LncRNA Malat1 suppresses pyroptosis and T cell-mediated killing of incipient metastatic cells.

The contribution of antitumor immunity to metastatic dormancy is poorly understood. Here we show that the long noncoding RNA Malat1 is required for tumor initiation and metastatic reactivation in mouse models of breast cancer and other tumor types. Malat1 localizes to nuclear speckles to couple transcription, splicing and mRNA maturation. In metastatic cells, Malat1 induces WNT ligands, autocrine loops to promote self-renewal and the expression of Serpin protease inhibitors. Through inhibition of caspase-1 and cathepsin G, SERPINB6B prevents gasdermin D-mediated induction of pyroptosis. In this way, SERPINB6B suppresses immunogenic cell death and confers evasion of T cell-mediated tumor lysis of incipient metastatic cells. On-target inhibition of Malat1 using therapeutic antisense nucleotides suppresses metastasis in a SERPINB6B-dependent manner. These results suggest that Malat1-induced expression of SERPINB6B can titrate pyroptosis and immune recognition at metastatic sites. Thus, Malat1 is at the nexus of tumor initiation, reactivation and immune evasion and represents a tractable and clinically relevant drug target.

Oncogenic KRAS Drives Lipofibrogenesis to Promote Angiogenesis and Colon Cancer Progression.

Oncogenic KRAS (KRAS*) contributes to many cancer hallmarks. In colorectal cancer, KRAS* suppresses antitumor immunity to promote tumor invasion and metastasis. Here, we uncovered that KRAS* transforms the phenotype of carcinoma-associated fibroblasts (CAF) into lipid-laden CAFs, promoting angiogenesis and tumor progression. Mechanistically, KRAS* activates the transcription factor CP2 (TFCP2) that upregulates the expression of the proadipogenic factors BMP4 and WNT5B, triggering the transformation of CAFs into lipid-rich CAFs. These lipid-rich CAFs, in turn, produce VEGFA to spur angiogenesis. In KRAS*-driven colorectal cancer mouse models, genetic or pharmacologic neutralization of TFCP2 reduced lipid-rich CAFs, lessened tumor angiogenesis, and improved overall survival. Correspondingly, in human colorectal cancer, lipid-rich CAF and TFCP2 signatures correlate with worse prognosis. This work unveils a new role for KRAS* in transforming CAFs, driving tumor angiogenesis and disease progression, providing an actionable therapeutic intervention for KRAS*-driven colorectal cancer. SIGNIFICANCE: This study identified a molecular mechanism contributing to KRAS*-driven colorectal cancer progression via fibroblast transformation in the tumor microenvironment to produce VEGFA driving tumor angiogenesis. In preclinical models, targeting the KRAS*-TFCP2-VEGFA axis impaired tumor progression, revealing a potential novel therapeutic option for patients with KRAS*-driven colorectal cancer. This article is featured in Selected Articles from This Issue, p. 2489.

Histone demethylase KDM5D upregulation drives sex differences in colon cancer.

Sex exerts a profound impact on cancer incidence, spectrum and outcomes, yet the molecular and genetic bases of such sex differences are ill-defined and presumptively ascribed to X-chromosome genes and sex hormones1. Such sex differences are particularly prominent in colorectal cancer (CRC) in which men experience higher metastases and mortality. A murine CRC model, engineered with an inducible transgene encoding oncogenic mutant KRASG12D and conditional null alleles of Apc and Trp53 tumour suppressors (designated iKAP)2, revealed higher metastases and worse outcomes specifically in males with oncogenic mutant KRAS (KRAS*) CRC. Integrated cross-species molecular and transcriptomic analyses identified Y-chromosome gene histone demethylase KDM5D as a transcriptionally upregulated gene driven by KRAS*-mediated activation of the STAT4 transcription factor. KDM5D-dependent chromatin mark and transcriptome changes showed repression of regulators of the epithelial cell tight junction and major histocompatibility complex class I complex components. Deletion of Kdm5d in iKAP cancer cells increased tight junction integrity, decreased cell invasiveness and enhanced cancer cell killing by CD8+ T cells. Conversely, iAP mice engineered with a Kdm5d transgene to provide constitutive Kdm5d expression specifically in iAP cancer cells showed an increased propensity for more invasive tumours in vivo. Thus, KRAS*-STAT4-mediated upregulation of Y chromosome KDM5D contributes substantially to the sex differences in KRAS* CRC by means of its disruption of cancer cell adhesion properties and tumour immunity, providing an actionable therapeutic strategy for metastasis risk reduction for men afflicted with KRAS* CRC.

