Project description:Mammary epithelium is hierarchically organized, with multipotent basal mammary stem cells (MaSCs) producing both luminal and basal cells during development or upon transplantation. Recent studies suggested that most breast cancers, including Basal-Like breast cancer (BLBC), might originate from luminal cells, and oncogenic events, such as ectopic expression of PIK3CA(H1047R), could induce multipotency in committed luminal cells. p53 is the most commonly mutated gene in human breast cancer; in particular, its inactivating mutations are found in most BLBCs, raising a question as to whether p53-loss plays a key role in acquisition of multipotent MaSC-like properties by luminal cells. By in situ lineage-tracing, we found that induced loss of p53 in Keratin 8 (K8)+ luminal cells led to their clonal expansion, due to increased cell cycle activity and attenuated apoptosis control, but did not directly affect their luminal identity. All induced mice eventually developed either Claudin-Low mammary tumors with 9qA1 (Yap1) amplification or Basal-Like tumors with 6qA1-A2 (Met) amplification. These data suggest that although p53 does not directly control the luminal fate, its loss facilitates acquisition of MaSC-like properties by luminal cells and predisposes them to development of mammary tumors with loss of luminal identity.
Project description:Mammary epithelium is hierarchically organized, with multipotent basal mammary stem cells (MaSCs) producing both luminal and basal cells during development or upon transplantation. Recent studies suggested that most breast cancers might originate from luminal cells, and oncogenic events, such as ectopic expression of PIK3CAH1047R, could induce multipotency in committed luminal cells. p53 is the most commonly mutated gene in human breast cancer; in particular, its inactivating mutations are found in most triple-negative breast cancers, raising a question as to whether p53-loss plays a key role in acquisition of MaSC-like properties by luminal cells. By in situ lineage tracing, we found that induced loss of p53 in Keratin 8 (K8)+ luminal cells led to their clonal expansion, in part due to increased proliferation, but did not directly affect their luminal identity. Expansion of luminal cells, in particular oestrogen receptor-positive luminal cells, was observed 3-4 weeks after induced p53-loss, which was accompanied by increased expression of cell cycle genes and downregulation of genes related to immune microenvironment, p53 downstream pathway and apoptosis control. All induced mice eventually developed mammary tumours with 9qA1 (Yap1) amplification and/or 6qA2 (Met) amplification. The resulting tumours exhibited a MaSC-like expression signature and most closely resembled Claudin-Low breast cancer. Overall, these data suggest that although p53 does not directly control the luminal fate, its loss facilitates acquisition of MaSC-like properties by luminal cells and predisposes them to development of mammary tumours with loss of luminal identity. Our data also suggest that Claudin-Low breast cancer can originate from luminal cells, possibly upon transition through a basal-like state.
Project description:Claudin-low breast cancer represents an aggressive molecular subtype that is comprised of mostly triple-negative mammary tumor cells that possess stem cell-like and mesenchymal features. Little is known about the cellular origin and oncogenic drivers that promote claudin-low breast cancer. In this study, we show that persistent oncogenic RAS signaling causes highly metastatic triple-negative mammary tumors in mice. More importantly, the activation of endogenous mutant KRAS and expression of exogenous KRAS specifically in luminal epithelial cells in a continuous and differentiation stage-independent manner induces preneoplastic lesions that evolve into basal-like and claudin-low mammary cancers. Further investigations demonstrate that the continuous signaling of oncogenic RAS as well as regulators of EMT play a crucial role in the cellular plasticity and maintenance of the mesenchymal and stem cell characteristics of claudin-low mammary cancer cells.
Project description:Mammary specific deletion of Lfng induces basal-like and claudin-low tumors with accumulation of Notch intracellular domain fragments, increased expression of proliferation-associated Notch targets, amplification of the Met/Caveolin locus, and elevated Met and Igf-1R signaling.
Project description:The claudin-low subtype is a recently identified rare molecular subtype of human breast cancer that expresses low levels of tight and adherens junction genes and shows high expression of epithelial-to-mesenchymal transition (EMT) genes. These tumors are enriched in gene expression signatures derived from human tumor initiating cells (TIC) and human mammary stem cells. Through cross-species analysis, we discovered mouse mammary tumors that have similar gene expression characteristics as human claudin-low tumors and were also enriched for the human TIC signature. Such claudin-low tumors were similarly rare, but came from a number of distinct mouse models including the p53 null transplant model. Here we present a molecular characterization of fifty p53 null mammary tumors as compared to other mouse models and human breast tumor subtypes. Similar to human tumors, the murine p53 null tumors fell into multiple molecular subtypes including two basal-like, a luminal, a claudin-low, and a subtype unique to this model. The claudin-low tumors also showed high gene expression of EMT inducers, low expression of the miR-200 family, and low to absent expression of both claudin 3 and E-cadherin. These murine subtypes also contained distinct genomic DNA copy number changes some of which are similarly altered in their cognate human subtype counterpart. Finally, limiting dilution transplantation revealed that p53 null claudin-low tumors are highly enriched for TICs as compared to the more common adenocarcinomas arising in the same model, thus providing a novel preclinical mouse model to investigate the therapeutic response of TICs. 107 Agilent CGH and expression microarrays
Project description:The claudin-low subtype is a recently identified rare molecular subtype of human breast cancer that expresses low levels of tight and adherens junction genes and shows high expression of epithelial-to-mesenchymal transition (EMT) genes. These tumors are enriched in gene expression signatures derived from human tumor initiating cells (TIC) and human mammary stem cells. Through cross-species analysis, we discovered mouse mammary tumors that have similar gene expression characteristics as human claudin-low tumors and were also enriched for the human TIC signature. Such claudin-low tumors were similarly rare, but came from a number of distinct mouse models including the p53 null transplant model. Here we present a molecular characterization of fifty p53 null mammary tumors as compared to other mouse models and human breast tumor subtypes. Similar to human tumors, the murine p53 null tumors fell into multiple molecular subtypes including two basal-like, a luminal, a claudin-low, and a subtype unique to this model. The claudin-low tumors also showed high gene expression of EMT inducers, low expression of the miR-200 family, and low to absent expression of both claudin 3 and E-cadherin. These murine subtypes also contained distinct genomic DNA copy number changes some of which are similarly altered in their cognate human subtype counterpart. Finally, limiting dilution transplantation revealed that p53 null claudin-low tumors are highly enriched for TICs as compared to the more common adenocarcinomas arising in the same model, thus providing a novel preclinical mouse model to investigate the therapeutic response of TICs.
Project description:Mammary specific deletion of Lfng induces basal-like and claudin-low tumors with accumulation of Notch intracellular domain fragments, increased expression of proliferation-associated Notch targets, amplification of the Met/Caveolin locus, and elevated Met and Igf-1R signaling. Tumor DNAs from Lfngflox/flox; MMTV-Cre conditional mutant mice are being compared to control DNAs from the same animals in order to identify common alterations associated with tumor progression