eIF4E1 Regulates Arabidopsis Embryo Development and Root Growth by Interacting With RopGEF7.

Eukaryotic translation initiation factor 4E1 (eIF4E1) is required for the initiation of protein synthesis. The biological function of eIF4E1 in plant-potyvirus interactions has been extensively studied. However, the role of eIF4E1 in Arabidopsis development remains unclear. In this study, we show that eIF4E1 is highly expressed in the embryo and root apical meristem. In addition, eIF4E1 expression is induced by auxin. eIF4E1 mutants show embryonic cell division defects and short primary roots, a result of reduced cell divisions. Furthermore, our results show that mutation in eIF4E1 severely reduces the accumulation of PIN-FORMED (PIN) proteins and decreases auxin-responsive gene expression at the root tip. Yeast two-hybrid assays identified that eIF4E1 interacts with an RAC/ROP GTPase activator, RopGEF7, which has been previously reported to be involved in the maintenance of the root apical meristem. The interaction between eIF4E1 and RopGEF7 is confirmed by protein pull-down and bimolecular fluorescent complementation assays in plant cells. Taken together, our results demonstrated that eIF4E1 is important for auxin-regulated embryo development and root growth. The eIF4E1-RopGEF7 interaction suggests that eIF4E1 may act through ROP signaling to regulate auxin transport, thus regulating auxin-dependent patterning.

p38α subtype is a potential target to inhibit eNOS activity and NO production in human endothelial cells.

Human endothelial nitric oxide synthase (eNOS) activity is important for maintaining blood pressure homeostasis and vascular integrity through nitric oxide (NO).The in vitro study aimed at investigating a role of p38α signaling in modulating NO production in human umbilical vein endothelial cell-12 (HUVEC-12). Consistent with the stimulation of lipopolysaccharide (LPS) or tumor necrosis factor (TNF)-α, the over-expression of p38α markedly down-regulated the eNOS promoter activity in HUVEC-12, which could be reversed by its negative mutant p38α (AF) or p38-specific inhibitor SB203580. Compared to the stimulation of LPS or TNF-α, p38α-targeting siRNA decreased the expressions of phosphorylated and non-phosphorylated p38α, and increased the promoter activity, an eNOS mRNA level and a phosphorylated eNOS protein expression with the enhancement of NO, which could be abrogated by the scrambled siRNA. The in situ eNOS protein expression in the cells treated by p38α-targeting siRNA was also higher than that of the control, following the corresponding attenuation of a p38 level, and mainly localized in the inner membrane and cytoplasm. These results indicate that the p38α subtype may be a potential target to down-regulate the eNOS activity and NO production in human endothelial cells.