Large-scale label-free comparative proteomics analysis of polo-like kinase 1 inhibition via the small-molecule inhibitor BI 6727 (Volasertib) in BRAF(V600E) mutant melanoma cells

Identification of RNA-binding protein hnRNP C targeting the 3'UTR of the TAP-associated glycoprotein tapasin in melanoma

Deregulation or loss of the human leukocyte antigen class I (HLA-I) molecules on tumor cells leading to inhibition of CD8+ T cell recognition is an important tumor immune escape strategy, which could be caused by a posttranscriptional control of molecules in the HLA-I pathway mediated by RNA-binding proteins (RBPs). So far, there exists only limited information about the interaction of RBPs with HLA-I-associated molecules, but own work demonstrated a binding of the heterogeneous ribonucleoprotein C (hnRNP C) to the 3' untranslated region (UTR) of the TAP-associated glycoprotein tapasin (tpn). In this study, in silico analysis of pan-cancer TCGA datasets revealed that hnRNP C is higher expressed in tumor specimens compared to corresponding normal tissues, which is negatively correlated to tpn expression, T cell infiltration and the overall survival of tumor patients. Functional analysis demonstrated an upregulation of tpn expression upon siRNA-mediated downregulation of hnRNP C, which is accompanied by an increased HLA-I surface expression. Thus, hnRNP C has been identified to target tpn and its inhibition could improve the HLA-I surface expression on melanoma cells suggesting its use as a possible biomarker for T-cell-based tumor immunotherapies.

Screening and anti-glioma activity of Chiloscyllium plagiosum anti-human IL-13Rα2 single-domain antibody

Glioblastoma is a common and fatal malignant tumour of the central nervous system, with high invasiveness. Conventional treatments for this disease, including comprehensive treatment of surgical resection combined with chemoradiotherapy, are ineffective, with low survival rate and extremely poor prognosis. Targeted therapy is promising in overcoming the difficulties in brain tumour treatment and IL-13Rα2 is a widely watched target. The development of new therapies for glioma, however, is challenged by factors, such as the unique location and immune microenvironment of gliomas. The unique advantages of single-domain antibodies (sdAbs) may provide a novel potential treatment for brain tumours. In this study, Chiloscyllium plagiosum was immunized with recombinant IL-13Rα2 protein to produce sdAb and sdAb sequences were screened by multi-omics. The targeted sdAb genes obtained were efficiently expressed in the Escherichia coli prokaryotic expression system, showing a significant binding capacity to IL-13Rα2 in vitro. The cell proliferation and migration inhibitory effects of recombinant variable domain of the new antigen receptor (VNAR) on glioma cells were detected by CCK-8 and cell scratch assays. The sdAb obtained in this study showed high in vitro activity and favourable cell proliferation inhibitory effect on glioma cells, with potential clinical application value. The present study also provides a new direction and experimental basis for the development of targeted therapies for glioma.

Proteomic investigation and understanding on IgY purification and product development

An increasing demand for the development of immunoglobin Y (IgY) illustrates the necessity of the component analysis in the process of conduction and quality control. This study investigated the proteomic changes in crude IgY extracts and purified IgY products obtained by sequential polyethylene glycol precipitation (PEG) of egg yolks followed by human mycoplasma protein-based affinity chromatography compared with intact egg yolks. After confirming the extraction efficiency and purity by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis, liquid chromatography tandem-mass spectrometry (LC-MS/MS) was performed with samples including fresh yolk, IgY extracted product and purified product. A total of 348 proteins were identified, with 36 proteins deleted and 209 newly detected proteins in the purified product compared to the intact egg yolk. The significantly decreased proteins mainly included phosvitin, albumin, and apolipoprotein B whereas the significantly increased proteins were mainly IgY-related proteins. GO analysis showed that the purified IgY product had ATPase activity and purine ribonucleoside triphosphate binding activity, and was mainly involved in purine and nucleic acid metabolism. This study will inevitably fasten the commercial application of IgY antibodies and is of greater significance for promotion, development and approval for new antibody derived drug products.

USP1 promotes the aerobic glycolysis and progression of T-cell acute lymphoblastic leukemia via PLK1/LDHA axis

The effect of aerobic glycolysis remains elusive in pediatric T-cell acute lymphoblastic leukemia (T-ALL). Increasing evidence has revealed that dysregulation of deubiquitination is involved in glycolysis, by targeting glycolytic rate-limiting enzymes. Here, we demonstrated that upregulated deubiquitinase ubiquitin-specific peptidase 1 (USP1) expression correlated with poor prognosis in pediatric primary T-ALL samples. USP1 depletion abolished cellular proliferation and attenuated glycolytic metabolism. In vivo experiments showed that USP1 suppression decreased leukemia progression in nude mice. Inhibition of USP1 caused a decrease in both mRNA and protein levels in lactate dehydrogenase A (LDHA), a critical glycolytic enzyme. Moreover, USP1 interacted with and deubiquitinated polo-like kinase 1 (PLK1), a critical regulator of glycolysis. Overexpression of USP1 with upregulated PLK1 was observed in most samples of patients with T-ALL. In addition, PLK1 inhibition reduced LDHA expression and abrogated the USP1-mediated increase of cell proliferation and lactate level. Ectopic expression of LDHA can rescue the suppressive effect of USP1 silencing on cell growth and lactate production. Pharmacological inhibition of USP1 by ML323 exhibited cell cytotoxicity in human T-ALL cells. Taken together, our results demonstrated that USP1 may be a promising therapeutic target in pediatric T-ALL.

