FUNCTION Tumor suppressor. Promotes rapid degradation of CTNNB1 and participates in Wnt signaling as a negative regulator. APC activity is correlated with its phosphorylation state. Activates the GEF activity of SPATA13 and ARHGEF4. Plays a role in hepatocyte growth factor (HGF)-induced cell migration. Required for MMP9 up-regulation via the JNK signaling pathway in colorectal tumor cells. Acts as a mediator of ERBB2-dependent stabilization of microtubules at the cell cortex. It is required for the localization of MACF1 to the cell membrane and this localization of MACF1 is critical for its function in microtubule stabilization.SUBUNIT Forms homooligomers and heterooligomers with APC2. Interacts with DIAPH1 and DIAPH2 (By similarity). Interacts with PDZ domains of DLG1 and DLG3. Associates with catenins. Binds axin. Interacts with ARHGEF4 (via N-terminus). Interacts with MAPRE1 (via C-terminus); probably required for APC targeting to the growing microtubule plus ends. Interacts with MAPRE2 and MAPRE3 (via C-terminus). Found in a complex consisting of ARHGEF4, APC and CTNNB1. Interacts with SCRIB; may mediate APC targeting to adherens junctions of epithelial cells. Interacts with SPATA13 (via N-terminus and SH3 domain). Interacts with ASAP1 (via SH3 domain). Found in a complex composed of MACF1, APC, AXIN1, CTNNB1 and GSK3B (By similarity). Interacts at the cell membrane with AMER1 and AMER2 (via ARM repeats). Interacts with KHDRBS1. The complex composed, at least, of APC, CTNNB1 and GSK3B interacts with JPT1; the interaction requires the inactive form of GSK3B (phosphorylated at 'Ser-9') (PubMed:25169422).TISSUE SPECIFICITY Expressed in a variety of tissues: brain, small intestine, colon, thymus, skeletal muscle, heart, prostate, lung, spleen, ovary, testis kidney, placenta, blood and liver (PubMed:21643010, PubMed:27217144). Isoform 1A: Very strongly expressed in brain but has relatively low expression levels in other tissues (PubMed:19527921, PubMed:21643010, PubMed:27217144). Isoform 1B: Predominant form in all tissues except for brain, including gastric mucosa and blood (PubMed:19527921, PubMed:21643010, PubMed:27217144).DOMAIN The microtubule tip localization signal (MtLS) motif; mediates interaction with MAPRE1 and targeting to the growing microtubule plus ends.PTM Phosphorylated by GSK3B.PTM Ubiquitinated, leading to its degradation by the proteasome. Ubiquitination is facilitated by Axin. Deubiquitinated by ZRANB1/TRABID.MISCELLANEOUS APC mutations have led to some interesting observations. (1) the great majority of the mutations found to date would result in truncation of the APC product. (2) almost all the mutations have occurred within the first half of the coding sequence, and somatic mutations in colorectal tumors are further clustered in a particular region, called MCR (mutation cluster region). (3) most identified point mutations in the APC gene are transitions from cytosine to other nucleotides. (4) the location of germline mutations tends to correlate with the number of colorectal polyps in FAP1 patients. Inactivation of both alleles of the APC gene seems to be required as an early event to develop most adenomas and carcinomas in the colon and rectum as well as some of those in the stomach.SIMILARITY Belongs to the adenomatous polyposis coli (APC) family.