Diagnostic rate of germline pathogenic variants in pancreatic ductal adenocarcinoma patients using whole genome sequencing.

Identification of germline pathogenic variants in cancer patients is critical for treatment planning, genetic counseling, and health policymaking. However, previous estimates of the prevalence of germline etiology of pancreatic ductal adenocarcinoma (PDAC) were biased because they were based only on sequencing data of protein-coding regions of known PDAC candidate genes. To determine the percentage of patients with PDAC carrying germline pathogenic variants, we enrolled the inpatients from the digestive health clinics, hematology and oncology clinics, and surgical clinics of a single tertiary medical center in Taiwan for whole genome sequencing (WGS) analysis of genomic DNA. The virtual gene panel of 750 genes comprised PDAC candidate genes and those listed in the COSMIC Cancer Gene Census. The genetic variant types under investigation included single nucleotide substitutions, small indels, structural variants, and mobile element insertions (MEIs). In 8 of 24 (33.3%) patients with PDAC, we identified pathogenic/likely pathogenic variants, including single nucleotide substitutions and small indels in ATM, BRCA1, BRCA2, POLQ, SPINK1 and CASP8, as well as structural variants in CDC25C and USP44. We identified additional patients carrying variants that could potentially affect splicing. This cohort study demonstrates that an extensive analysis of the abundant information yielded by the WGS approach can uncover many pathogenic variants that could be missed by traditional panel-based or whole exome sequencing-based approaches. The percentage of patients with PDAC carrying germline variants might be much higher than previously expected.

Targeting T cell checkpoints 41BB and LAG3 and myeloid cell CXCR1/CXCR2 results in antitumor immunity and durable response in pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDAC) is considered non-immunogenic, with trials showing its recalcitrance to PD1 and CTLA4 immune checkpoint therapies (ICTs). Here, we sought to systematically characterize the mechanisms underlying de novo ICT resistance and to identify effective therapeutic options for PDAC. We report that agonist 41BB and antagonist LAG3 ICT alone and in combination, increased survival and antitumor immunity, characterized by modulating T cell subsets with antitumor activity, increased T cell clonality and diversification, decreased immunosuppressive myeloid cells and increased antigen presentation/decreased immunosuppressive capability of myeloid cells. Translational analyses confirmed the expression of 41BB and LAG3 in human PDAC. Since single and dual ICTs were not curative, T cell-activating ICTs were combined with a CXCR1/2 inhibitor targeting immunosuppressive myeloid cells. Triple therapy resulted in durable complete responses. Given similar profiles in human PDAC and the availability of these agents for clinical testing, our findings provide a testable hypothesis for this lethal disease.

On the peptide binding affinity changes in population-specific HLA repertoires to the SARS-CoV-2 variants Delta and Omicron.

OBJECTIVE: To investigate the changes of Spike protein-HLA binding affinity profiles between the Wuhan strain and two dominant variants, the Delta and the Omicron strains, among the Taiwanese, the British and the Russian populations. METHODS: The HLA frequencies and the HLA-peptide binding affinity profiles in the T-CoV database were combined to conduct the study. We focused on the public alleles in the three populations (HLA-A, HLA-B, HLA-C, HLA-DRB1, and/or HLA-DPA1/DPB1 alleles) and the altered peptides of the spike protein (compared to the Wuhan strain) in the Delta G/478K·V1 (B.1.617.2 + AY.1 + AY.2) and the Omicron (BA.1) strains. RESULTS: For the Delta strain, tight bindings of the altered peptides to the HLA alleles decrease in all three populations and almost vanish in the Taiwanese population. For the Omicron strain, tight bindings are mostly preserved for both HLA classes and in the Taiwanese and the British populations, with a slight reduction in HLA class II in the Taiwanese (1.4%), while the Russian population preserves a relatively high fraction of tight bindings for both HLA classes. CONCLUSION: We comprehensively reported the changes in the HLA-associated SARS-CoV-2 Spike protein peptide binding profiles among the Taiwanese, the British, and the Russian populations. Further studies are needed to understand the immunological mechanisms and the clinical value of our findings.

