Inositol pyrophosphates mediate the DNA-PK/ATM-p53 cell death pathway by regulating CK2 phosphorylation of Tti1/Tel2.

The apoptotic actions of p53 require its phosphorylation by a family of phosphoinositide-3-kinase-related-kinases (PIKKs), which include DNA-PKcs and ATM. These kinases are stabilized by the TTT (Tel2, Tti1, Tti2) cochaperone family, whose actions are mediated by CK2 phosphorylation. The inositol pyrophosphates, such as 5-diphosphoinositol pentakisphosphate (IP7), are generated by a family of inositol hexakisphosphate kinases (IP6Ks), of which IP6K2 has been implicated in p53-associated cell death. In the present study we report an apoptotic signaling cascade linking CK2, TTT, the PIKKs, and p53. We demonstrate that IP7, formed by IP6K2, binds CK2 to enhance its phosphorylation of the TTT complex, thereby stabilizing DNA-PKcs and ATM. This process stimulates p53 phosphorylation at serine 15 to activate the cell death program in human cancer cells and in murine B cells.

Biliverdin reductase bridges focal adhesion kinase to Src to modulate synaptic signaling.

Synapses connect discrete neurons into vast networks that send, receive, and encode diverse forms of information. Synaptic function and plasticity, the neuronal process of adapting to diverse and variable inputs, depend on the dynamic nature of synaptic molecular components, which is mediated in part by cell adhesion signaling pathways. Here, we found that the enzyme biliverdin reductase (BVR) physically links together key focal adhesion signaling molecules at the synapse. BVR-null (BVR-/-) mice exhibited substantial deficits in learning and memory on neurocognitive tests, and hippocampal slices in which BVR was postsynaptically depleted showed deficits in electrophysiological responses to stimuli. RNA sequencing, biochemistry, and pathway analyses suggested that these deficits were mediated through the loss of focal adhesion signaling at both the transcriptional and biochemical level in the hippocampus. Independently of its catalytic function, BVR acted as a bridge between the primary focal adhesion signaling kinases FAK and Pyk2 and the effector kinase Src. Without BVR, FAK and Pyk2 did not bind to and stimulate Src, which then did not phosphorylate the N-methyl-d-aspartate (NMDA) receptor, a critical posttranslational modification for synaptic plasticity. Src itself is a molecular hub on which many signaling pathways converge to stimulate NMDAR-mediated neurotransmission, thus positioning BVR at a prominent intersection of synaptic signaling.

The full-length unprocessed hedgehog protein is an active signaling molecule.

The hedgehog (HH) family of ligands plays an important instructional role in metazoan development. HH proteins are initially produced as approximately 45-kDa full-length proteins, which undergo an intramolecular cleavage to generate an amino-terminal product that subsequently becomes cholesterol-modified (HH-Np). It is well accepted that this cholesterol-modified amino-terminal cleavage product is responsible for all HH-dependent signaling events. Contrary to this model we show here that full-length forms of HH proteins are able to traffic to the plasma membrane and participate directly in cell-cell signaling, both in vitro and in vivo. We were also able to rescue a Drosophila eye-specific hh loss of function phenotype by expressing a full-length form of hh that cannot be processed into HH-Np. These results suggest that in some physiological contexts full-length HH proteins may participate directly in HH signaling and that this novel activity of full-length HH may be evolutionarily conserved.

Hedgehog signaling regulates E-cadherin expression for the maintenance of the actin cytoskeleton and tight junctions.

In the stomach, strictly regulated cell adherens junctions are crucial in determining epithelial cell differentiation. Sonic Hedgehog (Shh) regulates epithelial cell differentiation in the adult stomach. We sought to identify whether Shh plays a role in regulating adherens junction protein E-cadherin as a mechanism for epithelial cell differentiation. Mouse nontumorigenic gastric epithelial (IMGE-5) cells treated with Hedgehog signaling inhibitor cyclopamine and anti-Shh 5E1 antibody or transduced with short hairpin RNA against Skinny Hedgehog (IMGE-5(Ski)) were cultured. A mouse model expressing a parietal cell-specific deletion of Shh (HKCre/Shh(KO)) was used to identify further changes in adherens and tight junctions. Inhibition of Hedgehog signaling in IMGE-5 cells caused loss of E-cadherin expression accompanied by disruption of F-actin cortical expression and relocalization of zonula occludens-1 (ZO-1). Loss of E-cadherin was also associated with increased proliferation in IMGE-5(Ski) cells and increased expression of the mucous neck cell lineage marker MUC6. Compared with membrane-expressed E-cadherin and ZO-1 protein in controls, dissociation of E-cadherin/ß-catenin and ZO-1/occludin protein complexes was observed in HKCre/Shh(KO) mice. In conclusion, we demonstrate that Hedgehog signaling regulates E-cadherin expression that is required for the maintenance of F-actin cortical expression and stability of tight junction protein ZO-1.

