RB1 and cancer: In MEK/ERK-activated cancer cells and hematopoietic stem cells, GRP75 depletion/targeting-induced cell cycle arrest was accompanied by increased expression of cyclin-dependent kinase inhibitor p21CIP1, tumor suppressor p53, and decreased expression of cyclin-dependent kinase inhibitor p27KIP1, S-phase transcription factor E2F-1, and Rb phosphorylation, indicating that GRP75 may regulate the cell cycle via cyclin-dependent kinas/TP53/Rb signaling [23, 26, 28, 30, 48].