To confirm the role of p300 in cellular senescence, we investigated the response to DNA damage induced by two different SIPS agents in an in vitro model of LCLs derived from patients with Rubinstein-Taybi syndrome type 2 (RSTS2, OMIM #613684) carrying germline mutations in EP300 (EP300mut) (Table 1, see Methods), which result in haploinsufficiency or defective p300 function26 (Fig. 1). The gene discussed is EP300; the disease is Rubinstein-Taybi syndrome due to EP300 haploinsufficiency.