Proteins In Human Cancer Cells Research Articles

Factors affecting the expression and stability of full-length and truncated SRSF3 proteins in human cancer cells

Alternative splicing plays a crucial role in increasing the diversity of mRNAs expressed in the genome. Serine/arginine-rich splicing factor 3 (SRSF3) is responsible for regulating the alternative splicing of its own mRNA and ensuring that its expression is balanced to maintain homeostasis. Moreover, the exon skipping of SRSF3 leads to the production of a truncated protein instead of a frameshift mutation that generates a premature termination codon (PTC). However, the precise regulatory mechanism involved in the splicing of SRSF3 remains unclear. In this study, we first established a platform for coexpressing full-length SRSF3 (SRSF3-FL) and SRSF3-PTC and further identified a specific antibody against the SRSF3-FL and truncated SRSF3 (SRSF3-TR) proteins. Next, we found that exogenously overexpressing SRSF3-FL or SRSF3-PTC failed to reverse the effects of digoxin, caffeine, or both in combination on this molecule and its targets. Endoplasmic reticulum-related pathways, transcription factors, and chemicals such as palmitic acid and phosphate were found to be involved in the regulation of SRSF3 expression. The downregulation of SRSF3-FL by palmitic acid and phosphate was mediated via different regulatory mechanisms in HeLa cells. In summary, we provide new insights into the altered expression of the SRSF3-FL and SRSF3-TR proteins for the identification of the functions of SRSF3 in cells.

Boningmycin induces AMPK-mediated endoplasmic reticulum-associated degradation of PD-L1 protein in human cancer cells

Anti-PD-1/PD-L1 monoclonal antibodies have displayed remarkable clinical benefits and revolutionized the treatment of multiple tumor types, but the low response rates and immune-related adverse events limit their application, which promoting the development of small molecule agents to improve the efficacy of PD-1/PD-L1 blockade therapy. Boningmycin (BON), a new small molecule belonging to bleomycin (BLM) family, exhibits potent anticancer activity in vitro and in vivo, as well as negligible lung toxicity, thereby can be an alternative of BLM. However, understandings about the anticancer mechanism of BLM-related compounds are extremely rare, it remains unclear if they affect PD-L1 level in a manner similar to that of other antitumor drugs. In this study, we discover that BON significantly reduces PD-L1 protein level in NCI-H460 and HT-1080 cells. Meanwhile, BON decreases the protein level of PD-L1 in a tumor xenograft model of NCI-H460 cells. Nevertheless, the mRNA level is not influenced after BON exposure. Furthermore, BON-induced PD-L1 reduction is proteasome- dependent. By using specific inhibitors and RNA interference technology, we confirm that the decline of PD-L1 protein by BON is mediated by AMPK-activated endoplasmic reticulum-associated degradation pathway, which is like to the action of metformin. Last but not the least, BON has synergism on gefitinib in vitro and in vivo. In conclusion, it is the first report demonstrating that BON decreases PD-L1 protein level through AMPK-mediated endoplasmic reticulum-associated degradation pathway. These findings will benefit the clinical transformation of BON and aid in the elucidation of molecular mechanism of BLM-related compounds.

Real-time monitoring of distinct binding kinetics of hot-spot mutant p53 protein in human cancer cells using an individual nanorod-based plasmonic biosensor

Hot-spot mutant p53 proteins are highly associated with cancer malignancy and chemotherapy resistance of various cancers. Precise detection of the hot-spot mutant protein is therefore important in predicting therapeutic effects in cancer. However, conventional analytical methods such as liquid chromatography couple with tandem mass spectrometry (LC–MS/MS) and immunohistochemistry (IHC) have limited sensitivity as well as accuracy and require labor-intensive pretreatment steps. Here, an efficient individual nanorod-based plasmonic biosensor has been developed to detect hot-spot mutant p53 protein with the growth arrest and DNA damage 45 (GADD45) promoter. DNA-protein interactions of wild-type/mutant p53 proteins are kinetically analyzed on the biosensor surface through real-time monitoring of the localized surface plasmon resonance shift, and their dissociation constants and relative transcriptional activities are estimated. Hot-spot mutant proteins exhibited 14.29-fold higher in the dissociation constants and 19.91-fold lower in the relative transcriptional activities as compared to the wild-type proteins. These distinct kinetic values of hot-spot mutants allowed precise detection of hot-spot mutant protein and identification of mutated site of the protein using very small volume of clinical samples. We also demonstrated the clinical validation of the sensor by evaluating its performance in human breast tumor surgical specimens. The sensor’s ability to identify the mutant protein with high specificity and extremely low detection limit (11.47 fM) in comparison with the LC–MS/MS and IHC. The results confirmed that our sensor could be characterized as an efficient biosensor for application in clinical assays in terms of analytical performance.

