Downregulation of CREB promotes cell proliferation of KMH2, L1236, L428, HDLM2, and L540 cells. (A) A quantitative PCR showed significant decrease in CREB expression in KMH2, L1236, L428, HDLM2, and L540 cells after CREB shRNA treatment. (B) Phase-contrast images of cells at day 4 after infection of shRNA-expressing lentivirus with or without shRNA-resistant CREB-expressing lentivirus. (C) Cell number was counted at day 4. *p < 0.001 versus control shRNA. #p < 0.001 versus CREB shRNA-1.