E2F1 and Alzheimer disease: Thus, the up regulation of the cell cycle proteins cyclin D1, cyclin E, cyclin A, Cdk2, and E2F transcription factor 1 (E2F-1), along with increased phosphorylation of the retinoblastoma tumour suppressor gene (Rb) protein, results in aberrant cell cycle re-entry and subsequent apoptosis [119], thereby contributing to AD progression [123], in which the cells are prone to dedifferentiation and degeneration [124].