Deep Intact Proteoform Characterization in Human Cell Lysate Using High-pH and Low-pH Reversed-Phase Liquid Chromatography.

Post-translational modifications (PTMs) play critical roles in biological processes and have significant effects on the structures and dynamics of proteins. Top-down proteomics methods were developed for and applied to the study of intact proteins and their PTMs in human samples. However, the large dynamic range and complexity of human samples makes the study of human proteins challenging. To address these challenges, we developed a 2D pH RP/RPLC-MS/MS technique that fuses high-resolution separation and intact protein characterization to study the human proteins in HeLa cell lysate. Our results provide a deep coverage of soluble proteins in human cancer cells. Compared to 225 proteoforms from 124 proteins identified when 1D separation was used, 2778 proteoforms from 628 proteins were detected and characterized using our 2D separation method. Many proteoforms with critically functional PTMs including phosphorylation were characterized. Additionally, we present the first detection of intact human GcvH proteoforms with rare modifications such as octanoylation and lipoylation. Overall, the increase in the number of proteoforms identified using 2DLC separation is largely due to the reduction in sample complexity through improved separation resolution, which enables the detection of low-abundance PTM-modified proteoforms. We demonstrate here that 2D pH RP/RPLC is an effective technique to analyze complex protein samples using top-down proteomics.

Abstract 1471: Short hairpin RNA-expressing oncolytic adenovirus-mediated inhibition of PDL1 significantly suppresses human cancer cell growth

Abstract In cancer immunotherapy, it is known that aberrant expression of immune checkpoint proteins in tumor cells and their resulting immunosuppression in surrounding tumor microenviroment and even in whole immune system represent the crucial limiting factors toward successful cancer treatment. Multiple studies evidenced that oncolytic viruses carrying biological molecule including cytokines, shRNAs and miRNAs relieve or attenuate immunosuppression, and may be a promising way toward curing tumor. In this study we generated an oncolytic adenovirus with expression of shRNA targeting human PDL1. The adenovirus exhibited proliferation activity more than two orders of magnitude higher in human cancer cells than in human normal primary cells. Western blot showed significantly decreased expressing levels of PDL1 protein in human cancer cells upon infection of the PDL1 shRNA expressing-oncolytic virus. FACS assay also showed decreased expression levels of PDL1 on the cell membrane after the infection of same viruses. In vivo experiments in two different genetic backgrounds mouse model <NOD-SCID mice and BALBC nude mice> demonstrated that the PDL1 shRNA expressing adenoviruses lysed the majority of the tumor cells derived from HCT116 colorectal cancer cells that were subcutaneously inoculated. Moreover, the adenoviruses downregulated PDL1 expression levels within the HCT116 colon cell-derived tumor cells, remarkably attenuated immunosuppression surrounding the HCT116 tumor. Consisted with these observations, TIL cell counts in the tumors derived from mice with shRNA expressing oncolytic adenovirus treatment were significantly higher than that from mice in other control groups. The growth of HCT116 colon cell-derived tumor in mice with oncolytic adenovirus treatment was greatly inhibited for a longer period compared with that in mice in other control groups. The oncolytic adenovirus described in this study features highly selective amplification in human tumor cells versus normal cells and inhibition of PDL1 expression in tumor cells, therefore it may be important toward developing novel method for cancer therapy. Citation Format: Jipo Sheng, Xue Wang, Xiaoming Dong, Jin Fu, Sanmao Kang, Fang Hu. Short hairpin RNA-expressing oncolytic adenovirus-mediated inhibition of PDL1 significantly suppresses human cancer cell growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1471.

Antiproliferative Benzoindazolequinones as Potential Cyclooxygenase-2 Inhibitors.