Dibutylstannanediyl (2Z,2'Z)-bis(4-(benzylamino)-4-oxobut-2-enoate inhibits prostate cancer progression by activating p38 MAPK/PPARα/SMAD4 signaling

Organotin (IV) compounds are a focus of research for potential use in cancer chemotherapy. Here, we established anticancer profile of dibutyltin (IV) carboxylate derivatives in prostate cancer (PCa) model. We determined cytotoxicity of a library of dibutyltin (IV) carboxylate derivatives and observed that dibutylstannanediyl (2Z,2'Z)-bis(4-(benzylamino)-4-oxobut-2-enoate (Ch-620; 10 μM) was minimally toxic to normal fibroblasts. Ch-620 (1-1.25 μM) inhibited proliferation of PCa and melanoma cells on short- and long-term exposures with induction of cell cycle arrest. Ch-620 treatment increased population of apoptotic cells, as assessed by flow cytometry, and activated caspase 3. Proteomics showed activation of PPARα, with repression of SMAD4 and integrin β5 (ITGB5) in Ch-620-treated PCa cells. Further analysis demonstrated that Ch-620 resulted in phosphorylation of p38 MAPK, upregulation of PPARα and decreased expression of SMAD4 and ITGB5 with reduced migration of PCa cells. In vivo studies in PC3M grafted athymic nude mice showed that Ch-620 (5 μg/week; 7 weeks) treatment reduced tumor growth as opposed to untreated controls. Immunoblot analysis of tumors demonstrated upregulated p-p38 MAPK and PPARα, followed by a decline in SMAD4 and ITGB5. Immunohistochemistry reinforced these results with increased caspase 3 and p-p38 MAPK and diminished Ki67 staining in Ch-620 treated animals. Taken together, our data indicate that Ch-620 inhibited proliferation of PCa through modulation of MAPK/PPARα/SMAD4 signaling. Organotin (IV) carboxylate compounds; specifically Ch-620 can be a potential anticancer agent for the treatment of PCa subject to detailed pre-clinical and clinical investigations. This unlocks prospects for the development of new tin-based drugs in cancer therapeutics.

Label-Free LC-MS/MS Analysis Reveals Different Proteomic Profiles between Egg Yolks of Silky Fowl and Ordinary Chickens

The proteomic profiles of Silky fowl egg yolk (SFEY) and Leghorn egg yolk (LEY) were analyzed by bottom-up label-free liquid chromatography–tandem mass spectrometry (LC-MS/MS). From a total of 186 identified proteins, 26 proteins were found significantly differentially abundant between two yolks, of which, 19 were up-regulated and 7 were down-regulated in SFEY, particularly, vitelline membrane outer layer protein 1, transthyretin and ovoinhibitor were up-regulated by 26, 25, and 16 times, respectively. In addition, there were 57 and 6 unique proteins in SFEY and LEY, respectively. Gene Ontology (GO) revealed SFEY contained relatively more abundant protease inhibitors and coagulation-related proteins. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed differentially abundant proteins in SFEY may be actively involved in the regulation of the neuroactive ligand–receptor interaction pathway. This study provides a theoretical basis for the understanding of proteomic and biological differences between these two yolks and can guide for further exploration of nutritional and biomedical use of Silky fowl egg.

Thermal proteome profiling identifies PIP4K2A and ZADH2 as off-targets of Polo-like kinase 1 inhibitor volasertib

Polo-like kinase 1 (PLK1) is an important cell cycle kinase and an attractive target for anticancer treatments. An ATP-competitive small molecular PLK1 inhibitor, volasertib, has reached phase III in clinical trials in patients with refractory acute myeloid leukemia as a combination treatment with cytarabine. However, severe side effects limited its use. The origin of the side effects is unclear and might be due to insufficient specificity of the drug. Thus, identifying potential off-targets to volasertib is important for future clinical trials and for the development of more specific drugs. In this study, we used thermal proteome profiling (TPP) to identify proteome-wide targets of volasertib. Apart from PLK1 and proteins regulated by PLK1, we identified about 200 potential volasertib off-targets. Comparison of this result with the mass-spectrometry analysis of volasertib-treated cells showed that phosphatidylinositol phosphate and prostaglandin metabolism pathways are affected by volasertib. We confirmed that PIP4K2A and ZADH2-marker proteins for these pathways-are, indeed, stabilized by volasertib. PIP4K2A, however, was not affected by another PLK1 inhibitor onvansertib, suggesting that PIP4K2A is a true off-target of volasertib. Inhibition of these proteins is known to impact both the immune response and fatty acid metabolism and could explain some of the side effects seen in volasertib-treated patients.

