Differential expression of the Tie-2 receptor and its ligands in human pancreatic tumors.

BACKGROUND: Derangements in the balance of the Tie-2 receptor ligands, angiopoietin-1 and angiopoietin-2 (Ang-1 and Ang-2), have been implicated in the growth and differentiation of several human tumors. To assess the potential role of angiogenesis factors in pancreatic tumorigenesis, we confirmed previously observed oligonucleotide-based microarray data by analyzing their expression in pancreatic tumors using semiquantitative reverse transcription polymerase chain reaction and immunohistochemistry.

STUDY DESIGN: RNA harvested from tissue samples obtained from patients with normal pancreata, adenocarcinoma of the pancreas, and neuroendocrine tumors of the pancreas (nine each) was grouped by tissue type, pooled, and hybridized to a cDNA microarray and global gene expression patterns were determined. Semiquantitative reverse transcription polymerase chain reaction was applied to individual pool components to specifically determine expression of Tie-2, Ang-1, and Ang-2. A separate set of tumors and matched normal pancreas were then stained for expression of Ang-2 protein using immunohistochemistry.

RESULTS: Microarray data showed that Ang-2 was upregulated in neuroendocrine tumors ( approximately 8 times more than normal) and adenocarcinoma of the pancreas ( approximately 5 times more than normal) although Ang-1 and Tie-2 were not differentially expressed. Reverse transcription polymerase chain reaction confirmed these findings showing strong Ang-2 expression in nine of nine neuroendocrine tumors, eight of nine adenocarcinoma of the pancreas, and weak expression in two of nine normal pancreata. Immunohistochemistry showed tumor-specific staining of Ang-2 in 10 of 15 matched adenocarcinoma of the pancreas (67%) and 6 of 8 neuroendocrine tumors (75%).

CONCLUSIONS: Although Tie-2 and Ang-1 are not differentially expressed in pancreatic tumors, Ang-2 gene and gene product are overexpressed, suggesting a significant role for Ang-2 in pancreatic tumorigenesis. Differential expression of Ang-2 in human tumors may be useful as a diagnostic and therapeutic target.