Quinones and nitrogen heterocyclic moieties have been recognized as important pharmacophores in the development of antitumor agents. This study aimed to establish whether there was any correlation between the in silico predicted parameters and the in vitro antiproliferative activity of a family of benzoindazolequinones (BIZQs), and to evaluate overexpressed proteins in human cancer cells as potential biomolecular targets of these compounds. For this purpose, this study was carried out using KATO-III and MCF-7 cell lines as in vitro models. Docking results showed that these BIZQs present better binding energies (ΔGbin) values for cyclooxygenase-2 (COX-2) than for other cancer-related proteins. The predicted ∆Gbin values of these BIZQs, classified in three series, positively correlated with IC50 measured in both cell lines (KATO-III: 0.72, 0.41, and 0.90; MCF-7: 0.79, 0.55, and 0.87 for Series I, II, and III, respectively). The results also indicated that compounds 2a, 2c, 6g, and 6k are the most prominent BIZQs, because they showed better IC50 and ∆Gbin values than the other derivatives. In silico drug absorption, distribution, metabolism, and excretion (ADME) properties of the three series were also analyzed and showed that several BIZQs could be selected as potential candidates for cancer pre-clinical assays.

Membrane-bound full-length Sonic Hedgehog identifies cancer stem cells in human non-small cell lung cancer.

The mechanism of Sonic Hedgehog (Shh) pathway activation in non-small cell lung cancer (NSCLC) is poorly described. Using an antibody against the Shh C-terminal domain, we found a small population of Shh-positive (Shh+) cells in NSCLC cells. The objective of this study was to characterize these Shh+ cells. Shh+ and Shh- cells were sorted by using Fluorescence Activated Cell Sorting (FACS) on 12 commercial NSCLC cell lines. Functional analyses on sorted cells were performed with gene expression assays (qRT-PCR and microarray) and cells were treated with cytotoxic chemotherapy and a targeted inhibitor of Shh signaling (GDC0449). We used in vivo models of nude mice inoculated with Shh+ and Shh- sorted cells and drug-treated cells. Finally, we confirmed our results in fresh human NSCLC samples (n=48) paired with normal lung tissue. We found that Shh+ cells produced an uncleaved, full-length Shh protein detected on the membranes of these cells. Shh+ cells exerted a paracrine effect on Shh- cells, inducing their proliferation and migration. Shh+ cells were chemo-resistant and showed features of cancer stem cells (CSCs) in vitro and in vivo. Pharmacological inhibition of the Shh pathway suppressed their CSC features. A high percentage of Shh+ cells was associated with poor prognosis in early-stage NSCLC patients. In conclusion, we describe for the first time the presence of an abnormal membrane-bound full-length Shh protein in human cancer cells that allows the identification of CSCs in vitro and in vivo.

Critical roles of SMYD2-mediated β-catenin methylation for nuclear translocation and activation of Wnt signaling.

Accumulation of β-catenin in the nucleus is a hallmark of activation of the Wnt/β-catenin signaling pathway, which drives development of a large proportion of human cancers. However, the mechanism of β-catenin nuclear translocation has not been well investigated. Here we report biological significance of SMYD2-mediated lysine 133 (K133) methylation of β-catenin on its nuclear translocation. Knockdown of SMYD2 attenuates the nuclear localization of β-catenin protein in human cancer cells. Consequently, transcriptional levels of well-known Wnt-signaling molecules, cMYC and CCND1, are significantly reduced. Substitution of lysine 133 to alanine in β-catenin almost completely abolishes its nuclear localization. We also demonstrate the K133 methylation is critical for the interaction of β-catenin with FOXM1. Furthermore, after treatment with a SMYD2 inhibitor, significant reduction of nuclear β-catenin and subsequent induction of cancer cell death are observed. Accordingly, our results imply that β-catenin methylation by SMYD2 promotes its nuclear translocation and activation of Wnt signaling.

Abstract 2153: Elephant p53 (EP53) expression induces apoptosis of human cancer cells

