Breast Center Baylor College of Medicine Houston, TX US
Baylor College of Medicine (Lab)
BCM-ABBR Room: R531B Houston, TX 77030 United States
THE HISTONE VARIANT MACROH2A IS A SUBSTRATE OF BRCA1 UBIQUITIN LIGASE
Beom-Jun Kim, Doug Chan, Sung Yun Jung, Yi Wang, Jun Qin
The breast and ovarian cancer specific tumor suppressor BRCA1 and its heterodimer partner BARD1 have an ubiquitin ligase activity and this activity can be compromised by cancer-associated mutations frequently. However, it remains unclear whether its ubiquitin ligase activity is important for cancer development or BRCA1 function. It is due in part to the lack of bona fide substrates despite extensive efforts to find them. We developed an approach that allows us to enrich ubiquitinated proteins and peptides from BRCA1/BARD1 overexpressed cells by two consecutive enrichment steps and identified a number of candidate substrates by mass spectrometry analysis. We confirmed BRCA1/BARD1-dependent enhancement of ubiquitination of these candidates in vivo and further confirmed that BRCA1/BARD1 specifically ubiquitinates histone variant macroH2A in vitro and in vivo. macroH2A ubiquitination plays a role in cellular senenscence as human fibroblast IMR90 cells underwent delayed senescence when ubiquitination-deficient form of macroH2A was expressed. Our findings show that macroH2A is an in vivo substrate of BRCA1/BARD1 ubiquitin ligase and its ubiquitination plays an important role in cellular senescence.