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Supplementary Material for: The Thioredoxin-Interacting Protein TXNIP Is a Putative Tumour Suppressor in Cutaneous T-Cell Lymphoma

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posted on 14.08.2020, 09:12 by Stolearenco V., Levring T.B., Nielsen H.M., Lindahl L., Fredholm S., Kongsbak-Wismann M., Willerslev-Olsen A., Buus T.B., Nastasi C., Hu T., Gluud M., Côme C.R.M., Krejsgaard T., Iversen L., Bonefeld C.M., Grønbæk K., Met Ö., Woetmann A., Ødum N., Geisler C.
Background: The thioredoxin-interacting protein (TXNIP) is involved in cellular metabolism and cell proliferation, and recently, deficient expression of TXNIP has been associated with progression and poor outcome for cancer patients. Objectives: To assess TXNIP expression and function in malignant T cells from cutaneous T-cell lymphoma (CTCL). Methods: CTCL-derived malignant (MyLa2059, PB2B) and non-malignant (MyLa1850) cell lines were analysed by Western blotting and qPCR for TXNIP expression. Subsequently, the malignant CTCL cell lines were treated with GSK126 – an inhibitor of enhancer of zeste homolog 2 (EZH2) methyltransferase activity or assessed by bisulphite sequencing for TXNIP promoter methylation. Methylation was also assessed with the demethylating agent 5-azacytidine (5AZA). Finally, TXNIP was overexpressed in the malignant PB2B cell line via plasmid transduction, and the effect of TXNIP was further analysed by flow cytometry. Results: We report on low expression of TXNIP protein in all cell lines representing different subtypes and stages of CTCL when compared to non-malignant T cells. Epigenetic silencing and other mechanisms were involved in the repression of TXNIP whereas forced expression of TXNIP strongly inhibited proliferation of malignant T cells. Conclusions: Epigenetic silencing and other as yet unknown mechanisms repress TXNIP expression in malignant T cells. As forced expression of TXNIP inhibits malignant proliferation, we propose that TXNIP is a putative tumour suppressor in CTCL.