Abstract The goal of our study was to determine if elephant TP53 (EP53) proteins contributing to increased apoptosis and possible cancer resistance in elephants could translate into human cancer cells as a future effective cancer treatment. We previously reported that elephants have a lower than expected rate of cancer, 20 copies of TP53 (1 ancestral gene with introns [EP53-anc] and 19 retrogenes [EP53-retro1-19]), and increased p53-mediated apoptosis induced by DNA damage in elephant cells compared to human cells (Abegglen JAMA 2015). For the current study, we expressed various EP53 proteins in human cancer cells with different p53 status, including osteosarcoma (U2-OS, Saos-2), glioblastoma (T98G), and breast cancer (MCF7). Western blot analysis confirmed EP53 expression. We compared apoptosis in the human cancer cells transfected/transduced with negative control vectors vs. epitope or protein-tagged EP53 exposed to doxorubicin (to induce DNA damage). Apoptosis was measured by cell viability, caspase activity, Propidium Iodide/Annexin V staining, and fluorescence microscopy. We observed a significant increase in caspase activity (normalized to cell viability) of U2-OS and T98G cells expressing EP53 compared to negative control treated cells as shown in Table 1, and apoptosis with p21 restoration in Saos-2. In U2-OS, which overexpress MDM2, EP53 was more effective at inducing apoptosis compared to human TP53. Taken together, we found that EP53-anc restored p53-mediated apoptosis and EP53-anc / EP53-retro9 enhanced p53-mediated apoptosis. These data suggest for the first time that EP53 functions in human cancer cells to promote cell death. Ongoing efforts are exploring the EP53 mechanism of action that leads to increased apoptosis, including expression of EP53 in additional cancer types (lung, melanoma, colon, prostate, and others) with a variety of genetic backgrounds to characterize its functional context. These results support the further exploration of EP53-based cancer therapeutics. Table 1:Increase in apoptosis with EP53 expression relative to EP53 empty vector control cellsCell TypeTP53 StatusEP53-ancEP53-retro9ConstructAssay ResultsNo Treatment (fold difference)P-value1uM doxorubicin (fold difference)P-valueU-2 OS (osteosarcoma)WTApoptosisApoptosismyc-EP53-retro9Increase in caspase relative to control1.730.00911.791.7x10^-5eGFP-EP53-retro9Increase in caspase relative to control1.686.7x10^-52.590.0041eGFP-EP53-retro9Percent decrease in GFP positive cells23% percent decrease4.8x10^-5--dyk-EP53-ancIncrease in caspase relative to control14.225.4x10^-73.311.0x10^-5dyk-huTP53Increase in caspase relative to control10.91.2x10^-72.475.8x10^-5MCF7 (breast cancer)WT-ApoptosiseGFP-EP53-retro9Cell death by Propidium Iodide staining0.15% GFP/surface area0.011--T98G (glioblastoma)MUTApoptosisNo Apoptosisdyk-EP53-ancIncrease in caspase relative to control3.077.9x10^-91.552.6x10^-5myc-EP53-ancIncrease in caspase relative to control3.460.000151.526.8x10^-5dyk-huTP53Increase in caspase relative to control2.821.2x10^-51.88.6x10^-5 Citation Format: Lisa M. Abegglen, Lauren N. Donovan, Genevieve Couldwell, Rosann Robinson, Cristhian Toruno, Mor Goldfeder, Wendy K. Kiso, Dennis L. Schmitt, Aleah F. Caulin, Katrin P. Guillen, Bryan E. Welm, Carlo C. Maley, Avi Schroeder, Joshua D. Schiffman. Elephant p53 (EP53) expression induces apoptosis of human cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2153. doi:10.1158/1538-7445.AM2017-2153

Membrane Androgen Receptor ZIP9 Induces Croaker Ovarian Cell Apoptosis via Stimulatory G Protein Alpha Subunit and MAP Kinase Signaling.

Recent studies show that androgen-induced apoptosis in Atlantic croaker primary granulosa and theca (G/T) cells and in human breast and prostate cancer cell lines is mediated by the membrane androgen receptor ZIP9, which belongs to the SLC39A zinc transporter family. However, the apoptotic signaling pathways remain unclear because ZIP9 activates an inhibitory G protein in human cancer cells, whereas recombinant croaker ZIP9 activates a stimulatory G protein (Gs) in transfected cancer cells. We investigated androgen-dependent apoptotic pathways to identify the signaling pathways regulated through wild-type croaker ZIP9 in ovarian follicle cells. We show that the ZIP9-mediated apoptotic signaling pathway in croaker G/T cells shares several proapoptotic members with those in human cancer cells, but is activated through a Gsα subunit-dependent pathway. Testosterone treatment of croaker G/T cells increased intracellular zinc levels, mitogen-activated protein (MAP) kinase activity, caspase 3 activity, messenger RNA levels of proapoptotic members Bax, p53, and c-Jun N-terminal kinase, and the incidence of apoptosis, similar to findings in mammalian cancer cells, but also increased cyclic adenosine monophosphate concentrations. Transfection with small interfering RNA targeting croaker ZIP9 blocked testosterone-induced increase in bax, p53, and jnk expression. Testosterone-induced apoptosis and caspase 3 activation depended on the presence of extracellular zinc and were effectively blocked with cotreatment of inhibitors of the Gsα subunit, adenylyl cyclase, protein kinase A, and MAP kinase (Erk1/2) activation. These results indicate that ZIP9-mediated testosterone signaling in croaker G/T cells involves multiple pathways, some of which differ from those activated through ZIP9 in human cancer cells even though a similar apoptotic response is observed.

