Widespread over-expression of the non-clustered homeobox gene HLX in acute myeloid leukemia

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.