MiR-181a is a novel player in the STAT3-mediated survival network of TCR\u03b1\u03b2+ CD8+ T large granular lymphocyte leukemia

Jorn L J C Assmann,Thomas P Loughran Jr,Stefan J Erkeland,Yorick Sandberg,Anton W Langerak,Sanne E Van Den Bogaerdt,Leticia G Leon,Joyce Schilperoord-Vermeulen,David J Feith,Christiaan J Stavast,Mar Bellido

doi:10.1038/s41375-021-01480-2

Abstract

T-LGL cells arise as a consequence of chronic antigenic stimulation and inflammation and thrive because of constitutive activation of the STAT3 and ERK pathway. Notably, in 40% of patients, constitutive STAT3 activation is due to STAT3 activating mutations, whereas in 60% this is unknown. As miRNAs are amongst the most potent regulators in health and disease, we hypothesized that aberrant miRNA expression could contribute to dysregulation of these pathways. miRNA sequencing in T-LGL leukemia cases and aged-matched healthy control TEMRA cells revealed overexpression of miR-181a. Furthermore, geneset enrichment analysis (GSEA) of downregulated targets of miR-181a implicated involvement in regulating STAT3 and ERK1/2 pathways. Flow cytometric analyses showed increased SOCS3+ and DUSP6+ T-LGL cells upon miR-181a inhibition. In addition, miR-181a-transfected human CD8+ T cells showed increased basal STAT3 and ERK1/2 phosphorylation. By using TL1, a human T-LGL cell line, we could show that miR-181a is an actor in T-LGL leukemia, driving STAT3 activation by SOCS3 inhibition and ERK1/2 phosphorylation by DUSP6 inhibition and verified this mechanism in an independent cell line. In addition, miR-181a inhibition resulted in a higher sensitivity to FAS-mediated apoptosis. Collectively, our data show that miR-181a could be the missing link to explain why STAT3-unmutated patients show hyperactive STAT3.

Highlights

T-cell large granular lymphocyte (T-LGL) leukemia is a rare hematological neoplasia that is characterized by an abnormal expansion of T-LGL cells in the peripheral blood (PB) [1]
Principal component analysis (PCA) revealed that T-LGL leukemia patient cells and healthy control TEMRA cells could be clearly distinguished by differential miRNA expression (Fig. 1B)
Keeping in mind that Suppressor of cytokine signaling 3 (SOCS3) and DUSP6 were found as primary targets, we focused on the signal transducer and activator of transcription 3 (STAT3) and extracellular signal‐regulated protein kinase 1/2 (ERK1/2) pathways, because these are postulated to be hyper-activated in T-LGL primary cells

Summary

Introduction

T-cell large granular lymphocyte (T-LGL) leukemia is a rare hematological neoplasia that is characterized by an abnormal expansion of T-LGL cells in the peripheral blood (PB) [1]. In 2017, Lamy et al proposed that the constitutive activation of signal transducer and activator of transcription 3 (STAT3) acts as a central hub in the proliferation and survival of the eventual clinically malignant monoclonal cell population. STAT3 has long been known for its fundamental pathogenic role in T-LGL leukemia because it acts on the expression of many genes related to cell survival. Specific inhibition of STAT3 with antisense oligos or through JAK inhibition with AG-490 in T-LGL leukemic cells restores their ability to go into apoptosis in vitro [3], clearly showcasing the importance of STAT3 in T-LGL survival. Suppressor of cytokine signaling 3 (SOCS3) is one of the targets of the STAT3 pathway and is readily expressed upon STAT3 dimerization. SOCS3 forms an important negative feedback loop by suppressing JAK activity and is an important regulator of the STAT3 pathway [5]. Teramo et al demonstrated that SOCS3 mRNA expression is low in T-LGL cells the gene was not epigenetically silenced and no clear mutation in the SOCS3 gene was found [6]

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Conclusion