Identifying Oncogenic Drivers of Poor Outcome in Triple Negative Breast Cancer


Year:

Session type:

Theme:

Shannon Beattie1
1CCRCB

Abstract

Background

Breast cancer is the most common type of cancer affecting women worldwide. Triple Negative Breast Cancers (TNBCs), which constitute 10-20% of all breast cancers, lack estrogen and progesterone receptors and HER2-overexpression. TNBCs have higher rates of chemoresistance, visceral metastases, and poorer prognosis compared to other subtypes. TNBC biology is poorly understood; however, it is known that the TGFβ pathway is overexpressed. TGFβ ligands bind to TGFβR1/2 leading to phosphorylation of transcriptional-coactivators SMAD2/3. In normal breast tissue, this leads to induction of cell-cycle-control genes p21WAF1, p27CIP1 and p57CIP2. However, in TNBCs, the Hedgehog-pathway-mediator GLI2 and shuttle protein YWHAZ/14-3-3ζ alter the SMAD2/3 transcriptional program, subverting the growth control effects of TGFβ towards Epithelial-Mesenchymal-Transition (EMT) and other oncogenic effects. Targeted inhibition of this pathway could downregulate EMT and metastasis and provide a therapy for poor prognosis patients.

Method

Microarray analyses, Western Blotting, qPCR, Migration Assay and Clonogenics were used in this study.

Results

Microarray analysis identified poor-outcome TNBC patients overexpress TGFβ2. In EMT-enriched TNBC lines, YWHAZ and GLI2 knockdowns reduced pSMAD2/3 protein levels, suggesting this pathway was less active following knockdown of these genes. Furthermore, knockdown of TGFβ2, YWHAZ and GLI2 reduced growth and migratory phenotypes in TNBC cell lines, but not in normal breast cells.

Conclusion

Preliminary results suggest TGFβ2 overexpression and SMAD-pathway dysregulation results in uncontrolled EMT in poor-outcome TNBCs. Additionally, the Hedgehog-pathway may collaborate with SMAD-signalling to drive EMT in TNBCs. The opposing roles of TGFβ2 in normal/cancer cells complicates potential use of a TGFβ2-specific inhibitor, as it may have unwanted effects on normal cells. Therefore, targeting GLI2 via an inhibitor, or indirectly via epigenetic intervention, may be an alternative strategy for treating poor-outcome TNBC patients. Future work for this project is to investigate other co-factors involved in this pathway, their localisation and invivo examination to analyse metastasis, EMT and possible targeted therapies.