Reduction-cleavable desferrioxamine B pulldown system enriches Ni(ii)-superoxide dismutase from a Streptomyces proteome.

Two resins with the hydroxamic acid siderophore desferrioxamine B (DFOB) immobilised as a free ligand or its Fe(iii) complex were prepared to screen the Streptomyces pilosus proteome for proteins involved in siderophore-mediated Fe(iii) uptake. The resin design included a disulfide bond to enable the release of bound proteins under mild reducing conditions. Proteomics analysis of the bound fractions did not identify proteins associated with siderophore-mediated Fe(iii) uptake, but identified nickel superoxide dismutase (NiSOD), which was enriched on the apo-DFOB-resin but not the Fe(iii)-DFOB-resin or the control resin. While DFOB is unable to sequester Fe(iii) from sites deeply buried in metalloproteins, the coordinatively unsaturated Ni(ii) ion in NiSOD is present in a surface-exposed loop region at the N-terminus, which might enable partial chelation. The results were consistent with the notion that the apo-DFOB-resin formed a ternary complex with NiSOD, which was not possible for either the coordinatively saturated Fe(iii)-DFOB-resin or the non-coordinating control resin systems. In support, ESI-TOF-MS measurements from a solution of a model Ni(ii)-SOD peptide and DFOB showed signals that correlated with a ternary Ni(ii)-SOD peptide-DFOB complex. Although any biological implications of a DFOB-NiSOD complex are unclear, the work shows that the metal coordination properties of siderophores might influence an array of metal-dependent biological processes beyond those established in iron uptake.

KLF5 inhibits angiogenesis in PTEN-deficient prostate cancer by attenuating AKT activation and subsequent HIF1α accumulation.

BACKGROUND: KLF5 is a basic transcriptional factor that regulates multiple physiopathological processes. Our recent study showed that deletion of Klf5 in mouse prostate promotes tumorigenesis initiated by the deletion of Pten. While molecular characterization of Klf5-null tumors suggested that angiogenesis was partially responsible for tumor promotion, the precise function and mechanism of KLF5 deletion in prostate tumor angiogenesis remain unclear. RESULTS: Applying histological staining to Pten-null mouse prostates, we observed that deletion of Klf5 significantly increased the number of microvessels, accompanied by the upregulation of multiple angiogenesis-related genes based on microarray analysis with MetaCore software. In human umbilical vein endothelial cells (HuVECs), tube formation and migration, both of which are indicators of angiogenic activities, were decreased by conditioned media from PC-3 and DU 145 human prostate cancer cells with KLF5 overexpression, but increased by media from cells with KLF5 knockdown. HIF1α, a key angiogenesis inducer, was upregulated by KLF5 loss at the protein but not the mRNA level in both mouse tissues and human cell lines, as determined by immunohistochemical staining, real-time RT-PCR and Western blotting. Consistently, KLF5 loss also upregulated VEGF and PDGF, two pro-angiogenic mediators of HIF1α function, as analyzed by immunohistochemical staining in mouse tissues and ELISA in conditioned media. Mechanistically, AKT activity, which caused the accumulation of HIF1α, was increased by KLF5 knockout or knockdown but decreased by KLF5 overexpression. PI3K/AKT inhibitors consistently abolished the effects of KLF5 knockdown on angiogenic activity, HIF1α accumulation, and VEGF and PDGF expression. CONCLUSION: KLF5 loss enhances tumor angiogenesis by attenuating PI3K/AKT signaling and subsequent accumulation of HIF1α in PTEN deficient prostate tumors.

Vemurafenib synergizes with nutlin-3 to deplete survivin and suppresses melanoma viability and tumor growth.

PURPOSE: For patients with advanced melanoma, primary and secondary resistance to selective BRAF inhibition remains one of the most critically compelling challenges. One rationale argues that novel biologically informed strategies are needed to maximally cripple melanoma cells up front before compensatory mechanisms emerge. As p53 is uncommonly mutated in melanoma, restoration of its function represents an attractive adjunct to selective BRAF inhibition. EXPERIMENTAL DESIGN: Thirty-seven BRAF(V600E)-mutated melanoma lines were subjected to synergy studies in vitro using a combination of vemurafenib and nutlin-3 (Nt-3). In addition, cellular responses and in vivo efficacy were also determined. We also analyzed changes in the levels of canonical apoptotic/survival factors in response to vemurafenib. RESULTS: Dual targeting of BRAF(V600E) and Hdm2 with vemurafenib and Nt-3, respectively, synergistically induced apoptosis and suppressed melanoma viability in vitro and tumor growth in vivo. Suppression of p53 in melanoma cells abrogated Nt-3's effects fully and vemurafenib's effects partially. A survey of canonical survival factors revealed that both vemurafenib and Nt-3 independently attenuated levels of the antiapoptotic protein, survivin. Genetic depletion of survivin reproduces the cytotoxic effects of the combination strategy. CONCLUSION: These results show preclinical feasibility for overcoming primary vemurafenib resistance by restoring p53 function. Moreover, it identifies survivin as one downstream mediator of the observed synergism and a potential secondary target.

Germline BAP1 inactivation is preferentially associated with metastatic ocular melanoma and cutaneous-ocular melanoma families.