Sonic hedgehog mutations identified in holoprosencephaly patients can act in a dominant negative manner.

Sonic hedgehog (SHH) plays an important instructional role in vertebrate development, as exemplified by the numerous developmental disorders that occur when the SHH pathway is disrupted. Mutations in the SHH gene are the most common cause of sporadic and inherited holoprosencephaly (HPE), a developmental disorder that is characterized by defective prosencephalon development. SHH HPE mutations provide a unique opportunity to better understand SHH biogenesis and signaling, and to decipher its role in the development of HPE. Here, we analyzed a panel of SHH HPE missense mutations that encode changes in the amino-terminal active domain of SHH. Our results show that SHH HPE mutations affect SHH biogenesis and signaling at multiple steps, which broadly results in low levels of protein expression, defective processing of SHH into its active form and protein with reduced activity. Additionally, we found that some inactive SHH proteins were able to modulate the activity of wt SHH in a dominant negative manner, both in vitro and in vivo. These findings show for the first time the susceptibility of SHH driven developmental processes to perturbations by low-activity forms of SHH. In conclusion, we demonstrate that SHH mutations found in HPE patients affect distinct steps of SHH biogenesis to attenuate SHH activity to different levels, and suggest that these variable levels of SHH activity might contribute to some of the phenotypic variation found in HPE patients.

Bilirubin Links Heme Metabolism to Neuroprotection by Scavenging Superoxide.

Bilirubin is one of the most frequently measured metabolites in medicine, yet its physiologic roles remain unclear. Bilirubin can act as an antioxidant in vitro, but whether its redox activity is physiologically relevant is unclear because many other antioxidants are far more abundant in vivo. Here, we report that depleting endogenous bilirubin renders mice hypersensitive to oxidative stress. We find that mice lacking bilirubin are particularly vulnerable to superoxide (O2⋅-) over other tested reactive oxidants and electrophiles. Whereas major antioxidants such as glutathione and cysteine exhibit little to no reactivity toward O2⋅-, bilirubin readily scavenges O2⋅-. We find that bilirubin's redox activity is particularly important in the brain, where it prevents excitotoxicity and neuronal death by scavenging O2⋅- during NMDA neurotransmission. Bilirubin's unique redox activity toward O2⋅- may underlie a prominent physiologic role despite being significantly less abundant than other endogenous and exogenous antioxidants.

Diels-alder adducts of 3,6-dibromophencyclone with symmetrical 1,4-disubstituted-cis-2-butenes: comparisons with the adduct of phencyclone and N-benzylmaleimide, and one-dimensional and two-dimensional nuclear magnetic resonance studies and ab initio structure calculations.

Hindered Diels-Alder adducts have been prepared from 3,6-dibromophencyclone, 2, with cis-1,4-diacetoxy-2-butene, 3; cis-2-butene-1,4-diol, 4; and N-benzylmaleimide, 5. The adduct from the parent phencyclone, 1, with N-benzylmaleimide was prepared for comparison. One- and two-dimensional (1D and 2D) proton and carbon-13 NMR studies (at 7.05 tesla, ambient temperatures), including high-resolution COSY45 and HETCOR (XHCORR) chemical shift correlation spectra, were performed, allowing extensive rigorous assignments for protons and protonated carbons. Substantial anisotropic shielding was seen for the ortho protons of the N-benzyl group in the adducts of 5 with 1 or 2, with these aryl protons resonating at 6.25 ppm (CDCl3) for each adduct. The unsubstituted bridgehead phenyls of all four adducts showed slow exchange limit (SEL) 1H and 13C spectra. Greater shift dispersions for the bridge-head phenyl protons in the adducts from 5 relative to those from 3 or 4 suggested the role of the imide carbonyls for anisotropic contributions or for influences on adduct geometry. Ab initio geometry optimizations were performed at the Hartree-Fock level with the 6-31G* basis set (or the LACVP* basis set for the bromine-containing compounds) for each of the adducts. For the two adducts from benzylmaleimide, separate minima were located corresponding to conformers in which the benzyl group was directed into the adduct cavity (syn) or out of the adduct cavity (anti). Calculated energies and geometric parameters for the adducts are presented, and these suggested a significantly different structure for the dibromo diacetate adduct, in terms of general symmetry and bridgehead phenyl geometries, compared to the other adducts.