Identification of ALDH6A1 as a Potential Molecular Signature in Hepatocellular Carcinoma via Quantitative Profiling of the Mitochondrial Proteome

Various liver diseases, including hepatocellular carcinoma (HCC), have been linked to mitochondrial dysfunction, reduction of reactive oxygen species (ROS), and elevation of nitric oxide (NO). In this study, we subjected the human liver mitochondrial proteome to extensive quantitative proteomic profiling analysis and molecular characterization to identify potential signatures indicative of cancer cell growth and progression. Sequential proteomic analysis identified 2452 mitochondrial proteins, of which 1464 and 2010 were classified as nontumor and tumor (HCC) mitochondrial proteins, respectively, with 1022 overlaps. Further metabolic mapping of the HCC mitochondrial proteins narrowed our biological characterization to four proteins, namely, ALDH4A1, LRPPRC, ATP5C1, and ALDH6A1. The latter protein, a mitochondrial methylmalonate semialdehyde dehydrogenase (ALDH6A1), was most strongly suppressed in HCC tumor regions (∼10-fold decrease) in contrast to LRPPRC (∼6-fold increase) and was predicted to be present in plasma. Accordingly, we selected ALDH6A1 for functional analysis and engineered Hep3B cells to overexpress this protein, called ALDH6A1-O/E cells. Since ALDH6A1 is predicted to be involved in mitochondrial respiration, we assessed changes in the levels of NO and ROS in the overexpressed cell lines. Surprisingly, in ALDH6A1-O/E cells, NO was decreased nearly 50% but ROS was increased at a similar level, while the former was restored by treatment with S-nitroso-N-acetyl-penicillamine. The lactate levels were also decreased relative to control cells. Propidium iodide and Rhodamine-123 staining suggested that the decrease in NO and increase in ROS in ALDH6A1-O/E cells could be caused by depolarization of the mitochondrial membrane potential (ΔΨ). Taken together, our results suggest that hepatic neoplastic transformation appears to suppress the expression of ALDH6A1, which is accompanied by a respective increase and decrease in NO and ROS in cancer cells. Given the close link between ALDH6A1 suppression and abnormal cancer cell growth, this protein may serve as a potential molecular signature or biomarker of hepatocarcinogenesis and treatment responses.

Identification of proteins that mediate the role of androgens in antler regeneration using label free proteomics in sika deer (Cervus nippon)

Deer antlers offer a unique model to study organ regeneration in mammals. Antler regeneration relies on the pedicle periosteum (PP) cells and is triggered by a decrease in circulating testosterone (T). The molecular mechanism for antler regeneration is however, unclear. Label-free liquid chromatography-mass spectrometry (LC-MS/MS) was used to identify differentially-expressed proteins (DEPs) in the regeneration-potentiated PP (under low T environment) over the non-regeneration-potentiated PP (under high T environment). Out of total 273 DEPs, 189 were significantly up-regulated and 84 were down-regulated from these comparisons: after castration vs before castration, natural T vs before castration, and exogenous T vs before castration. We focused on the analysis only of those DEPs that were present in fully permissive environment to antler regeneration (low T). Nine transduction pathways were identified through the Kyoto Encyclopedia of Genes and Genomes (KEGG) database, including the estrogen signaling pathway. A total of 639 gene ontology terms were found to be significantly enriched in regeneration-potentiated PP (low T) from the DEPs. Reliability of the label free LC-MS/MS was determined by qRT-PCR to estimate the expression level of selected genes. The results suggest that up-regulated heat shock proteins (HSP90AB1, HSP90B1), peptidyl-prolyl cis-trans isomerase 4 (FKBP4), mitogen-activated protein kinase 3 (MAPK3) and calreticulin (CALR) and down-regulated SHC-transforming protein 1 (SHC1), heat shock protein family A member 1A (HSPA1A) and proto-oncogene tyrosine-protein kinase (SRC) may be associated directly or indirectly with antler regeneration. Further studies are required to investigate the roles of these proteins in regeneration using appropriate in vivo models.

Participation of PLK1 and FOXM1 in the hyperplastic proliferation of pulmonary artery smooth muscle cells in pulmonary arterial hypertension

