Up-regulated A20 promotes proliferation, regulates cell cycle progression and induces chemotherapy resistance of acute lymphoblastic leukemia cells

Highlights

• The protein expression of A20 is upregulated in ALL patients and cell lines.

• A20 depletion decreases proliferation of ALL cells both in vivo and in vitro.

• A20 depletion induces cell cycle arrest at G0/G1 stage of ALL cells.

• A20 depletion increases the sensitivity of ALL cells to chemotherapy.

• The regulation mechanism of A20 was associated with p-ERK and p53 signal pathways.

Abstract

A20, also known as tumor necrosis factor-α (TNFα)-induced protein 3 (TNFAIP3), has been identified as a key regulator of cell survival in many solid tumors. However, little is known about the protein expression level and function of A20 in acute lymphoblastic leukemia (ALL). In this study, we found that A20 is up-regulated in ALL patients and several cell lines. Knockdown of A20 in Jurkat, Nalm-6, and Reh cells resulted in reduced cell proliferation, which was associated with cell cycle arrest. Phospho-ERK (p-ERK) was also down-regulated, while p53 and p21 were up-regulated in A20 knockdown cells. In addition, A20 knockdown induced apoptosis in Jurkat and Reh cells and enhanced the sensitivity of these cell lines to chemotherapeutic drugs. These results indicate that A20 may stimulate cell proliferation by regulating cell cycle progression. A20 inhibited apoptosis in some types of ALL cells, thereby enhancing their resistance to chemotherapy. This effect was abolished through A20 silencing. These findings suggest that A20 may contribute to the pathogenesis of ALL and that it may be used as a new therapeutic target for ALL treatment.

Introduction

Acute lymphoblastic leukemia (ALL) is a hematological malignancy characterized by an accumulation of immature cells in the bone marrow and peripheral blood. It is recognized as the most common type of childhood leukemia [1], [2]. Although great improvements have been made in the treatment of pediatric leukemia, adult ALL remains a high burden [3]. This burden is partly due to uncontrolled cell proliferation and poor response to chemotherapy in adult patients [4]. Leukemic cells abnormally express numerous genes that are associated with proliferation and apoptosis compared to normal hematopoietic cells, and these genes are thought to be the main cause of drug resistance [5]. An examination of abnormally expressed genes in leukemic cells, and of the pathogenic mechanisms associated with these genes, would therefore have great value for the development of targeted therapies.

The zinc-finger protein A20, also known as tumor necrosis factor-α-induced protein 3(TNFAIP3), was first identified as a cytokine-induced gene in human umbilical vein endothelial cells [6]. Many studies have suggested that A20 is an ubiquitin editing protein that regulates inflammation signaling pathways [7] and negatively regulates the nuclear factor kappa B (NF-κB) activation pathway [8]. Some autoimmune diseases, including systemic lupus erythematosus and rheumatoid arthritis, are closely related with A20. Growing evidence also supports a role for A20 in the pathogenesis of cancer [9]. Dysregulation of A20 expression was observed in many types of solid tumor cells; for example, A20 expression is increased in glioblastoma cells [10], [11], hepatocellular carcinoma cells [12], estrogen receptor(ER)-negative or tamoxifen-resistant ER-positive breast cancer cells [13], [14], undifferentiated nasopharyngeal carcinoma cells, and poorly differentiated head and neck cancer cells [15]. These studies suggest an oncogenic role for A20 in these tumors and also suggest that A20 may be a useful new biomarker. However, little is known about the role of A20 in ALL.

In this study, we investigated the expression and biological function of A20 in several types of ALL cells. The results revealed that there was a significantly higher level of A20 protein in cell lines and in bone marrow mononuclear cells (BMMNC) obtained from ALL patients than in cells obtained from healthy donors. In addition, A20 promoted cell proliferation, induced cell cycle arrest, and reduced the sensitivity of three ALL cell lines to daunorubicin via a mechanism involving the ERK, p53 and p21 signal pathways. However, the role of A20 in different ALL cells varied, and the mechanisms by which A20 acted were not completely consistent. This suggests that the effects of A20 are pleotropic and complex in ALL.