A modular master regulator landscape controls cancer transcriptional identity.

Despite considerable efforts, the mechanisms linking genomic alterations to the transcriptional identity of cancer cells remain elusive. Integrative genomic analysis, using a network-based approach, identified 407 master regulator (MR) proteins responsible for canalizing the genetics of individual samples from 20 cohorts in The Cancer Genome Atlas (TCGA) into 112 transcriptionally distinct tumor subtypes. MR proteins could be further organized into 24 pan-cancer, master regulator block modules (MRBs), each regulating key cancer hallmarks and predictive of patient outcome in multiple cohorts. Of all somatic alterations detected in each individual sample, >50% were predicted to induce aberrant MR activity, yielding insight into mechanisms linking tumor genetics and transcriptional identity and establishing non-oncogene dependencies. Genetic and pharmacological validation assays confirmed the predicted effect of upstream mutations and MR activity on downstream cellular identity and phenotype. Thus, co-analysis of mutational and gene expression profiles identified elusive subtypes and provided testable hypothesis for mechanisms mediating the effect of genetic alterations.

Network-based elucidation of colon cancer drug resistance mechanisms by phosphoproteomic time-series analysis.

Aberrant signaling pathway activity is a hallmark of tumorigenesis and progression, which has guided targeted inhibitor design for over 30 years. Yet, adaptive resistance mechanisms, induced by rapid, context-specific signaling network rewiring, continue to challenge therapeutic efficacy. Leveraging progress in proteomic technologies and network-based methodologies, we introduce Virtual Enrichment-based Signaling Protein-activity Analysis (VESPA)-an algorithm designed to elucidate mechanisms of cell response and adaptation to drug perturbations-and use it to analyze 7-point phosphoproteomic time series from colorectal cancer cells treated with clinically-relevant inhibitors and control media. Interrogating tumor-specific enzyme/substrate interactions accurately infers kinase and phosphatase activity, based on their substrate phosphorylation state, effectively accounting for signal crosstalk and sparse phosphoproteome coverage. The analysis elucidates time-dependent signaling pathway response to each drug perturbation and, more importantly, cell adaptive response and rewiring, experimentally confirmed by CRISPR knock-out assays, suggesting broad applicability to cancer and other diseases.

Network-based elucidation of colon cancer drug resistance by phosphoproteomic time-series analysis.

Aberrant signaling pathway activity is a hallmark of tumorigenesis and progression, which has guided targeted inhibitor design for over 30 years. Yet, adaptive resistance mechanisms, induced by rapid, context-specific signaling network rewiring, continue to challenge therapeutic efficacy. By leveraging progress in proteomic technologies and network-based methodologies, over the past decade, we developed VESPA-an algorithm designed to elucidate mechanisms of cell response and adaptation to drug perturbations-and used it to analyze 7-point phosphoproteomic time series from colorectal cancer cells treated with clinically-relevant inhibitors and control media. Interrogation of tumor-specific enzyme/substrate interactions accurately inferred kinase and phosphatase activity, based on their inferred substrate phosphorylation state, effectively accounting for signal cross-talk and sparse phosphoproteome coverage. The analysis elucidated time-dependent signaling pathway response to each drug perturbation and, more importantly, cell adaptive response and rewiring that was experimentally confirmed by CRISPRko assays, suggesting broad applicability to cancer and other diseases.

Interferon gamma is recognised by importin alpha/beta: enhanced nuclear localising and transactivation activities of an interferon gamma mimetic.

Interferon (IFN) gamma's ability to localise in the nucleus and function in gene activation has been known for some time, although the role of the conventional nuclear transporting importin molecules is unclear. Here, we demonstrate for the first time the direct recognition of IFNgamma and an IFNgamma mimetic peptide by IMPalpha and the IMPalpha/beta heterodimer, where the IFNgamma mimetic shows higher affinity. Significantly, this correlates well both with in vivo ability to target green fluorescent protein to the nucleus in transfected cells as determined by quantitative confocal laser scanning microscopy, as well as GAS promoter activity of a luciferase reporter. This has important implications for IFNgamma's anti-viral action, and the potential use of the IFNgamma mimetic in antiviral therapies.

A precision oncology approach to the pharmacological targeting of mechanistic dependencies in neuroendocrine tumors.

