Michaela Schlederer

TGF-β IL-6 axis mediates selective and adaptive mechanisms of resistance to molecular targeted therapy in lung cancer

The epidermal growth-factor receptor (EGFR) tyrosine kinase inhibitor erlotinib has been proven to be highly effective in the treatment of nonsmall cell lung cancer (NSCLC) harboring oncogenic EGFR mutations. The majority of patients, however, will eventually develop resistance and succumb to the disease. Recent studies have identified secondary mutations in the EGFR (EGFR T790M) and amplification of the N-Methyl-N′-nitro-N-nitroso-guanidine (MNNG) HOS transforming gene (MET) oncogene as two principal mechanisms of acquired resistance. Although they can account for approximately 50% of acquired resistance cases together, in the remaining 50%, the mechanism remains unknown. In NSCLC-derived cell lines and early-stage tumors before erlotinib treatment, we have uncovered the existence of a subpopulation of cells that are intrinsically resistant to erlotinib and display features suggestive of epithelial-to-mesenchymal transition (EMT). We showed that activation of TGF-β–mediated signaling was sufficient to induce these phenotypes. In particular, we determined that an increased TGF-β–dependent IL-6 secretion unleashed previously addicted lung tumor cells from their EGFR dependency. Because IL-6 and TGF-β are prominently produced during inflammatory response, we used a mouse model system to determine whether inflammation might impair erlotinib sensitivity. Indeed, induction of inflammation not only stimulated IL-6 secretion but was sufficient to decrease the tumor response to erlotinib. Our data, thus, argue that both tumor cell-autonomous mechanisms and/or activation of the tumor microenvironment could contribute to primary and acquired erlotinib resistance, and as such, treatments based on EGFR inhibition may not be sufficient for the effective treatment of lung-cancer patients harboring mutant EGFR.

A dual role for autophagy in a murine model of lung cancer

Autophagy is a mechanism by which starving cells can control their energy requirements and metabolic states, thus facilitating the survival of cells in stressful environments, in particular in the pathogenesis of cancer. Here we report that tissue-specific inactivation of Atg5, essential for the formation of autophagosomes, markedly impairs the progression of KRas(G12D)-driven lung cancer, resulting in a significant survival advantage of tumour-bearing mice. Autophagy-defective lung cancers exhibit impaired mitochondrial energy homoeostasis, oxidative stress and a constitutively active DNA damage response. Genetic deletion of the tumour suppressor p53 reinstates cancer progression of autophagy-deficient tumours. Although there is improved survival, the onset of Atg5-mutant KRas(G12D)-driven lung tumours is markedly accelerated. Mechanistically, increased oncogenesis maps to regulatory T cells. These results demonstrate that, in KRas(G12D)-driven lung cancer, Atg5-regulated autophagy accelerates tumour progression; however, autophagy also represses early oncogenesis, suggesting a link between deregulated autophagy and regulatory T cell controlled anticancer immunity.

Neutralization of Osteopontin Inhibits Obesity-Induced Inflammation and Insulin Resistance

OBJECTIVE Obesity is associated with a state of chronic low-grade inflammation mediated by immune cells that are primarily located to adipose tissue and liver. The chronic inflammatory response appears to underlie obesity-induced metabolic deterioration including insulin resistance and type 2 diabetes. Osteopontin (OPN) is an inflammatory cytokine, the expression of which is strongly upregulated in adipose tissue and liver upon obesity. Here, we studied OPN effects in obesity-induced inflammation and insulin resistance by targeting OPN action in vivo. RESEARCH DESIGN AND METHODS C57BL/6J mice were fed a high-fat diet to induce obesity and were then intravenously treated with an OPN-neutralizing or control antibody. Insulin sensitivity and inflammatory alterations in adipose tissue and liver were assessed. RESULTS Interference with OPN action by a neutralizing antibody for 5 days significantly improved insulin sensitivity in diet-induced obese mice. Anti-OPN treatment attenuated liver and adipose tissue macrophage infiltration and inflammatory gene expression by increasing macrophage apoptosis and significantly reducing c-Jun NH2-terminal kinase activation. Moreover, we report OPN as a novel negative regulator for the activation of hepatic signal transducer and activator of transcription 3 (STAT3), which is essential for glucose homeostasis and insulin sensitivity. Consequently, OPN neutralization decreased expression of hepatic gluconeogenic markers, which are targets of STAT3-mediated downregulation. CONCLUSIONS These findings demonstrate that antibody-mediated neutralization of OPN action significantly reduces insulin resistance in obesity. OPN neutralization partially decreases obesity-associated inflammation in adipose tissue and liver and reverses signal transduction related to insulin resistance and glucose homeostasis. Hence, targeting OPN could provide a novel approach for the treatment of obesity-related metabolic disorders.

