Tightly regulated Ca2+ homeostasis is a prerequisite for proper cardiac function. To dissect the regulatory network of cardiac Ca2+ handling, we performed a chemical suppressor screen on zebrafish tremblor embryos, which suffer from Ca2+ extrusion defects. Efsevin was identified based on its potent activity to restore coordinated contractions in tremblor. We show that efsevin binds to VDAC2, potentiates mitochondrial Ca2+ uptake and accelerates the transfer of Ca2+ from intracellular stores into mitochondria. In cardiomyocytes, efsevin restricts the temporal and spatial boundaries of Ca2+ sparks and thereby inhibits Ca2+ overload-induced erratic Ca2+ waves and irregular contractions. We further show that overexpression of VDAC2 recapitulates the suppressive effect of efsevin on tremblor embryos whereas VDAC2 deficiency attenuates efsevin's rescue effect and that VDAC2 functions synergistically with MCU to suppress cardiac fibrillation in tremblor. Together, these findings demonstrate a critical modulatory role for VDAC2-dependent mitochondrial Ca2+ uptake in the regulation of cardiac rhythmicity.DOI: http://dx.doi.org/10.7554/eLife.04801.001

Protein geranylgeranylation is critical for the function of a number of proteins such as RhoA, Rac, and Rab. Protein geranylgeranyltransferase I (GGTase-I) and Rab geranylgeranyltransferase (RabGGTase) catalyze these modifications. In this work, we first describe the identification and characterization of small molecule inhibitors of GGTase-I (GGTI) with two novel scaffolds from a library consisting of allenoate-derived compounds. These compounds exhibit specific inhibition of GGTase-I and act by competing with a substrate protein. Derivatization of a carboxylic acid emanating from the core ring of one of the GGTI compounds dramatically improves their cellular activity. The improved GGTI compounds inhibit proliferation of a variety of human cancer cell lines and cause G 1 cell cycle arrest and induction of p21 CIP1/WAF1 . We also report the identification of novel small molecule inhibitors of RabGGTase. These compounds were identified first by screening our GGTI compounds for those that also exhibited RabGGTase inhibition. This led to the discovery of a common structural feature for RabGGTase inhibitors: the presence of a characteristic six-atom aliphatic tail attached to the penta-substituted pyrrolidine core. Further screening led to the identification of compounds with preferential inhibition of RabGGTase. These compounds inhibit RabGGTase activity by competing with the substrate protein. These novel compounds may provide valuable reagents to study protein geranylgeranylation.

Small molecules that inhibit the geranylgeranylation of K-Ras4B and RhoA by protein geranylgeranyltransferase type I (GGTase-I) were identified from chemical genetic screens of heterocycles synthesized through phosphine catalysis of allenes. To further improve the efficacy of the GGTase-I inhibitors (GGTIs), 4288 related compounds bearing core dihydropyrrole/pyrrolidine and tetrahydropyrdine/piperidine scaffolds were synthesized on SynPhase Lanterns in a split-pool manner through phosphine-catalyzed [3+2] and [4+2] annulations of resin-bound allenoates. Testing of the 4288 analogs resulted in several GGTIs exhibiting submicromolar IC 50 values. Because proteins such as Ras and Rho GTPases are implicated in oncogenesis and metastasis, these GGTIs might ultimately lead to the development of novel antitumor therapeutics.Although library approaches to the discovery of small-molecule enzyme inhibitors or receptor ligands are well established, 1 many reactions continue to pose challenges when applied to solid phase synthesis for the generation of compound libraries. From our development of phosphine catalysis of allenoates, 2 we envisioned that these reactions might be adaptable to solid phase synthesis for the generation of heterocycle libraries using resin-bound allenoates. Before embarking on the potentially time-consuming development of solid phase processes, however, we decided to screen our model compounds synthesized through solution-phase reactions. If we could identify a biologically important molecule from the preliminary screen, it would then be worthwhile pursuing a library generated through solid phase split-pool synthesis. Herein, we report the first example of phosphine catalysis of polymer-bound allenoates and a combinatorial library approach to the development of potent inhibitors of protein geranylgeranyltransferase type I (GGTase-I).Protein prenylation, a posttranslational modification of nascent proteins by either the farnesyl or geranylgeranyl isoprenoid at the C-terminus cysteine residue, is a key event in the regulation of many protein functions. 3 Of particular interest is the farnesylation of the oncogenic forms E-mail: ohyun@chem.ucla With this premise in mind, we screened a collection of 138 heterocycles 9 for their ability to inhibit the activity of human GGTase-I to geranylgeranylate K-Ras4B or RhoA. Purified GGTase-I was incubated with its substrate protein K-Ras4B or RhoA, [ 3 H]GGPP, and the 138 compounds. After 30 min, the degree of incorporation of tritiated geranylgeranyl groups was measured using a scintillation counter. We identified a number of compounds as GGTIs ( Figure 1).This discovery of promising lead GGTI compounds and their moderate activity warranted the development of efficient and rapid syntheses and evaluations of analogous structures in the search for better inhibitors; we envisioned a short, modular synthetic route (Scheme 1), using SynPhase™ lanterns as the solid support. 10 Validation of the synthetic route on the polymer support commenced with formation o...

Arterial and venous endothelial cells exhibit distinct molecular characteristics at early developmental stages. These lineage-specific molecular programs are instructive to the development of distinct vascular architectures and physiological conditions of arteries and veins, but their roles in angiogenesis remain unexplored. Here, we show that the caudal vein plexus in zebrafish forms by endothelial cell sprouting, migration and anastomosis, providing a venous-specific angiogenesis model. Using this model, we have identified a novel compound, aplexone, which effectively suppresses venous, but not arterial, angiogenesis. Multiple lines of evidence indicate that aplexone differentially regulates arteriovenous angiogenesis by targeting the HMG-CoA reductase (HMGCR) pathway. Treatment with aplexone affects the transcription of enzymes in the HMGCR pathway and reduces cellular cholesterol levels. Injecting mevalonate, a metabolic product of HMGCR, reverses the inhibitory effect of aplexone on venous angiogenesis. In addition, aplexone treatment inhibits protein prenylation and blocking the activity of geranylgeranyl transferase induces a venous angiogenesis phenotype resembling that observed in aplexone-treated embryos. Furthermore, endothelial cells of venous origin have higher levels of proteins requiring geranylgeranylation than arterial endothelial cells and inhibiting the activity of Rac or Rho kinase effectively reduces the migration of venous, but not arterial, endothelial cells. Taken together, our findings indicate that angiogenesis is differentially regulated by the HMGCR pathway via an arteriovenous-dependent requirement for protein prenylation in zebrafish and human endothelial cells.

Protein geranylgeranyltransferase-I (GGTase-I) catalyzes protein geranylgeranylation, which is critical for the function of proteins such as Rho, Rac, and Ral. We previously identified several small-molecule inhibitors of GGTase