Antagonizing functions of BARD1 and its alternatively spliced variant BARD1δ in telomere stability

// Maxim Pilyugin 1 , Pierre-Alain Andre 1 , Magdalena Ratajska 2, 4 , Alina Kuzniacka 2 , Janusz Limon 2 , Benjamin B. Tournier 3 , Julien Colas 1 , Geoff Laurent 4 , Irmgard Irminger-Finger 1, 4, 5 1 Department of Gynecology and Obstetrics Geneva University Hospitals, Geneva, Switzerland 2 Department of Biology and Genetics, Medical University of Gdansk, Poland 3 Department of Neuropsychiatry, Vulnerability Biomarkers Unit, University Hospital of Geneva, Geneva, Switzerland 4 Centre for Cell Therapy and Regenerative Medicine, University of Western Australia and Institute of Respiratory Health, Nedlands, Australia 5 Department of Genetic and Laboratory Medicine, Geneva University Hospitals, Geneva, Switzerland Correspondence to: Maxm Pilyugin, email: maxim.pilyugin@unige.ch Keywords: BARD1, alternative splicing, telomere alteration, shelterin, genome permutator Received: October 20, 2016      Accepted: December 15, 2016      Published: December 21, 2016 ABSTRACT Previous reports have shown that expression of BARD1δ, a deletion-bearing isoform of BARD1, correlates with tumor aggressiveness and progression. We show that expression of BARD1δ induces cell cycle arrest in vitro and in vivo in non-malignant cells. We investigated the mechanism that leads to proliferation arrest and found that BARD1δ overexpression induced mitotic arrest with chromosome and telomere aberrations in cell cultures, in transgenic mice, and in cells from human breast and ovarian cancer patients with BARD1 mutations. BARD1δ binds more efficiently than BARD1 to telomere binding proteins and causes their depletion from telomeres, leading to telomere and chromosomal instability. While this induces cell cycle arrest, cancer cells lacking G2/M checkpoint controls might continue to proliferate despite the BARD1δ-induced chromosomal instability. These features of BARD1δ may make it a genome permutator and a driver of continuous uncontrolled proliferation of cancer cells.