Impaired Proteasome Function Activates GATA3 in T Cells and Upregulates CTLA-4: Relevance for Sézary Syndrome

Abstract

Highly regulated expression of the negative co-stimulatory molecule CTLA-4 on T-cells modulates T-cell activation and proliferation. CTLA-4 is preferentially expressed in Th2 T-cells, whose differentiation depends on the transcriptional regulator GATA3. Sezary syndrome (SS) is a T-cell malignancy characterized by Th2 cytokine skewing, impaired T-cell responses, and over-expression of GATA3 and CTLA-4. GATA3 is regulated by phosphorylation and ubiquitination. In SS cells, we detected increased polyubiquitinated proteins and activated GATA3. We hypothesized that proteasome dysfunction in SS T cells may lead to GATA3, and CTLA-4 over-expression. To test this hypothesis, we blocked proteasome function with bortezomib in normal T-cells, and observed sustained GATA3 and CTLA-4 upregulation. The increased CTLA-4 was functionally inhibitory in a mixed lymphocyte reaction (MLR). GATA3 directly transactivated the CTLA-4 promoter, and knockdown of GATA3 mRNA and protein inhibited CTLA-4 induction mediated by bortezomib. Finally, knockdown of GATA3 in patient’s malignant T-cells suppressed CTLA-4 expression. Here we demonstrate a new T-cell regulatory pathway that directly links decreased proteasome degradation of GATA-3, CTLA-4 upregulation, and inhibition of T-cell responses. We also demonstrate the presence of the GATA3/CTLA-4 regulatory pathway in fresh neoplastic CD4+ T-cells. Targeting of this pathway may be beneficial in SS and other CTLA-4-overexpressing T-cell neoplasms.

Evidence of an oncogenic role of aberrant TOX activation in cutaneous T-cell lymphoma

“…Aberrations in signal transducers and transcription factors have been reported in SS studies, such as Jun B, JunD, TGFBR2, STAT3, STAT4, CDKN1C, CTLA-4, GATA3, AHI-1, SATB1, PDCD10, and NOTCH1. 4,16,17,[32][33][34][35][36] Several of these dysregulated genes (TGFBR2, GATA3, STAT3, SATB1, and NOTCH1) are involved in the signal cascades governing T-cell development. [37][38][39][40][41] Our recent observation of aberrant TOX upregulation in MF, subsequently confirmed by McGirt et al, 10 prompted us to ask whether TOX is also upregulated in SS, the advanced CTCL, and whether TOX contributes to the development of CTCL.…”

GATA3 in Breast Cancer: Tumor Suppressor or Oncogene?

“…In adipocyte differentiation induced by rosiglitazone in cell lines, increased GATA3 turnover downstream of prolyl hydroxylase function and eventual ubiquitination are required (31). Finally, stabilization of GATA3 at the protein level is associated with the skewed cytokine profile characteristic of Sezary Syndrome (32). …”

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“…Sezary syndrome and other T-cell lymphomas upregulate the production of CTLA-4, a pathway inhibitor, and thus avoid destruction via T-cells. [12][13][14] The other pathways have a similar disregulation. Epstein-Barr virus-associated malignancies upregulate PD-L1 and several cancers, such as Hodgkin's lymphoma, produce an aberrant, stable form of the PD-L1 to increase the inhibitory signal, and evade the immune system.…”