Multi-modal molecular programs regulate melanoma cell state.

Melanoma cells display distinct intrinsic phenotypic states. Here, we seek to characterize the molecular regulation of these states using multi-omic analyses of whole exome, transcriptome, microRNA, long non-coding RNA and DNA methylation data together with reverse-phase protein array data on a panel of 68 highly annotated early passage melanoma cell lines. We demonstrate that clearly defined cancer cell intrinsic transcriptomic programs are maintained in melanoma cells ex vivo and remain highly conserved within melanoma tumors, are associated with distinct immune features within tumors, and differentially correlate with checkpoint inhibitor and adoptive T cell therapy efficacy. Through integrative analyses we demonstrate highly complex multi-omic regulation of melanoma cell intrinsic programs that provide key insights into the molecular maintenance of phenotypic states. These findings have implications for cancer biology and the identification of new therapeutic strategies. Further, these deeply characterized cell lines will serve as an invaluable resource for future research in the field.

Oncogenic collagen I homotrimers from cancer cells bind to α3ß1 integrin and impact tumor microbiome and immunity to promote pancreatic cancer.

In contrast to normal type I collagen (Col1) heterotrimer (α1/α2/α1) produced by fibroblasts, pancreatic cancer cells specifically produce unique Col1 homotrimer (α1/α1/α1). Col1 homotrimer results from epigenetic suppression of the Col1a2 gene and promotes oncogenic signaling, cancer cell proliferation, tumor organoid formation, and growth via α3ß1 integrin on cancer cells, associated with tumor microbiome enriched in anaerobic Bacteroidales in hypoxic and immunosuppressive tumors. Deletion of Col1 homotrimers increases overall survival of mice with pancreatic ductal adenocarcinoma (PDAC), associated with reprograming of the tumor microbiome with increased microaerophilic Campylobacterales, which can be reversed with broad-spectrum antibiotics. Deletion of Col1 homotrimers enhances T cell infiltration and enables efficacy of anti-PD-1 immunotherapy. This study identifies the functional impact of Col1 homotrimers on tumor microbiome and tumor immunity, implicating Col1 homotrimer-α3ß1 integrin signaling axis as a cancer-specific therapeutic target.

Synthetic Essentiality of Tryptophan 2,3-Dioxygenase 2 in APC-Mutated Colorectal Cancer.

Inactivation of adenomatous polyposis coli (APC) is common across many cancer types and serves as a critical initiating event in most sporadic colorectal cancers. APC deficiency activates WNT signaling, which remains an elusive target for cancer therapy, prompting us to apply the synthetic essentiality framework to identify druggable vulnerabilities for APC-deficient cancers. Tryptophan 2,3-dioxygenase 2 (TDO2) was identified as a synthetic essential effector of APC-deficient colorectal cancer. Mechanistically, APC deficiency results in the TCF4/ß-catenin-mediated upregulation of TDO2 gene transcription. TDO2 in turn activates the Kyn-AhR pathway, which increases glycolysis to drive anabolic cancer cell growth and CXCL5 secretion to recruit macrophages into the tumor microenvironment. Therapeutically, APC-deficient colorectal cancer models were susceptible to TDO2 depletion or pharmacologic inhibition, which impaired cancer cell proliferation and enhanced antitumor immune profiles. Thus, APC deficiency activates a TCF4-TDO2-AhR-CXCL5 circuit that affects multiple cancer hallmarks via autonomous and nonautonomous mechanisms and illuminates a genotype-specific vulnerability in colorectal cancer. SIGNIFICANCE: This study identifies critical effectors in the maintenance of APC-deficient colorectal cancer and demonstrates the relationship between APC/WNT pathway and kynurenine pathway signaling. It further determines the tumor-associated macrophage biology in APC-deficient colorectal cancer, informing genotype-specific therapeutic targets and the use of TDO2 inhibitors. This article is highlighted in the In This Issue feature, p. 1599.

