Cyclic AMP-Induced p53 Destabilization is Independent of CREB in Pre-B Acute Lymphoblastic Leukemia Cells

Elevated cAMP levels in B-cell precursor acute lymphoblastic leukemia (BCP-ALL) cells attenuate the doxorubicin-induced p53 accumulation and protect cells against apoptosis. cAMP responsive element binding protein (CREB) is a cAMP-stimulated transcription factor that regulates genes whose deregulated expression cooperate in oncogenesis. In the present study, we investigated the role of CREB on inhibitory effect of cAMP on apoptosis and p53 accumulation in BCP-ALL NALM-6 cells. To determine whether targeting CREB can modulate the effect of cAMP on doxorubicin-induced apoptosis, we knocked down CREB in NALM-6 cells using lentiviral CREB shRNA. Knocked down cells were treated with doxorubicin in the presence or absence of cAMP-elevating agents. p53 protein level and apoptosis were assessed by western blot analysis and flow cytometry, respectively. p53 protein expression was reduced in cells treated with combination of cAMPelevating agents and doxorubicin in contrast to cells treated with doxorubicin alone even in CREB-knocked down cells. Apoptosis assay showed that the cAMP-elevating agents decreased doxorubicin-induced apoptosis in CREB-knocked down and control cells. Although, CREB plays a particularly important role in cAMP signaling pathway our data suggest that CREB does not mediate the inhibitory effect of cAMP on doxorubicin-induced apoptosis and p53 accumulation in BCP-ALL NALM-6 cells.