Vascular smooth muscle cells from the pulmonary arteries (HPASMC) of subjects with pulmonary arterial hypertension (PAH) exhibit hyperplastic growth. The PAH HPASMC display an increased sensitivity to fetal bovine serum (FBS) and undergo growth at a very low, 0.2%, FBS concentration. On the other hand, normal HPASMC (obtained from non-PAH donors) do not proliferate at low FBS (0.2%). A previous genomic study suggested that the nuclear factor, FOXM1 and the polo like kinase 1 (PLK1) are involved in promoting this hyperplastic growth of the PAH HPASMC. Here we find that limiting the action of FOXM1 or PLK1 not only restricts the hyperplastic proliferation of the PAH HPASMC but also modulates the FBS stimulated growth of normal HPASMC. The PAH HPASMC exhibit significantly elevated PLK1 and FOXM1 expression and decreased p27 (quiescence protein) levels compared to normal HPASMC. Regulation of the expression of FOXM1 and PLK1 is accompanied by the regulation of downstream expression of cell cycle components, Aurora B, cyclin B1 and cyclin D1. Expression of these cell cycle components is reversed by the knockdown of FOXM1 or PLK1 expression/activity. Furthermore, the knockdown of PLK1 expression lowers the protein level of FOXM1. On the other hand, inhibiting the action of FOXO1, a growth inhibitor, further increases the expression of FOXM1 in PAH HPASMC. Although PLK1 and FOXM1 clearly participate in PAH HPASMC hyperplasia, at this time it is not clear whether their increased activity is the primary driver of the hyperplastic behavior of the PAH HPASMC or merely a component of the pathway(s) leading to this response.

Molecular and enzoinformatics perspectives of targeting Polo-like kinase 1 in cancer therapy

Cancer is a disease that has been the focus of scientific research and discovery and continues to remain so. Polo-like kinases (PLKs) are basically serine/threonine kinase enzymes that control cell cycle from yeast to humans. PLK-1 stands for 'Polo-like kinase-1'. It is the most investigated protein among PLKs. It is crucial for intracellular processes, hence a 'hot' anticancer drug-target. Accelerating innovations in Enzoinformatics and associated molecular visualization tools have made it possible to literally perform a 'molecular level walk' traversing through and observing the minutest contours of the active site of relevant enzymes. PLK-1 as a protein consists of a kinase domain at the protein N-terminal and a Polo Box Domain (PBD) at the C-terminal connected by a short inter-domain linking region. PBD has two Polo-Boxes. PBD of PLK-1 gives the impression of "a small clamp sandwiched between two clips", where the two Polo Boxes are the 'clips' and the 'phosphopeptide' is the small 'clamp'. Broadly, two major sites of PLK-1 can be potential targets: one is the adenosine-5'-triphosphate (ATP)-binding site in the kinase domain and the other is PBD (more preferred due to specificity). Targeting PLK-1 RNA and the interaction of PLK-1 with a key binding partner can also be approached. However, the list of potent small molecule inhibitors targeting the PBD site of PLK-1 is still not long enough and needs due input from the scientific community. Recently, eminent scientists have proposed targeting the 'Y'-shaped pocket of PLK-1-PBD and encouraged design of ligands that should be able to concurrently bind to two or more modules of the 'Y' pocket. Hence, it is suggested that during molecular interaction analyses, particular focus should be kept on the moiety in each ligand/drug candidate which directly interacts with the amino acid residue(s) that belong(s) to one of the three binding modules which together create this Y-shaped cavity. This obviously includes (but it is not limited to) the 'shallow cleft'-forming residues i.e. Trp414, H538 and K540, as significance of these binding residues has been consistently highlighted by many studies. The present article attempts to give a concise yet critically updated overview of targeting PLK-1 for cancer therapy.

Label-Free Quantitative Proteomics of Lysine Acetylome Identifies Substrates of Gcn5 in Magnaporthe oryzae Autophagy and Epigenetic Regulation

Gcn5 is a histone acetyltransferase that was previously shown to regulate phototropic and starvation-induced autophagy in the rice blast fungus Magnaporthe oryzae, likely via modification on autophagy protein Atg7. In this study, we identified more potential substrates of Gcn5-mediated acetylation by quantitative and comparative acetylome analyses. By epifluorescence microscopy and biochemistry experiments, we verified that Gcn5 may regulate autophagy induction at both the epigenetic and posttranslational levels and regulate autophagic degradation of a critical metabolic enzyme pyruvate kinase (Pk) likely via acetylation. Overall, our findings reveal comprehensive posttranslational modification executed by Gcn5, in response to various external stimuli, to synergistically promote cellular differentiation in a fungal pathogen.

The rice blast fungus Magnaporthe oryzae poses a great threat to global food security. During its conidiation (asexual spore formation) and appressorium (infecting structure) formation, autophagy is induced, serving glycogen breakdown or programmed cell death function, both essential for M. oryzae pathogenicity. Recently, we identified an M. oryzae histone acetyltransferase (HAT) Gcn5 as a key regulator in phototropic induction of autophagy and asexual spore formation while serving a cellular function other than autophagy induction during M. oryzae infection. To further understand the regulatory mechanism of Gcn5 on M. oryzae pathogenicity, we set out to identify more Gcn5 substrates by comparative acetylome between the wild-type (WT) and GCN5 overexpression (OX) mutant and between OX mutant and GCN5 deletion (knockout [KO]) mutant. Our results showed that Gcn5 regulates autophagy induction and other important aspects of fungal pathogenicity, including energy metabolism, stress response, cell toxicity and death, likely via both epigenetic regulation (histone acetylation) and posttranslational modification (nonhistone protein acetylation).

