RESUMO
Tumor suppressor SMARCA4 (BRG1), a key SWI/SNF chromatin remodeling gene, is frequently inactivated in cancers and is not directly druggable. We recently uncovered that SMARCA4 loss in an ovarian cancer subtype causes cyclin D1 deficiency leading to susceptibility to CDK4/6 inhibition. Here, we show that this vulnerability is conserved in non-small cell lung cancer (NSCLC), where SMARCA4 loss also results in reduced cyclin D1 expression and selective sensitivity to CDK4/6 inhibitors. In addition, SMARCA2, another SWI/SNF subunit lost in a subset of NSCLCs, also regulates cyclin D1 and drug response when SMARCA4 is absent. Mechanistically, SMARCA4/2 loss reduces cyclin D1 expression by a combination of restricting CCND1 chromatin accessibility and suppressing c-Jun, a transcription activator of CCND1. Furthermore, SMARCA4 loss is synthetic lethal with CDK4/6 inhibition both in vitro and in vivo, suggesting that FDA-approved CDK4/6 inhibitors could be effective to treat this significant subgroup of NSCLCs.
Assuntos
Carcinoma Pulmonar de Células não Pequenas/metabolismo , Quinase 4 Dependente de Ciclina/metabolismo , Quinase 6 Dependente de Ciclina/metabolismo , DNA Helicases/metabolismo , Neoplasias Pulmonares/metabolismo , Proteínas Nucleares/metabolismo , Fatores de Transcrição/metabolismo , Animais , Carcinoma Pulmonar de Células não Pequenas/genética , Sobrevivência Celular/genética , Sobrevivência Celular/fisiologia , Imunoprecipitação da Cromatina , Quinase 4 Dependente de Ciclina/genética , Quinase 6 Dependente de Ciclina/genética , DNA Helicases/genética , Feminino , Humanos , Imuno-Histoquímica , Neoplasias Pulmonares/genética , Camundongos , Camundongos SCID , Proteínas Nucleares/genética , Fatores de Transcrição/genéticaRESUMO
Inactivating mutations in SMARCA4 (BRG1), a key SWI/SNF chromatin remodelling gene, underlie small cell carcinoma of the ovary, hypercalcemic type (SCCOHT). To reveal its druggable vulnerabilities, we perform kinase-focused RNAi screens and uncover that SMARCA4-deficient SCCOHT cells are highly sensitive to the inhibition of cyclin-dependent kinase 4/6 (CDK4/6). SMARCA4 loss causes profound downregulation of cyclin D1, which limits CDK4/6 kinase activity in SCCOHT cells and leads to in vitro and in vivo susceptibility to CDK4/6 inhibitors. SCCOHT patient tumors are deficient in cyclin D1 yet retain the retinoblastoma-proficient/p16INK4a-deficient profile associated with positive responses to CDK4/6 inhibitors. Thus, our findings indicate that CDK4/6 inhibitors, approved for a breast cancer subtype addicted to CDK4/6 activation, could be repurposed to treat SCCOHT. Moreover, our study suggests a novel paradigm whereby critically low oncogene levels, caused by loss of a driver tumor suppressor, may also be exploited therapeutically.
