The adenomatous polyposis coli tumor suppressor protein localizes to plasma membrane sites involved in active cell migration.

Abstract

Abstract. Mutations in the adenomatous polyposis coli (APC) gene are linked to polyp formation in familial and sporadic colon cancer, but the functions of the protein are not known. We show that APC protein localizes mainly to clusters of puncta near the ends of microtubules that extend into actively migrating regions of epithelial cell membranes. This subcellular distribution of APC protein requires microtubules, but not actin filaments. APC protein-containing membranes are actively involved in cell migration in response to wounding epithelial monolayers, addition of the motorgen hepatocyte growth factor, and during the formation of cell-cell contacts. In the intestine, APC protein levels increase at the crypt/villus boundary, where cell migration is crucial for enterocyte exit from the crypt and where cells accumulate during polyp formation that is linked to mutations in the microtubule-binding domain of APC protein. Together, these data indicate that APC protein has a role in directed cell migration.

Regulation and function of the interaction between the APC tumour suppressor protein and EB1

“…Our work also, however, con®rms a role for the basic domain in the microtubule association of APC. In the context of full-length APC, our observations could mean that EB1 targets APC to the extending microtubule tip (NaÈ thke et al, 1996;Morrison et al, 1997). Once there, the APC basic domain could exert a stabilizing e ect upon microtubule structure and/or assembly (Deka et al, 1998), perhaps by decreasing the catastrophe rate of the extending microtubule.…”

“…From previous studies (NaÈ thke et al, 1996;Morrison et al, 1997Morrison et al, , 1998a it seemed plausible that the interaction between APC and EB1 served to target APC to microtubule tips. To test this hypothesis a number of expression constructs consisting of de®ned regions from the C-terminus of APC fused to eGFP were produced.…”

“…Interestingly, several yeast homologues of EB1 have been shown to play a role in mitotic spindle function, in the maintenance of chromosomal transmission ®delity and in a novel late mitotic checkpoint (Beinhauer et al, 1997;Schwartz et al, 1997;Muhua et al, 1998). We have suggested that the interaction between EB1 and APC may be downregulated during mitosis (Morrison et al, 1998a), a hypothesis based in part on the observation that no association of APC with the mitotic spindle has yet been reported despite the cytoplasmic localization of APC in interphase cells being dependent upon microtubules (NaÈ thke et al, 1996;Morrison et al, 1997). We have further speculated that the phosphorylation of APC at mitosis, for example by the p34 cdc2 mitotic kinase (Trzepacz et al, 1997), may negatively regulate the association with EB1.…”

“…APC has been shown to associate with EB1 (Su et al, 1995), a 30 kDa protein which we (Morrison et al, 1998a) and others (Berrueta et al, 1998;Juwana et al, 1999) have recently shown to be associated with microtubule tips. APC is itself a microtubule tip-associated protein (Munemitsu et al, 1994;Smith et al, 1994;NaÈ thke et al, 1996;Morrison et al, 1997), a feature ascribed to the presence of a microtubule-binding basic domain towards the Cterminus of the protein. Aberrant cell migration is an early feature of tumorigenesis initiated by APC mutation (Oshima et al, 1995), and the forced overexpression of APC also causes disordered cell migration in the intestinal epithelium (Wong et al, 1996).…”

“…Aberrant cell migration is an early feature of tumorigenesis initiated by APC mutation (Oshima et al, 1995), and the forced overexpression of APC also causes disordered cell migration in the intestinal epithelium (Wong et al, 1996). It has therefore been hypothesized that APC may play a role in directed microtubule assembly during cell migration via the stabilization of extending microtubule tips (NaÈ thke et al, 1996;Morrison et al, 1997;Pollock et al, 1997). Interestingly, several yeast homologues of EB1 have been shown to play a role in mitotic spindle function, in the maintenance of chromosomal transmission ®delity and in a novel late mitotic checkpoint (Beinhauer et al, 1997;Schwartz et al, 1997;Muhua et al, 1998).…”