IMPORTANCE Gcn5 is a histone acetyltransferase that was previously shown to regulate phototropic and starvation-induced autophagy in the rice blast fungus Magnaporthe oryzae, likely via modification on autophagy protein Atg7. In this study, we identified more potential substrates of Gcn5-mediated acetylation by quantitative and comparative acetylome analyses. By epifluorescence microscopy and biochemistry experiments, we verified that Gcn5 may regulate autophagy induction at both the epigenetic and posttranslational levels and regulate autophagic degradation of a critical metabolic enzyme pyruvate kinase (Pk) likely via acetylation. Overall, our findings reveal comprehensive posttranslational modification executed by Gcn5, in response to various external stimuli, to synergistically promote cellular differentiation in a fungal pathogen.

Proteomic Analysis of Plasma Membrane Proteins of Antler Stem Cells Using Label-Free LC⁻MS/MS

Deer antlers are unusual mammalian organs that can fully regenerate after annual shedding. Stem cells resident in the pedicle periosteum (PPCs) provide the main cell source for antler regeneration. Central to various cellular processes are plasma membrane proteins, but the expression of these proteins has not been well documented in antler regeneration. In the present study, plasma membrane proteins of PPCs and facial periosteal cells (FPCs) were analyzed using label-free liquid chromatography⁻mass spetrometry (LC⁻MS/MS). A total of 1739 proteins were identified. Of these proteins, 53 were found solely in the PPCs, 100 solely in the FPCs, and 1576 co-existed in both PPCs and FPCs; and 39 were significantly up-regulated in PPCs and 49 up-regulated in FPCs. In total, 226 gene ontology (GO) terms were significantly enriched from the differentially expressed proteins (DEPs). Five clusters of biological processes from these GO terms comprised responses to external stimuli, signal transduction, membrane transport, regulation of tissue regeneration, and protein modification processes. Further studies are required to demonstrate the relevancy of these DEPs in antler stem cell biology and antler regeneration.

Targeting Polo-like kinase 1 in SMARCB1 deleted atypical teratoid rhabdoid tumor

Atypical teratoid rhabdoid tumor (ATRT) is an aggressive and malignant pediatric brain tumor. Polo-like kinase 1 (PLK1) is highly expressed in many cancers and essential for mitosis. Overexpression of PLK1 promotes chromosome instability and aneuploidy by overriding the G2-M DNA damage and spindle checkpoints. Recent studies suggest that targeting PLK1 by small molecule inhibitors is a promising approach to tumor therapy. We investigated the effect of PLK1 inhibition in ATRT. Gene expression analysis showed that PLK1 was overexpressed in ATRT patient samples and tumor cell lines. Genetic inhibition of PLK1 with shRNA potently suppressed ATRT cell growth in vitro. Treatment with the PLK1 inhibitor BI 6727 (Volasertib) significantly decreased cell growth, inhibited clonogenic potential, and induced apoptosis. BI6727 treatment led to G2-M phase arrest, consistent with PLK1's role as a critical regulator of mitosis. Moreover, inhibition of PLK1 by BI6727 suppressed the tumor-sphere formation of ATRT cells. Treatment also significantly decreased levels of the DNA damage proteins Ku80 and RAD51 and increased γ-H2AX expression, indicating that BI 6727 can induce DNA damage. Importantly, BI6727 significantly enhanced radiation sensitivity of ATRT cells. In vivo, BI6727 slowed growth of ATRT tumors and prolonged survival in a xenograft model. PLK1 inhibition is a compelling new therapeutic approach for treating ATRT, and the use of BI6727 should be evaluated in clinical studies.

Genetic Mechanisms Contribute to the Development of Heart Failure in Patients with Atrioventricular Block and Right Ventricular Apical Pacing

Right ventricular apical (RVA) pacing can lead to progressive left ventricular dysfunction and heart failure (HF), even in patients with normal cardiac structure and function. Our study conducted candidate gene screening and lentivirus transfected neonatal rat cardiomyocytes (NRCMs) to explore the genetic and pathogenic mechanisms of RVA pacing induced cardiomyopathy in third degree atrioventricular block (III AVB) patients. We followed 887 III AVB patients with baseline normal cardiac function and RVA pacing. After a median follow-up of 2.5 years, 10 patients (four males, mean age 47.6 ± 10.0 years) were diagnosed with RVA pacing induced HF with left ventricular ejection fraction (LVEF) reducing dramatically to 37.8 ± 7.1% (P  < 0.05). Candidate genes sequencing found cardiomyopathy associated genetic variations in all ten HF patients and six SCN5A variations in 6 of 20 control patients. Transfected NRCMs of Lamin A/C mutations (R216C and L379F) disrupted Lamin A/C location on nucleus membrane and finally resulted in increased apoptotic rate after serum starvation. In conclusion, cardiomyopathy associated genetic variations play an essential role in occurrence of newly onset HF in the III AVB patients with RVA pacing. RVA pacing, serving as extra stimulator, might accelerate the deterioration of cardiac structure and function.

