Endothelial cells contribute to a subset of cardiac fibroblasts by undergoing endothelial-to-mesenchymal-transition, but whether cardiac fibroblasts can adopt an endothelial cell fate and directly contribute to neovascularization after cardiac injury is not known. Here, using genetic fate map techniques, we demonstrate that cardiac fibroblasts rapidly adopt an endothelial cell like phenotype after acute ischemic cardiac injury. Fibroblast derived endothelial cells exhibit anatomical and functional characteristics of native endothelial cells. We show that the transcription factor p53 regulates such a switch in cardiac fibroblast fate. Loss of p53 in cardiac fibroblasts severely decreases the formation of fibroblast derived endothelial cells, reduces post infarct vascular density and worsens cardiac function. Conversely, stimulation of the p53 pathway in cardiac fibroblasts augments mesenchymal to endothelial transition, enhances vascularity and improves cardiac function. These observations demonstrate that mesenchymal-to-endothelial-transition contributes to neovascularization of the injured heart and represents a potential therapeutic target for enhancing cardiac repair.
Tyro3, Axl, Mer (TAM) receptor tyrosine kinases reduce inflammatory, innate immune responses. We demonstrate that tumor-secreted protein S (Pros1), a Mer/Tyro3 ligand, decreased macrophage M1 cytokine expression in vitro and in vivo. In contrast, tumor cells with CRISPR-based deletion of Pros1 failed to inhibit M1 polarization. Tumor cell-associated Pros1 action was abrogated in macrophages from Mer- and Tyro3- but not Axl-KO mice. In addition, several other murine and human tumor cell lines suppressed macrophage M1 cytokine expression induced by IFN-γ and LPS. Investigation of the suppressive pathway demonstrated a role for PTP1b complexing with Mer. Substantiating the role of PTP1b, M1 cytokine suppression was also lost in macrophages from PTP1b-KO mice. Mice bearing Pros1-deficient tumors showed increased innate and adaptive immune infiltration, as well as increased median survival. TAM activation can also inhibit TLR-mediated M1 polarization. Treatment with resiquimod, a TLR7/8 agonist, did not improve survival in mice bearing Pros1-secreting tumors but doubled survival for Pros1-deleted tumors. The tumor-derived Pros1 immune suppressive system, like PD-L1, was cytokine responsive, with IFN-γ inducing Pros1 transcription and secretion. Inhibition of Pros1/TAM interaction represents a potential novel strategy to block tumor-derived immune suppression.
Myeloid cell receptor tyrosine kinases (RTK) TYRO3, AXL and MERTK and their ligands, Gas 6 and Protein S, physiologically suppress innate immune responses, including in the tumor microenvironment. Here, we showed that myeloid-derived suppressor cells (MDSCs) dramatically upregulated TYRO3, AXL and MERTK and their ligands (M-MDSCs>20-fold, PMN-MDSCs>15-fold) in tumor-bearing mice. MDSCs from tumor bearing Mertk −/− , Axl −/− and Tyro3 −/− mice exhibited diminished suppressive enzymatic capabilities, displayed deficits in T cell suppression and migrated poorly to tumor-draining lymph nodes (TDLNs). In co-implantation experiments, using TYRO3 −/− , AXL −/− and MERTK −/− MDSCs, we showed the absence of these RTKs reversed the pro-tumorigenic properties of MDSCs in vivo. Consistent with these findings, in vivo pharmacologic TYRO3, AXL and MERTK inhibition diminished MDSCs' suppressive capability, slowed tumor growth, increased CD8 + T cell infiltration and augmented anti-PD-1 checkpoint inhibitor immunotherapy. Mechanistically, MERTK regulated MDSC suppression and differentiation in part through regulation of STAT3 serine phosphorylation and nuclear localization. Analysis of metastatic melanoma patients demonstrated an enrichment of circulating MERTK + and TYRO3 + M-MDSCs, PMN-MDSCs and e-MDSCs relative to these MDSC populations in healthy controls. These studies demonstrated that TYRO3, AXL and MERTK
Macrophages are a specialized class of innate immune cells with multifaceted roles in modulation of the inflammatory response, homeostasis, and wound healing. While developmentally derived or originating from circulating monocytes, naïve macrophages can adopt a spectrum of context-dependent activation states ranging from pro-inflammatory (classically activated, M1) to pro-wound healing (alternatively activated, M2). Tumors are known to exploit macrophage polarization states to foster a tumor-permissive milieu, particularly by skewing macrophages toward a pro-tumor (M2) phenotype. These pro-tumoral macrophages can support cancer progression by several mechanisms including immune suppression, growth factor production, promotion of angiogenesis and tissue remodeling. By preventing the adoption of this pro-tumor phenotype or reprogramming these macrophages to a more pro-inflammatory state, it may be possible to inhibit tumor growth. Here, we describe types of tumor-derived signaling that facilitate macrophage reprogramming, including paracrine signaling and activation of innate immune checkpoints. We also describe intervention strategies targeting macrophage plasticity to limit disease progression and address their implications in cancer chemo- and immunotherapy.