The multi-target drug BAI induces apoptosis in various human cancer cells through modulation of Bcl-xL protein.

Previous studies have demonstrated the anticancer effects of the newly developed cyclin-dependent kinase inhibitor BAI in various cancer cells. However, the molecular mechanisms of the cellular effects induced by BAI have not been fully elucidated. The objective of this study was to investigate the mechanisms underlying the regulation of B cell lymphoma-2 (Bcl-2) family proteins in BAI-induced apoptosis of cancer cells. BAI induced poly(ADP-ribose) polymerase cleavage and DEVDase activation dose- and time-dependently. However, BAI-induced apoptosis was not involved in reactive oxygen species generation or mitogen-activated protein kinases pathways. On the other hand, BAI reduced the mitochondrial membrane potential (∆ψm) dose- and time-dependently, and induced the release of apoptosis-inducing factor (AIF) and cytochromec from mitochondria in A549 and Caki cells. Furthermore, BAI-induced apoptosis was strongly associated with downregulation of B-cell lymphoma-extra large (Bcl-xL), but not Bcl-2, and BAI modulated the interactions among p53 and Bcl-2 family proteins in human cancer cells. Taken together, these results revealed that the regulations of Bcl-2 family proteins are correlated with BAI-induced apoptosis, suggesting that BAI is a potential multi-target agent of cancer.

Abstract A24: Characterizing a novel “Minimalist Hybrid Protein” inhibitor designed to target Myc activity in cancer

Abstract When deregulated, the c-Myc oncoprotein plays a key role in the development and progression of over 50% of all human cancers. As such, innovative and effective therapeutics are urgently needed to improve the treatment and survival of cancer patients, and we believe that directly modulating the activity of Myc would fill this important gap. Recent studies using a dominant negative protein, Omomyc, have provided evidence regarding the therapeutic value of inhibiting Myc activity in cancer. Specifically, perturbing Myc activity in vivo eradicates tumors without irreversible damage to normal cells, as demonstrated in mouse models of cancer. Using a similar yet novel strategy, we have generated a minimalist hybrid protein inhibitor known as MaxE47 (ME47), which is composed of the subdomains of different b-HLH-LZ and b-HLH transcription factor families. ME47 is designed to act as a competitive inhibitor of DNA E-box binding by the Myc/Max heterodimer. We hypothesize that ME47 can be used as a tool to better understand how best to interfere with oncogenic Myc and will lead to the development of Myc-targeted therapeutics. Using our prototype inhibitor, ME47, with Omomyc as a proof-of-concept control, we have established the cell systems and assays necessary to (1) evaluate the anti-cancer efficacy of our Minimalist Hybrid Proteins in human cancer cells, and (2) to determine their mechanism of action and specificity. Here we have demonstrated that ME47 significantly reduces anchorage-independent growth in soft agar and cell viability in tumor-derived breast cancer cell line MDA-MB-231, but not the non-transformed MCF10A breast cells. ME47 also significantly decreases tumor formation in xenograft mice. To begin to characterize the specificity and mechanism of action of ME47, luciferase reporter and chromatin immunoprecipitation assays were used to evaluate whether ME47 is Myc and/or E-box specific. Using luciferase reporter constructs fused to the promoters of established Myc target genes such as Nucleolin, we have also demonstrated that MaxE47 decreases the ability of Myc to activate target gene transcription. While this work is focused on the development of a Myc/Max E-box interaction inhibitor, Dr. Linda Penn's research group is also implementing BioID mass spectrometry to identify novel Myc interacting partners (see Penn lab abstract Dingar et al.). This work could potentially reveal new targets for a similar mode of disruptive inhibition, where a Minimalist Hybrid Protein designed to inhibit the association of the novel interacting partner and Myc would disrupt Myc activity. A direct inhibitor of Myc activity in cancer would re-define the field of Myc therapeutics and could develop into a valuable tool for personalized cancer medicine in those patients with deregulated Myc. The success we have had with our ME47 inhibitor suggests that we are progressing along the path to such an inhibitor, and we look forward to continuing our work with this inhibitor and other Minimalist Hybrid Proteins. Citation Format: K. Ashley Hickman, Lindsay C. Lustig, Dharmendra Dingar, Romina Ponzielli, Christina Bros, Warren W.C Chan, Jumi Shin, Linda J.Z Penn. Characterizing a novel “Minimalist Hybrid Protein” inhibitor designed to target Myc activity in cancer. [abstract]. In: Proceedings of the AACR Special Conference on Myc: From Biology to Therapy; Jan 7-10, 2015; La Jolla, CA. Philadelphia (PA): AACR; Mol Cancer Res 2015;13(10 Suppl):Abstract nr A24.

