Epsins are endocytic adaptors with putative functions in general aspects of clathrin-mediated endocytosis as well as in the internalization of specific membrane proteins. We have now tested the role of the ubiquitously expressed epsin genes, Epn1 and Epn2, by a genetic approach in mice. While either gene is dispensable for life, their combined inactivation results in embryonic lethality at E9.5-E10, i.e., at the beginning of organogenesis. Consistent with studies in Drosophila, where epsin endocytic function was linked to Notch activation, developmental defects observed in epsin 1/2 double knockout (DKO) embryos recapitulated those produced by a global impairment of Notch signaling. Accordingly, expression of Notch primary target genes was severely reduced in DKO embryos. However, housekeeping forms of clathrin-mediated endocytosis were not impaired in cells derived from these embryos. These findings support a role of epsin as a specialized endocytic adaptor, with a critical role in the activation of Notch signaling in mammals.cell signaling ͉ endocytosis ͉ gene targeting

Humans lack the enzymes needed to directly metabolise oxalate, and this potentially toxic compound is, therefore, managed using alternative pathways. As oxalate-degrading bacteria are present in the endogenous microbiota of the human intestine, although with significant individual differences, it is possible to hypothesise that the administration of selected oxalate-degrading probiotics could be an alternative and innovative approach to reducing the intestinal absorption of oxalate and the resulting urinary excretion.

Neuroblastoma is the most common type of cancer in infants. In children this tumor is particularly aggressive; despite various new therapeutic approaches, it is associated with poor prognosis. Given the importance of endosomallysosomal proteolysis in cellular metabolism, we hypothesized that inhibition of lysosomal protease would impact negatively on neuroblastoma cell survival. Treatment with E-64 or CA074Me (2 specific inhibitors of cathepsin B) or with pepstatin A (a specific inhibitor of cathepsin D) was cytotoxic for 2 neuroblastoma cell lines having different degrees of malignancy. Cell death was associated with condensation and fragmentation of chromatin and externalization of plasma membrane phosphatidylserine, 2 hallmarks of apoptosis. Concomitant inhibition of the caspase cascade protected neuroblastoma cells from cathepsin inhibitor-induced cytotoxicity. These data indicate that prolonged inhibition of the lysosomal proteolytic pathway is incompatible with cell survival, leading to apoptosis of neuroblastoma cells, and that the cathepsin-mediated and caspase-mediated proteolytic systems are connected and cooperate in the regulation of such an event. Since modern antitumor chemotherapy is aimed at restoring the normal rate of apoptosis in neoplastic tissues, the demonstration that endosomal-lysosomal cathepsins are involved in this process may constitute a basis for novel strategies that include cathepsin inhibitors in the therapeutic regimen. © 2002 Wiley-Liss, Inc. Key words: apoptosis; neuroblastoma; caspases; cathepsins; protease inhibitorsAltered regulation of cell survival and death, including apoptosis, is considered an important factor in tumor development and progression, as well as in the response to antineoplastic therapy. 1,2 The molecular pathways controlling apoptosis include a complex network of intracellular proteases that act in an orderly sequence on cellular substrates and lead to characteristic modifications of cell morphology with eventual DNA cleavage and apoptotic body formation. Several proteolytic systems have been shown to participate in the apoptotic process, depending on the cell type and stimuli adopted. With few exceptions, the caspase system seems to be the most universally involved one. 3,4 Recently, proteases resident within the endosomal-lysosomal compartment (cathepsins) have also been associated with apoptosis. 5-9 These studies demonstrated the need for a cathepsin-mediated proteolytic event in the apoptotic pathway triggered by cytokines or antiblastic drugs. In addition, the active participation of the autophagic proteolytic pathway, particularly of lysosomal cathepsins B and D (CB, CD), has been envisaged in rat pheochromocytoma PC12 cell death after nutrient and serum factor deprivation. In this model of caspasedependent apoptosis, CD acted as a death factor, whereas CB acted as a pro-survival factor. 10 We followed an opposite approach, assuming that the endosomal-lysosomal proteolytic pathway serves crucial functions for cell viability. Indeed, experiments usi...

The expression of different protein kinase C (PKC) isoenzymes has been shown to vary with proliferation rates, differentiation or apoptosis in normal colon crypts. In addition, the activity of some PKC isoenzymes appears to be reduced in colorectal cancer. The aim of the present work was to determine whether modulation of PKC expression would affect the susceptibility of a p53-defective colon carcinoma cell line to different apoptotic treatments. HT-29 cells exhibited sensitivity to paclitaxel (Taxol) and tumor necrosis factor ␣ (TNF␣) in a dose-and time-dependent manner but were relatively resistant to etoposide. Inhibition of PKC activity augmented the susceptibility of HT-29 cells to apoptosis, and phorbol ester induction of PKC reduced such susceptibility. Key words: protein kinase C; TNF␣; paclitaxel; apoptosis; colon carcinomaColorectal cancer is one of the most common solid tumors world-wide. Due to its high metastatic potential and the frequent onset of resistance to chemotherapy, it is one of the four major causes of death by neoplasia in westernized countries. Loss of function of p53 occurs in more than 75% of human colorectal cancers. Since p53 regulates a complex array of cellular responses to DNA damage, including cell cycle arrest and apoptosis, its loss of function is also expected to affect the sensitivity of tumor cells to DNA-damaging antiblastic drugs. 1,2The expression of different protein kinase C (PKC) isoenzymes varies with proliferation rates, differentiation or apoptosis in normal colon crypts, [3][4][5][6] and the activity of some PKC isoenzymes is reduced in colorectal cancer. [7][8][9] Whether, in addition to loss of function of p53, altered functioning of PKCs contributes to the low sensitivity of colon carcinomas to apoptosis-based chemotherapy remains to be established. In the present work we addressed this issue by examining the effect of various apoptotic treatments on HT-29 colon cancer cells that lack functional p53 10 and either do or do not express abnormal levels of the isoform ␤1 of PKC. We found that paclitaxel (Taxol) and TNF␣, but not etoposide, efficiently induced apoptosis of HT-29 cells in a dose-and timedependent manner.The involvement of PKC in the apoptotic pathways triggered by paclitaxel or TNF␣ was assessed by using a myristoylated pseudosubstrate as inhibitor at doses not affecting cell viability. In HT-29 cells, inhibition of PKC (␣ and ␤ isoforms) activity augmented by twofold the cytotoxicity of both drugs. Induction of PKC by the phorbol ester phorbol myristate acetate (PMA) decreased the susceptibility of HT-29 cells to both TNF␣ and paclitaxel treatments. Resistance to apoptotic treatments was consistently observed in transfected HT-29 cells hyper-expressing PKC␤1. The present data implicate PKC (␣ and ␤) as a component of the mechanism responsible for the resistance of colon carcinoma cells to apoptotic drugs. MATERIAL AND METHODS Cells and chemicalsThe HT-29 human colon cancer cell line was obtained from the American Type Culture Collection (ATCC, Rock...