An increased high-mobility group A2 expression level is associated with malignant phenotype in pancreatic exocrine tissue

Abstract

The altered form of the high-mobility group A2 (HMGA2) gene is somehow related to the generation of human benign and malignant tumours of mesenchymal origin. However, only a few data on the expression of HMGA2 in malignant tumour originating from epithelial tissue are available. In this study, we examined the HMGA2 expression level in pancreatic carcinoma, and investigated whether alterations in the HMGA2 expression level are associated with a malignant phenotype in pancreatic tissue. High-mobility group A2 mRNA and protein expression was determined in eight surgically resected specimens of non-neoplastic tissue (six specimens of normal pancreatic tissue and two of chronic pancreatitis tissue) and 27 pancreatic carcinomas by highly sensitive reverse transcriptase-polymerase chain reaction (RT-PCR) techniques and immunohistochemical staining, respectively. Reverse transcriptase-polymerase chain reaction analysis revealed the expression of the HMGA2 gene in non-neoplastic pancreatic tissue, although its expression level was significantly lower than that in carcinoma. Immunohistochemical analysis indicated that the presence of the HMGA2 gene in non-neoplastic pancreatic tissue observed in RT-PCR reflects its abundant expression in islet cells, together with its focal expression in duct epithelial cells. Intense and multifocal or diffuse HMGA2 immunoreactivity was noted in all the pancreatic carcinoma examined. A strong correlation between HMGA2 overexpression and the diagnosis of carcinoma was statistically verified. Based on these findings, we propose that an increased expression level of the HMGA2 protein is closely associated with the malignant phenotype in the pancreatic exocrine system, and accordingly, HMGA2 could serve as a potential diagnostic molecular marker for distinguishing pancreatic malignant cells from non-neoplastic pancreatic exocrine cells.

Figure 1

Reverse transcriptase–polymerase chain reaction products of HMGA2 after gel electrophoresis and ethidium bromide staining. Results show specific 220-bp bands. DL, DNA molecular weight marker; lane 1, positive control (hepatoma cell line HEP3B, which is known to express high level of HMGA2); lane 2, normal pancreas; lane 3, chronic pancreatitis; lane 4–11, pancreatic carcinomas.

Figure 2

Immunohistochemical demonstration of the HMGA2 protein expression in pancreatic cancer cell lines. (A) AsPC-1 (Mayer's haematoxylin; original magnification × 200). (B) PANC-I (Mayer's haematoxylin; original magnification × 200). (C) MIA PaCa-2 (Mayer's haematoxylin; original magnification × 100). (D) BxPC-3 (Mayer's haematoxylin; original magnification × 200). Intense multifocal or diffuse HMGA2 nuclear immunoreactivity (brown colour) was characteristically observed in cancer cells.

Figure 3

Immunohistochemical demonstration of the HMGA2 protein expression in surgically resected specimens of non-neoplastic pancreatic tissues and pancreatic carcinomas. (A) Non-neoplastic epithelial cells of the main pancreatic duct. A small proportion of duct epithelial cells show HMGA2 immunoreactivity (arrows). (Mayer's haematoxylin; original magnification × 200). (B) Epithelial cells of branch pancreatic duct and islets in chronic pancreatitis tissue. Islet cells showed intense and diffuse HMGA2 immunoreactivity (arrows), while epithelial cells of the branch pancreatic duct did not exhibit any detectable HMGA2 immunoreactivity (arrowhead) (Mayer's haematoxylin; original magnification × 100). (C) Primary pancreatic carcinoma exhibiting well-differentiated tubular adenocarcinoma (Mayer's haematoxylin; original magnification × 200). (D) Primary pancreatic carcinoma exhibiting adenosquamous carcinoma (Mayer's haematoxylin; original magnification × 200). (E) Metastatic lesion in the liver (Mayer's haematoxylin; original magnification × 200). Intense and multifocal or diffuse HMGA2 immunoreactivity was noted in all the pancreatic carcinomas (C–E). (F) Section including both carcinoma cells and islet cells (Mayer's haematoxylin; original magnification × 200). Islet cells showed intense and diffuse HMGA2 immunoreactivity (arrows), which was almost equivalent to that observed in carcinoma cells (arrowheads).