RNA interference-mediated knockdown of SIRT1 and/or SIRT2 in melanoma: Identification of downstream targets by large-scale proteomics analysis

Melanoma is the most notorious and fatal of all skin cancers and the existing treatment options have not been proven to effectively manage this neoplasm, especially the metastatic disease. Sirtuin (SIRT) proteins have been shown to be differentially expressed in melanoma. We have shown that SIRTs 1 and 2 were overexpressed in melanoma and inhibition of SIRT1 imparts anti-proliferative responses in human melanoma cells. To elucidate the impact of SIRT 1 and/or 2 in melanoma, we created stable knockdowns of SIRTs 1, 2, and their combination using shRNA mediated RNA interference in A375 human melanoma cells. We found that SIRT1 and SIRT1&2 combination knockdown caused a decreased cellular proliferation in melanoma cells. Further, the knockdown of SIRT 1 and/or 2 resulted in a decreased colony formation in melanoma cells. To explore the downstream targets of SIRTs 1 and/or 2, we employed a label-free quantitative nano-LC-MS/MS proteomics analysis using the stable lines. We found aberrant levels of proteins involved in many vital cellular processes, including cytoskeletal organization, ribosomal activity, oxidative stress response, and angiogenesis. These findings provide clear evidence of cellular systems undergoing alterations in response to sirtuin inhibition, and have unveiled several excellent candidates for future study.

SIGNIFICANCE

Melanoma is the deadliest form of skin cancer, due to its aggressive nature, metastatic potential, and a lack of sufficient treatment options for advanced disease. Therefore, detailed investigations into the molecular mechanisms of melanoma growth and progression are needed. In the search for candidate genes to serve as therapeutic targets, the sirtuins show promise as they have been found to be upregulated in melanoma and they regulate a large number of proteins involved in cellular processes known to affect tumor growth, such as DNA damage repair, cell cycle arrest, and apoptosis. In this study, we used a large-scale label-free comparative proteomics system to identify novel protein targets that are affected following knockdown of SIRT1 and/or 2 in A375 metastatic melanoma cell line. Our study offers important insight into the potential downstream targets of SIRTs 1 and/or 2. This may unravel new potential areas of exploration in melanoma research.

Targeted knockdown of polo-like kinase 1 alters metabolic regulation in melanoma

A limited number of studies have indicated an association of the mitotic kinase polo-like kinase 1 (PLK1) and cellular metabolism. Here, employing an inducible RNA interference approach in A375 melanoma cells coupled with a PCR array and multiple validation approaches, we demonstrated that PLK1 alters a number of genes associated with cellular metabolism. PLK1 knockdown resulted in a significant downregulation of IDH1, PDP2 and PCK1 and upregulation of FBP1. Ingenuity Pathway Analysis (IPA) identified that 1) glycolysis and the pentose phosphate pathway are major canonical pathways associated with PLK1, and 2) PLK1 inhibition-modulated genes were largely associated with cellular proliferation, with FBP1 being the key modulator. Further, BI 6727-mediated inhibition of PLK1 caused a decrease in PCK1 and increase in FBP1 in A375 melanoma cell implanted xenografts in vivo. Furthermore, an inverse correlation between PLK1 and FBP1 was found in melanoma cells, with FBP1 expression significantly downregulated in a panel of melanoma cells. In addition, BI 6727 treatment resulted in an upregulation in FBP1 in A375, Hs294T and G361 melanoma cells. Overall, our study suggests that PLK1 may be an important regulator of metabolism maintenance in melanoma cells.

PLK1, A Potential Target for Cancer Therapy

Polo-like kinase 1 (PLK1) plays an important role in the initiation, maintenance, and completion of mitosis. Dysfunction of PLK1 may promote cancerous transformation and drive its progression. PLK1 overexpression has been found in a variety of human cancers and was associated with poor prognoses in cancers. Many studies have showed that inhibition of PLK1 could lead to death of cancer cells by interfering with multiple stages of mitosis. Thus, PLK1 is expected to be a potential target for cancer therapy. In this article, we examined PLK1’s structural characteristics, its regulatory roles in cell mitosis, PLK1 expression, and its association with survival prognoses of cancer patients in a wide variety of cancer types, PLK1 interaction networks, and PLK1 inhibitors under investigation. Finally, we discussed the key issues in the development of PLK1-targeted cancer therapy.

Activity-Based Protein Profiling Shows Heterogeneous Signaling Adaptations to BRAF Inhibition