Cold and heterogeneous T cell repertoire is associated with copy number aberrations and loss of immune genes in small-cell lung cancer.

Small-cell lung cancer (SCLC) is speculated to harbor complex genomic intratumor heterogeneity (ITH) associated with high recurrence rate and suboptimal response to immunotherapy. Here, using multi-region whole exome/T cell receptor (TCR) sequencing as well as immunohistochemistry, we reveal a rather homogeneous mutational landscape but extremely cold and heterogeneous TCR repertoire in limited-stage SCLC tumors (LS-SCLCs). Compared to localized non-small cell lung cancers, LS-SCLCs have similar predicted neoantigen burden and genomic ITH, but significantly colder and more heterogeneous TCR repertoire associated with higher chromosomal copy number aberration (CNA) burden. Furthermore, copy number loss of IFN-γ pathway genes is frequently observed and positively correlates with CNA burden. Higher mutational burden, higher T cell infiltration and positive PD-L1 expression are associated with longer overall survival (OS), while higher CNA burden is associated with shorter OS in patients with LS-SCLC.

USP21 deubiquitinase elevates macropinocytosis to enable oncogenic KRAS bypass in pancreatic cancer.

Activating mutations in KRAS (KRAS*) are present in nearly all pancreatic ductal adenocarcinoma (PDAC) cases and critical for tumor maintenance. By using an inducible KRAS* PDAC mouse model, we identified a deubiquitinase USP21-driven resistance mechanism to anti-KRAS* therapy. USP21 promotes KRAS*-independent tumor growth via its regulation of MARK3-induced macropinocytosis, which serves to maintain intracellular amino acid levels for anabolic growth. The USP21-mediated KRAS* bypass, coupled with the frequent amplification of USP21 in human PDAC tumors, encourages the assessment of USP21 as a novel drug target as well as a potential parameter that may affect responsiveness to emergent anti-KRAS* therapy.

AR-negative prostate cancer is vulnerable to loss of JMJD1C demethylase.

Prostate cancer is a leading cause of cancer-related mortality in men. The widespread use of androgen receptor (AR) inhibitors has generated an increased incidence of AR-negative prostate cancer, triggering the need for effective therapies for such patients. Here, analysis of public genome-wide CRISPR screens in human prostate cancer cell lines identified histone demethylase JMJD1C (KDM3C) as an AR-negative context-specific vulnerability. Secondary validation studies in multiple cell lines and organoids, including isogenic models, confirmed that small hairpin RNA (shRNA)-mediated depletion of JMJD1C potently inhibited growth specifically in AR-negative prostate cancer cells. To explore the cooperative interactions of AR and JMJD1C, we performed comparative transcriptomics of 1) isogenic AR-positive versus AR-negative prostate cancer cells, 2) AR-positive versus AR-negative prostate cancer tumors, and 3) isogenic JMJD1C-expressing versus JMJD1C-depleted AR-negative prostate cancer cells. Loss of AR or JMJD1C generates a modest tumor necrosis factor alpha (TNFα) signature, whereas combined loss of AR and JMJD1C strongly up-regulates the TNFα signature in human prostate cancer, suggesting TNFα signaling as a point of convergence for the combined actions of AR and JMJD1C. Correspondingly, AR-negative prostate cancer cells showed exquisite sensitivity to TNFα treatment and, conversely, TNFα pathway inhibition via inhibition of its downstream effector MAP4K4 partially reversed the growth defect of JMJD1C-depleted AR-negative prostate cancer cells. Given the deleterious systemic side effects of TNFα therapy in humans and the viability of JMJD1C-knockout mice, the identification of JMJD1C inhibition as a specific vulnerability in AR-negative prostate cancer may provide an alternative drug target for prostate cancer patients progressing on AR inhibitor therapy.

Oncogene-specific differences in tumor mutational burden, PD-L1 expression, and outcomes from immunotherapy in non-small cell lung cancer.

