TK1 and pulmonary arterial hypertension: Importantly, we found that numerous transcripts of genes already known to be implicated in the pro-proliferative and apoptosis-resistant phenotype of PAH-PASMCs, such as Survivin [21], ADAMTS8 [35], PBK [20], TK1 [36], and E2F1 [37], were significantly repressed under EZH2 inhibition, which is consistent with the hypothesis that EZH2 plays a critical role in the abnormal phenotype of disease cells.