metallothionein and Lymphoma--B-Cell

Several clinical trials have shown gallium nitrate to be an active agent in the treatment of lymphoma. Whereas gallium is known to target cellular iron homeostasis, the basis for lymphoma cell resistance to gallium is not known. Understanding mechanisms of resistance may suggest strategies to enhance the clinical efficacy of gallium. In the present study, we used a focused DNA microarray to compare the expression of genes related to metal metabolism in gallium-resistant and gallium-sensitive lymphoma cell lines developed by us. Gallium-resistant cells were found to display a marked increase in gene expression for metallothionein-2A and the zinc transporter ZnT-1. Cells exposed to gallium nitrate displayed an increase in the binding of metal-responsive transcription factor-1 to metal response element sequences involved in the transcriptional regulation of metallothionein and ZnT-1 genes. Gallium nitrate induced metallothionein-2A and ZnT-1 expression in cells. A role for metallothionein in modulating the antineoplastic activity of gallium was confirmed by showing that the induction of metallothionein expression by zinc provided partial protection against the cytotoxicity of gallium and by showing that the level of endogenous metallothionein in lymphoma cell lines correlated with their sensitivity to gallium nitrate. Immunohistochemical staining of lymphomatous tissues revealed metallothionein protein to be variably expressed in different lymphomas. Our studies show for the first time that gallium acts on pathways related to zinc metabolism and that metal-responsive transcription factor-1 activity and metallothionein expression contribute to the development of gallium drug resistance. Furthermore, the endogenous level of metallothionein in lymphoma may be an important determinant of clinical response to gallium nitrate.

Topics: Antineoplastic Agents; Blotting, Northern; Cation Transport Proteins; Cell Proliferation; DNA-Binding Proteins; DNA, Complementary; Drug Resistance, Neoplasm; Electrophoretic Mobility Shift Assay; Gallium; Gene Expression Profiling; Gene Expression Regulation, Neoplastic; Humans; Immunoenzyme Techniques; Immunosuppressive Agents; Leukemia, Lymphoid; Lymphoma, B-Cell; Lymphoma, Large B-Cell, Diffuse; Metallothionein; Oligonucleotide Array Sequence Analysis; Transcription Factor MTF-1; Transcription Factors; Transcription, Genetic

We have investigated metallothionein (MT) I and II mRNA and protein in B-cell lymphomas with particular reference to diffuse large B-cell lymphoma (DLBCL). The mRNA profiling was performed on Affymetrix arrays and showed up-regulated MT mRNA in 15 of 48 DLBCLs, including 12 of 23 activated B-cell (ABC) and 3 of 9 type-3 lesions. In contrast, MT mRNA was low to undetectable in 16 germinal center B-cell (GCB)-type DLBCLs. Only 1 of 15 patients with up-regulated MT mRNA achieved a sustained remission, suggesting that up-regulated MT mRNA constitutes a significant risk factor for treatment failure. This was confirmed in 2 independent series, which showed significantly shorter 5-year survival in DLBCL with high versus low MT-IIa levels. By immunohistology, MT was shown to be present in both macrophages and lymphoma cells. The proportion of MT-positive macrophages did not correlate with the survival. In contrast, in 115 DLBCLs, MT labeling of more than 20% lymphoma cells was associated with a significantly poorer 5-year survival, independent of the age, stage, or International Prognostic Index. Taken together, it is suggested that both increased MT mRNA and MT protein expression by more than 20% lymphoma cells constitute independent risk factors in DLBCL.

Topics: Gene Expression Profiling; Gene Expression Regulation, Neoplastic; Humans; Lymphoma, B-Cell; Lymphoma, Large B-Cell, Diffuse; Metallothionein; Predictive Value of Tests; Prognosis; RNA, Messenger; Survival Analysis; Treatment Failure; Up-Regulation

Metallothionein (MT) is a metal-binding protein with functional roles in cell growth, repair and differentiation. MT is reported to be differentially expressed in lymphocytes of malignant gastrointestinal lesions. The level of MT protein was examined by immunohistochemical analysis at light microscopic and ultrastructural level in infiltrating lymphocytes from 20 cases of undifferentiated nasopharyngeal carcinoma (NPC). MT expression was found to be absent in the infiltrating lymphocytes of NPC and in reactive lymphocytes of lymphoid hyperplasia in nasopharyngeal tissues. Ultrastructural examination confirmed the absence of MT immunoreactivity in the lymphoid infiltrate of NPC. On the other hand, malignant lymphoblasts of diffuse large cell lymphoma, showed MT-immunopositivity by immunoelectron microscopy. This study demonstrates a lack of MT expression in the lymphoid stroma of undifferentiated NPC, a further characteristic of its non-neoplastic nature.

Topics: Adult; Aged; Carcinoma; Female; Humans; Immunohistochemistry; Lymphocytes, Tumor-Infiltrating; Lymphoma, B-Cell; Male; Metallothionein; Microscopy, Electron; Microscopy, Immunoelectron; Middle Aged; Nasopharyngeal Neoplasms