HLX in AML: novel prognostic and therapeutic target

HLX affects cell cycle and proliferation in AML cells via the JAK/STAT signaling pathway

Acute myelogenous leukemia (AML) is a class of malignant tumors derived from hematopoietic stem or progenitor cells. The H2.0-like homeobox gene (HLX) encodes transcription factors that function in promoting normal hematopoietic cell proliferation and tumor immunity. The present study analyzed the effect of downregulating the HLX on cell cycle distribution and cell proliferation in AML. Moreover, the current study detected changes in the expression of genes and proteins in the Janus kinase (JAK)/STAT signaling pathway to investigate the mechanism of the action of HLX in tumor immunity in AML. HLX expression in AML cell lines was silenced using small interfering siRNA, and MTS/PMS-assay colorimetric assays were used to assess the effect of knockdown of HLX on AML cell proliferation. Flow cytometry was used to analyze changes in cell cycle distribution, while reverse transcription-quantitative PCR and western blotting were used to detect changes in the expression levels of key components of the JAK/STAT signaling pathway, such as p21-activated kinase 1 (PAK1), neuropilin 1 (NRP1), B-cell translocation gene 1 (BTG1) and STAT5. It was found that HLX was differentially expressed in AML cell lines of various subtypes, and HLX expression was higher in the AML/M3 subtype NB4 cell line compared with the control group. Knockdown of HLX in NB4 cells significantly inhibited cell proliferation and arrested cells in the G₀/G₁ phase. Moreover, STAT5 protein expression, as well as NRP1 and PAK1 expression levels were downregulated, while BTG1 expression was upregulated when HLX was knocked out by siRNA. Collectively, the results suggested that downregulation of HLX may cause G₀/G₁ phase arrest and inhibit the proliferation of AML cells by activating the JAK/STAT signaling pathway.

A metabolic interplay coordinated by HLX regulates myeloid differentiation and AML through partly overlapping pathways

The H2.0-like homeobox transcription factor (HLX) regulates hematopoietic differentiation and is overexpressed in Acute Myeloid Leukemia (AML), but the mechanisms underlying these functions remain unclear. We demonstrate here that HLX overexpression leads to a myeloid differentiation block both in zebrafish and human hematopoietic stem and progenitor cells (HSPCs). We show that HLX overexpression leads to downregulation of genes encoding electron transport chain (ETC) components and upregulation of PPARδ gene expression in zebrafish and human HSPCs. HLX overexpression also results in AMPK activation. Pharmacological modulation of PPARδ signaling relieves the HLX-induced myeloid differentiation block and rescues HSPC loss upon HLX knockdown but it has no effect on AML cell lines. In contrast, AMPK inhibition results in reduced viability of AML cell lines, but minimally affects myeloid progenitors. This newly described role of HLX in regulating the metabolic state of hematopoietic cells may have important therapeutic implications.

HLX transcription factor regulates haematopoietic stem and progenitor cell (HSPC) differentiation and is overexpressed in acute myeloid leukemia. Here the authors show that HLX overexpression leads to myeloid differentiation block in zebrafish and human HSPCs by direct regulation of metabolic pathways.

DNMT3A and TET2 in the Pre-Leukemic Phase of Hematopoietic Disorders

In recent years, advances in next-generation sequencing (NGS) technology have provided the opportunity to detect putative genetic drivers of disease, particularly cancers, with very high sensitivity. This knowledge has substantially improved our understanding of tumor pathogenesis. In hematological malignancies such as acute myeloid leukemia and myelodysplastic syndromes, pioneering work combining multi-parameter flow cytometry and targeted resequencing in leukemia have clearly shown that different classes of mutations appear to be acquired in particular sequences along the hematopoietic differentiation hierarchy. Moreover, as these mutations can be found in “normal” cells recovered during remission and can be detected at relapse, there is strong evidence for the existence of “pre-leukemic” stem cells (pre-LSC). These cells, while phenotypically normal by flow cytometry, morphology, and functional studies, are speculated to be molecularly poised to transform owing to a limited number of predisposing mutations. Identifying these “pre-leukemic” mutations and how they propagate a pre-malignant state has important implications for understanding the etiology of these disorders and for the development of novel therapeutics. NGS studies have found a substantial enrichment for mutations in epigenetic/chromatin remodeling regulators in pre-LSC, and elegant genetic models have confirmed that these mutations can predispose to a variety of hematological malignancies. In this review, we will discuss the current understanding of pre-leukemic biology in myeloid malignancies, and how mutations in two key epigenetic regulators, DNMT3A and TET2, may contribute to disease pathogenesis.

H2.0-like homeobox 1 acts as a tumor suppressor in hepatocellular carcinoma

H2.0-like homeobox 1 (HLX1) is a homeobox transcription factor gene expressed primarily in cytotrophoblast cell types in the early pregnancy human placenta and involved in the development of enteric nervous system. However, the biological function of HLX1 in hepatocellular carcinoma (HCC) remains unclear. In the present study, semiquantitative reverse transcription-polymerase chain reaction (RT-PCR), quantitative real-time RT-PCR, western blot, and immunohistochemical staining were used to examine the expression level of HLX1 in a total of 125 cases of HCC tissues and their matched adjacent nontumorous tissues (ANLTs), and its correlation with clinical features of HCC patients was analyzed. Our findings showed that the expression level of HLX1 was significantly reduced in HCCs compared to ANLTs. Besides, it was also remarkably downregulated in HCC cell lines compared to normal liver cell line. We further found that the HLX1 level was significantly associated with the tumor size (p = 0.016), tumor number (p = 0.004), vascular invasion (p = 0.031), Edmondson-Steiner grade (p = 0.041), tumor-node-metastasis (TNM) stage (p < 0.001), and Barcelona clinic liver cancer (BCLC) stage (p = 0.008). Moreover, HLX1 was an independent risk factor for overall survival (OS, p = 0.020) and disease-free survival (DFS, p = 0.024) of HCC patients. In vitro experiments showed that overexpression of HLX1 markedly suppressed the invasion, migration, proliferation, and colony formation of HCC cells; in contrast, downregulation of HLX1 significantly promoted the invasion, migration, proliferation, and colony formation of HCC cells. In vivo study indicated that overexpression of HLX1 significantly inhibited the tumorigenic capacity of HCC cells in nude mice. Based on these findings, we suggest that HLX1 acts as a tumor suppressor in HCC.