Stat3 Is a Negative Regulator of Intestinal Tumor Progression in ApcMin Mice

BACKGROUND AND AIMS The transcription factor signal transducer and activator of transcription 3 (Stat3) has been considered to promote progression and metastasis of intestinal cancers. METHODS We investigated the role of Stat3 in intestinal tumors using mice with conditional ablation of Stat3 in intestinal epithelial cells (Stat3(DeltaIEC)). RESULTS In the Apc(Min) mouse model of intestinal cancer, genetic ablation of Stat3 reduced the multiplicity of early adenomas. However, loss of Stat3 promoted tumor progression at later stages, leading to formation of invasive carcinomas, which significantly shortened the lifespan of Stat3(DeltaIEC)Apc(Min/+) mice. Interestingly, loss of Stat3 in tumors of Apc(Min/+) mice had no significant impact on cell survival and angiogenesis, but promoted cell proliferation. A genome-wide expression analysis of Stat3-deficient tumors suggested that Stat3 might negatively regulate intestinal cancer progression via the cell adhesion molecule CEACAM1. CONCLUSIONS Our data suggest that Stat3 impairs invasiveness of intestinal tumors. Therefore, therapeutic targeting of the Stat3 signaling pathway in intestinal cancer should be evaluated for adverse effects on tumor progression.

A Kinase-Independent Function of CDK6 Links the Cell Cycle to Tumor Angiogenesis.

Summary In contrast to its close homolog CDK4, the cell cycle kinase CDK6 is expressed at high levels in lymphoid malignancies. In a model for p185BCR-ABL+ B-acute lymphoid leukemia, we show that CDK6 is part of a transcription complex that induces the expression of the tumor suppressor p16INK4a and the pro-angiogenic factor VEGF-A. This function is independent of CDK6’s kinase activity. High CDK6 expression thus suppresses proliferation by upregulating p16INK4a, providing an internal safeguard. However, in the absence of p16INK4a, CDK6 can exert its full tumor-promoting function by enhancing proliferation and stimulating angiogenesis. The finding that CDK6 connects cell-cycle progression to angiogenesis confirms CDK6’s central role in hematopoietic malignancies and could underlie the selection pressure to upregulate CDK6 and silence p16INK4a.

PDGFR blockade is a rational and effective therapy for NPM-ALK-driven lymphomas

Anaplastic large cell lymphoma (ALCL) is an aggressive non-Hodgkins lymphoma found in children and young adults. ALCLs frequently carry a chromosomal translocation that results in expression of the oncoprotein nucleophosmin–anaplastic lymphoma kinase (NPM-ALK). The key molecular downstream events required for NPM-ALK–triggered lymphoma growth have been only partly unveiled. Here we show that the activator protein 1 family members JUN and JUNB promote lymphoma development and tumor dissemination through transcriptional regulation of platelet-derived growth factor receptor-β (PDGFRB) in a mouse model of NPM-ALK–triggered lymphomagenesis. Therapeutic inhibition of PDGFRB markedly prolonged survival of NPM-ALK transgenic mice and increased the efficacy of an ALK-specific inhibitor in transplanted NPM-ALK tumors. Notably, inhibition of PDGFRA and PDGFRB in a patient with refractory late-stage NPM-ALK+ ALCL resulted in rapid, complete and sustained remission. Together, our data identify PDGFRB as a previously unknown JUN and JUNB target that could be a highly effective therapy for ALCL.

Epidermal loss of JunB leads to a SLE phenotype due to hyper IL-6 signaling

Systemic lupus erythematosus (SLE) is a complex autoimmune disease affecting various tissues. Involvement of B and T cells as well as increased cytokine levels have been associated with disease manifestation. Recently, we demonstrated that mice with epidermal loss of JunB (JunBΔep) develop a myeloproliferative syndrome (MPS) due to high levels of G-CSF which are secreted by JunB-deficient keratinocytes. In addition, we show that JunBΔep mice develop a SLE phenotype linked to increased epidermal interleukin 6 (IL-6) secretion. Intercrosses with IL-6-deficient mice could rescue the SLE phenotype. Furthermore, we show that JunB binds to the IL-6 promoter and transcriptionally suppresses IL-6. Facial skin biopsies of human SLE patients similarly revealed low JunB protein expression and high IL-6, activated Stat3, Socs-1, and Socs-3 levels within lupus lesions. Thus, keratinocyte-induced IL-6 secretion can cause SLE and systemic autoimmunity. Our results support trials to use α-IL-6 receptor antibody therapy for treatment of SLE.

