Sanguinarine suppresses IgE induced inflammatory responses through inhibition of type II PtdIns 4-kinase(s)

• Sanguinarine inhibits type II Phosphatidylinositol (PtdIns) 4-kinase α and β isoforms.
• Sanguinarine does not inhibit phosphatidylinositol 3-kinases.
• Sanguinarine competes with phosphatidylinositol in binding with type II PtdIns 4-kinases.
• Sanguinarine inhibits β-hexosaminidase release in RBL 2H3 cells.

The effects of sanguinarine on IgE mediated early signaling mechanisms leading to inflammatory mediators release were investigated. Pretreatment of RBL 2H3 cells with sanguinarine inhibited IgE induced activation of type II PtdIns 4-kinase activity. Concomitant with type II PtdIns 4-kinase inhibition, sanguinarine also inhibited IgE induced degranulation and β hexosaminidase release in RBL 2H3 cells. In vitro assays showed sanguinarine inhibited type II PtdIns 4-kinase activity in a dose dependent fashion with no effect on PtdIns 3-kinase activity. Fluorescence spectroscopic studies suggested that sanguinarine binds to type II PtdIns 4-kinases α and β isoforms with a Kd of 2.4 and 1.8 μM, respectively. Kinetic studies showed that sanguinarine competes with PtdIns binding site of type II PtdIns 4-kinase β. These results suggest that the anti-inflammatory effects of sanguinarine on PtdIns 3-kinase signaling pathway are more likely an indirect effect and emphasize the importance of the cross talk between type II PtdIns 4-kinases and PtdIns 3-kinases.