Expression Of Tumor Suppressor Gene NDRG2 In Lymphoma And Its Clinical Significance

【Objective】Lymphoma represents an entity of malignancies originated in the lymph nodes or other lymphoid tissues which consists of two subsets: Hodgkin's disease (referred to as HD)and non-Hodgkin's lymphoma (NHL), and NHL comprises T-cell lymphoma , B-cell lymphoma and NK cell lymphoma. The NK/T cell lymphoma is an independent disease in lymphoma, as the majority of tumor cells are derived from mature NK cells and the minority of tumor cells from NK-like T cells so referred to as NK/T cell lymphoma.The NDRG2 (N-myc downstream regulated gene 2) is a novel tumor suppressor gene candidate which was identified by using Anchor-PCR method from the human brain cDNA library in our lab. The accession number of the NDRG2 in gene bank is AF159092Hj and the structural properities of this gene is not yet well defined . we found that NDRG2 was obviously expressed in a variety of normal human tissues, and had no expression or low expression in the corresponding tumor tissues. However, in order to explore wether NDRG2 was involved in the incidence and development of lymphoma, this study was conducted to detect the expression of NDRG2 in lymphoma by using immunohistochemical method.【Method】1. The lymphoma tissue microarray purchased from Shaanxi CHAOYING Biological Company. Chip ID: CC15-17-001, CC15-19-001. this lymphoma tissue microarray provided 81 samples of lymphoma tissue, 36 of which are T-cell lymphoma, while 45 are B-cell lymphoma, and 40 cases of benign lesions of lymph node and 40 cases of normal lymph tissues.2. There are 48 cases of paraffin embedded NK/T Lymphoma tissue which had been previously diagnosed as malignant lymphoma from the Pathology department of Xi Jing Hospital. These patients had not been pretreated with radiotherapy or chemotherapy before their diagnosis and had been undoubtedly diagnosed as NK/T lymphoma according to the new working formulation of WHO updated in 2008. All patients had complete clinical data and totally belonged to the clinical stageⅠandⅡ, 29 male cases and 19 female cases. The average age is 52.87±15.02 year old. The thickness of the tissue slice is 4μmThe protocol of immunohistochemical staining was briefly addressed as following: the paraffin embedded tissue was dewaxed by xylene , stained with mouse anti-NDRG2 monoclonal antibody (dilution is 1:75) and developed with DAB.3. The pathologist assessed the intensity of positive signal according to the staining degree and percentage of staining cells by using semi-quantitative method for ten times under the optical microscope. Non-staining cells were judged to be 0 points, Positive cells with yellow staining to be 1 point, brown staining 2 point and tan staining 3 point; The percentage of staining cells in accounted cell is less than 5% was calculated to be 0 point, 5%~25% 1 point, 26%~50% 2 points, 50%~75% 3 points, over 75% 4 points. the sum of the two scores was finally used to determine the positivity of NDRG2 expression : 0 is negative (-), 1~4 is weakly positive expression (+), 5~8 medium positive expression (++), 9~12 is strongly positive expression (+++).5. SPSS software was unilitized for statistical analysis.【Result】1. The positive signal exclusively dsiplayed in the cytoplasm, and no positive signal was observed in the cells nuclear.2. The results showed that the rates of NDRG2 positive expression in normal lymph nodes, benign lesions of lymph nodes and lymphoma were 92.5% (37 / 40), 67.5% (27 / 40), and 16.2% (18/111) respectively, which indicated a statistical differences among these three groups(P<0.05). The differences of NDRG2 expression between lymphoma and benign lesion lymph nodes was of statistical significance (P<0.05). The differences of NDRG2 expression between lymphoma and normal lymph nodes was also of statistical significance (P<0.05).3. The expression level of NDRG2 was not related to patient's age, gender, and clinical staging in the NK/T cell lymphoma group (P>0.05)..4. The positive expression rate in paraffin-embedded NK/T cell lymphoma tissues was 6.2% (3 / 48); positive rate of B-cell and T-cell lymphoma containing in the tissue microarray were 13.3% (9 / 36) and 25.0% (6 / 45), which was suggestive of no statistical significance between these three groups. The positive expression rate of NDRG2 in NK/T cell lymphoma is quite lower than that in the B-cell and T-cell lymphoma.【Conclusion】1. The immunohistochemical results suggested that although the NDRG2 was a novel tumor suppressor gene candidate, it might also has very low level expressions in the lymphoma tissues. The immunohistochemical score based on the results of statistical analysis showed that the NDRG2 protein expression in normal tissues are higher than that in tumor tissues.2. There were small differences between different types of lymphoma in positive expression rates; in general, the positive expression rate of lymphoma was quite low. It had been proved that the NDRG2 has low expression or no expression in majority of lymphomas, suggesting that the NDRG2 might be involved in the occurrence and development of lymphoma. This would not only provide clues for researching the pathogenesis of lymphoma, but also have certain significance for the diagnosis and treatment of lymphoma.