During kidney organogenesis, tubular epithelial cells proliferate until a functional tubule is formed as sensed by cilia bending in response to fluid flow. This flow-induced ciliary mechanosensation opens the calcium (Ca 2؉ ) channel polycystin-2 (PC2), resulting in a calcium flux-mediated cell cycle arrest. Loss or mutation of either PC2 or its regulatory protein polycystin-1 (PC1) results in autosomal dominant polycystic kidney disease (ADPKD), characterized by cyst formation and growth and often leading to renal failure and death. Here we show that triptolide, the active diterpene in the traditional Chinese medicine Lei Gong Teng, induces Ca 2؉ release by a PC2-dependent mechanism. Furthermore, in a murine model of ADPKD, triptolide arrests cellular proliferation and attenuates overall cyst formation by restoring Ca 2؉ signaling in these cells. We anticipate that small molecule induction of PC2-dependent calcium release is likely to be a valid therapeutic strategy for ADPKD.ADPKD ͉ calcium ͉ natural product ͉ polycystin ͉ renal cyst

The antiangiogenic agent fumagillin (Fg) and its analog TNP-470 bind to intracellular metalloprotease methionine aminopeptidase-2 (MetAP-2) and inhibit endothelial cell growth in a p53-dependent manner. To confirm the role of MetAP-2 in endothelial cell proliferation and to validate it as a physiological target for the Fg class of antiangiogenic agents, we have generated a conditional MetAP-2 knockout mouse. Ubiquitous deletion of the MetAP-2 gene (MAP2) resulted in an early gastrulation defect, which is bypassed in double MetAP-2͞p53 knockout embryos. Targeted deletion of MAP2 specifically in the hemangioblast lineage resulted in abnormal vascular development, and these embryos die at the midsomite stage. In addition, knockdown of MetAP-2 using small interfering RNA or homologous recombination specifically suppresses the proliferation of cultured endothelial cells. Together, these results demonstrate an essential role for MetAP-2 in angiogenesis and indicate that MetAP-2 is responsible for the endothelial cell growth arrest induced by Fg and its derivatives.angiogenesis ͉ TNP-470 T he methionine aminopeptidase (MetAPs) family of cytosolic metalloproteases are responsible for the cleavage of the initial methionine from the N termini of nascent proteins (1, 2). Eukaryotes express two forms of MetAPs, types 1 and 2, which possess similar in vitro substrate specificities. Removal of the N-terminal methionine by MetAP activity is important for subsequent Nterminal modifications, such as myristoylation (3) and acetylation (4). In addition, MetAP activity may affect protein stability according to the N-end rule proposed by Varshavsky and coworkers (5). It has been shown that MetAP function is essential for growth and survival of prokaryotes (which express only MetAP-1) and of the budding yeast Saccharomyces cerevisiae (6, 7). However, the physiological roles of MetAPs have not yet been identified in vertebrates.MetAP-2 is specifically inhibited by TNP-470, a synthetic derivative of the Aspergillus fumigatus natural product fumagillin (Fg; see refs. 8 and 9). TNP-470 selectively inhibits endothelial cell growth in vitro with picomolar efficacy and has a potent antiangiogenic effect in vivo (10, 11). Because of the requirement of angiogenesis for solid tumor growth, MetAP-2 is currently being targeted with small-molecule inhibitors for anticancer and other angiogenesisrelated diseases therapy, even though the mode of action of TNP-470 is not entirely clear (12-16). Several lines of evidence suggest that MetAP-2 is important for the antiangiogenic effect of TNP-470. First, we have recently demonstrated that an A362T variant of human MetAP-2 confers resistance to the cytostatic effect of a Fg analog in MAP1-null yeast (17). In addition, it has been shown that the ability of various Fg analogues to inhibit endothelial cell growth correlates with their MetAP-2 enzymatic inhibitory activity in vitro (9). However, a recent report using RNA interference (RNAi)-mediated MetAP-2 down-regulation contradicts our results and thus r...

Natural products have long proven useful in drug development. The cytotoxic activity of many natural products have been exploited to develop novel anti‐tumor chemotherapeutics. However, several cytotoxic compounds also have non‐lethal biological activities well below their cytotoxic concentrations. Here, we discuss the cytotoxic diterpene, triptolide, isolated from the Chinese Medicinal Herb, Lei Gong Teng, which has been tested in antitumor Phase I clinical trials. At concentrations below its cytotoxic concentrations, we have found that triptolide induces a calcium‐mediated cytostatic signal via the calcium channel polycystin 2. Moreover, we show that triptolide can reduce cyst formation in a murine model of Autosomal Dominant Polycystic Kidney Disease (ADPKD) indicating that this natural product has multiple clinical potential depending on the concentration administered.