BACKGROUND: Non-small cell lung cancer (NSCLC) patients bearing targetable oncogene alterations typically derive limited benefit from immune checkpoint blockade (ICB), which has been attributed to low tumor mutation burden (TMB) and/or PD-L1 levels. We investigated oncogene-specific differences in these markers and clinical outcome. METHODS: Three cohorts of NSCLC patients with oncogene alterations (n=4189 total) were analyzed. Two clinical cohorts of advanced NSCLC patients treated with ICB monotherapy [MD Anderson (MDACC; n=172) and Flatiron Health-Foundation Medicine Clinico-Genomic Database (CGDB; n=894 patients)] were analyzed for clinical outcome. The FMI biomarker cohort (n=4017) was used to assess the association of oncogene alterations with TMB and PD-L1 expression. RESULTS: High PD-L1 expression (PD-L1 ≥50%) rate was 19%-20% in classic EGFR, EGFR exon 20 and HER2-mutant tumors, and 34%-55% in tumors with ALK, BRAF V600E, ROS1, RET, or MET alterations. Compared with KRAS-mutant tumors, BRAF non-V600E group had higher TMB (9.6 vs KRAS 7.8 mutations/Mb, p=0.003), while all other oncogene groups had lower TMB (p<0.001). In the two clinical cohorts treated with ICB, molecular groups with EGFR, HER2, ALK, ROS1, RET, or MET alterations had short progression-free survival (PFS; 1.8-3.7 months), while BRAF V600E group was associated with greater clinical benefit from ICB (CGDB cohort: PFS 9.8 months vs KRAS 3.7 months, HR 0.66, p=0.099; MDACC cohort: response rate 62% vs KRAS 24%; PFS 7.4 vs KRAS 2.8 months, HR 0.36, p=0.026). KRAS G12C and non-G12C subgroups had similar clinical benefit from ICB in both cohorts. In a multivariable analysis, BRAF V600E mutation (HR 0.58, p=0.041), PD-L1 expression (HR 0.57, p=0.022), and high TMB (HR 0.66, p<0.001) were associated with longer PFS. CONCLUSIONS: High TMB and PD-L1 expression are predictive for benefit from ICB treatment in oncogene-driven NSCLCs. NSCLC harboring BRAF mutations demonstrated superior benefit from ICB that may be attributed to higher TMB and higher PD-L1 expression in these tumors. Meanwhile EGFR and HER2 mutations and ALK, ROS1, RET, and MET fusions define NSCLC subsets with minimal benefit from ICB despite high PD-L1 expression in NSCLC harboring oncogene fusions. These findings indicate a TMB/PD-L1-independent impact on sensitivity to ICB for certain oncogene alterations.

Telomere dysfunction instigates inflammation in inflammatory bowel disease.

Inflammatory bowel disease (IBD) is a chronic inflammatory condition driven by diverse genetic and nongenetic programs that converge to disrupt immune homeostasis in the intestine. We have reported that, in murine intestinal epithelium with telomere dysfunction, DNA damage-induced activation of ataxia-telangiectasia mutated (ATM) results in ATM-mediated phosphorylation and activation of the YAP1 transcriptional coactivator, which in turn up-regulates pro-IL-18, a pivotal immune regulator in IBD pathogenesis. Moreover, individuals with germline defects in telomere maintenance genes experience increased occurrence of intestinal inflammation and show activation of the ATM/YAP1/pro-IL-18 pathway in the intestinal epithelium. Here, we sought to determine the relevance of the ATM/YAP1/pro-IL-18 pathway as a potential driver of IBD, particularly older-onset IBD. Analysis of intestinal biopsy specimens and organoids from older-onset IBD patients documented the presence of telomere dysfunction and activation of the ATM/YAP1/precursor of interleukin 18 (pro-IL-18) pathway in the intestinal epithelium. Employing intestinal organoids from healthy individuals, we demonstrated that experimental induction of telomere dysfunction activates this inflammatory pathway. In organoid models from ulcerative colitis and Crohn's disease patients, pharmacological interventions of telomerase reactivation, suppression of DNA damage signaling, or YAP1 inhibition reduced pro-IL-18 production. Together, these findings support a model wherein telomere dysfunction in the intestinal epithelium can initiate the inflammatory process in IBD, pointing to therapeutic interventions for this disease.

