a b s t r a c tReceptor-interacting protein 3 (RIP3) has been implicated in ischemic necrosis of retinal cells. An in silico analysis followed by experimental validation identified death associated protein (Daxx) as a novel substrate of RIP3. In vitro binding studies revealed that RIP3 binds to the serine/proline/threonine-rich domain (amino acid 625-740) of Daxx. Upon ischemic insult, RIP3 phosphorylated Daxx at Ser-668 in the retinal ganglion cells, triggering nuclear export of Daxx. Depletion of RIP3 significantly inhibited nuclear export of Daxx and attenuated cell death to a great extent. Collectively, the findings of this study demonstrate that phosphorylation of Daxx by RIP3 comprises an important part of ischemic necrosis in rat retinal ganglion cells. Structured summary of protein interactions:Daxx binds to Rip3 by pull down (View Interaction: 1, 2) Rip3 and Daxx colocalize by fluorescence microscopy (View interaction) Rip3 physically interacts with Daxx by anti bait coimmunoprecipitation (View interaction) Daxx binds to Rip1 bypull down (View interaction)
High-content screening (HCS) using RNA interference (RNAi) in combination with automated microscopy is a powerful investigative tool to explore complex biological processes. However, despite the plethora of data generated from these screens, little progress has been made in analyzing HC data using multivariate methods that exploit the full richness of multidimensional data. We developed a novel multivariate method for HCS, Multivariate Robust Analysis Method (M-RAM), integrating image feature selection with ranking of perturbations for hit identification, and applied this method to a HC RNAi screen to discover novel components of the DNA damage response in an osteosarcoma cell line. M-RAM automatically selects the most informative phenotypic readouts and time points to facilitate the more efficient design of follow-up experiments and enhance biological understanding. Our method outperforms univariate hit identification and identifies relevant genes that these approaches would have missed. We found that statistical cell-to-cell variation in phenotypic responses is an important predictor of ‘hits’ in RNAi-directed image-based screens. Genes that we identified as modulators of DNA damage signaling in U2OS cells include B-Raf, a cancer driver gene in multiple tumor types, whose role in DNA damage signaling we confirm experimentally, and multiple subunits of protein kinase A.
Dynamic re-wiring of signaling networks is a prominent mechanism responsible for the development of resistance to many molecular-targeted anti-cancer agents. Here we show how this same dynamic re-wiring process can be used therapeutically to enhance the response of tumors to cytotoxic anti-cancer agents. Using cell lines and murine tumor models of triple-negative breast cancer, non-small cell lung cancer, and head and neck cancer, we show that chronic inhibition of EGFR and/or FGFR driver oncogenes dramatically enhances cell death in response to topoisomerase inhibitors and platinum DNA crosslinking drugs. In marked contrast, no such sensitization is observed when the growth factor receptor inhibitors are co-administered with the cytotoxic agents. The molecular mechanism responsible for this time-dependent growth factor inhibitor-induced tumor cell sensitization was explored using a systems biology-based model of DNA damage signaling in which protein kinase activities, substrate phosphorylation, and phosphoprotein-binding events for multiple signaling pathways were quantitatively measured at densely sampled points in time, and mathematically correlated with tumor cell responses including cell cycle arrest, cytokine production, autophagy, and apoptosis. This analysis revealed that sustained EGFR/FGFR suppression unmasks an apoptotic network involving Caspase-8 that is normally suppressed by oncogene addiction, resulting in an enhanced apoptotic response to equivalent amounts of DNA damage. This discovery demonstrates that the timing interval between administration of different drugs in combination chemotherapy can have profound effects on the tumor response through the dynamic re-wiring of cell signaling pathways in real time. Finally, we take advantage of this dynamic re-wiring process by developing tumor-targeted time-staggered release nanoparticles that deliver EGFR inhibitors at early times followed by the delayed release of doxorubicin. We show that these nanoparticles cause dramatic regression of murine NSCLC and TNBC tumor xenografts in vivo, substantiating the utility of therapeutic network re-wiring for anti-cancer therapy in the clinic. Citation Format: Michael J. Lee, Yogesh Dayma, Anne-Margriet Heijinks, Stephen W. Morton, Erik C. Dreaden, Paula T. Hammond, Michael B. Yaffe. Therapeutic network re-wiring of the DNA damage response can be used to enhance tumor killing by cytotoxic chemotherapy. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr SY19-01. doi:10.1158/1538-7445.AM2015-SY19-01
We have previously shown that a subset of triple-negative breast cancers can be dramatically sensitized to killing by DNA-damaging chemotherapy by time-staggered inhibition of EGFR. This sensitization effect results from dynamic re-wiring of apoptotic signaling pathways to engage a caspase-8-dependent cell death mechanism (Figure 1). Here we explored whether combined EGFR and/or FGFR inhibition could enhance the killing of head and neck squamous cell cancers by DNA damaging treatments through a similar re-wiring mechanism. The epidermal growth factor receptor (EGFR) and FGFR pathways are two of the most dysregulated molecular pathways in human head-and-neck squamous cell carcinoma (HNSCC). Despite overexpression in approximately 90% of HNSCC tumors, EGFR inhibitors alone have not exerted a major therapeutic impact on tumor response or patient survival. A recent study provides evidence that the insensitivity of the majority of HNSCC to EGFR inhibitors is mediated by dominant activity of alternative receptor tyrosine kinase (RTK) systems such as FGFR signaling (Clinical Cancer Research 2011). We have found that time-staggered administration of either EGFR inhibitors, or FGFR inhibitors, can dramatically enhance the apoptotic response of HNSCCs to DNA damage from doxorubicin. Importantly, combined inhibition of both the EGFR and FGFR pathways was more effective than inhibition of either pathway alone, at inducing sensitization to cytotoxic chemotherapy through dynamic network re-rewiring. Enhanced cell death by dual EGFR/FGFR inhibition and subsequent genotoxic injury results from greater activation of Caspase-8 than that seen by either EGFR or FGFR inhibitors alone. This enhanced Caspase-8 acitivty, together with Caspase-9 activation, accounts for the majority of apoptotic death. Our data further suggest that Src family kinases are a critical downstream node of EGFR/FGFR activity since treatment of HNSCC cell lines with Src kinase inhibitors resulted in similar sensitization to doxorubicin treatment. In summary, our data extend the utility of therapeutic dynamic rewiring for the targeting of tumors with redundant receptor signaling pathways as well as their critical downstream nodes. Citation Format: Yogesh Dayma, Michael B. Yaffe. Dynamic rewiring of apoptotic signaling networks by combined EGFR/FRGR inhibition enhances killing of head and neck squamous tumor by DNA damage [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Optimizing Survival and Quality of Life through Basic, Clinical, and Translational Research; April 23-25, 2017; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(23_Suppl):Abstract nr 52.
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