El-Rifai Wa'el, Smith Michael F, Li Guolian, Beckler Andy, Carl Virginia S, Montgomery Elizabeth, Knuutila Sakari, Moskaluk Christopher A, Frierson Henry F, Powell Steven M
Department of Medicine, University of Virginia Health System, Charlottesville, Virginia 22908-0708, USA.
Cancer Res. 2002 Jul 15;62(14):4061-4.
Gastric carcinoma is the second most common cause of cancer-related death worldwide. Recently, we have demonstrated that expressed sequence tag AA552509 was frequently amplified and the most consistently overexpressed target at 17q in gastric cancers. Herein, we report that DARPP-32 (dopamine and cAMP-regulated phosphoprotein of M(r) 32,000) is the target gene for overexpression of expressed sequence tag AA552509. In addition, we have identified full-length cDNA of DARPP-32 (GenBank accession number AF464196) with 467 bp of additional untranslated mRNA nucleotides upstream of the previously known translation start site in exon 1. Additionally, we have discovered a novel truncated isoform of DARPP-32 that we named t-DARPP (GenBank accession number AY070271), which is also overexpressed in gastric cancers. Using quantitative real-time reverse transcription-PCR, Western blots, and staining of tumor tissue arrays, the two DARPP mRNA transcripts and proteins were overexpressed in gastric cancer cells and exhibited abundant protein overexpression in neoplastic but not normal gastric epithelial cells. DARPP-32 is the only known protein that acts as a protein phosphatase 1 inhibitor or a protein kinase A inhibitor. The novel truncated isoform, t-DARPP, lacks the phosphorylation site related to protein phosphatase 1 inhibition but maintains the phosphorylation site with the protein kinase A inhibitory effect. Our results reveal for the first time the presence of these signaling molecules in human cancer and suggest that they may be important for gastric tumorigenesis.
胃癌是全球癌症相关死亡的第二大常见原因。最近，我们已经证明，表达序列标签AA552509在胃癌中经常扩增，并且是17号染色体上最持续过度表达的靶点。在此，我们报告DARPP - 32（分子量为32,000的多巴胺和cAMP调节磷蛋白）是表达序列标签AA552509过度表达的靶基因。此外，我们已经鉴定出DARPP - 32的全长cDNA（GenBank登录号AF464196），其在第1外显子中先前已知的翻译起始位点上游有467 bp的额外非翻译mRNA核苷酸。此外，我们发现了一种新的DARPP - 32截短异构体，我们将其命名为t - DARPP（GenBank登录号AY070271），它在胃癌中也过度表达。使用定量实时逆转录PCR、蛋白质免疫印迹和肿瘤组织芯片染色，这两种DARPP mRNA转录本和蛋白质在胃癌细胞中过度表达，并在肿瘤性而非正常胃上皮细胞中表现出丰富的蛋白质过度表达。DARPP - 32是唯一已知的作为蛋白磷酸酶1抑制剂或蛋白激酶A抑制剂的蛋白质。这种新的截短异构体t - DARPP缺乏与蛋白磷酸酶1抑制相关的磷酸化位点，但保留了具有蛋白激酶A抑制作用的磷酸化位点。我们的结果首次揭示了这些信号分子在人类癌症中的存在，并表明它们可能对胃癌发生很重要。