Akt plays indispensable roles in cell proliferation, survival and metabolism. Mechanisms underlying posttranslational modification-mediated Akt activation have been extensively studied yet the Akt interactome is less understood. Here, we report that SAV1, a Hippo signaling component, inhibits Akt, a function independent of its role in Hippo signaling. Binding to a proline-tyrosine motif in the Akt-PH domain, SAV1 suppresses Akt activation by blocking Akt’s movement to plasma membrane. We further identify cancer-associated SAV1 mutations with impaired ability to bind Akt, leading to Akt hyperactivation. We also determine that MERTK phosphorylates Akt1-Y26, releasing SAV1 binding and allowing Akt responsiveness to canonical PI-3K pathway activation. This work provides a mechanism underlying MERTK-mediated Akt activation and survival signaling in kidney cancer. Akt activation drives oncogenesis and therapeutic resistance; this mechanism of Akt regulation by MERTK/SAV1 provides yet another complexity in an extensively studied pathway, and may yield prognostic information and therapeutic targets.
The ORFDB (http://orf.invitrogen.com/) represents an ongoing effort at Invitrogen Corporation to integrate relevant scientific data with an evolving collection of human and mouse Open Reading Frame (ORF) clones (Ultimate ORF Clones). The ORFDB serves as a central data warehouse enabling researchers to search the ORF collection through its web portal ORFBrowser, allowing researchers to find the Ultimate ORF clones by blast, keyword, GenBank accession, gene symbol, clone ID, Unigene ID, LocusLink ID or through functional relationships by browsing the collection via the Gene Ontology (GO) Browser. As of October 2003, the ORFDB contains 6200 human and 2870 mouse Ultimate ORF clones. All Ultimate ORF clones have been fully sequenced with high quality, and are matched to public reference protein sequences. In addition, the cloned ORFs have been extensively annotated across six categories: Gene, ORF, Clone Format, Protein, SNP and Genomic links, with the information assembled in a format termed the ORFCard. The ORFCard represents an information repository that documents the sequence quality, alignment with respect to public protein sequences, and the latest publicly available information associated with each human and mouse gene represented in the collection.
Multiple mechanisms restrain inflammation in neonates, most likely to prevent tissue damage caused by overly robust immune responses against newly encountered pathogens. Here, we identify a population of pulmonary dendritic cells (DCs) that express intermediate levels of CD103 (CD103 int ) and appear in the lungs and lung-draining lymph nodes of mice between birth and 2 weeks of age. CD103 int DCs express XCR1 and CD205 and require expression of the transcription factor BATF3 for development, suggesting that they belong to the cDC1 lineage. In addition, CD103 int DCs express CCR7 constitutively and spontaneously migrate to the lung-draining lymph node, where they promote stromal cell maturation and lymph node expansion. CD103 int DCs mature independently of microbial exposure and TRIF- or MyD88-dependent signaling and are transcriptionally related to efferocytic and tolerogenic DCs as well as mature, regulatory DCs. Correlating with this, CD103 int DCs show limited ability to stimulate proliferation and IFN-γ production by CD8 + T cells. Moreover, CD103 int DCs acquire apoptotic cells efficiently, in a process that is dependent on the expression of the TAM receptor, Mertk, which drives their homeostatic maturation. The appearance of CD103 int DCs coincides with a temporal wave of apoptosis in developing lungs and explains, in part, dampened pulmonary immunity in neonatal mice. Together, these data suggest a mechanism by which DCs sense apoptotic cells at sites of noninflammatory tissue remodeling, such as tumors or the developing lungs, and limit local T cell responses.
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