Targeting the cancer cell state

It can be argued that the development of effective anti-bacterial agents have shaped the history of the twentieth century. The success of these drugs is largely driven by the availability of unique bacterial proteins that are absent in human cells. Drugs that inhibit these proteins induce bacterial killing without significant toxicity to the patient. In contrast, cancer is a disease that is indelibly and undeniably human. With few exceptions,1 there are no unique proteins in human cancer cells that are absent in normal cells and would trigger irreversible cancer death upon inhibition. The discovery of oncogenic “driver” mutations led to the hypothesis that cancer cells may be uniquely dependent on onco-proteins encoded by these mutated genes.2 However, the clinical experiences with drugs that selectively inhibit these proteins have been largely disappointing.3 Efforts devoted to better understanding these “targeted” agents have taught us the following. Most oncogenes are members of large families of proto-oncogenes, and there are significant degrees of functional degeneracy between oncogenes and cellular proto-oncogenes. Consequently, cancer cells can circumvent the inhibition of onco-proteins through activation of alternative proto-oncogenes.3 It is in this context that the work reported by Ying et al is of importance.4 The authors studied glioblastoma, the most common form of primary brain cancer.5 Hyper-activation of Epidermal Growth Factor Receptor (EGFR) is a critical step in the pathogenesis of glioblastomas.6 However, when treated with EGFR inhibitors, EGFR expressing glioblastoma cells quickly acquire resistance by activating proto-oncogenes that substitute for EGFR.4 Unfortunately, a wide spectrum of proto-oncogenes is activated during this process such that simultaneous inhibition of these gene products would not be feasible.3 The critical observation made by the authors is that EGFR activation in glioblastoma triggers a cell state characterized by excessive accumulation of DNA damage, requiring increased utilization of DNA repair in order to ensure cell viability.7 The authors showed that, once this cell state is established, it is preserved even when EGFR is inhibited and another proto-oncogene is activated. The authors isolated independent glioblastoma clones that developed distinct mechanisms of resistance to 2 clinically used EGFR inhibitors, Erlotnib and Gefitnib. Notably, all clones isolated remained universally sensitive to an inhibitor of DNA repair targeting the Polo-Like Kinase 1(PLK1). These results suggest that activating an alternate proto-oncogene to drive the existing cellular circuit would be less costly than a complete realignment of fundamental cellular processes. The work suggests potential change in therapeutic paradigm at fundamental level from one targeting unique protein to one targeting unique cell states (Fig. 1). Because EGFR inhibitors have not been shown to alter DNA damage response and DNA repair inhibitors have not been shown to alter EGFR signaling, the authors propose that these therapeutic approaches impose parallel and orthogonal selection pressures on glioblastoma cells. Accordingly, therapeutic synergy was observed in this combined approach. These results establish a sound foundation for combinatorial therapeutic approaches integrating inhibitors directed against oncogenes and oncogene associated cell-states. It is likely that oncogenes functionally intersect other fundamental cellular processes, such as DNA replication, transcription, or mitosis. Importantly, the aggregate of work over the past 50 years have yielded effective inhibitors to many of these processes. Characterizing the therapeutic efficacy of these inhibitors with molecular targeted agents should afford opportunities for meaningful improvement in the clinical outcome cancer patients and contribute to human history for the upcoming century. Figure 1. Multiple oncogenes and proto-oncogenes induce similar forms of cellular stress (e.g., DNA damage). On the left: to ensure cell survival despite this stress, the oncogenes and proto-oncogenes activate cellular processes (e.g., DNA repair) to compensate ...

