APC BINDS TO THE NOVEL PROTEIN EB1

Mutations of the APC gene play a critical role in both sporadic and fa milial forms of colorectal cancer. The vast majority of these mutation s result in the loss of the carboxyl terminus of the protein. To furth er elucidate the function of APC, we searched for cellular proteins th at associate with its carboxyl terminus. One million human cDNA clones were screened with the use of the interaction trap two-hybrid system, and 67 clones were found to have a phenotype suggestive of an APC-int eracting protein. Nucleotide sequence analysis revealed that 48 of the se clones were derived from a single novel gene named EB1. The associa tion of APC and EB1 proteins was confirmed with in vitro binding assay s. mAbs against EB1 were then produced and used to demonstrate the ass ociation of APC and EB1 in vivo. The EB1 gene was predicted to encode a 268-amino acid protein without significant homology to proteins with known function. However, searches of nucleotide databases did identif y evidence for at least two related human genes and a yeast homologue. This conservation suggests an essential function for EB1 that might p rovide clues to the mechanism through which APC suppresses colonic neo plasia.