Darpp-32: a novel antiapoptotic gene in upper gastrointestinal carcinomas.

Belkhiri A, Zaika A, Pidkovka N, Knuutila S, Moskaluk C, El-Rifai W
Cancer Res. 2005 65 (15): 6583-92

PMID: 16061638 · DOI:10.1158/0008-5472.CAN-05-1433

We show the molecular mechanisms involved in Darpp-32 overexpression and its biological role in upper gastrointestinal adenocarcinomas (UGC). A tumor tissue array of 377 samples was developed and used to detect DARPP-32 DNA amplification and protein overexpression, which occurred in 32% and 60% of UGCs, respectively. Concomitant overexpression of mRNA for Darpp-32 and its truncated isoform t-Darpp was observed in 68% of tumors (P < 0.001). When Darpp-32 and t-Darpp were overexpressed in AGS and RKO gastrointestinal cells, up to a 4-fold reduction in the apoptosis rate was observed (terminal deoxynucleotidyl transferase-mediated nick-end labeling and Annexin V assays) in response to camptothecin, sodium butyrate, and ceramide. However, the introduction of mutations in phosphorylation sites abrogated this effect. Expression of Darpp-32 and t-Darpp preserved the mitochondrial transmembrane potential and was associated with increased levels of Bcl2 protein. A reversal of Bcl2 protein level was obtained using small interfering RNAs for Darpp-32 and t-Darpp. Luciferase assays using the p53 and p21 reporter plasmids and probing of immunoblots with antibodies specific for p53 transcriptional targets, such as Hdm2 and p21, indicated that neither Darpp-32 nor t-Darpp interfere with p53 function. Altogether, we show more frequent mRNA and protein overexpression of Darpp-32 than DNA amplification, suggesting that, in addition to amplification, transcriptional or posttranscriptional mechanisms may play an important role. The expression of Darpp-32 and t-Darpp is associated with a potent antiapoptotic advantage for cancer cells through a p53-independent mechanism that involves preservation of mitochondrial potential and increased Bcl2 levels.

MeSH Terms (18)

Adenocarcinoma Antineoplastic Agents, Phytogenic Apoptosis Camptothecin Dopamine and cAMP-Regulated Phosphoprotein 32 Esophageal Neoplasms Gene Dosage Humans Intracellular Membranes Membrane Potentials Mitochondria Nerve Tissue Proteins Phosphoproteins Proto-Oncogene Proteins c-bcl-2 RNA, Messenger Stomach Neoplasms Tumor Suppressor Protein p53 Up-Regulation

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