PI3K and PTEN lipid phosphatase control the level of cellular phosphatidylinositol (3,4,5)-trisphosphate, an activator of AKT kinases that promotes cell growth and survival. Mutations activating AKT are commonly observed in human cancers. We report here that ENTPD5, an endoplasmic reticulum (ER) enzyme, is upregulated in cell lines and primary human tumor samples with active AKT. ENTPD5 hydrolyzes UDP to UMP to promote protein N-glycosylation and folding in ER. Knockdown of ENTPD5 in PTEN null cells causes ER stress and loss of growth factor receptors. ENTPD5, together with cytidine monophosphate kinase-1 and adenylate kinase-1, constitute an ATP hydrolysis cycle that converts ATP to AMP, resulting in a compensatory increase in aerobic glycolysis known as the Warburg effect. The growth of PTEN null cells is inhibited both in vitro and in mouse xenograft tumor models. ENTPD5 is therefore an integral part of the PI3K/PTEN regulatory loop and a potential target for anticancer therapy.

Intrinsic apoptotic stimuli initiate mammalian cells' apoptotic program by first activating the proteins that have only Bcl-2 homology domain 3 (BH3), such as Bcl-2 interacting mediator of cell death (Bim) and truncated BH3 interacting death domain agonist (tBid), which in turn trigger conformational changes in BCL2-associated X (Bax) and BCL2-antagonist/killer (Bak) proteins that enable oligomer formation on the mitochondria, causing cytochrome c and other apoptogenic proteins in the intermembrane space to leak out. Leaked cytochrome c then initiates apoptotic caspase activation through a well-defined biochemical pathway. However, how oligomerized Bax and Bak cause cytochrome c release from mitochondria remains unknown. We report here the establishment of cell lines in which Bim or tBid can be inducibly expressed to initiate apoptosis in a controlled, quantitative manner. We used these cell lines to examine apoptotic events after Bax and Bak oligomerization but before cytochrome c release. The mitochondrial metalloprotease OMA1 was activated in this system in a Bax-and Bak-dependent fashion. Activated OMA1 cleaved the dynamin-like GTPase, optical nerve atrophy 1, an event that is critical for remodeling of mitochondrial cristae. Knockdown or knockout of OMA1 in these cells attenuated cytochrome c release. Thus it is clear that oligomerized Bax and Bak trigger apoptosis by causing both the permeabilization of the mitochondrial outer membrane and activation OMA1.Smac | permeability | membrane potential | caspase

Receptor-interacting protein kinase 3, RIP3, and a pseudokinase mixed lineage kinase-domain like protein, MLKL, constitute the core components of the necroptosis pathway, which causes programmed necrotic death in mammalian cells. Latent RIP3 in the cytosol is activated by several upstream signals including the related kinase RIP1, which transduces signals from the tumor necrosis factor (TNF) family of cytokines. We report here that RIP3 activation following the induction of necroptosis requires the activity of an HSP90 and CDC37 cochaperone complex. This complex physically associates with RIP3. Chemical inhibitors of HSP90 efficiently block necroptosis by preventing RIP3 activation. Cells with knocked down CDC37 were unable to respond to necroptosis stimuli. Moreover, an HSP90 inhibitor that is currently under clinical development as a cancer therapy was able to prevent systemic inflammatory response syndrome in rats treated with TNF-α. HSP90 and CDC37 cochaperone complex-mediated protein folding is thus an important part of the RIP3 activation process during necroptosis.

In yeast, activation of ATG1/ATG13 kinase complex initiates autophagy. This mechanism of autophagy initiation is conserved, as unc-51-like kinase 1 (ULK1) and unc-51-like kinase 2 (ULK2) are two mammalian functional homologues of ATG1 and form similar complex with mammalian ATG13. Here, we report that both ULK1 and ULK2 are transcriptional targets of tumor suppressor p53. In response to DNA damage, ULK1 and ULK2 are upregulated by p53. The upregulation of ULK1 (ULK2)/ATG13 complex by p53 is necessary for the sustained autophagy activity induced by DNA damage. In this context, elevated autophagy contributes to subsequent cell death. These findings suggest that ULK1 and ULK2 may mediate part of tumor suppression activity in mammalian cells and contribute to the efficacy of genotoxic chemotherapeutic drugs.

