Epithelial cell adhesion molecule (EpCAM) is a cell-surface protein highly expressed in embryonic tissues and in malignant carcinomas. We report that EpCAM acts as a potent inhibitor of novel protein kinase C (nPKC) in both embryos and cancer cells. We observed dramatic effects of loss of EpCAM on amphibian embryonic tissues, which include sequentially strong overstimulation of PKC activity and of the Erk pathway, leading to exacerbated myosin contractility, loss of cadherin-mediated adhesion, tissue dissociation, and, ultimately, cell death. We show that PKC inhibition is caused by a short segment of the EpCAM cytoplasmic tail. This motif resembles the pseudosubstrate inhibitory domains of PKCs and binds nPKCs with high affinity. A bioinformatics search reveals the existence of similar motifs in other plasma membrane proteins, most of which are cell-cell adhesion molecules. Thus, direct inhibition of PKC by EpCAM represents a general mode of regulation of signal transduction by cell-surface proteins.

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Total antioxidant capacities, 2,2-diphenyl-1-picrylhydrazyl (DPPH.), hydroxyl (HO.), scavenging activities, and total phenolic values were determined in extracts of Cucurbita pepo L. female and male flowers. Powdered C. pepo L. samples were extracted in aqueous ethyl acetate (EA: W1, 17:3), ethanol (E), and water (W) by agitating in magnetic stirrer for 80 degrees C, 15 min and also by in aqueous ethyl acetate (EA: W2, 17:3) at 25 degrees C, 15 min. DPPH., HO. scavenging capacities and total phenolic values of C. pepo L. female and male were higher in EA:W2 than in other extracts. In addition, all determined antioxidant capacities of female were significantly higher than male.