title: Cooperation of Notch and Ras/MAPK signaling pathways in human breast carcinogenesis.
abstract: BACKGROUND
  Recent studies have implicated aberrant Notch signaling in breast cancers. Yet, relatively little is known about the pattern of expression of various components of the Notch pathway, or its mechanism of action. To better understand the role of the Notch pathway in breast cancer, we have undertaken a detailed expression analysis of various Notch receptors, their ligands, and downstream targets at different stages of breast cancer progression.
  
  
  RESULTS
  We report here that there is a general increase in the expression levels of Notch 1, 2, 4, Jagged1, Jagged2, and Delta-like 4 proteins in breast cancers, with simultaneous upregulation of multiple Notch receptors and ligands in a given cancer tissue. While Notch3 and Delta-like1 were undetectable in normal tissues, moderate to high expression was detected in several cancers. We detected the presence of active, cleaved Notch1, along with downstream targets of the Notch pathway, Hes1/Hes5, in approximately 75% of breast cancers, clearly indicating that in a large proportion of breast cancers Notch signaling is aberrantly activated. Furthermore, we detected cleaved Notch1 and Hes1/5 in early precursors of breast cancers - hyperplasia and ductal carcinoma in situ - suggesting that aberrant Notch activation may be an early event in breast cancer progression. Mechanistically, while constitutively active Notch1 alone failed to transform immortalized breast cells, it synergized with the Ras/MAPK pathway to mediate transformation. This cooperation is reflected in vivo, as a subset of cleaved Notch positive tumors additionally expressed phopsho-Erk1/2 in the nuclei. Such cases exhibited high node positivity, suggesting that Notch-Ras cooperation may lead to poor prognosis.
  
  
  CONCLUSIONS
  High level expression of Notch receptors and ligands, and its increased activation in several breast cancers and early precursors, places Notch signaling as a key player in breast cancer pathogenesis. Its cooperation with the Ras/MAPK pathway in transformation offers combined inhibition of the two pathways as a new modality for breast cancer treatment.
authors.affiliation: Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore 560 012, Karnataka, India. suruchi.mittal@gmail.com
authors.forename: Suruchi
authors.initials: S
authors.lastname: Mittal
authors.forename: Deepa
authors.initials: D
authors.lastname: Subramanyam
authors.forename: Devaveena
authors.initials: D
authors.lastname: Dey
authors.forename: Rekha V
authors.initials: RV
authors.lastname: Kumar
authors.forename: Annapoorni
authors.initials: A
authors.lastname: Rangarajan
mesh_terms: D001943:Breast Neoplasms / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D002471:Cell Transformation, Neoplastic; D018450:Disease Progression; D006801:Humans; D008024:Ligands; D020935:MAP Kinase Signaling System; D015689:Oncogene Protein p21(ras) / Q000378:metabolism*; D051880:Receptors, Notch / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D008024:Ligands; D051880:Receptors, Notch; D015689:Oncogene Protein p21(ras)