Distal 11q arm breakage and reduction of H2AX copy number in breast cancer

Chromosome 11q alterations are frequent in hormone-positive luminal breast cancer (LBC). The 11q13 locus where the CCND1 oncogene is located is frequently amplified and the distal 11q arm is often lost. Several DNA damage response (DDR) genes, namely MRE11, RSF1, ATM, H2AX and CHEK1 map to the 11q arm. Heterozygous loss of the 11q arm may reduce DDR gene expression and promote chromosomal instability but render the tumour more sensitive to radiation and treatment through synthetic lethality approaches. Recently, complete H2AX loss in cell lines was shown to activate the epithelial-mesenchymal transition (EMT), a cellular program which allows cancer cells to metastasize to distant sites. LBC cell lines with 11q13 amplification and distal 11q loss were selected and characterised. Cytogenetic analysis revealed 11q alterations, distal 11q loss, and CCND1 amplification, likely arising through the breakage-fusion-bridge mechanism. 11q mRNA expression did not correlate with gene copy number, however cell lines with distal 11q loss exhibited increased sensitivity to ionizing radiation. T47D WT and H2AX-targeted cell pools, obtained from Synthego, allowed us to study the effects of H2AX loss on EMT. H2AX-deficient clones showed minor morphology changes, but EMT activation was not robust. These clones failed to form MDC1 foci after DNA damage, indicating DDR defects worthy of future investigation. Our study underscores the importance of in-house cytogenetic analysis to validate genomic database findings. Cell lines with distal 11q loss exhibit potential radiation sensitivity, suggesting targeted treatments for this LBC subgroup. Unexpectedly, H2AX-deficient clones did not strongly activate EMT, challenging published literature and hinting at cell-type-specific H2AX regulation of EMT. These findings contribute valuable insights into the genomic and functional aspects of 11q alterations in LBC, emphasizing the need for personalized approaches in understanding and treating this subtype of breast cancer.

Funder

Hardiman PhD research scholarship

Publisher

University of Galway

Rights

Attribution-NonCommercial-NoDerivatives 4.0 International

cbn

Collections

University of Galway Theses (PhD Theses)