TY - JOUR
T1 - t-Darpp promotes cancer cell survival by up-regulation of Bcl2 through Akt-dependent mechanism
AU - Belkhiri, Abbes
AU - Dar, Altaf A.
AU - Zaika, Alexander
AU - Kelley, Mark
AU - El-Rifai, Wael
N1 - Copyright:
Copyright 2008 Elsevier B.V., All rights reserved.
PY - 2008/1/15
Y1 - 2008/1/15
N2 - t-Darpp is a cancer-related truncated isoform of Darpp-32 (dopamine and cyclic-AMP-regulated phosphoprotein of Mr 32,000). We detected overexpression of t-Darpp mRNA in two thirds of gastric cancers compared with normal samples (P = 0.004). Using 20 μmol/L ceramide treatment as a model for induction of apoptosis in AGS cancer cells, we found that expression of t-Darpp led to an increase in Bcl2 protein levels and blocked the activation of caspase-3 and caspase-9. The MitoCapture mitochondrial apoptosis and cytochrome c release assays indicated that t-Darpp expression enforces the mitochondrial transmembrane potential and protects against ceramide-induced apoptosis. Interestingly, the expression of t-Darpp in AGS cells led to ≥2-fold increase in Akt kinase activity with an increase in protein levels of p-Ser 473 Akt and p-Ser9 GSK3β. These findings were further confirmed using tetracycline-inducible AGS cells stably expressing t-Darpp. We also showed transcriptional up-regulation of Bcl2 using the luciferase assay with Bcl2 reporter containing P1 full promoter, quantitative reverse transcription-PCR, and t-Darpp small interfering RNA. The Bcl2 promoter contains binding sites for cyclic AMP-responsive element binding protein CREB/ATF1 transcription factors and using the electrophoretic mobility shift assay with a CREB response element, we detected a stronger binding in t-Darpp-expressing cells. The t-Darpp expression led to an increase in expression and phosphorylation of CREB and ATF-1 transcription factors that were required for up-regulating Bcl2 levels. Indeed, knockdown of Akt, CREB, or ATF1 in t-Darpp-expressing cells reduced Bcl2 protein levels. In conclusion, the t-Darpp/Akt axis underscores a novel oncogenic potential of t-Darpp in gastric carcinogenesis and resistance to drug-induced apoptosis.
AB - t-Darpp is a cancer-related truncated isoform of Darpp-32 (dopamine and cyclic-AMP-regulated phosphoprotein of Mr 32,000). We detected overexpression of t-Darpp mRNA in two thirds of gastric cancers compared with normal samples (P = 0.004). Using 20 μmol/L ceramide treatment as a model for induction of apoptosis in AGS cancer cells, we found that expression of t-Darpp led to an increase in Bcl2 protein levels and blocked the activation of caspase-3 and caspase-9. The MitoCapture mitochondrial apoptosis and cytochrome c release assays indicated that t-Darpp expression enforces the mitochondrial transmembrane potential and protects against ceramide-induced apoptosis. Interestingly, the expression of t-Darpp in AGS cells led to ≥2-fold increase in Akt kinase activity with an increase in protein levels of p-Ser 473 Akt and p-Ser9 GSK3β. These findings were further confirmed using tetracycline-inducible AGS cells stably expressing t-Darpp. We also showed transcriptional up-regulation of Bcl2 using the luciferase assay with Bcl2 reporter containing P1 full promoter, quantitative reverse transcription-PCR, and t-Darpp small interfering RNA. The Bcl2 promoter contains binding sites for cyclic AMP-responsive element binding protein CREB/ATF1 transcription factors and using the electrophoretic mobility shift assay with a CREB response element, we detected a stronger binding in t-Darpp-expressing cells. The t-Darpp expression led to an increase in expression and phosphorylation of CREB and ATF-1 transcription factors that were required for up-regulating Bcl2 levels. Indeed, knockdown of Akt, CREB, or ATF1 in t-Darpp-expressing cells reduced Bcl2 protein levels. In conclusion, the t-Darpp/Akt axis underscores a novel oncogenic potential of t-Darpp in gastric carcinogenesis and resistance to drug-induced apoptosis.
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U2 - 10.1158/0008-5472.CAN-07-1580
DO - 10.1158/0008-5472.CAN-07-1580
M3 - Article
C2 - 18199533
AN - SCOPUS:39049122786
VL - 68
SP - 395
EP - 403
JO - Cancer Research
JF - Cancer Research
SN - 0008-5472
IS - 2
ER -