WILD-TYPE BUT NOT MUTANT APC ASSOCIATES WITH THE MICROTUBULE CYTOSKELETON

The adenomatous polyposis coli protein (APC) is mutated in familial ad enomatous polyposis patients as well as in sporadic colorectal tumors. In an attempt to further understand the function of APC, the subcellu lar localization of APC was examined. Wild-type and mutant forms of AP C were expressed in mammalian cells and protein detected by immunofluo rescence using monoclonal and polyclonal antibodies. Staining of wildt ype APC protein revealed a filamentous network which extended througho ut the cytoplasm and colocalized with microtubules. In striking contra st, mutant APC protein gave a diffuse cytoplasmic staining pattern. Tr eatment with a microtubule depolymerizing agent, nocodazole, caused AP C as well as tubulin to become diffusely cytoplasmic. In addition, imm unoperoxidaze staining of transfected APC protein followed by transmis sion electron microscopy revealed staining of microtubules. These resu lts suggest that wild-type but not mutant APC protein may be associate d with the microtubule cytoskeleton.