We introduce and validate a new precision oncology framework for the systematic prioritization of drugs targeting mechanistic tumor dependencies in individual patients. Compounds are prioritized on the basis of their ability to invert the concerted activity of master regulator proteins that mechanistically regulate tumor cell state, as assessed from systematic drug perturbation assays. We validated the approach on a cohort of 212 gastroenteropancreatic neuroendocrine tumors (GEP-NETs), a rare malignancy originating in the pancreas and gastrointestinal tract. The analysis identified several master regulator proteins, including key regulators of neuroendocrine lineage progenitor state and immunoevasion, whose role as critical tumor dependencies was experimentally confirmed. Transcriptome analysis of GEP-NET-derived cells, perturbed with a library of 107 compounds, identified the HDAC class I inhibitor entinostat as a potent inhibitor of master regulator activity for 42% of metastatic GEP-NET patients, abrogating tumor growth in vivo. This approach may thus complement current efforts in precision oncology.

A SOCS-1 peptide mimetic inhibits both constitutive and IL-6 induced activation of STAT3 in prostate cancer cells.

Prostate cancer is the second highest cause of cancer-related deaths of men in the US. Signal transducers and activators of transcription (STATs) proteins are a small family of latent cytoplasmic transcription factors that act downstream of Janus kinase (JAK) activation and mediate intracellular signaling from a wide variety of cytokines, growth factors, and hormones. Aberrant activation of STAT3 has been implicated in the progression of many human carcinomas, including prostate cancer. Previously, we have characterized a novel tyrosine kinase inhibitor peptide, Tkip, that is a mimetic of suppressor of cytokine signaling 1 (SOCS-1). Similar to SOCS-1, Tkip binds to the autophosphorylation site of JAK2 and inhibits phosphorylation of STAT1alpha. In this study, we determined the inhibitory effects of Tkip on the human prostate cancer cell lines DU145 and LNCaP. Tkip inhibited cellular proliferation of both DU145 and LNCaP cells, with a slightly greater antiproliferative effect on DU145 cells. Cell cycle analysis using flow cytometry showed Tkip blockage of progression into the S phase of the cell cycle. Tkip also inhibited constitutive (DU145) and IL-6-induced (LNCaP) activation of STAT3, consistent with the fact that STAT3 activation is mediated by JAK2. Tkip also slightly reduced the levels of cyclin D1, an important regulator of cell cycle progression into S phase, in DU145 and LNCaP cancer cell lines. These data describe a potentially important therapeutic that targets both constitutive and IL-6-induced STAT3 activation in human prostate cancer cell lines.

Dclk1 Defines Quiescent Pancreatic Progenitors that Promote Injury-Induced Regeneration and Tumorigenesis.

The existence of adult pancreatic progenitor cells has been debated. While some favor the concept of facultative progenitors involved in homeostasis and repair, neither a location nor markers for such cells have been defined. Using genetic lineage tracing, we show that Doublecortin-like kinase-1 (Dclk1) labels a rare population of long-lived, quiescent pancreatic cells. In vitro, Dclk1+ cells proliferate readily and sustain pancreatic organoid growth. In vivo, Dclk1+ cells are necessary for pancreatic regeneration following injury and chronic inflammation. Accordingly, their loss has detrimental effects after cerulein-induced pancreatitis. Expression of mutant Kras in Dclk1+ cells does not affect their quiescence or longevity. However, experimental pancreatitis converts Kras mutant Dclk1+ cells into potent cancer-initiating cells. As a potential effector of Kras, Dclk1 contributes functionally to the pathogenesis of pancreatic cancer. Taken together, these observations indicate that Dclk1 marks quiescent pancreatic progenitors that are candidates for the origin of pancreatic cancer.

The IFNAR1 subunit of the type I IFN receptor complex contains a functional nuclear localization sequence.

A nuclear localization sequence (NLS) in the type II interferon (IFN) IFN gamma, which is responsible for the nuclear translocation of both the ligand and the alpha-subunit (IFNGR1) of the receptor complex, has previously been characterized and its role in signaling examined in detail. We have now identified an NLS in the type I IFN receptor (IFNAR) common subunit IFNAR1 from humans and show that the human IFNAR1 subunit can translocate to the nucleus following human IFN beta stimulation. An NLS in human IFNAR1 is located in the extracellular domain of IFNAR1 within the sequence (382)RKIIEKKT (numbered for the precursor form). Nuclear import by the NLS functions in a conventional fashion requiring cytosolic import factors, is energy-dependent and inhibited by the prototypical NLS of the SV40 large T-antigen. These studies provide a mechanism for nuclear import of IFNAR1, as well as for type I IFN ligands, and a starting point for studying an alternate role for IFNAR1 in nuclear signaling within the type I IFN system.

