Collagen Density Modulates the Immunosuppressive Functions of Macrophages.

Tumor-associated macrophages (TAMs) support tumor growth by suppressing the activity of tumor-infiltrating T cells. Consistently, TAMs are considered a major limitation for the efficacy of cancer immunotherapy. However, the molecular reason behind the acquisition of an immunosuppressive TAM phenotype is not fully clarified. During tumor growth, the extracellular matrix (ECM) is degraded and substituted with a tumor-specific collagen-rich ECM. The collagen density of this tumor ECM has been associated with poor patient prognosis but the reason for this is not well understood. In this study, we investigated whether the collagen density could modulate the immunosuppressive activity of TAMs. The murine macrophage cell line RAW 264.7 was three-dimensionally cultured in collagen matrices of low and high collagen densities mimicking healthy and tumor tissue, respectively. Collagen density did not affect proliferation or viability of the macrophages. However, whole-transcriptome analysis revealed a striking response to the surrounding collagen density, including the regulation of immune regulatory genes and genes encoding chemokines. These transcriptional changes were shown to be similar in murine bone marrow-derived macrophages and TAMs isolated from murine tumors. Strikingly, coculture assays with primary T cells showed that macrophages cultured in high-density collagen were less efficient at attracting cytotoxic T cells and capable of inhibiting T cell proliferation more than macrophages cultured in low-density collagen. Our study demonstrates that a high collagen density can instruct macrophages to acquire an immunosuppressive phenotype. This mechanism could reduce the efficacy of immunotherapy and explain the link between high collagen density and poor prognosis.

The ASXL1-G643W variant accelerates the development of CEBPA mutant acute myeloid leukemia.

ASXL1 is one of the most commonly mutated genes in myeloid malignancies, including Myelodysplastic Syndrome (MDS) and Acute Myeloid Leukemia (AML). In order to further our understanding of the role of ASXL1 lesions in malignant hematopoiesis, we generated a novel knock-in mouse model carrying the most frequent ASXL1 mutation identified in MDS patients, p.G643WfsX12. Mutant mice did not display any major hematopoietic defects nor developed any apparent hematological disease. In AML patients, ASXL1 mutations co-occur with mutations in CEBPA and we therefore generated compound Cebpa and Asxl1 mutated mice. Using a transplantation model, we found that the mutated Asxl1 allele significantly accelerated disease development in a CEBPA mutant context. Importantly, we demonstrated that, similar to the human setting, Asxl1 mutated mice responded poorly to chemotherapy. This model therefore constitutes an excellent experimental system for further studies into the clinically important question of chemotherapy resistance mediated by mutant ASXL1.

Insulin signaling and reduced glucocorticoid receptor activity attenuate postprandial gene expression in liver.

Hepatic circadian gene transcription is tightly coupled to feeding behavior, which has a profound impact on metabolic disorders associated with diet-induced obesity. Here, we describe a genomics approach to uncover mechanisms controlling hepatic postprandial gene expression. Combined transcriptomic and cistromic analysis identified hundreds of circadian-regulated genes and enhancers controlled by feeding. Postprandial suppression of enhancer activity was associated with reduced glucocorticoid receptor (GR) and Forkhead box O1 (FOXO1) occupancy of chromatin correlating with reduced serum corticosterone levels and increased serum insulin levels. Despite substantial co-occupancy of feeding-regulated enhancers by GR and FOXO1, selective disruption of corticosteroid and/or insulin signaling resulted in dysregulation of specific postprandial regulated gene programs. In combination, these signaling pathways operate a major part of the genes suppressed by feeding. Importantly, the feeding response was disrupted in diet-induced obese animals, which was associated with dysregulation of several corticosteroid- and insulin-regulated genes, providing mechanistic insights to dysregulated circadian gene transcription associated with obesity.

The histone demethylase KDM5C functions as a tumor suppressor in AML by repression of bivalently marked immature genes.

Epigenetic regulators are frequently mutated in hematological malignancies including acute myeloid leukemia (AML). Thus, the identification and characterization of novel epigenetic drivers affecting AML biology holds potential to improve our basic understanding of AML and to uncover novel options for therapeutic intervention. To identify novel tumor suppressive epigenetic regulators in AML, we performed an in vivo short hairpin RNA (shRNA) screen in the context of CEBPA mutant AML. This identified the Histone 3 Lysine 4 (H3K4) demethylase KDM5C as a tumor suppressor, and we show that reduced Kdm5c/KDM5C expression results in accelerated growth both in human and murine AML cell lines, as well as in vivo in Cebpa mutant and inv(16) AML mouse models. Mechanistically, we show that KDM5C act as a transcriptional repressor through its demethylase activity at promoters. Specifically, KDM5C knockdown results in globally increased H3K4me3 levels associated with up-regulation of bivalently marked immature genes. This is accompanied by a de-differentiation phenotype that could be reversed by modulating levels of several direct and indirect downstream mediators. Finally, the association of KDM5C levels with long-term disease-free survival of female AML patients emphasizes the clinical relevance of our findings and identifies KDM5C as a novel female-biased tumor suppressor in AML.

H3K9 dimethylation safeguards cancer cells against activation of the interferon pathway.

