Department of Pathology and Laboratory Medicine, Rutgers Biomedical and Health Sciences, Newark, New Jersey.
J Cell Physiol. 2014 Jul;229(7):856-67. doi: 10.1002/jcp.24513.
Mitogen-activated protein kinases (MAPKs) are important transducers of external signals for cell growth, survival, and other cellular responses including cell differentiation. Several MAPK cascades are known with the MEK1/2-ERK1/2, JNK, and p38MAPKs receiving most attention, but the role of MEK5-ERK5 in intracellular signaling deserves more scrutiny, as this pathway transmits signals that can complement ERK/2 signaling. We hypothesized that the ERK5 pathway plays a role in the control of monocytic differentiation, which is disturbed in myeloid leukemia. We therefore examined the cellular phenotype and key molecular events which occur when human myeloid leukemia cells, acute (AML) or chronic (CML), are forced to differentiate by vitamin D derivatives (VDDs). This study was performed using established cell lines HL60 and U937, and primary cultures of blasts from 10 patients with ML. We found that ERK5 and its direct downstream target transcription factor MEF2C are upregulated by 1,25D in parallel with monocytic differentiation. Further, inhibition of ERK5 activity by specific pharmacological agents BIX02189 and XMD8-92 alters the phenotype of these cells by reducing the abundance of the VDD-induced surface monocytic marker CD14, and concomitantly increasing surface expression of the general myeloid marker CD11b. Similar results were obtained when the expression of ERK5 was reduced by siRNA or short hairpin (sh) RNA. ERK5 inhibition resulted in an expected decrease in MEF2C activation. We also found that in AML cells the transcription factor C/EBPβ is positively regulated, while C/EBPα is negatively regulated by ERK5. These findings provide new understanding of dysregulated differentiation in human myeloid leukemia.
丝裂原活化蛋白激酶（MAPKs）是细胞生长、存活和其他细胞反应（包括细胞分化）的外部信号的重要转导因子。目前已知有几种 MAPK 级联反应，其中 MEK1/2-ERK1/2、JNK 和 p38MAPKs 受到了最多的关注，但 MEK5-ERK5 在细胞内信号转导中的作用值得更深入的研究，因为这条途径传递的信号可以补充 ERK/2 信号。我们假设 ERK5 途径在单核细胞分化的控制中发挥作用，而髓系白血病中这种分化受到了干扰。因此，我们研究了当人髓系白血病细胞（急性髓系白血病（AML）或慢性髓系白血病（CML））被维生素 D 衍生物（VDDs）强制分化时，细胞表型和关键分子事件的变化。这项研究使用了已建立的 HL60 和 U937 细胞系以及 10 例白血病患者的原始细胞培养物进行。我们发现，ERK5 及其直接下游靶转录因子 MEF2C 与单核细胞分化平行被 1,25D 上调。此外，通过特异性药理学药物 BIX02189 和 XMD8-92 抑制 ERK5 活性，通过降低 VDD 诱导的表面单核细胞标记物 CD14 的丰度，同时增加一般髓样标记物 CD11b 的表面表达，改变这些细胞的表型。当通过 siRNA 或短发夹（sh）RNA 降低 ERK5 的表达时，也得到了类似的结果。ERK5 抑制导致 MEF2C 激活的预期下降。我们还发现，在 AML 细胞中，转录因子 C/EBPβ 受到 ERK5 的正调控，而 C/EBPα 受到 ERK5 的负调控。这些发现为理解人类髓系白血病中失调分化提供了新的认识。