Identification of a family of fatty-acid-speciated sonic hedgehog proteins, whose members display differential biological properties.

Hedgehog (HH) proteins are proteolytically processed into a biologically active form that is covalently modified by cholesterol and palmitate. However, most studies of HH biogenesis have characterized protein from cells in which HH is overexpressed. We purified Sonic Hedgehog (SHH) from cells expressing physiologically relevant levels and showed that it was more potent than SHH isolated from overexpressing cells. Furthermore, the SHH in our preparations was modified with a diverse spectrum of fatty acids on its amino termini, and this spectrum of fatty acids varied dramatically depending on the growth conditions of the cells. The fatty acid composition of SHH affected its trafficking to lipid rafts as well as its potency. Our results suggest that HH proteins exist as a family of diverse lipid-speciated proteins that might be altered in different physiological and pathological contexts in order to regulate distinct properties of HH proteins.

Hedgehog signaling regulates bladder cancer growth and tumorigenicity.

The role of Hedgehog (HH) signaling in bladder cancer remains controversial. The gene encoding the HH receptor and negative regulator PATCHED1 (PTCH1) resides on a region of chromosome 9q, one copy of which is frequently lost in bladder cancer. Inconsistent with PTCH1 functioning as a classic tumor suppressor gene, loss-of-function mutations in the remaining copy of PTCH1 are not commonly found. Here, we provide direct evidence for a critical role of HH signaling in bladder carcinogenesis. We show that transformed human urothelial cells and many urothelial carcinoma cell lines exhibit constitutive HH signaling, which is required for their growth and tumorigenic properties. Surprisingly, rather than originating from loss of PTCH1, the constitutive HH activity observed in urothelial carcinoma cell lines was HH ligand dependent. Consistent with this finding, increased levels of HH and the HH target gene product GLI1 were found in resected human primary bladder tumors. Furthermore, on the basis of the difference in intrinsic HH dependence of urothelial carcinoma cell lines, a gene expression signature was identified that correlated with bladder cancer progression. Our findings therefore indicate that therapeutic targeting of the HH signaling pathway may be beneficial in the clinical management of bladder cancer.

Hedgehog-producing cancer cells respond to and require autocrine Hedgehog activity.

A number of Smoothened (SMO) pathway antagonists are currently undergoing clinical trials as anticancer agents. These drugs are proposed to attenuate tumor growth solely through inhibition of Hedgehog (HH), which is produced in tumor cells but acts on tumor stromal cells. The pivotal argument underlying this model is that the growth-inhibitory properties of SMO antagonists on HH-producing cancer cells are due to their off-target effects. Here, we show that the tumorigenic properties of such lung cancer cells depend on their intrinsic level of HH activity. Notably, reducing HH signaling in these tumor cells decreases HH target gene expression. Taken together, these results question the dogma that autocrine HH signaling plays no role in HH-dependent cancers, and does so without using SMO antagonists.

Selective inhibitor of proteasome's caspase-like sites sensitizes cells to specific inhibition of chymotrypsin-like sites.

Proteasomes degrade most proteins in mammalian cells and are established targets of anticancer drugs. All eukaryotic proteasomes have three types of active sites: chymotrypsin-like, trypsin-like, and caspase-like. Chymotrypsin-like sites are the most important in protein degradation and are the primary target of most proteasome inhibitors. The biological roles of trypsin-like and caspase-like sites and their potential as cotargets of antineoplastic agents are not well defined. Here we describe the development of site-specific inhibitors and active-site probes of chymotrypsin-like and caspase-like sites. Using these compounds, we show that cytotoxicity of proteasome inhibitors does not correlate with inhibition of chymotrypsin-like sites and that coinhibition of either trypsin-like and/or caspase-like sites is needed to achieve maximal cytotoxicity. Thus, caspase-like and trypsin-like sites must be considered as cotargets of anticancer drugs.