[Show abstract][Hide abstract] ABSTRACT: Understanding stage-dependent oncogenic mechanisms is critical to develop not only targeted therapies, but also diagnostic markers and preventive strategies. The mechanisms acting during cancer initiation remain elusive, largely owing to a lack of suitable animal models and limited availability of human precancerous lesions. Here we show using genetic mouse models specific for liver cancer initiation, that survival of initiated cancer cells is controlled by c-Jun, independently of p53, through suppressing c-Fos-mediated apoptosis. Mechanistically, c-Fos induces SIRT6 transcription, which represses survivin by reducing histone H3K9 acetylation and NF-κB activation. Importantly, increasing the level of SIRT6 or targeting the anti-apoptotic activity of survivin at the initiation stage markedly impairs cancer development. Moreover, in human dysplastic liver nodules, but not in malignant tumours, a specific expression pattern with increased c-Jun-survivin and attenuated c-Fos-SIRT6 levels was identified. These results reveal a regulatory network connecting stress response and histone modification in liver tumour initiation, which could be targeted to prevent liver tumorigenesis.
[Show abstract][Hide abstract] ABSTRACT: Squamous cell carcinomas (SCCs) are heterogeneous and aggressive skin tumors for which innovative, targeted therapies are needed. Here, we identify a p53/TACE pathway that is negatively regulated by FOS and show that the FOS/p53/TACE axis suppresses SCC by inducing differentiation. We found that epidermal Fos deletion in mouse tumor models or pharmacological FOS/AP-1 inhibition in human SCC cell lines induced p53 expression. Epidermal cell differentiation and skin tumor suppression were caused by a p53-dependent transcriptional activation of the metalloprotease TACE/ADAM17 (TNF-α-converting enzyme), a previously unknown p53 target gene that was required for NOTCH1 activation. Although half of cutaneous human SCCs display p53-inactivating mutations, restoring p53/TACE activity in mouse and human skin SCCs induced tumor cell differentiation independently of the p53 status. We propose FOS/AP-1 inhibition or p53/TACE reactivating strategies as differentiation-inducing therapies for SCCs.
The Journal of clinical investigation 07/2012; 122(8):2898-910. · 15.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Immediate early genes (IEGs) are widely used as markers to delineate neuronal circuits because they show fast and transient expression induced by various behavioral paradigms. In this study, we investigated the expression of the IEGs c-fos and Arc in the auditory cortex of the mouse after auditory cued fear conditioning using quantitative polymerase chain reaction and microarray analysis. To test for the specificity of the IEG induction, we included several control groups that allowed us to test for factors other than associative learning to sounds that could lead to an induction of IEGs. We found that both c-fos and Arc showed strong and robust induction after auditory fear conditioning. However, we also observed increased expression of both genes in any control paradigm that involved shocks, even when no sounds were presented. Using mRNA microarrays and comparing the effect of the various behavioral paradigms on mRNA expression levels, we did not find genes being selectively upregulated in the auditory fear conditioned group. In summary, our results indicate that the use of IEGs to identify neuronal circuits involved specifically in processing of sound cues in the fear conditioning paradigm can be limited by the effects of the aversive unconditional stimulus and that activity levels in a particular primary sensory cortical area can be strongly influenced by stimuli mediated by other modalities.
Genes Brain and Behavior 12/2011; 11(3):314-24. · 3.60 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Inducible epidermal deletion of JunB and c-Jun in adult mice causes a psoriasis-like inflammatory skin disease. Increased levels of the proinflammatory cytokine TNFalpha play a major role in this phenotype. Here we define the underlying molecular mechanism using genetic mouse models. We show that Jun proteins control TNFalpha shedding in the epidermis by direct transcriptional activation of tissue inhibitor of metalloproteinase-3 (TIMP-3), an inhibitor of the TNFalpha-converting enzyme (TACE). TIMP-3 is down-regulated and TACE activity is specifically increased, leading to massive, cell-autonomous TNFalpha shedding upon loss of both JunB and c-Jun. Consequently, a prominent TNFalpha-dependent cytokine cascade is initiated in the epidermis, inducing severe skin inflammation and perinatal death of newborns from exhaustion of energy reservoirs such as glycogen and lipids. Importantly, this metabolic "cachectic" phenotype can be genetically rescued in a TNFR1-deficient background or by epidermis-specific re-expression of TIMP-3. These findings reveal that Jun proteins are essential physiological regulators of TNFalpha shedding by controlling the TIMP-3/TACE pathway. This novel mechanism describing how Jun proteins control skin inflammation offers potential targets for the treatment of skin pathologies associated with increased TNFalpha levels.
