Extracts of Koelreuteria henryi Dummer induce apoptosis and autophagy by inhibiting dihydrodiol dehydrogenase, thus enhancing anticancer effects.

Dihydrodiol dehydrogenase (DDH) is frequently detected in cancer cells, and its overexpression correlates with drug resistance, the downregulation of DNA repair mechanisms, increased frequency of tumor recurrence, cancer cell metastasis and poor prognosis. The silencing of DDH expression using siRNA, on the other hand, reduces drug resistance and cancer cell mobility. These data suggest that DDH may be an oncogene-related protein. However, no specific DDH inhibitor has been identified to date. Thus, in this study, we used DDH as a target enzyme in a live-cell enzyme-linked immunosorbent assay to screen Chinese medicinal herb extracts (CMHEs) with the aim of identifying a DDH inhibitor. Using this method, we found 49 among 796 CMHEs that inhibited DDH expression. We selected three potential extracts, which had the highest activity against DDH, for further fractionation using high-performance liquid chromatography. The active ingredient was identified by immunoblot analysis. The function of the active ingredient was characterized by cell function analysis. Our results revealed that the CMHE-purified compounds targeted DDH, inducing autophagy and reducing DNA repair, which in turn enhanced the cytotoxic effects of the anticancer drugs and irradiation.

Differential phosphorylation of the docking protein Gab1 by c-Src and the hepatocyte growth factor receptor regulates different aspects of cell functions.

The docking protein Grb2-associated binder1 (Gab1) has a central role in the integration of the growth-factor signaling. In this study, we aimed to examine the significance of Src-mediated Gab1 phosphorylation in the hepatocyte growth factor (HGF) signaling. Using both mutagenesis and mass spectrometry approaches, Y242, Y259, Y317, Y373 and Y627 of Gab1 were identified to be phosphorylated by c-Src. It is interesting to note that the binding of the tyrosine phosphatase SHP2 to the Y627 antagonized the effect of c-Src on the phosphorylation of the other four tyrosine residues. Moreover, the tyrosine residues predominantly phosphorylated by c-Src were different from those predominantly phosphorylated by the HGF receptor. Gab1 overexpression potentiated both mitogenic and motogenic activities of HGF. However, a Gab1 mutant with substitutions of the Src phosphorylation sites (Y242, Y259, Y317 and Y373) failed to promote HGF-induced DNA synthesis, but retained its ability to facilitate HGF-induced chemotaxis. Taken together, our results not only suggest that the phosphorylation of Gab1 by c-Src is important for HGF-induced DNA synthesis, but also provide an example to illustrate how a docking protein (for example, Gab1) is differentially phosphorylated by c-Src and a receptor tyrosine kinase to emanate full spectrum of signals to the downstream.