Impairment of hepatic growth hormone and glucocorticoid receptor signaling causes steatosis and hepatocellular carcinoma in mice

Growth hormone (GH)‐activated signal transducer and activator of transcription 5 (STAT5) and the glucocorticoid (GC)‐responsive glucocorticoid receptor (GR) are important signal integrators in the liver during metabolic and physiologic stress. Their deregulation has been implicated in the development of metabolic liver diseases, such as steatosis and progression to fibrosis. Using liver‐specific STAT5 and GR knockout mice, we addressed their role in metabolism and liver cancer onset. STAT5 single and STAT5/GR double mutants developed steatosis, but only double‐mutant mice progressed to liver cancer. Mechanistically, STAT5 deficiency led to the up‐regulation of prolipogenic sterol regulatory element binding protein 1 (SREBP‐1) and peroxisome proliferator activated receptor gamma (PPAR‐γ) signaling. Combined loss of STAT5/GR resulted in GH resistance and hypercortisolism. The combination of both induced expression of adipose tissue lipases, adipose tissue lipid mobilization, and lipid flux to the liver, thereby aggravating STAT5‐dependent steatosis. The metabolic dysfunctions in STAT5/GR compound knockout animals led to the development of hepatic dysplasia at 9 months of age. At 12 months, 35% of STAT5/GR‐deficient livers harbored dysplastic nodules and ∼60% hepatocellular carcinomas (HCCs). HCC development was associated with GH and insulin resistance, enhanced tumor necrosis factor alpha (TNF‐α) expression, high reactive oxygen species levels, and augmented liver and DNA damage parameters. Moreover, activation of the c‐Jun N‐terminal kinase 1 (JNK1) and STAT3 was prominent. Conclusion: Hepatic STAT5/GR signaling is crucial for the maintenance of systemic lipid homeostasis. Impairment of both signaling cascades causes severe metabolic liver disease and promotes spontaneous hepatic tumorigenesis. (HEPATOLOGY 2011;54:1398–1409)

STAT3 regulated ARF expression suppresses prostate cancer metastasis.

Prostate cancer (PCa) is the most prevalent cancer in men. Hyperactive STAT3 is thought to be oncogenic in PCa. However, targeting of the IL-6/STAT3 axis in PCa patients has failed to provide therapeutic benefit. Here we show that genetic inactivation of Stat3 or IL-6 signalling in a Pten-deficient PCa mouse model accelerates cancer progression leading to metastasis. Mechanistically, we identify p19ARF as a direct Stat3 target. Loss of Stat3 signalling disrupts the ARF–Mdm2–p53 tumour suppressor axis bypassing senescence. Strikingly, we also identify STAT3 and CDKN2A mutations in primary human PCa. STAT3 and CDKN2A deletions co-occurred with high frequency in PCa metastases. In accordance, loss of STAT3 and p14ARF expression in patient tumours correlates with increased risk of disease recurrence and metastatic PCa. Thus, STAT3 and ARF may be prognostic markers to stratify high from low risk PCa patients. Our findings challenge the current discussion on therapeutic benefit or risk of IL-6/STAT3 inhibition.

Histone acetyl transferase 1 is essential for mammalian development, genome stability, and the processing of newly synthesized histones H3 and H4.

Histone acetyltransferase 1 is an evolutionarily conserved type B histone acetyltransferase that is thought to be responsible for the diacetylation of newly synthesized histone H4 on lysines 5 and 12 during chromatin assembly. To understand the function of this enzyme in a complex organism, we have constructed a conditional mouse knockout model of Hat1. Murine Hat1 is essential for viability, as homozygous deletion of Hat1 results in neonatal lethality. The lungs of embryos and pups genetically deficient in Hat1 were much less mature upon histological evaluation. The neonatal lethality is due to severe defects in lung development that result in less aeration and respiratory distress. Many of the Hat1−/− neonates also display significant craniofacial defects with abnormalities in the bones of the skull and jaw. Hat1−/− mouse embryonic fibroblasts (MEFs) are defective in cell proliferation and are sensitive to DNA damaging agents. In addition, the Hat1−/− MEFs display a marked increase in genome instability. Analysis of histone dynamics at sites of replication-coupled chromatin assembly demonstrates that Hat1 is not only responsible for the acetylation of newly synthesized histone H4 but is also required to maintain the acetylation of histone H3 on lysines 9, 18, and 27 during replication-coupled chromatin assembly.