Targeting nonclassical oncogenes for therapy in T-ALL.

Constitutive phosphoinositide 3-kinase (PI3K)/Akt activation is common in T cell acute lymphoblastic leukemia (T-ALL). Although four distinct class I PI3K isoforms (α, ß, γ, δ) could participate in T-ALL pathogenesis, none has been implicated in this process. We report that in the absence of PTEN phosphatase tumor suppressor function, PI3Kγ or PI3Kδ alone can support leukemogenesis, whereas inactivation of both isoforms suppressed tumor formation. The reliance of PTEN null T-ALL on the combined activities of PI3Kγ/δ was further demonstrated by the ability of a dual inhibitor to reduce disease burden and prolong survival in mice as well as prevent proliferation and promote activation of proapoptotic pathways in human tumors. These results support combined inhibition of PI3Kγ/δ as therapy for T-ALL.

Peptide mimetics of gamma interferon possess antiviral properties against vaccinia virus and other viruses in the presence of poxvirus B8R protein.

We have developed peptide mimetics of gamma interferon (IFN-gamma) that play a direct role in the activation and nuclear translocation of STAT1alpha transcription factor. These mimetics do not act through recognition by the extracellular domain of IFN-gamma receptor but rather bind to the cytoplasmic domain of the receptor chain 1, IFNGR-1, and thereby initiate the cellular signaling. Thus, we hypothesized that these mimetics would bypass the poxvirus virulence factor B8R protein that binds to intact IFN-gamma and prevents its interaction with the receptor. Human and murine IFN-gamma mimetic peptides were introduced into an adenoviral vector for intracellular expression. Murine IFN-gamma mimetic peptide was also expressed via chemical synthesis with an attached lipophilic group for penetration of cell plasma membrane. In contrast to intact human IFN-gamma, the mimetics did not bind poxvirus B8R protein, a homolog of the IFN-gamma receptor extracellular domain. Expression of B8R protein in WISH cells did not block the antiviral effect of the mimetics against encephalomyocarditis or vesicular stomatitis virus, while the antiviral activity of human IFN-gamma was neutralized. Consistent with the antiviral activity, the upregulation of MHC class I molecules on WISH cells by the IFN-gamma mimetics was not affected by B8R protein, while IFN-gamma-induced upregulation was blocked. Finally, the mimetics, but not IFN-gamma, inhibited vaccinia virus replication in African green monkey kidney BSC-40 cells. The data presented demonstrate that small peptide mimetics of IFN-gamma can avoid the B8R virulence factor for poxviruses and, thus, are potential candidates for antivirals against smallpox virus.

Lipid microdomains are required sites for the selective endocytosis and nuclear translocation of IFN-gamma, its receptor chain IFN-gamma receptor-1, and the phosphorylation and nuclear translocation of STAT1alpha.

IFN-gamma contains a nuclear localization sequence that may play a role in the nuclear transport of activated STAT1alpha via a complex of IFN-gamma/IFN-gamma receptor (IFNGR)-1/STAT1alpha with the nuclear importer nucleoprotein interactor 1. In this study, we examine the mechanism of endocytosis of IFNGR-1 and the relationship of its nuclear translocation to that of STAT1alpha. In untreated WISH cells, both IFNGR-1 and IFNGR-2 were constitutively localized within caveolae-like microdomains isolated from plasma membrane. However, treatment of cells with IFN-gamma resulted in rapid migration of IFNGR-1, but not IFNGR-2, from these microdomains. Filipin pretreatment, which specifically inhibits endocytosis from caveolae-like microdomains, inhibited the nuclear translocation of IFN-gamma and IFNGR-1 as well as the tyrosine phosphorylation and nuclear translocation of STAT1alpha, but did not affect the binding of IFN-gamma to these cells. In the Jurkat T lymphocyte cell line, which does not express caveolin-1, nuclear translocation of IFNGR-1 and STAT1alpha were similarly inhibited by filipin pretreatment. Isolation of lipid microdomains from Jurkat cells showed that both IFNGR-1 and IFNGR-2 were associated with lipid microdomains only after stimulation with IFN-gamma, suggesting that the IFNGR subunits are recruited to lipid microdomains by IFN-gamma binding in lymphocytes (Jurkat) in contrast to their constitutive presence in epithelial (WISH) cells. In contrast, treatments that block clathrin-dependent endocytosis did not inhibit either activation or nuclear translocation of STAT1alpha or the nuclear translocation of IFN-gamma or IFNGR-1. Thus, membrane lipid microdomains play an important role in IFN-gamma-initiated endocytic events involving IFNGR-1, and the nuclear translocation of IFN-gamma, IFNGR-1, and STAT1alpha.

