Expression and significance of Id1 helix–loop–helix protein overexpression in gastric cancer

The Id family of helix–loop–helix proteins is involved in a variety of biological processes, including development, proliferation, and angiogenesis. There is emerging evidence for deregulation of Id proteins in some cancers. Hence we determined Id expression in gastric cancer. To elucidate the involvement of Id1 in gastric carcinogenesis, Immunohistochemistry was carried out on paraffin-embedded gastric cancer sections. By analyzing the relationship between the Id1 staining index of individual tumors and the patientʹs clinical parameters, including histological grade, clinical stage, and presence of metastases, we found that strong Id1 expression was associated with poorer differentiation and more aggressive behavior of tumor cells. To further explore Id1 expression in human gastric carcinomas, Western blot analysis was performed to analyze Id1 protein expression in 15 pairs of gastric tissues and cancers and in gastric cell lines. Id1 was found to be expressed at higher levels in 11/15 cancer tissues compared to adjacent tissues. Id1 was upregulated more prominently in the poorly differentiated cell lines than in the well-differentiated ones. Semiquantitative RT-PCR was carried out to investigate the expression of mRNA of Id1 in gastric cancer cell lines and it was upregulated in most of them. Our results demonstrate that Id1 protein may play an important role in the process of gastric carcinogenesis and high-level Id1 expression may be related to the malignant potential of tumor cells.