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Hdm2 is regulated by K-Ras and mediates p53-independent functions in pancreatic cancer cells

Oncogene volume 28, pages 709–720 (2009)Cite this article

Abstract

There is emerging evidence that the oncogenic potential of hdm2 (human and/or murine double minute-2 protein) stems not only from its ability to counteract tumor suppressor p53 but also from its less understood p53-independent functions. Surprisingly, little is known about the role and regulation of hdm2 in pancreatic tumors, a large proportion (50–75%) of which contain mutant p53. In this study, we determined that hdm2 was expressed in a Ras-signaling-dependent manner in various pancreatic cancer cell lines. As p53 was mutated and inactive in these cells, the expression of hdm2 was seemingly redundant. Indeed, the proliferation and survival of cell lines such as Panc-1 and Panc-28 could be inhibited by PRIMA-1 (mutant p53 activator) but not by Nutlin-3 (inhibitor of the hdm2–p53 interaction). Unexpectedly, however, the proliferation of both cell lines was strongly inhibited by hdm2-specific RNAi. Our data also revealed cyclin D1, c-Jun and c-Myc to be novel targets of hdm2 and suggested that they might mediate hdm2's role in cellular proliferation and/or survival. We conclude from our results that hdm2 is expressed in pancreatic cancer cells as a result of activated Ras signaling, and that it regulates cellular proliferation and the expression of three novel target genes by p53-independent mechanisms.

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Abbreviations

hdm2:

human and/or murine double minute-2 protein

MEK:

mitogen and extracellular signal-regulated protein kinase

p53:

tumor suppressor p53

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Acknowledgements

We are grateful to Drs Frank McCormick and Martin McMahon (University of California, San Francisco, CA, USA) for the hdm2 P2 promoter reporter constructs, Johannes Bos (Utrecht University) for the Raf1 GST-RBD plasmid and Gigi Lozano (M.D. Anderson Cancer Center, Houston, TX, USA) for the p53 and pCMV-hdm2 expression vectors. We also thank Pfizer (CI-1040), Dr Bryant Darnay (pMX-BGD vector) and Dr F-X Claret (pSRα-c-Jun) for other reagents; Dr Baoan Ji for assistance with the qPCR assays and Beth L Notzon and Angelique L Geehan (M.D. Anderson Cancer Center) for editorial assistance. This work was supported by the Lustgarten Foundation for Pancreatic Cancer Research (SAGR), the Topfer Fund for Pancreatic Cancer Research (SAGR), the University Cancer Foundation at The University of Texas M.D. Anderson Cancer Center (SAGR), NCI SPORE CA101936 in Pancreatic Cancer (JLA) and NCI Grant CA016672 (DNA sequencing and media preparation facilities, The University of Texas M.D. Anderson Cancer Center).

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Author notes

  1. S Shin

    Present address: 3Current address: Department of Internal Medicine, East Tennessee State University, Johnson City, TN 37614-70622, USA.,

  2. P F Firozi

    Present address: 4Current address: Center for Cell and Gene Therapy, Baylor College of Medicine, Houston, TX 77030, USA.,

  3. L Yang

    Present address: 5Current address: Department of Biology and Biochemistry, University of Houston, Houston, TX 77204, USA.,

  4. X Sui and S Shin: These authors contributed equally to this work.

Authors and Affiliations

  1. Department of Gastrointestinal Medical Oncology, The University of Texas M.D. Anderson Cancer Center, Houston, TX, USA

    X Sui, S Shin, R Zhang, P F Firozi, L Yang, J L Abbruzzese & S A G Reddy

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  1. X Sui
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Correspondence to S A G Reddy.

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Supplementary Information accompanies the paper on the Oncogene website (http://www.nature.com/onc)

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Sui, X., Shin, S., Zhang, R. et al. Hdm2 is regulated by K-Ras and mediates p53-independent functions in pancreatic cancer cells. Oncogene 28, 709–720 (2009). https://doi.org/10.1038/onc.2008.423

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