Trafficking and signaling pathways of nuclear localizing protein ligands and their receptors.

Interaction of ligands such as epidermal growth factor and interferon-gamma with the extracellular domains of their plasma membrane receptors results in internalization followed by translocation into the nucleus of the ligand and/or receptor. There has been reluctance, however, to ascribe signaling importance to this, the focus instead being on second messenger pathways, including mobilization of kinases and inducible transcription factors (TFs). The latter, however, fails to explain the fact that so many ligands stimulate the same second messenger cascades/TFs, and yet show distinct gene activation profiles. This is particularly apt in the case of the seven STAT TFs that are held to be the mediators of the distinct cellular functions of over 60 ligands. The current review focuses on five representative nuclear localizing ligands for which there is documentation of translocation into the cytosol and nucleus through well-characterized pathways, in addition to a role in gene activation by ligand/receptor in the nucleus.

Signal transduction mechanism of a peptide mimetic of interferon-gamma.

The C-terminus of interferon-gamma (IFNgamma) contains a nuclear localization sequence (NLS) required for the activation and nuclear translocation of the transcription factor STAT1alpha and induction of IFNgamma-activated genes. On the basis of this and other studies, we developed a peptide mimetic of IFNgamma that possesses the IFNgamma functions of antiviral activity and upregulation of MHC class II molecules. The mimetic also shares with IFNgamma the ability to induce the activation and nuclear translocation of STAT1alpha and the IFNgamma receptor (IFNGR)-1 subunit. The mimetic, IFNgamma(95-132), is a peptide that consists of the C-terminal residues 95-132 of murine IFNgamma and contains a required alpha-helical domain and the NLS of IFNgamma. In this study, we determined the mechanism of the intracellular action of the mimetic at the level of signal transduction. We show that the mimetic mediates the nuclear transport of IFNGR-1 through its interaction with IFNGR-1 cytoplasmic region 253-287 via both the helical region and the NLS of IFNgamma(95-132). Alanine substitutions of the NLS of the mimetic showed that the NLS was required for nuclear translocation and that the nuclear transport properties of the mimetic correlated with its ability to bind IFNGR-1. These data also show that the NLS of IFNgamma(95-132) can interact simultaneously with IFNGR-1 and the nuclear import machinery. We found that in in vitro nuclear transport assays tyrosine-phosphorylated STAT1alpha failed to undergo nuclear translocation in the presence of nuclear import factors, but was transported to nucleus in the presence of IFNgamma(95-132) and JAK2-phosphorylated IFNGR-1, to which STAT1alpha binds, as a complex of IFNgamma(95-132)/IFNGR-1/STAT1alpha. Thus, the mimetic, which possesses IFNgamma function, is directly involved as a chaperone in the nuclear transport of STAT1alpha and shares this mechanism of action with that previously described for IFNgamma. The mimetic, like IFNgamma, is able to upregulate the tumor suppressor p21WAF1/CIP1, a direct target of STAT1alpha, and this ability requires the NLS of the mimetic. However, unlike IFNgamma, the mimetic is unable to downregulate c-myc and hence does not inhibit the cycling of cells. This suggests that IFNgamma has additional functions that are not tied directly to the nuclear translocation of STAT1alpha.

Superantigen enhancement of specific immunity: antibody production and signaling pathways.

