The mammalian proapoptotic protein Bax confers a lethal phenotype when expressed in yeast. By exploiting this phenotype, we have identified a novel human Bax inhibitor, BI-1. BI-1 is an evolutionarily conserved integral membrane protein containing multiple membrane-spanning segments and is predominantly localized to intracellular membranes, similar to Bcl-2 family proteins. Moreover, BI-1 can interact with Bcl-2 and Bcl-XL but Bax or Bak, as demonstrated by in vivo cross-linking and coimmunoprecipitation studies. When overexpressed in mammalian cells, BI-1 suppressed apoptosis included by Bax, etoposide, staurosporine, and growth factor deprivation, but not by Fas (CD95). Conversely, BI-1 antisense induced apoptosis. BI-1 thus represents a new type of regulator of cell death pathways controlled by Bcl-2 and Bax.

The proapoptotic mammalian protein Bax associates with mitochondrial membranes and confers a lethal phenotype when expressed in yeast. By generating Bax-resistant mutant yeast and using classical complementation cloning methods, subunits of the mitochondrial F0F1-ATPase proton pump were determined to be critical for Bax-mediated killing in S. cerevisiae. A pharmacological inhibitor of the proton pump, oligomycin, also partially abrogated the cytotoxic actions of Bax in yeast. In mammalian cells, oligomycin also inhibited Bax-induced apoptosis and activation of cell death proteases. The findings imply that an intact F0F1-ATPase in the inner membrane of mitochondria is necessary for optimal function of Bax in both yeast and mammalian cells.

The p53 tumor suppressor is a key mediator of the cellular response to stress. Phosphorylation induced by multiple stress-activated kinases has been proposed to be essential for p53 stabilization, interaction with transcriptional co-activators, and activation of p53 target genes. However, genetic studies suggest that stress-activated phosphorylation may not be essential for p53 activation. We therefore investigated the role of p53 phosphorylation on six key serine residues (Ser 6 , Ser 15 , Ser 20 , Ser 37 , Ser 46 , and Ser 392 ) for p53 activation using nutlin-3, a recently developed small molecule MDM2 antagonist. We show here that nutlin does not induce the phosphorylation of p53. Comparison of the activity of unphosphorylated and phosphorylated p53 induced by the genotoxic drugs doxorubicin and etoposide in HCT116 and RKO cells revealed no difference in their sequence-specific DNA binding and ability to transactivate p53 target genes and to induce p53-dependent apoptosis. We conclude that p53 phosphorylation on six major serine sites is not required for activation of p53 target genes or biological responses in vivo.

Despite the prevalence of the N-H aziridine motif in bioactive natural products and the clear advantages of this unprotected parent structure over N-protected derivatives as a synthetic building block, no practical methods have emerged for direct synthesis of this compound class from unfunctionalized olefins. Here, we present a mild, versatile method for the direct stereospecific conversion of structurally diverse mono-, di-, tri- and tetra-substituted olefins to N-H aziridines using O-(2,4-dinitrophenyl)hydroxylamine (DPH) via homogeneous rhodium catalysis with no external oxidants. This method is operationally simple (i.e., one-pot), scalable and fast at ambient temperature, furnishing N-H aziridines in good-to-excellent yields. Likewise, N-alkyl aziridines are prepared from N-alkylated DPH derivatives. Quantum-mechanical calculations suggest a plausible Rh-nitrene pathway.

The goal of targeted therapy is to match a selective drug with a genetic lesion that predicts for drug sensitivity. In a diverse panel of cancer cell lines, we found that the cells most sensitive to focal adhesion kinase (FAK) inhibition are deficient in the expression of the NF2 tumor suppressor gene product, Merlin. Merlin expression is often lost in malignant pleural mesothelioma (MPM), an asbestos-induced aggressive cancer with limited treatment options. Our data demonstrate that low Merlin expression predicts for increased sensitivity of MPM cells to a FAK inhibitor, VS-4718, in vitro and in tumor xenograft models. Disruption of MPM cell-cell or cell-extracellular matrix (ECM) contacts with blocking antibodies suggests that weak cell-cell adhesions in Merlin-negative MPM cells lead to their greater dependence on cell-ECM-induced FAK signaling. This provides one explanation of why Merlin-negative cells are vulnerable to FAK inhibitor treatment. Furthermore, we validated ALDH as a marker of cancer stem cells (CSCs) in MPM, a cell population thought to mediate tumor relapse after chemotherapy. Whereas pemetrexed and cisplatin, standard-of-care agents for MPM, enrich for CSCs, FAK inhibitor treatment preferentially eliminates these cells. These preclinical results provide the rationale for a clinical trial in MPM patients using a FAK inhibitor as a single agent after first-line chemotherapy. With this design, the FAK inhibitor could potentially induce a more durable clinical response due to reduction of CSCs along with a strong antitumor effect. Furthermore, our data suggest that patients with Merlin-negative tumors may especially benefit from FAK inhibitor treatment.

Two major pathways for induction of apoptosis have been identified-intrinsic and extrinsic. The extrinsic pathway is represented by tumor necrosis factor family receptors, which utilize protein interaction modules known as death domains and death effector domains (DEDs) to assemble receptor signaling complexes that recruit and activate certain caspase-family cell death proteases, namely procaspases-8 and -10. The intrinsic pathway for apoptosis involves the participation of mitochondria, which release caspase-activating proteins. Bcl-2 family proteins govern this mitochondria-dependent apoptosis pathway, with proteins such as Bax functioning as inducers and proteins such as Bcl-2 and Bcl-X L serving as suppressors of cell death. An apoptosis regulator, BAR, was identified by using a yeast-based screen for inhibitors of Bax-induced cell death. The BAR protein contains a SAM domain, which is required for its interactions with Bcl-2 and Bcl-X L and for suppression of Bax-induced cell death in both mammalian cells and yeast. In addition, BAR contains a DED-like domain responsible for its interaction with DED-containing procaspases and suppression of Fas-induced apoptosis. Furthermore, BAR can bridge procaspase-8 and Bcl-2 into a protein complex. The BAR protein is anchored in intracellular membranes where Bcl-2 resides. BAR therefore may represent a scaffold protein capable of bridging two major apoptosis pathways.

High-throughput synthesis of well-defined polymer nano-objects has long been an attractive yet challenging topic in the area of polymer chemistry and material science. Herein, we report an enzyme-assisted photoinitiated polymerizationinduced self-assembly (photo-PISA) approach to prepare well-defined AB diblock or ABC triblock copolymer nano-objects at room temperature in open vessels and multiwell plates. Kinetic studies indicated that the presence of glucose oxidase (GOx) endowed the polymerizations with excellent oxygen tolerance. Good control was maintained during the enzyme-assisted photo-PISA process. This method facilitates high-throughput PISA, allowing for the construction of a detailed phase diagram in a rather short time. We also demonstrate the potential bio-related application of this method by the successful encapsulation of horseradish peroxidase (HRP) and bovine serum albumin (BSA) into self-assembled polymer vesicles without compromising protein activities. This robust oxygen-tolerant PISA approach leads to unprecedented access to well-defined polymer nanoobjects for nonexperts.

Photoinitiated polymerization-induced self-assembly (photo-PISA) is utilized to investigate the sole effect of reaction temperature on PISA.