XRCC6 and pulmonary arterial hypertension: To demonstrate that HDAC6 inhibits Ku70 acetylation, enhancing Ku70-Bax binding and preventing stress-induced apoptosis, we first measured the acetylation level of Ku70 at lysine 539 (a critical acetylation site that influences Ku70-Bax binding)16, 34 in PAH-PASMCs exposed to HDAC6 inhibitors.