DARPP32 Up-regulates ANGPT2 And Angiogenesis By Activating STAT3 In Gastric Cancer

Objective:Angiogenesis is one of the main hallmarks of cancer. Overexpression of dopamine and cAMP-regulated phosphoprotein, Mr 32000 (DARPP-32) and its truncated isoform (t-DARPP), are associated with gastric tumorigenesis. In the present study, we investigated the mechanisms of DARPP32 in promoting gastric cancer angiogenesis.Methods:Gene expressions were tested using RT-PCR. Transcriptional factors’ activities were analyzed by luciferase reporter assay. Proteins cellular localizations and expression were determined using Immunofluorescence assay, Western blot, immunohistochemistry and Enzyme-Linked Immunosorbent Assay. Angiogenesis was tested by HUVEC tube formation assay. Tumor formation ability was determined using in vivo tumor formation assay in nude mouse.Results:DARPP-32 proteins can regulate the levels of angiopoietin 2 (ANGPT2) and promote angiogenesis. This unique function for DARPP-32 proteins was independent of its N-terminal domain where DARPP-32, DARPP-32 T34A mutant, and the N-terminal truncated isoform, t-DARPP, led to similar effects. The increase in ANGPT2 was detectable in the secreted form which was functionally active and induced angiogenesis; antibody blocking of the secreted ANGPT2 abrogated these effects. Because of the close link between inflammation, angiogenesis, and gastric carcinogenesis we next examined NF-κB and STAT3 activities. We found that DARPP-32 proteins did not affect the phosphorylation or activity of NF-κB but induced significant phosphorylation, activation, and nuclear localization of STAT3. Inhibition or knockdown of STAT3 significantly attenuated the induction of ANGPT2 by DARPP-32. In vivo xenografts models demonstrated that overexpression of DARPP-32 markedly increases angiogenesis and tumor growth. Analyses of human gastric tissues showed a strong correlation between DARPP-32 and ANGPT2.Conclusion:This study establishes the role of DARPP-32-STAT3-ANGPT2 axis in regulating angiogenesis; a novel finding that could have a significant impact on tumorigenesis in different cancer types.Objective:MicroRNAs (miRNAs) play critical roles in tumor development and progression. The finding that a single miRNA can regulate hundreds of genes places miRNAs at critical hubs of signaling pathways. For the current study, the authors investigated the miRNA expression profile of non cardia gastric adenocarcinomas and compared it with cardia gastric adenocarcinomas to better identify a unique miRNA signature of non cardia gastric adenocarcinoma.Methods:miRNA expression profiles were obtained using 2 different proprietary microarray platforms on primary non cardia gastric adenocarcinoma tissue samples. The cross comparison of results identified 17 up-regulated miRNAs and 12 down-regulated miRNAs that overlapped in both platforms. Quantitative real-time polymerase chain reaction was performed for independent validation of a representative set of 8 miRNAs in non cardia gastric and cardia gastric adenocarcinomas compared with normal non cardia gastric mucosa or cardia gastric mucosa, respectively.Results:The deregulation of miRNA-146b-5p, miRNA-375, miRNA-148a, miRNA-31, and miRNA-451 was associated significantly with non cardia gastric adenocarcinomas. Conversely, deregulation of miRNA-21 (up-regulation) and miRNA- 133b (down-regulation) was detectable in both non cardia gastric and cardia gastric adenocarcinomas. It was noteworthy that miRNA-200a was significantly down-regulated in non cardia gastric adenocarcinoma samples (P<0.04) but was up-regulated in cardia gastric adenocarcinoma samples (P<0.001). In addition, the expression level of miRNA-146b-5p displayed a strong correlation with the tumor stage of non cardia gastric cancer.Conclusion:Non cardia gastric adenocarcinoma displayed a unique miRNA signature that distinguished it from cardia gastric adenocarcinoma. This specific signature may reflect differences in the etiology and/or molecular signaling in these 2 closely related cancers. The current findings suggest important miRNA candidates that can be investigated for their biological functions and for their possible diagnostic, prognostic, and therapeutic role in gastric adenocarcinoma.