Activation of interferon genes constitutes an important anticancer pathway able to restrict proliferation of cancer cells. Here, we demonstrate that the H3K9me3 histone methyltransferase (HMT) suppressor of variegation 3-9 homolog 1 (SUV39H1) is required for the proliferation of acute myeloid leukemia (AML) and find that its loss leads to activation of the interferon pathway. Mechanistically, we show that this occurs via destabilization of a complex composed of SUV39H1 and the two H3K9me2 HMTs, G9A and GLP. Indeed, loss of H3K9me2 correlated with the activation of key interferon pathway genes, and interference with the activities of G9A/GLP largely phenocopied loss of SUV39H1. Last, we demonstrate that inhibition of G9A/GLP synergized with DNA demethylating agents and that SUV39H1 constitutes a potential biomarker for the response to hypomethylation treatment. Collectively, we uncovered a clinically relevant role for H3K9me2 in safeguarding cancer cells against activation of the interferon pathway.

Collagen density regulates the activity of tumor-infiltrating T cells.

BACKGROUND: Tumor progression is accompanied by dramatic remodeling of the surrounding extracellular matrix leading to the formation of a tumor-specific ECM, which is often more collagen-rich and of increased stiffness. The altered ECM of the tumor supports cancer growth and metastasis, but it is unknown if this effect involves modulation of T cell activity. To investigate if a high-density tumor-specific ECM could influence the ability of T cells to kill cancer cells, we here studied how T cells respond to 3D culture in different collagen densities. METHODS: T cells cultured in 3D conditions surrounded by a high or low collagen density were imaged using confocal fluorescent microscopy. The effects of the different collagen densities on T cell proliferation, survival, and differentiation were examined using flow cytometry. Cancer cell proliferation in similar 3D conditions was also measured. Triple-negative breast cancer specimens were analyzed for the number of infiltrating CD8+ T cells and for the collagen density. Whole-transcriptome analyses were applied to investigate in detail the effects of collagen density on T cells. Computational analyses were used to identify transcription factors involved in the collagen density-induced gene regulation. Observed changes were confirmed by qRT-PCR analysis. RESULTS: T cell proliferation was significantly reduced in a high-density matrix compared to a low-density matrix and prolonged culture in a high-density matrix led to a higher ratio of CD4+ to CD8+ T cells. The proliferation of cancer cells was unaffected by the surrounding collagen-density. Consistently, we observed a reduction in the number of infiltrating CD8+ T-cells in mammary tumors with high collagen-density indicating that collagen-density has a role in regulating T cell abundance in human breast cancer. Whole-transcriptome analysis of 3D-cultured T cells revealed that a high-density matrix induces downregulation of cytotoxic activity markers and upregulation of regulatory T cell markers. These transcriptional changes were predicted to involve autocrine TGF-ß signaling and they were accompanied by an impaired ability of tumor-infiltrating T cells to kill autologous cancer cells. CONCLUSIONS: Our study identifies a new immune modulatory mechanism, which could be essential for suppression of T cell activity in the tumor microenvironment.

MIRU-VNTR genotype diversity and indications of homoplasy in M. avium strains isolated from humans and slaughter pigs in Latvia.

Diseases which are caused by non-tuberculous mycobacteria (NTM) are an increasing problem in the developed countries. In Latvia, one of the most clinically important members of NTM is Mycobacterium avium (M. avium), an opportunistic pathogen which has been isolated from several lung disease patients and tissue samples of slaughter pigs. This study was designed to characterize the genetic diversity of the M. avium isolates in Latvia and to compare the distribution of genotypic patterns among humans and pigs. Eleven (Hall and Salipante, 2010) clinical M. avium samples, isolated from patients of Center of Tuberculosis and Lung Diseases (years 2003-2010), and 32 isolates from pig necrotic mesenterial lymph nodes in different regions (years 2003-2007) were analyzed. The majority (42 of 43) of samples were identified as M. avium subsp. hominissuis; one porcine isolate belonged to M. avium subsp. avium. MIRU-VNTR genotyping revealed 13 distinct genotypes, among which nine genotype patterns, including M. avium subsp. avium isolate, were newly identified. IS1245 RFLP fingerprinting of 25 M. avium subsp. hominissuis samples yielded 17 different IS1245 RFLP patterns, allowing an efficient discrimination of isolates. Clusters of identical RFLP profiles were observed within host species, geographical locations and time frame of several years. Additional in silico analysis on simulated MIRU-VNTR genotype population datasets showed that the MIRU-VNTR pattern similarity could partly arise due to probabilistic increase of acquiring homoplasy among subpopulations, thus the similar MIRU-VNTR profiles of M. avium strains even in close geographical proximity should be interpreted with caution.

Genotypic and phenotypic characteristics of aminoglycoside-resistant Mycobacterium tuberculosis isolates in Latvia.

Mutations causing resistance to aminoglycosides, such as kanamycin (KAN), amikacin (AMK), and streptomycin, are not completely understood. In this study, polymorphisms of aminoglycoside resistance influencing genes such as rrs, eis, rpsL, and gidB in 41 drug-resistant and 17 pan-sensitive Mycobacterium tuberculosis clinical isolates in Latvia were analyzed. Mutation A1400G in rrs gene was detected in 92% isolates with high resistance level to KAN and diverse MIC level to AMK. Mutations in promoter region of eis were detected in 80% isolates with low-level MIC of KAN. The association of K43R mutation in rpsL gene, a mutation in the rrs gene at position 513, and various polymorphisms in gidB gene with distinct genetic lineages of M. tuberculosis was observed. The results of this study suggest that association of different controversial mutations of M. tuberculosis genes to the drug resistance phenotype should be done in respect to genetic lineages.