Genes & development 11/2009; 23(22):2663-74. · 12.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: JNK proteins have been shown to be involved in liver carcinogenesis in mice, but the extent of their involvement in the development of human liver cancers is unknown. Here, we show that activation of JNK1 but not JNK2 was increased in human primary hepatocellular carcinomas (HCCs). Further, JNK1 was required for human HCC cell proliferation in vitro and tumorigenesis after xenotransplantation. Importantly, mice lacking JNK1 displayed decreased tumor cell proliferation in a mouse model of liver carcinogenesis and decreased hepatocyte proliferation in a mouse model of liver regeneration. In both cases, impaired proliferation was caused by increased expression of p21, a cell-cycle inhibitor, and reduced expression of c-Myc, a negative regulator of p21. Genetic inactivation of p21 in JNK1-/- mice restored hepatocyte proliferation in models of both liver carcinogenesis and liver regeneration, and overexpression of c-Myc increased proliferation of JNK1-/- liver cells. Similarly, JNK1 was found to control the proliferation of human HCC cells by affecting p21 and c-Myc expression. Pharmacologic inhibition of JNK reduced the growth of both xenografted human HCC cells and chemically induced mouse liver cancers. These findings provide a mechanistic link between JNK activity and liver cell proliferation via p21 and c-Myc and suggest JNK targeting can be considered as a new therapeutic approach for HCC treatment.
Journal of Clinical Investigation 01/2009; 118(12):3943-53. · 12.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Osteoclasts are multinucleated haematopoietic cells that resorb bone. Increased osteoclast activity causes osteoporosis, a disorder resulting in a low bone mass and a high risk of fractures. Increased osteoclast size and numbers are also a hallmark of other disorders, such as Paget's disease and multiple myeloma. The protein c-Fos, a component of the AP-1 transcription factor complex, is essential for osteoclast differentiation. Here we show that the Fos-related protein Fra-2 controls osteoclast survival and size. The bones of Fra-2-deficient newborn mice have giant osteoclasts, and signalling through leukaemia inhibitory factor (LIF) and its receptor is impaired. Similarly, newborn animals lacking LIF have giant osteoclasts, and we show that LIF is a direct transcriptional target of Fra-2 and c-Jun. Moreover, bones deficient in Fra-2 and LIF are hypoxic and express increased levels of hypoxia-induced factor 1alpha (HIF1alpha) and Bcl-2. Overexpression of Bcl-2 is sufficient to induce giant osteoclasts in vivo, whereas Fra-2 and LIF affect HIF1alpha through transcriptional modulation of the HIF prolyl hydroxylase PHD2. This pathway is operative in the placenta, because specific inactivation of Fra-2 in the embryo alone does not cause hypoxia or the giant osteoclast phenotype. Thus placenta-induced hypoxia during embryogenesis leads to the formation of giant osteoclasts in young pups. These findings offer potential targets for the treatment of syndromes associated with increased osteoclastogenesis.
