Transcriptomic Profiling of Early Metastatic Transition in Breast Carcinomas
PL Fernandez, J Calvo, L Gelabert, M Marin, JJ Lozano, R Bermudo, TM Thomson. Hospital Clinic/IDIBAPS, University of Barcelona, Barcelona, Spain; Instituto de Biologa Molecular, CSIC, Barcelona, Spain; Hospital Clinic/IDIBAPS, Barcelona, Spain
Background: Lymph node (LN) involvement by tumor cells is the first metastatic event in breast carcinoma and the single most important prognostic factor.Yet, little is known about the molecular events and alterations in biochemical pathways leading to the initial acquisition of the metastatic capacity and the role of hypothetical breast cancer stem cell (CSC) in tumor progression.
Design: Comparative whole-genome transcriptomic profiling of 18 carefully selected pairs of frozen primary invasive ductal carcinoma and their lymph node mestastases as well as 7 non-metastatic tumors was performed on Affymetrix U133 Plus 2.0 chips. Genes differentially expressed among the 3 groups were selected for experimental validation by Reverse Transcription and Quantitative Real-Time PCR (QRT-PCR) with Taqman LDA cards. Laser microdissection was used in a subset of samples in order to confirm the epithelial origin of the transcripts differentially expressed.
Results: Pathway analysis indicated activation of TGF- and Wnt responses in all primary tumors, but not in metastases. Also, all primary tumors, but not LN metastases, expressed markers and effectors of epithelial-mesenchymal transition (EMT), in particular TWIST1 and SNAI2. In contrast, stemness factors such as EZH2, PITX2, SOX12 or SPDEF were more strongly expressed in primary tumors which metastatized, and also in their corresponding metastases, than in primary tumors that had not metastatized. Interestingly, our analysis also showed that all primary tumors (metastatizing and not metastatizing), but not the LN metastases, expressed basal-type keratins 5, 6, 14 and 17, while metastatizing primary tumors and also their LN metastases expressed keratin 18, GATA3 and ESR1, suggestive of a luminal phenotype.
Conclusions: The activation of the TGF- and Wnt signalling pathways seems to plays a major role in the early acquisition of local invasive phenotypes of breast tumors through induction of EMT, and the capacity of metastasis to the LN is associated with a stronger representation of cells with CSC features.We hypothesize that tumors capable of metastatizing to the LN contain a double tumor cell phenotype (luminal and basal, and also CSC and EMT), which could reflect either the prevalence of a bipotent cell in such tumors, or a mixture of two distinct cell populations.
Monday, March 9, 2009 1:00 PM
Poster Session II # 31, Monday Afternoon