Quantitative comparison of a human cancer cell surface proteome between interphase and mitosis

The cell surface is the cellular compartment responsible for communication with the environment. The interior of mammalian cells undergoes dramatic reorganization when cells enter mitosis. These changes are triggered by activation of the CDK1 kinase and have been studied extensively. In contrast, very little is known of the cell surface changes during cell division. We undertook a quantitative proteomic comparison of cell surface-exposed proteins in human cancer cells that were tightly synchronized in mitosis or interphase. Six hundred and twenty-eight surface and surface-associated proteins in HeLa cells were identified; of these, 27 were significantly enriched at the cell surface in mitosis and 37 in interphase. Using imaging techniques, we confirmed the mitosis-selective cell surface localization of protocadherin PCDH7, a member of a family with anti-adhesive roles in embryos. We show that PCDH7 is required for development of full mitotic rounding pressure at the onset of mitosis. Our analysis provided basic information on how cell cycle progression affects the cell surface. It also provides potential pharmacodynamic biomarkers for anti-mitotic cancer chemotherapy.

Quantification of XRCC and DNA-PK proteins in cancer cell lines and human tumors by LC-MS/MS.

The x-ray repair cross-complementing (XRCC) proteins and a catalytic subunit of nuclear DNA-dependent serine/threonine protein kinase (DNA-PK) play important roles in cancer biology. Understanding the protein expression levels allows us to reconstruct in vivo functionality and to qualify protein biomarkers. XRCC and DNA-PK proteins in human cancer cells and tumor tissues have been identified and quantified by selected peptides using NanoLC and high-resolution mass spectrometry. The stable isotope-labeled full-length protein XRCC4 ([(13)C6, (15)N4]-arginine and [(13)C6, (15)N2]-lysine) uses as the internal standard. The assay range is 0.140-450 fmol (coefficient of variation: 25%) for XRCC4 in bovine serum albumen. The quantitative protein expression levels for XRCC and DNA-PK in HeLa, Ramos and HEK-293 cells and tumor tissues (lung and lymphoma) are reported.

Distinct and overlapping control of 5-methylcytosine and 5-hydroxymethylcytosine by the TET proteins in human cancer cells.

BackgroundThe TET family of dioxygenases catalyze conversion of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), but their involvement in establishing normal 5mC patterns during mammalian development and their contributions to aberrant control of 5mC during cellular transformation remain largely unknown. We depleted TET1, TET2, and TET3 in a pluripotent embryonic carcinoma cell model and examined the impact on genome-wide 5mC, 5hmC, and transcriptional patterns.ResultsTET1 depletion yields widespread reduction of 5hmC, while depletion of TET2 and TET3 reduces 5hmC at a subset of TET1 targets suggesting functional co-dependence. TET2 or TET3 depletion also causes increased 5hmC, suggesting these proteins play a major role in 5hmC removal. All TETs prevent hypermethylation throughout the genome, a finding dramatically illustrated in CpG island shores, where TET depletion results in prolific hypermethylation. Surprisingly, TETs also promote methylation, as hypomethylation was associated with 5hmC reduction. TET function is highly specific to chromatin environment: 5hmC maintenance by all TETs occurs at polycomb-marked chromatin and genes expressed at moderate levels; 5hmC removal by TET2 is associated with highly transcribed genes enriched for H3K4me3 and H3K36me3. Importantly, genes prone to hypermethylation in cancer become depleted of 5hmC with TET deficiency, suggesting that TETs normally promote 5hmC at these loci. Finally, all three TETs, but especially TET2, are required for 5hmC enrichment at enhancers, a condition necessary for expression of adjacent genes.ConclusionsThese results provide novel insight into the division of labor among TET proteins and reveal important connections between TET activity, the chromatin landscape, and gene expression.