BackgroundAuditory neuropathy spectrum disorder (ANSD) is a form of hearing loss in which auditory signal transmission from the inner ear to the auditory nerve and brain stem is distorted, giving rise to speech perception difficulties beyond that expected for the observed degree of hearing loss. For many cases of ANSD, the underlying molecular pathology and the site of lesion remain unclear. The X-linked form of the condition, AUNX1, has been mapped to Xq23-q27.3, although the causative gene has yet to be identified.MethodsWe performed whole-exome sequencing on DNA samples from the AUNX1 family and another small phenotypically similar but unrelated ANSD family.ResultsWe identified two missense mutations in AIFM1 in these families: c.1352G>A (p.R451Q) in the AUNX1 family and c.1030C>T (p.L344F) in the second ANSD family. Mutation screening in a large cohort of 3 additional unrelated families and 93 sporadic cases with ANSD identified 9 more missense mutations in AIFM1. Bioinformatics analysis and expression studies support this gene as being causative of ANSD.ConclusionsVariants in AIFM1 gene are a common cause of familial and sporadic ANSD and provide insight into the expanded spectrum of AIFM1-associated diseases. The finding of cochlear nerve hypoplasia in some patients was AIFM1-related ANSD implies that MRI may be of value in localising the site of lesion and suggests that cochlea implantation in these patients may have limited success.

RIP3-dependent necroptosis has recently garnered significant interest because of the unique signaling mechanisms and pathologic functions involved in this process. Accordingly, a number of chemical screens have identified several effective small-molecule inhibitors that specifically block necroptosis. Here, we report the discovery that kongensin A (KA), a natural product isolated from Croton kongensis, is a potent inhibitor of necroptosis and an inducer of apoptosis. Using a new bioorthogonal ligation method (TQ ligation), we reveal that the direct cellular target of KA is heat shock protein 90 (HSP90). Further studies demonstrate that KA covalently binds to a previously uncharacterized cysteine 420 in the middle domain of HSP90 and dissociates HSP90 from its cochaperone CDC37, which leads to inhibition of RIP3-dependent necroptosis and promotion of apoptosis in multiple cancer cell lines. Collectively, our findings demonstrate that KA is an effective HSP90 inhibitor that has potential anti-necroptosis and anti-inflammation applications.

Class III PI3-kinase (PI3KC3) is essential for autophagy initiation, but whether PI3KC3 participates in other steps of autophagy remains unknown. The HOPS complex mediates the fusion of intracellular vesicles to lysosome, but how HOPS specifically tethers autophagosome to lysosome remains elusive. Here, we report Pacer (protein associated with UVRAG as autophagy enhancer) as a regulator of autophagy. Pacer localizes to autophagic structures and positively regulates autophagosome maturation. Mechanistically, Pacer antagonizes Rubicon to stimulate Vps34 kinase activity. Next, Pacer recruits PI3KC3 and HOPS complexes to the autophagosome for their site-specific activation by anchoring to the autophagosomal SNARE Stx17. Furthermore, Pacer is crucial for the degradation of hepatic lipid droplets, the suppression of Salmonella infection, and the clearance of protein aggregates. These results not only identify Pacer as a crucial multifunctional enhancer in autophagy but also uncover both the involvement of PI3KC3 and the mediators of HOPS's specific tethering activity in autophagosome maturation.

Pamiparib, an investigational Poly (ADP-ribose) polymerase (PARP) inhibitor in clinical development, demonstrates excellent selectivity for both PARP1 and PARP2, and superb anti-proliferation activities in tumor cell lines with BRCA1/2 mutations or HR pathway deficiency (HRD). Pamiparib has good bioavailability and is 16-fold more potent than olaparib in an efficacy study using BRCA1 mutated MDA-MB-436 breast cancer xenograft model. Pamiparib also shows strong anti-tumor synergy with temozolomide (TMZ), a DNA alkylating agent used to treat brain tumors. Compared to other PARP inhibitors, pamiparib demonstrated improved penetration across the blood brain barrier (BBB) in mice. Oral administration of pamiparib at a dose as low as 3 mg/kg is sufficient to abrogate PARylation in brain tumor tissues. In SCLC-derived, TMZ-resistant H209 intracranial xenograft model, combination of pamiparib with TMZ overcomes its resistance and shows significant tumor inhibitory effects and prolonged life span. Our data suggests that combination of pamiparib with TMZ has unique potential for treatment of brain tumors. Currently, the combination therapy of pamiparib with TMZ is evaluated in clinical trial [NCT03150862].