Novel PKC signaling is required for LPS-induced soluble Flt-1 expression in macrophages

Ming-Cheng Lee^*, Shu-Chen Wei, Jyy-Jih Tsai-Wu, C. H. Herbert Wu^* and Po-Nien Tsao^,1

Departments of Pediatrics,
Internal Medicine, and
Medical Research, National Taiwan University Hospital, and
^* Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan

¹ Correspondence: Department of Pediatrics, National Taiwan University Hospital, Taipei 100, Taiwan. E-mail: tsaopn{at}ntu.edu.tw

In vitro activation of macrophages by LPS induces rapid releaseof vascular endothelial growth factor (VEGF) and soluble fms-liketyrosine kinase-1 receptor (sFlt-1), which are thought to bethe effectors to cause sepsis. However, the signal pathway thatcontrols the VEGF and sFlt-1 expressions in LPS-activated macrophagesremains unclear. In this study, we demonstrated that phosphorylationof protein kinase C (PKC) ${delta}$ played a key role in the VEGF andsFlt-1 signaling pathway of LPS-activated macrophages. PKC isa family of serine-threonine kinases, which are classified intothree major groups based on homology and cofactor requirements:conventional PKCs, novel PKCs, and atypical PKCs. In the murineRAW264.7 cells, as well as in primary human monocytes/macrophages,pretreatment with a general PKC inhibitor GF109203X or witha novel PKC ${delta}$ inhibitor rottlerin or overexpression of a kinase-inactiveform of PKC ${delta}$ (K376R) eliminated LPS-induced sFlt-1 expressionand augmented LPS-induced VEGF expression at the protein andthe transcription levels. In contrast, Gö6976, an inhibitorfor the conventional PKCs, or myristoylated PKC ${zeta}$ pseudosubstratepeptide, an inhibitor for the atypical PKCs, failed to exertthe same effects. These data suggest that PKC ${delta}$ signaling is involvedin LPS-induced sFlt-1 expression and serves as a negative mediatorin LPS-induced VEGF expression in macrophages. A novel strategycontrolling the LPS-induced PKC pathways, especially the PKC ${delta}$ isoform, may be developed based on this study.

Key Words: sepsis • inflammation • vascular endothelial growth factor