1,25-Dihydroxyvitamin D3 induces monocytic differentiation of human myeloid leukemia cells by regulating C/EBPβ expression through MEF2C

Abstract

Myogenic enhancer factor2 (Mef2) consists of a family of transcription factors involved in morphogenesis of skeletal, cardiac and smooth muscle cells. Among the four isoforms (Mef2A, 2B, 2C, and 2D), Mef2C was also found to play important roles in hematopoiesis. At myeloid progenitor level, Mef2C expression favors monocytic differentiation. Previous studies from our laboratory demonstrated that ERK5 was activated in 1,25-dihydroxyvitamin D3 (1,25D)-induced monocytic differentiation in AML cells and ERK5 activation was accompanied by increased Mef2C phosphorylation. We therefore examined the role of Mef2C in 1,25D-induced monocytic differentiation in AML cell lines (HL60, U937 and THP1) and found that knockdown of Mef2C with small interfering RNA (siRNA) significantly decreases the expression of the monocytic marker, CD14, without affecting the expression of the general myeloid marker, CD11b. CCAAT/Enhancer-binding protein (C/EBP) β, which can bind to CD14 promoter and increase its transcription, has been shown to be the downstream effector of 1,25D-induced monocytic differentiation in AML cells. When Mef2C was knocked down, expression of C/EBPβ was reduced at both mRNA and protein levels. The protein expression levels of cell cycle regulators, p27Kip1 and cyclin D1, were not affected by Mef2C knockdown, nor the monopoiesis related transcription factor, ATF2 (Activating Transcription Factor 2). Thus, we conclude that 1,25D-induced monocytic differentiation, and CD14 expression in particular, is mediated through activation of ERK5-Mef2C-C/EBPβ signaling pathway, and that Mef2C does not seem to modulate cell cycle progression.

Exposure top,p′-DDE Induces Morphological Changes and Activation of the PKCα-p38-C/EBPβPathway in Human Promyelocytic HL-60 Cells

“…We evaluated the effect of p , p ′ - DDE on intracellular molecules that are involved in activation of C/EBP β , a transcription factor activated during myeloid differentiation [30–32]. Our results demonstrate that p , p ′ - DDE induced an increase in nuclear levels of C/EBP β , an effect that was dependent on p38 activation and is consistent with data previously reported [52].…”

“…CCAAT/enhancer binding protein β (C/EBP β ) is involved in gene expression and regulates differentiation in haematopoietic cells [29]. C/EBP β expression is induced in myeloid progenitors when emergency granulopoiesis is required and during monocyte differentiation [30–32]. Its function is regulated by posttranslational modifications including phosphorylation [33].…”

The MEK5/ERK5 signalling pathway in cancer: a promising novel therapeutic target

“…However, further studies have generated controversial and unclear results. Recently, ERK5 was shown to be involved in the monocytic differentiation of human AML cells upon cell treatment with 1,25D vitamin D3 [68]. In agreement with this study, others demonstrated that, in human AML cells, both established cultures and AML blasts ex vivo, ERK5 directly promoted the optimal monocytic differentiation of AML cells when exposed to differentiating agents [65].…”

The role of VDR and BIM in potentiation of cytarabine-induced cell death in human AML blasts

“…Increased mRNA levels of both CD11b and CD14 markers in AML blasts, though modest, suggested monocytic type of differentiation (Figure 3A). This was supported by the increased expression of the C/EBPβ transcription factor (TF), linked to signaling of monocytic differentiation [28] in AML blasts, but not in non-differentiating normal bone marrow cells treated in the same way (Figure 3B). Similarly, the expression of the vitamin D-regulated TF VDR was found to be enhanced at mRNA and protein levels by the AraC-D2/CA combination (Figure 3C and 3D).…”