DOC-2/hDab2 Expression Is Up-Regulated in Primary Pancreatic Cancer but Reduced in Metastasis

Abstract

SUMMARY:DOC-2/hDab2 (DOC-2) has tumor suppressive functions in ovarian cancer and choriocarcinoma. In these tumors, it negatively influences mitogenic signal transduction of growth factors and blocks ras activity. Pancreatic cancer exhibits a high frequency of K-ras gene mutations; however, it is not known whether DOC-2 expression is altered in these tumors. Therefore, we investigated DOC-2 expression in 22 pancreatic adenocarcinomas and in 6 pancreatic cancer cell lines. Findings in human tumors were compared with normal controls and correlated with clinicopathological data. Additionally, the influence of K-ras on DOC-2 transcription was investigated. Northern blot and Western blot analyses both demonstrated an increase of DOC-2 mRNA and protein levels in primary pancreatic cancers in comparison with normal controls. In situ hybridization showed DOC-2 mRNA expression in the majority of cancer cells of primary tumors, as well as in chronic pancreatitis-like lesions surrounding the cancer mass. Immunohistochemistry mirrored the in situ hybridization findings. In contrast, levels of expression of DOC-2 in lymph node metastases were markedly decreased in comparison with levels in primary tumors. In addition, in 5 metastatic pancreatic cancer cell lines, DOC-2 mRNA and protein levels were low, whereas quantitative RT-PCR demonstrated relatively higher levels in a nonmetastatic pancreatic cancer cell line. In conclusion, DOC-2 is overexpressed in primary pancreatic adenocarcinoma but down-regulated in metastatic disease, suggesting a tumor suppressor function of DOC-2 in the late steps of pancreatic carcinogenesis. (Lab Invest 2001, 81:863-873).P ancreatic adenocarcinomas are the fourth or fifth leading cause of cancer-related death in developed countries, with an average 5-year survival rate of less than 0.5% (Gudjonsson, 1995). The poor prognosis of pancreatic cancer manifests itself by low resection rates, nonresponsiveness to adjuvant or palliative therapy, and a high incidence of recurrence and early metastasis formation following potentially curative resection.It is known that various genetic and epigenetic alterations are involved in the pathogenesis of pancreatic cancer, including overexpression of mitogenic growth factors and growth factor receptors (Friess et al, 1993;Korc et al, 1992), as well as mutations of the K-ras proto-oncogene and p53 and Smad4 tumor suppressor genes (Friess et al, 1998). A better understanding of the underlying molecular mechanisms, including those related to metastasis in this malignancy, will hopefully contribute to improvement of early diagnosis and effective therapy in the future. DOC-2/hDab2(DOC-2) is a candidate tumor suppressor gene that was first isolated by differential RNA display techniques (Liang and Pardee, 1992;Mok et al, 1994). In 1995, Albertsen and coworkers (Albertsen et al, 1996) reported the complete gene sequence of the 3.2-kb DOC-2 transcript and its localization at chromosome 5p13. It was shown that DOC-2 is the human homolog of mouse Dab2, which was cloned f...

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Identification of differentially expressed genes in pulmonary adenocarcinoma by using cDNA array

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