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 cAMP-
elevating 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.