Reprogramming of bivalent chromatin states in NRAS mutant melanoma suggests PRC2 inhibition as a therapeutic strategy.

The dynamic evolution of chromatin state patterns during metastasis, their relationship with bona fide genetic drivers, and their therapeutic vulnerabilities are not completely understood. Combinatorial chromatin state profiling of 46 melanoma samples reveals an association of NRAS mutants with bivalent histone H3 lysine 27 trimethylation (H3K27me3) and Polycomb repressive complex 2. Reprogramming of bivalent domains during metastasis occurs on master transcription factors of a mesenchymal phenotype, including ZEB1, TWIST1, and CDH1. Resolution of bivalency using pharmacological inhibition of EZH2 decreases invasive capacity of melanoma cells and markedly reduces tumor burden in vivo, specifically in NRAS mutants. Coincident with bivalent reprogramming, the increased expression of pro-metastatic and melanocyte-specific cell-identity genes is associated with exceptionally wide H3K4me3 domains, suggesting a role for this epigenetic element. Overall, we demonstrate that reprogramming of bivalent and broad domains represents key epigenetic alterations in metastatic melanoma and that EZH2 plus MEK inhibition may provide a promising therapeutic strategy for NRAS mutant melanoma patients.

Type I collagen deletion in αSMA+ myofibroblasts augments immune suppression and accelerates progression of pancreatic cancer.

Stromal desmoplastic reaction in pancreatic ductal adenocarcinoma (PDAC) involves significant accumulation of type I collagen (Col1). However, the precise molecular and mechanistic contribution of Col1 in PDAC progression remains unknown. Activated pancreatic stellate cells/αSMA+ myofibroblasts are major contributors of Col1 in the PDAC stroma. We use a dual-recombinase genetic mouse model of spontaneous PDAC to delete Col1 specifically in myofibroblasts. This results in significant reduction of total stromal Col1 content and accelerates the emergence of PanINs and PDAC, decreasing overall survival. Col1 deletion leads to Cxcl5 upregulation in cancer cells via SOX9. Increase in Cxcl5 is associated with recruitment of myeloid-derived suppressor cells and suppression of CD8+ T cells, which can be attenuated with combined targeting of CXCR2 and CCR2 to restrain accelerated PDAC progression in the setting of stromal Col1 deletion. Our results unravel the fundamental role of myofibroblast-derived Co1l in regulating tumor immunity and restraining PDAC progression.

Telomerase Reverse Transcriptase Preserves Neuron Survival and Cognition in Alzheimer's Disease Models.

Amyloid-induced neurodegeneration plays a central role in Alzheimer's disease (AD) pathogenesis. Here, we show that telomerase reverse transcriptase (TERT) haploinsufficiency decreases BDNF and increases amyloid-ß (Aß) precursor in murine brain. Moreover, prior to disease onset, the TERT locus sustains accumulation of repressive epigenetic marks in murine and human AD neurons, implicating TERT repression in amyloid-induced neurodegeneration. To test the impact of sustained TERT expression on AD pathobiology, AD mouse models were engineered to maintain physiological levels of TERT in adult neurons, resulting in reduced Aß accumulation, improved spine morphology, and preserved cognitive function. Mechanistically, integrated profiling revealed that TERT interacts with ß-catenin and RNA polymerase II at gene promoters and upregulates gene networks governing synaptic signaling and learning processes. These TERT-directed transcriptional activities do not require its catalytic activity nor telomerase RNA. These findings provide genetic proof-of-concept for somatic TERT gene activation therapy in attenuating AD progression including cognitive decline.

Multiomics profiling of primary lung cancers and distant metastases reveals immunosuppression as a common characteristic of tumor cells with metastatic plasticity.