Patients with BRAF V600E mutant melanoma are typically treated with targeted BRAF kinase inhibitors, such as vemurafenib and dabrafenib. Although these drugs are initially effective, they are not curative. Most of the focus to date has been upon genetic mechanisms of acquired resistance; therefore, we must better understand the global signaling adaptations that mediate escape from BRAF inhibition. In the current study, we have used activity-based protein profiling (ABPP) with ATP-analogue probes to enrich kinases and other enzyme classes that contribute to BRAF inhibitor (BRAFi) resistance in four paired isogenic BRAFi-naïve/resistant cell line models. Our analysis showed these cell line models, which also differ in their PTEN status, have considerable heterogeneity in their kinase ATP probe uptake in comparing both naïve cells and adaptations to chronic drug exposure. A number of kinases including FAK1, SLK, and TAOK2 had increased ATP probe uptake in BRAFi resistant cells, while KHS1 (M4K5) and BRAF had decreased ATP probe uptake in the BRAFi-resistant cells. Gene ontology (GO) enrichment analysis revealed BRAFi resistance is associated with a significant enhancement in ATP probe uptake in proteins implicated in cytoskeletal organization and adhesion, and decreases in ATP probe uptake in proteins associated with cell metabolic processes. The ABPP approach was able to identify key phenotypic mediators critical for each BRAFi resistant cell line. Together, these data show that common phenotypic adaptations to BRAF inhibition can be mediated through very different signaling networks, suggesting considerable redundancy within the signaling of BRAF mutant melanoma cells.

Spotlight on Volasertib: Preclinical and Clinical Evaluation of a Promising Plk1 Inhibitor

Considering the important side effects of conventional microtubule targeting agents, more and more research focuses on regulatory proteins for the development of mitosis-specific agents. Polo-like kinase 1 (Plk1), a master regulator of several cell cycle events, has arisen as an intriguing target in this research field. The observed overexpression of Plk1 in a broad range of human malignancies has given rise to the development of several potent and specific small molecule inhibitors targeting the kinase. In this review, we focus on volasertib (BI6727), the lead agent in category of Plk1 inhibitors at the moment. Numerous preclinical experiments have demonstrated that BI6727 is highly active across a variety of carcinoma cell lines, and the inhibitor has been reported to induce tumor regression in several xenograft models. Moreover, volasertib has shown clinical efficacy in multiple tumor types. As a result, Food and Drug Administration (FDA) has recently awarded volasertib the Breakthrough Therapy status after significant benefit was observed in acute myeloid leukemia (AML) patients treated with the Plk1 inhibitor. Here, we discuss both preclinical and clinical data available for volasertib administered as monotherapy or in combination with other anticancer therapies in a broad range of tumor types.

Proteomic Findings in Melanoma

Although the emergence of proteomics as an independent branch of science is fairly recent, within a short period of time it has contributed substantially in various disciplines. The tool of mass spectrometry has become indispensable in the analysis of complex biological samples. Clinical applications of proteomics include detection of predictive and diagnostic markers, understanding mechanism of action of drugs as well as resistance mechanisms against them and assessment of therapeutic efficacy and toxicity of drugs in patients. Here, we have summarized the major contributions of proteomics towards the study of melanoma, which is a deadly variety of skin cancer with a high mortality rate.

Targeting mutant NRAS signaling pathways in melanoma

Cutaneous melanoma is a devastating form of skin cancer and its incidence is increasing faster than any other preventable cancer in the United States. The mutant NRAS subset of melanoma is more aggressive and associated with poorer outcomes compared to non-NRAS mutant melanoma. The aggressive nature and complex molecular signaling conferred by this transformation has evaded clinically effective treatment options. This review examines the major downstream effectors of NRAS relevant in melanoma and the associated advances made in targeted therapies that focus on these effector pathways. We outline the history of MEK inhibition in mutant NRAS melanoma and recent advances with newer MEK inhibitors. Since MEK inhibitors will likely be optimized when combined with other targeted therapies, we focus on recently identified targets that can be used in combination with MEK inhibitors.

Volasertib Versus Chemotherapy in Platinum-Resistant or -Refractory Ovarian Cancer: A Randomized Phase II Groupe des Investigateurs Nationaux pour l'Etude des Cancers de l'Ovaire Study

PURPOSE

Volasertib is a potent and selective cell-cycle kinase inhibitor that induces mitotic arrest and apoptosis by targeting Polo-like kinase. This phase II trial evaluated volasertib or single-agent chemotherapy in patients with platinum-resistant or -refractory ovarian cancer who experienced failure after treatment with two or three therapy lines.

PATIENTS AND METHODS

Patients were randomly assigned to receive either volasertib 300 mg by intravenous infusion every 3 weeks or an investigator's choice of single-agent, nonplatinum, cytotoxic chemotherapy. The primary end point was 24-week disease control rate. Secondary end points included best overall response, progression-free survival (PFS), safety, quality of life, and exploratory biomarker analyses.

RESULTS

Of the 109 patients receiving treatment, 54 received volasertib and 55 received chemotherapy; demographics were well balanced. The 24-week disease control rates for volasertib and chemotherapy were 30.6% (95% CI, 18.0% to 43.2%) and 43.1% (95% CI, 29.6% to 56.7%), respectively, with partial responses in seven (13.0%) and eight (14.5%) patients, respectively. Median PFS was 13.1 weeks and 20.6 weeks for volasertib and chemotherapy (hazard ratio, 1.01; 95% CI, 0.66 to 1.53). Six patients (11%) receiving volasertib achieved PFS fore more than 1 year, whereas no patient receiving chemotherapy achieved PFS greater than 1 year. No relationship between the expression of the biomarkers tested and their response was determined. Patients treated with volasertib experienced more grade 3 and 4 drug-related hematologic adverse events (AEs) and fewer nonhematologic AEs than did patients receiving chemotherapy. Discontinuation resulting from AEs occurred in seven (13.0%) and 15 (27.3%) patients in the volasertib and chemotherapy arms, respectively. Both arms showed similar effects on quality of life.

