Scale bar=100 m. such as altered FAK/Src/JNK signaling. == Introduction == Mutation of theAdenomatous Polyposis Coli(APC) tumor suppressor has been implicated in breast cancer; yet how it cooperates with oncogenic events to drive breast cancer pathogenesis is usually unknown. Numerous studies have demonstratedAPCmutation or loss in human sporadic breast cancer (reviewed in[1]). APC inactivation has been reported in 570% of tumors, varying widely because of power constraints, the type of analysis performed, and specific molecular subtypes examined (reviewed in[1]). Unlike colorectal cancer where mutation is the main mechanism for APC loss, APC expression is frequently down-regulated through transcriptional silencing via gene promoter methylation in breast cancer. For example,APCpromoter hypermethylation has been observed in approximately 70% of inflammatory human breast tumors[2]and in 7% of metaplastic breast carcinomas[3].APCpromoter methylation also correlates with MSC1094308 decreased MSC1094308 disease-free and SDF-5 overall survival[4], providing evidence that APC down-regulation is not a passive bystander but, rather, contributes significantly to breast cancer. Mouse models have further supported the importance of APC in breast cancer. Female mice transporting a germline heterozygous nonsense mutation inApc, designatedApcMin/+, develop spontaneous and carcinogen- or radiation-induced mammary tumorigenesis, although spontaneous mammary tumors develop at a low frequency[5],[6],[7]]. Our laboratory exhibited that mammary hyperplasia and squamous metaplasia are common inApcMin/+mice, and APC is required for normal lobuloaloveolar development during pregnancy and lactation[8]. Other alleles, includingApc1638, also develop spontaneous mammary tumors and are sensitive to radiation or chemical carcinogens[9],[10]. Spontaneous tumors inApc474mice resemble squamous MSC1094308 cell carcinomas[11], a pathological phenotype that has been observed often in mammary tumors in which Wnt/-catenin signaling is usually aberrantly activated[12]. While whey acidic protein (WAP)- and -lactoglobulin-cre-inducedApcdeletion increased squamous metaplasias[13],[14], keratin-14 (K-14)-mediatedApcdeletion led to mammary tumor formation[14], suggesting that this cell type in which APC is usually inactivated is critical for the associated phenotypes. Recently, truncation at codon 1572 in APC (Apc1572T) was shown to be sufficient for metastatic mammary tumors MSC1094308 that resemble human metaplastic breast cancers[15]. It is right now appreciated that most breast cancers contain more than 80 non-silent mutations[16]. These tumor models have addressed the importance ofApcmutation or deletion alone in mammary tumor initiation, but not the contribution of APC loss in the context of other oncogenic events. In this study, we addressed howApcmutation cooperates with known breast cancer oncogenes to mimic more closely human sporadic breast cancer using mouse models. MMTV-PyMT transgenic females develop metastatic mammary tumors with high penetrance[17]. Despite the quick development of aggressive tumors by using this model, multiple studies have demonstrated the ability to enhance tumorigenesis[18],[19],[20]. Tumor progression in MSC1094308 the MMTV-PyMT model follows a pattern much like human sporadic breast cancer[21]. Further, signaling pathways activated downstream of PyMT overexpression, including the Src family of kinases, are commonly dysregulated in human breast cancers[22]. MMTV-c-Neu mammary tumors mimic HER2-positive human breast cancer and develop with lower penetrance and significantly longer latency[23]. The current study demonstrates thatApcmutation enhances PyMT-, but not Neu- induced mammary tumorigenesis, where it drives the squamous adenocarcinoma phenotype and provides a significant proliferation advantage. Importantly, these differences are associated with increased signaling through the FAK/Src/JNK network. These data support a model in whichAPCmutation may promote breast cancer by cooperating with other oncogenic changes to alter their histopathological and growth characteristics via the activation of signaling pathways downstream of cell-matrix interactions. == Methods == == Ethics Statement == All procedures were performed with prior approval (protocol #71828) from your University of Chicago Institutional Animal Care and Use Committee, which has full accreditation from your Association for Assessment and.