E2F1 and non-small cell lung carcinoma: After the NSCLC cells were treated with the CDK4/6 inhibitor, PD 0332991, CYCLIND1-CDK4/6 complexes could not be formed, and the downstream target, pRb, could not be phosphorylated and bind to the E2F1 transcriptional regulator, thus suppressing target gene transcription [42].