CONCLUSION

Single-agent volasertib showed antitumor activity in patients with ovarian cancer. AEs in patients receiving volasertib were mainly hematologic and manageable.

miR-296-5p suppresses cell viability by directly targeting PLK1 in non-small cell lung cancer

Polo-like kinase 1 (PLK1), a critical kinase for mitotic progression, is overexpressed in a wide range of cancers. MicroRNAs (miRNAs) are a class of small non-coding RNA molecules and proposed to play important roles in the regulation of tumor progression and invasion. However, the relationship between PLK1 and miRNAs have remained unclear. In the present study, the association between PLK1 and miR-296-5p was investigated. The upregulation of PLK1 mRNA expression levels combined with the downregulation of miR-296-5p levels were detected in both non-small cell lung cancer (NSCLC) tissues and cell lines. Functional studies showed that knockdown of PLK1 by siRNA inhibited NSCLC cells proliferation. Impressively, overexpression of miR-296-5p showed the same phenocopy as the effect of PLK1 knockdown in NSCLC cells, indicating that PLK1 was a major target of miR-296-5p. Furthermore, using western blot analysis and luciferase reporter assay, PLK1 protein expression was proved to be regulated by miR-296-5p through binding to the putative binding sites in its 3'-untranslated region (3'-UTR). Taken together, the present study indicated that miR-296-5p regulated PLK1 expression and could function as a tumor suppressor in NSCLC progression, which provides a potential target for gene therapy of NSCLC.

Combined Inhibition of MEK and Plk1 Has Synergistic Antitumor Activity in NRAS Mutant Melanoma

About one-third of cancers harbor activating mutations in rat sarcoma viral oncogene homolog (RAS) oncogenes. In melanoma, aberrant neuroblastoma-RAS (NRAS) signaling fuels tumor progression in about 20% of patients. Current therapeutics for NRAS-driven malignancies barely affect overall survival. To date, pathway interference downstream of mutant NRAS seems to be the most promising approach. In this study, data revealed that mutant NRAS induced Polo-like kinase 1 (Plk1) expression, and pharmacologic inhibition of Plk1 stabilized the size of NRAS mutant melanoma xenografts. The combination of mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK) and Plk1 inhibitors resulted in a significant growth reduction of NRAS mutant melanoma cells in vitro, and regression of xenografted NRAS mutant melanoma in vivo. Independent cell cycle arrest and increased induction of apoptosis underlies the synergistic effect of this combination. Data further suggest that the p53 signaling pathway is of key importance to the observed therapeutic efficacy. This study provides in vitro, in vivo, and first mechanistic data that an MEK/Plk1 inhibitor combination might be a promising treatment approach for patients with NRAS-driven melanoma. As mutant NRAS signaling is similar across different malignancies, this inhibitor combination could also offer a previously unreported treatment modality for NRAS mutant tumors of other cell origins.

DNA microarray and signal transduction analysis in pulmonary artery smooth muscle cells from heritable and idiopathic pulmonary arterial hypertension subjects

Pulmonary arterial hypertension (PAH) is characterized by increased pulmonary vascular smooth muscle contraction and proliferation. Here, we analyze genome-wide mRNA expression in human pulmonary arterial smooth muscle cells (HPASMC) isolated from three control, three hereditary (HPAH), and three idiopathic PAH (IPAH) subjects using the Affymetrix Human Gene ST 1.0 chip. The microarray analysis reveals the expression of 537 genes in HPAH and 1024 genes in IPAH changed compared with control HPASMC. Among those genes, 227 genes show similar directionality of expression in both HPAH and IPAH HPASMC. Ingenuity™ Pathway Analysis (IPA) suggests that many of those genes are involved in cellular growth/proliferation and cell cycle regulation and that signaling pathways such as the mitotic activators, polo-like kinases, ATM signaling are activated under PAH conditions. Furthermore, the analysis demonstrates downregulated mRNA expression of certain vasoactive receptors such as bradykinin receptor B2 (BKB2R). Using real time PCR, we verified the downregulated BKB2R expression in the PAH cells. Bradykinin-stimulated calcium influx is also decreased in PAH PASMC. IPA also identified transcriptional factors such p53 and Rb as downregulated, and FoxM1 and Myc as upregulated in both HPAH and IPAH HPASMC. The decreased level of phospho-p53 in PAH cells was confirmed with a phospho-protein array; and we experimentally show a dysregulated proliferation of both HPAH and IPAH PASMC. Together, the microarray experiments and bioinformatics analysis highlight an aberrant proliferation and cell cycle regulation in HPASMC from PAH subjects. These newly identified pathways may provide new targets for the treatment of both hereditary and idiopathic PAH.