Abstract 44P
Background
In breast cancer, the oestrogen receptor expressing subtype (ER+) is the most frequent. Those tumours frequently become resistant to hormonotherapy and metastasise. In this case, chemotherapy needs to be administrated. The CDK4/6 inhibitors in combination with hormonotherapy are the new standard treatment for metastatic disease and allows the postponement of chemotherapy. These drugs play the same role as the endogenous p16-p15 proteins, and patients who have lost expression of these proteins are expected to be those who will respond best to treatment. However, none of the currently tested biomarkers are predictive of treatment response. The INK locus, where p16/p14-p15 proteins are encoded, is involved in the cell cycle and is often altered in cancers. Expression of p16/p14-p15 is negatively regulated by ANRIL, a non-coding RNA (ncRNA). ANRIL interacts with Polycomb Repressive Complexes and guides them to methylate and silence this locus. In cancer, aberrant methylation is involved in tumorigenesis. Understanding the molecular mechanisms between ncRNA and regulation of the expression of p16/p14-p15 may highlight potential biomarkers of treatment response in ER+ breast cancer.
Methods
In Vitro: Expression data were collected by RT-qPCR in MDAMB468 and T47D cell lines and RNAseq was used to identify other ncRNA in this locus. DNA methylation was detected by immunoprecipitation after deoxyazacytidine treatment. In Vivo: Expression was measured by RNAseq of breast cancer tumours biopsies treated with adjuvant and neoadjuvant chemotherapy.
Results
MDAMB468 (triple negative) and T47D (ER+) cells show different methylation and expression profiles, showing a link between the expression of the locus and its methylation. ANRIL and methylation of gene promoters influence locus silencing. DNA methylation around or after the stop codon of a gene are poorly described in the literature but seem to also play a role in regulation of RNA expression. RNAseq reveals little-known transcripts highly expressed in MDAMB468; it’s possible effect and its relevance in vivo is currently studied.
Conclusions
Understanding the role of DNA methylation and ncRNA in this locus could help to adapt and identify effective treatments in ER+ breast cancer.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
University of Liège.
Funding
F.R.S-FNRS.
Disclosure
All authors have declared no conflicts of interest.