BACKGROUND: Metastasis is the primary cause of cancer mortality accounting for 90% of cancer deaths. Our understanding of the molecular mechanisms driving metastasis is rudimentary. RESULTS: We perform whole exome sequencing (WES), RNA sequencing, methylation microarray, and immunohistochemistry (IHC) on 8 pairs of non-small cell lung cancer (NSCLC) primary tumors and matched distant metastases. Furthermore, we analyze published WES data from 35 primary NSCLC and metastasis pairs, and transcriptomic data from 4 autopsy cases with metastatic NSCLC and one metastatic lung cancer mouse model. The majority of somatic mutations are shared between primary tumors and paired distant metastases although mutational signatures suggest different mutagenesis processes in play before and after metastatic spread. Subclonal analysis reveals evidence of monoclonal seeding in 41 of 42 patients. Pathway analysis of transcriptomic data reveals that downregulated pathways in metastases are mainly immune-related. Further deconvolution analysis reveals significantly lower infiltration of various immune cell types in metastases with the exception of CD4+ T cells and M2 macrophages. These results are in line with lower densities of immune cells and higher CD4/CD8 ratios in metastases shown by IHC. Analysis of transcriptomic data from autopsy cases and animal models confirms that immunosuppression is also present in extracranial metastases. Significantly higher somatic copy number aberration and allelic imbalance burdens are identified in metastases. CONCLUSIONS: Metastasis is a molecularly late event, and immunosuppression driven by different molecular events, including somatic copy number aberration, may be a common characteristic of tumors with metastatic plasticity.

Endothelial-to-mesenchymal transition compromises vascular integrity to induce Myc-mediated metabolic reprogramming in kidney fibrosis.

Endothelial-to-mesenchymal transition (EndMT) is a cellular transdifferentiation program in which endothelial cells partially lose their endothelial identity and acquire mesenchymal-like features. Renal capillary endothelial cells can undergo EndMT in association with persistent damage of the renal parenchyma. The functional consequence(s) of EndMT in kidney fibrosis remains unexplored. Here, we studied the effect of Twist or Snail deficiency in endothelial cells on EndMT in kidney fibrosis. Conditional deletion of Twist1 (which encodes Twist) or Snai1 (which encodes Snail) in VE-cadherin+ or Tie1+ endothelial cells inhibited the emergence of EndMT and improved kidney fibrosis in two different kidney injury/fibrosis mouse models. Suppression of EndMT limited peritubular vascular leakage, reduced tissue hypoxia, and preserved tubular epithelial health and function. Hypoxia, which was exacerbated by EndMT, resulted in increased Myc abundance in tubular epithelial cells, enhanced glycolysis, and suppression of fatty acid oxidation. Pharmacological suppression or epithelial-specific genetic ablation of Myc in tubular epithelial cells ameliorated fibrosis and restored renal parenchymal function and metabolic homeostasis. Together, these findings demonstrate a functional role for EndMT in the response to kidney capillary endothelial injury and highlight the contribution of endothelial-epithelial cross-talk in the development of kidney fibrosis with a potential for therapeutic intervention.

Chromatin Regulator CHD1 Remodels the Immunosuppressive Tumor Microenvironment in PTEN-Deficient Prostate Cancer.

Genetic inactivation of PTEN is common in prostate cancer and correlates with poorer prognosis. We previously identified CHD1 as an essential gene in PTEN-deficient cancer cells. Here, we sought definitive in vivo genetic evidence for, and mechanistic understanding of, the essential role of CHD1 in PTEN-deficient prostate cancer. In Pten and Pten/Smad4 genetically engineered mouse models, prostate-specific deletion of Chd1 resulted in markedly delayed tumor progression and prolonged survival. Chd1 deletion was associated with profound tumor microenvironment (TME) remodeling characterized by reduced myeloid-derived suppressor cells (MDSC) and increased CD8+ T cells. Further analysis identified IL6 as a key transcriptional target of CHD1, which plays a major role in recruitment of immunosuppressive MDSCs. Given the prominent role of MDSCs in suppressing responsiveness to immune checkpoint inhibitors (ICI), our genetic and tumor biological findings support combined testing of anti-IL6 and ICI therapies, specifically in PTEN-deficient prostate cancer. SIGNIFICANCE: We demonstrate a critical role of CHD1 in MDSC recruitment and discover CHD1/IL6 as a major regulator of the immunosuppressive TME of PTEN-deficient prostate cancer. Pharmacologic inhibition of IL6 in combination with immune checkpoint blockade elicits robust antitumor responses in prostate cancer.This article is highlighted in the In This Issue feature, p. 1241.