Abstract 5656: Preclinical evaluation of cytotoxic effect of photosensitive fluorescent protein in human cancer cells

Abstract Photodynamic therapy (PDT) is an anticancer therapy to induce tumor-specific cytotoxicity by accumulation of photosensitizers (PSs) and following non-toxic light irradiation to tumor tissues. Non-toxic light irradiation induces the PS-mediated generation of reactive oxygen species (ROS) and subsequent cytotoxicity in tumor cells. For clinical application, some kinds of PSs, such as photofrin and laserphyrin, are intravenously injected before light irradiation in anticancer PDT. However, the lack of sufficient and continuous accumulation of PSs in tumor tissues makes difficult to eradicate tumor cells by PDT. Therefore, the development of novel PSs that accumulate to tumor tissues more efficiently and persistently is required to improve the antitumor effect of PDT. Recently, a bioengineered fluorescent protein KillerRed has been reported to generate ROS upon green light irradiation, suggesting a potential of KillerRed fluorescent protein as a novel PS. In this study, we investigated the antitumor effect of KillerRed fluorescent protein in human cancer cells in combination with PDT. Transient transfection with KillerRed expression vector induced the photosensitive cytotoxicity upon green light irradiation within a few hours in human cancer HeLa and OST cells. To further evaluate the cytotoxic effect of KillerRed fluorescent protein in human cancer cells, we obtained the stable transfectants expressing cytotoxic KillerRed or non-cytotoxic Katushka fluorescent protein from human lung cancer H1299 cells. Green light irradiation induced the cytotoxic effect within one hour in H1299-KillerRed cells, but not in H1299-Katushka or H1299 cells. H1299-KillerRed cells irradiated with green light showed significantly higher levels of ROS, which was confirmed by intracellular fluorescence level of 2′,7′-Dichlorodihydrofluorescein Diacetate, than H1299-Katushka or H1299 cells. Immunocytochemistry further revealed that green light-irradiated H1299-KillerRed cells showed the apoptotic cell death with the cleavage of caspase-3 24 hours after irradiation. These results suggest that KillerRed fluorescent protein is a potent novel PS inducing ROS generation and apoptotic cell death in tumor cells in anticancer PDT. The development of virus-mediated delivery system for tumor-specific induction of KillerRed fluorescent protein is under way. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5656. doi:1538-7445.AM2012-5656

Decreased MCM2-6 in Drosophila S2 Cells Does Not Generate Significant DNA Damage or Cause a Marked Increase in Sensitivity to Replication Interference

A reduction in the level of some MCM proteins in human cancer cells (MCM5 in U20S cells or MCM3 in Hela cells) causes a rapid increase in the level of DNA damage under normal conditions of cell proliferation and a loss of viability when the cells are subjected to replication interference. Here we show that Drosophila S2 cells do not appear to show the same degree of sensitivity to MCM2-6 reduction. Under normal cell growth conditions a reduction of >95% in the levels of MCM3, 5, and 6 causes no significant short term alteration in the parameters of DNA replication or increase in DNA damage. MCM depleted cells challenged with HU do show a decrease in the density of replication forks compared to cells with normal levels of MCM proteins, but this produces no consistent change in the levels of DNA damage observed. In contrast a comparable reduction of MCM7 levels has marked effects on viability, replication parameters and DNA damage in the absence of HU treatment.

Anti-neoplastic agent thymoquinone induces degradation of α and β tubulin proteins in human cancer cells without affecting their level in normal human fibroblasts

The microtubule-targeting agents derived from natural products, such as vinca-alkaloids and taxanes are an important family of efficient anti-cancer drugs with therapeutic benefits in both haematological and solid tumors. These drugs interfere with the assembly of microtubules of α/β tubulin heterodimers without altering their expression level. The aim of the present study was to investigate the effect of thymoquinone (TQ), a natural product present in black cumin seed oil known to exhibit putative anti-cancer activities, on α/β tubulin expression in human astrocytoma cells (cell line U87, solid tumor model) and in Jurkat cells (T lymphoblastic leukaemia cells). TQ induced a concentration- and time-dependent degradation of α/β tubulin in both cancer cell types. This degradation was associated with the up-regulation of the tumor suppressor p73 with subsequent induction of apoptosis. Interestingly, TQ had no effect on α/β tubulin protein expression in normal human fibroblast cells, which were used as a non-cancerous cell model. These data indicate that TQ exerts a selective effect towards α/β tubulin in cancer cells. In conclusion, the present findings indicate that TQ is a novel anti-microtubule drug which targets the level of α/β tubulin proteins in cancer cells. Furthermore, they highlight the interest of developing anti-cancer therapies that target directly tubulin rather than microtubules dynamics.

A day in the half-life of a protein

Researchers describe a method called bleach-chase to quantitatively measure the half-lives of fluorescently tagged proteins in human cancer cells.