BACKGROUND: BAP1 has been shown to be a target of both somatic alteration in high-risk ocular melanomas (OM) and germline inactivation in a few individuals from cancer-prone families. These findings suggest that constitutional BAP1 changes may predispose individuals to metastatic OM and that familial permeation of deleterious alleles could delineate a new cancer syndrome. DESIGN: To characterize BAP1's contribution to melanoma risk, we sequenced BAP1 in a set of 100 patients with OM, including 50 metastatic OM cases and 50 matched non-metastatic OM controls, and 200 individuals with cutaneous melanoma (CM) including 7 CM patients from CM-OM families and 193 CM patients from CM-non-OM kindreds. RESULTS: Germline BAP1 mutations were detected in 4/50 patients with metastatic OM and 0/50 cases of non-metastatic OM (8% vs. 0%, p = 0.059). Since 2/4 of the BAP1 carriers reported a family history of CM, we analyzed 200 additional hereditary CM patients and found mutations in 2/7 CM probands from CM-OM families and 1/193 probands from CM-non-OM kindreds (29% vs. 0.52%, p = .003). Germline mutations co-segregated with both CM and OM phenotypes and were associated with the presence of unique nevoid melanomas and highly atypical nevoid melanoma-like melanocytic proliferations (NEMMPs). Interestingly, 7/14 germline variants identified to date reside in C-terminus suggesting that the BRCA1 binding domain is important in cancer predisposition. CONCLUSION: Germline BAP1 mutations are associated with a more aggressive OM phenotype and a recurrent phenotypic complex of cutaneous/ocular melanoma, atypical melanocytic proliferations and other internal neoplasms (ie. COMMON syndrome), which could be a useful clinical marker for constitutive BAP1 inactivation.

Selective BRAFV600E inhibition enhances T-cell recognition of melanoma without affecting lymphocyte function.

Targeted therapy against the BRAF/mitogen-activated protein kinase (MAPK) pathway is a promising new therapeutic approach for the treatment of melanoma. Treatment with selective BRAF inhibitors results in a high initial response rate but limited duration of response. To counter this, investigators propose combining this therapy with other targeted agents, addressing the issue of redundancy and signaling through different oncogenic pathways. An alternative approach is combining BRAF/MAPK-targeted agents with immunotherapy. Preliminary evidence suggests that oncogenic BRAF (BRAF(V600E)) contributes to immune escape and that blocking its activity via MAPK pathway inhibition leads to increased expression of melanocyte differentiation antigens (MDA). Recognition of MDAs is a critical component of the immunologic response to melanoma, and several forms of immunotherapy capitalize on this recognition. Among the various approaches to inhibiting BRAF/MAPK, broad MAPK pathway inhibition may have deleterious effects on T lymphocyte function. Here, we corroborate the role of oncogenic BRAF in immune evasion by melanoma cells through suppression of MDAs. We show that inhibition of the MAPK pathway with MAPK/extracellular signal-regulated kinase kinase (MEK) inhibitors or a specific inhibitor of BRAF(V600E) in melanoma cell lines and tumor digests results in increased levels of MDAs, which is associated with improved recognition by antigen-specific T lymphocytes. However, treatment with MEK inhibitors impairs T lymphocyte function, whereas T-cell function is preserved after treatment with a specific inhibitor of BRAF(V600E). These findings suggest that immune evasion of melanomas mediated by oncogenic BRAF may be reversed by targeted BRAF inhibition without compromising T-cell function. These findings have important implications for combined kinase-targeted therapy plus immunotherapy for melanoma.

Dynamic gene expression analysis links melanocyte growth arrest with nevogenesis.

Like all primary cells in vitro, normal human melanocytes exhibit a physiologic decay in proliferative potential as it transitions to a growth-arrested state. The underlying transcriptional program(s) that regulate this phenotypic change is largely unknown. To identify molecular determinants of this process, we performed a Bayesian-based dynamic gene expression analysis on primary melanocytes undergoing proliferative arrest. This analysis revealed several related clusters whose expression behavior correlated with the melanocyte growth kinetics; we designated these clusters the melanocyte growth arrest program (MGAP). These MGAP genes were preferentially represented in benign melanocytic nevi over melanomas and selectively mapped to the hepatocyte fibrosis pathway. This transcriptional relationship between melanocyte growth stasis, nevus biology, and fibrogenic signaling was further validated in vivo by the demonstration of strong pericellular collagen deposition within benign nevi but not melanomas. Taken together, our study provides a novel view of fibroplasia in both melanocyte biology and nevogenesis.

Crystal structure of the lambda repressor and a model for pairwise cooperative operator binding.

Bacteriophage lambda has for many years been a model system for understanding mechanisms of gene regulation. A 'genetic switch' enables the phage to transition from lysogenic growth to lytic development when triggered by specific environmental conditions. The key component of the switch is the cI repressor, which binds to two sets of three operator sites on the lambda chromosome that are separated by about 2,400 base pairs (bp). A hallmark of the lambda system is the pairwise cooperativity of repressor binding. In the absence of detailed structural information, it has been difficult to understand fully how repressor molecules establish the cooperativity complex. Here we present the X-ray crystal structure of the intact lambda cI repressor dimer bound to a DNA operator site. The structure of the repressor, determined by multiple isomorphous replacement methods, reveals an unusual overall architecture that allows it to adopt a conformation that appears to facilitate pairwise cooperative binding to adjacent operator sites.