Analysis of the Regulatory Mechanism and Function of a Novel Class of Phospholipase C, PLCε

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1, We constructed phospholipase C_ε(PLC_ε) knockout mice and showed that the hearts of these mice develop ventricular dilation, which is caused by a volume overload resulting from marked regurgitation and mild stenosis of the semilunar (aortic and pulmonic) valves. We analysed the mechanism of the congenital semilunar valvulogenesis defect causing these phenotypes and concluded that the abnormal thickening and morphology of the semilunar valve leaflets in PLC_ε knockout mice were caused by aberrant cellular proliferation in valve remodeling at the late stages of semilunar valvulogenesis. By analogy with the phenotypes of mice carrying an attenuated epidermal growth factor (EGF) receptor or deficient in heparin-binding EGF, we speculated a crucial role of PLC_ε, as a Ras effector downstream of the EGF receptor, in inhibition of valvular cell proliferation. In fact, we observed increased phosphorylation of Smad1/5/8, which induce valvular cell proliferation downstream of the BMP receptor, in PLC_ε knockout mice.2, By applying the two stage skin chemical carcinogenesis protocol using DMBA as an initiator and a phorbor ester TPA as a promoter to PLC_ε knockout mice, we showed that PLC_ε plays a crucial role in ras oncogene-induced development of benign tumors as well as in their malignant progression. We further analysed the mechanism of action of PLC_ε. PLC_ε knockout mice showed marked reduction in proliferation of basal layer cells and epidermal hyperplasia induced by TPA, suggesting a crucial role of PLC_ε in downstream signaling from TPA.3, We disrupted the PLC_ε gene in a model organism Caenorhabditis elegans and observed a sterile phenotype, caused by abnormal contraction of sphincter muscles of the spermatheca.4, By using BaF3 cells expressing a PDGF receptor mutant lacking the PLC_γ-binding sites, we showed the importance of PH and RA domains by establishing an assay system for Ca^<2+> increase induced by PDGF-dependent PLC_ε activation.