As the fourth leading cause of cancer deaths in the United States, pancreatic cancer is one of the most lethal forms of cancer diagnosed. Despite advances in understanding the underlying mechanisms driving disease progression, median survival time following diagnosis remains <6 months, with a five year survival rate of only 3-5%. Part of this is due to the rapid metastasis of pancreatic cancer to the lymphatic system, as well as other organs such as the liver and lungs. In addition, its resistance to conventional chemotherapy makes it difficult to treat. The properties which endow a tumor cell with the ability to metastasize are similar to those possessed by normal stem cells, including self-renewal, migratory capability and drug-effluxing ability, leading to the theory that cancer arises from a putative cancer stem cell. Cells which efflux the dye Hoechst 33342, termed the side population, have been shown to be rich in stem cells, and have now been isolated from many organs, including the bone marrow, skin and mammary gland. Since pancreatic cancer recapitulates many of these same characteristics, it has also been postulated that it too arises from a stem cell or stem cell-like precursor cell. Transcriptional profiling of side population cells reveals that they express multiple mRNAs which function to restrain growth-stimulatory signaling pathways, including the putative tumor suppressor Disabled-2 (Dab2). We have previously identified that Dab2 plays an important role in transducing TGF? signaling. Mutation or deletion of SMAD4, a key intracellular mediator of the Smad-dependent arm of TGF? signaling, is observed in ~50% of PDAC cases and is associated with aggressive progression of pancreatic cancer. While a recent study has demonstrated that normal adult pancreas expresses low levels of Dab2, its expression increases in primary pancreatic cancer samples. Examination of lymph node metastases of the same tumors, as well as in metastatic PDAC cell lines, however, reveals a striking loss of Dab2 expression at this stage in tumor progression. We observe a correlation between loss of Dab2 expression and appearance of an epithelial-to-mesenchymal transition (EMT) in pancreatic cancer cell lines. EMT has been associated with poor prognosis in pancreatic cancer patients. Based on this, we hypothesize that Dab2 plays an important role in preventing pancreatic tumor progression by modulation of the TGF? signaling pathway and the process of EMT. Loss of Dab2 would therefore lead to pancreatic tumor progression and metastasis. To test our hypothesis, the following specific aims are proposed: (1) to determine the effects of ablation or restoration of Dab2 expression on pancreatic cancer cell line growth and tumorigenicity and (2) to define the activity and regulation of the Dab2 promoter in pancreatic cancer cell lines. Completion of these studies will further our long-term goal of understanding the role of the putative tumor suppressor Dab2 in cancer progression which may potentially lead to novel therapeutic options for treatment of pancreatic and other human cancers.
Pancreatic cancer remains the one of the most lethal forms of human cancer, with a 5 year survival rate of only 3-5%, due to its rapid metastatic spread as well as its resistance to standard chemotherapeutic regimens. We show that pancreatic cell lines which display decreased levels of a protein called Disabled-2 exhibit the characteristics of cells which are primed to undergo metastasis, suggesting that Dab2 plays a role in suppression of pancreatic cancer. The studies proposed here will provide prelimary evidence to support a role of Disabled-2 in prevention of pancreatic tumor progression and metastasis which may lead to improved diagnosis and treatment of pancreatic cancer.
| Duckworth, C; Zhang, L; Carroll, S L et al. (2016) Overexpression of GAB2 in ovarian cancer cells promotes tumor growth and angiogenesis by upregulating chemokine expression. Oncogene 35:4036-47 |
| Martin, J C; Herbert, B-S; Hocevar, B A (2010) Disabled-2 downregulation promotes epithelial-to-mesenchymal transition. Br J Cancer 103:1716-23 |
