocodazole, an agent that disrupts microtubu
les; upon drug removal, EB1 localized to the microtubule-organizing ce
nter. Immunofluorescence analysis of SW480, a colon cancer cell line t
hat expresses only carboxyl-terminal-deleted APC unable to interact wi
th EB1, demonstrated that EB1 remained localized to the microtubule cy
toskeleton, suggesting that this pattern of subcellular distribution i
s not mediated by its interaction with APC, rn vitro cosedimentation w
ith taxol-stabilized microtubules demonstrated that a significant frac
tion of EB1 associated with microtubules, Recent studies of the yeast
EB1 homologues Mal3 and Bim1p have demonstrated that both proteins loc
alize to microtubules and are important in vivo for microtubule functi
on. Our results demonstrate that EB1 is a novel component of the micro
tubule cytoskeleton in mammalian cells. Associating with the mitotic a
pparatus, EB1 may play a physiologic role connecting APC to cellular d
ivision, coordinating the control of normal growth and differentiation
processes in the colonic epithelium.