Superantigens are microbial proteins that induce massive activation, proliferation, and cytokine production by CD4+ T cells via specific Vbeta elements on the TCR. In this study we examine superantigen enhancement of Ag-specific CD4+ T cell activity for humoral B cell responses to T-dependent Ags BSA and HIV gp120 envelope, type I T-independent Ag LPS, and type II T-independent Ag pneumococcal polysaccharides. Injection of BSA followed by a combination of superantigens staphylococcal enterotoxin A and staphylococcal enterotoxin B (SEB) 7 days later enhanced the anti-BSA Ab response in mice approximately 4-fold as compared with mice given BSA alone. The anti-gp120 response was enhanced approximately 3-fold by superantigens. The type II T-independent Ag pneumococcal polysaccharide response was enhanced approximately 2.3-fold by superantigens, whereas no effect was observed on the response to the type I T-independent Ag LPS. The superantigen effect was completely blocked by the CD4+ T cell inhibitory cytokine IL-10. SEB-stimulated human CD4+ T cells were examined to determine the role of the mitogen-activated protein (MAP) kinase signal transduction pathway in superantigen activation of T cells. Inhibitors of the mitogen pathway of MAP kinase blocked SEB-induced proliferation and IFN-gamma production, while an inhibitor of the p38 stress pathway had no effect. Consistent with this, SEB activated extracellular signal-regulated kinase/MAP kinase as well as MAP kinase-interacting kinase, a kinase that phosphorylates eIF4E, which is an important component of the eukaryotic protein synthesis initiation complex. Both kinases were inhibited by IL-10. Thus, superantigens enhance humoral immunity via Ag-specific CD4+ T cells involving the stress-independent pathway of MAP kinase.

The role of IFNgamma nuclear localization sequence in intracellular function.

Intracellularly expressed interferon gamma (IFNgamma) has been reported to possess biological activity similar to that of IFNgamma added to cells. This study addresses the mechanisms for such similar biological effects. Adenoviral vectors were used to express a non-secreted form of human IFNgamma or a non-secreted mutant form in which a previously demonstrated nuclear localization sequence (NLS), 128KTGKRKR134, was replaced with alanines at K and R positions. With the vector expressing non-secreted wild-type IFNgamma, biological responses normally associated with extracellular IFNgamma, such as antiviral activity and MHC class I upregulation, were observed, although the mutant IFNgamma did not possess biological activity. Intracellular human IFNgamma possessed biological activity in mouse L cells, which do not recognize extracellularly added human IFNgamma. Thus, the biological activity was not due to leakage of IFNgamma to the surroundings and subsequent interaction with the receptor on the cell surface. Biological function was associated with activation of STAT1alpha and nuclear translocation of IFNgamma, IFNGR1 and STAT1alpha. Immunoprecipitation of cellular extracts with antibody to the nuclear transporter NPI-1 showed the formation of a complex with IFNgamma-IFNGR1-STAT1alpha. To provide the physiological basis for these effects we show that extracellularly added IFNgamma possesses intracellular signaling activity that is NLS dependent, as suggested by our previous studies, and that this activity occurs via the receptor-mediated endocytosis of IFNgamma. The data are consistent with previous observations that the NLS of extracellularly added IFNgamma plays a role in IFNgamma signaling.

Characterization of a peptide inhibitor of Janus kinase 2 that mimics suppressor of cytokine signaling 1 function.

Positive and negative regulation of cytokines such as IFN-gamma are key to normal homeostatic function. Negative regulation of IFN-gamma in cells occurs via proteins called suppressors of cytokine signaling (SOCS)1 and -3. SOCS-1 inhibits IFN-gamma function by binding to the autophosphorylation site of the tyrosine kinase Janus kinase (JAK)2. We have developed a short 12-mer peptide, WLVFFVIFYFFR, that binds to the autophosphorylation site of JAK2, resulting in inhibition of its autophosphorylation as well as its phosphorylation of IFN-gamma receptor subunit IFNGR-1. The JAK2 tyrosine kinase inhibitor peptide (Tkip) did not bind to or inhibit tyrosine autophosphorylation of vascular endothelial growth factor receptor or phosphorylation of a substrate peptide by the protooncogene tyrosine kinase c-src. Tkip also inhibited epidermal growth factor receptor autophosphorylation, consistent with the fact that epidermal growth factor receptor is regulated by SOCS-1 and SOCS-3, similar to JAK2. Although Tkip binds to unphosphorylated JAK2 autophosphorylation site peptide, it binds significantly better to tyrosine-1007 phosphorylated JAK2 autophosphorylation site peptide. SOCS-1 only recognizes the JAK2 site in its phosphorylated state. Thus, Tkip recognizes the JAK2 autophosphorylation site similar to SOCS-1, but not precisely the same way. Consistent with inhibition of JAK2, Tkip inhibited the ability of IFN-gamma to induce an antiviral state as well as up-regulate MHC class I molecules on cells at a concentration of approximately 10 microM. This is similar to the K(d) of SOCS-3 for the erythropoietin receptor. These data represent a proof-of-concept demonstration of a peptide mimetic of SOCS-1 that regulates JAK2 tyrosine kinase function.