Fig. 7.

EZH2 depletion with DZNep sensitizes SCLC to cisplatin in vitro and in vivo and model for EZH2 in NER. a H128 cells are sensitized to cisplatin through EZH2 depletion but not through S-Adenosyl-l-methionine (SAM) competitive inhibition. H128 cells were treated with DZNep, EPZ-6438, or DMSO for 72 hours followed by cisplatin treatment for 72 hours prior to assaying for cell viability. b DZNep-mediated EZH2 depletion destabilizes DDB2. H128 cells were treated with DZNep or DMSO for 6 days followed by 2 hours of CHX pretreatment and 30 J/m² UV damage, and allowed to recover at the times indicated. Cells were then harvested, lysed, and run on SDS-PAGE. c-e The combination of DZNep and cisplatin synergistically suppresses SCLC tumor growth in vivo. c and d Nu/Nu mice with H128 lung cancer xenografts were treated with DZNep (2.5mg/kg; 2 times per week), cisplatin (2.5mg/kg; 2 times per week), or the combination i.p. for 28 days. Each group included 5 mice. Tumor volumes were measured once every 2 days. The error bars indicate ± SD. e Weights corresponding to figure c were measured once every 2 days. The error bars indicate ± SD. * indicates p<0.05, by 2-tailed t test. **indicates p<0.01, by 2-tailed t test. f Model for EZH2 function in NER. Following cisplatin or UV damage, EZH2 mobilizes to DNA damage sites where it complexes with DDB1-DDB2 and promotes DDB2 stability by preventing its ubiquitination independent of its methyltransferase activity or PRC2. EZH2 stabilization of DDB2 may facilitate DDB2 binding and assembly of CRL4 at the site of the NER lesion, which in turn promotes the ubiquitination of critical downstream NER targets to facilitate NER. In the absence of EZH2 or with EZH2 depletion by DZNep, there is increased ubiquitination of DDB2 leading to its degradation and impaired NER and thereby causing sensitization to cisplatin and UV damage. (For b, a representative blot from 3 independent experiments (n=3) is shown).