[Show abstract][Hide abstract] ABSTRACT: Mice that lack JunB in epidermal cells are born with normal skin; however, keratinocytes hyperproliferate in vitro and on TPA treatment in vivo. Loss of JunB expression in the epidermis of adult mice affects the skin, the proliferation of haematopoietic cells and bone formation. G-CSF is a direct transcriptional target of JunB and mutant epidermis releases large amounts of G-CSF that reach high systemic levels and cause skin ulcerations, myeloproliferative disease and low bone mass. The absence of G-CSF significantly improves hyperkeratosis and prevents the development of myeloproliferative disease, but does not affect bone loss. This study describes a mechanism by which the absence of JunB in epithelial cells causes multi-organ disease, suggesting that the epidermis can act as an endocrine-like organ.
[Show abstract][Hide abstract] ABSTRACT: The mitogen-activated protein kinase (MAPK) p38alpha controls inflammatory responses and cell proliferation. Using mice carrying conditional Mapk14 (also known as p38alpha) alleles, we investigated its function in postnatal development and tumorigenesis. When we specifically deleted Mapk14 in the mouse embryo, fetuses developed to term but died shortly after birth, probably owing to lung dysfunction. Fetal hematopoietic cells and embryonic fibroblasts deficient in p38alpha showed increased proliferation resulting from sustained activation of the c-Jun N-terminal kinase (JNK)-c-Jun pathway. Notably, in chemical-induced liver cancer development, mice with liver-specific deletion of Mapk14 showed enhanced hepatocyte proliferation and tumor development that correlated with upregulation of the JNK-c-Jun pathway. Furthermore, inactivation of JNK or c-Jun suppressed the increased proliferation of Mapk14-deficient hepatocytes and tumor cells. These results demonstrate a new mechanism whereby p38alpha negatively regulates cell proliferation by antagonizing the JNK-c-Jun pathway in multiple cell types and in liver cancer development.
[Show abstract][Hide abstract] ABSTRACT: Psoriasis is a frequent, inflammatory disease of skin and joints with considerable morbidity. Here we report that in psoriatic lesions, epidermal keratinocytes have decreased expression of JunB, a gene localized in the psoriasis susceptibility region PSORS6. Likewise, inducible epidermal deletion of JunB and its functional companion c-Jun in adult mice leads (within two weeks) to a phenotype resembling the histological and molecular hallmarks of psoriasis, including arthritic lesions. In contrast to the skin phenotype, the development of arthritic lesions requires T and B cells and signalling through tumour necrosis factor receptor 1 (TNFR1). Prior to the disease onset, two chemotactic proteins (S100A8 and S100A9) previously mapped to the psoriasis susceptibility region PSORS4, are strongly induced in mutant keratinocytes in vivo and in vitro. We propose that the abrogation of JunB/activator protein 1 (AP-1) in keratinocytes triggers chemokine/cytokine expression, which recruits neutrophils and macrophages to the epidermis thereby contributing to the phenotypic changes observed in psoriasis. Thus, these data support the hypothesis that epidermal alterations are sufficient to initiate both skin lesions and arthritis in psoriasis.
[Show abstract][Hide abstract] ABSTRACT: The Fos-related AP1 transcription factor Fra2 (encoded by Fosl2) is expressed in various epithelial cells as well as in cartilaginous structures. We studied the role of Fra2 in cartilage development. The absence of Fra2 in embryos and newborns leads to reduced zones of hypertrophic chondrocytes and impaired matrix deposition in femoral and tibial growth plates, probably owing to impaired differentiation into hypertrophic chondrocytes. In addition, hypertrophic differentiation and ossification of primordial arches of the developing vertebrae are delayed in Fra2-deficient embryos. Primary Fosl2-/- chondrocytes exhibit decreased hypertrophic differentiation and remain in a proliferative state longer than wild-type cells. As pups lacking Fra2 die shortly after birth, we generated mice carrying 'floxed' Fosl2 alleles and crossed them to coll2a1-Cre mice, allowing investigation of postnatal cartilage development. The coll2a1-Cre, Fosl2f/f mice die between 10 and 25 days after birth, are growth retarded and display smaller growth plates similar to Fosl2-/- embryos. In addition, these mice suffer from a kyphosis-like phenotype, an abnormal bending of the spine. Hence, Fra2 is a novel transcription factor important for skeletogenesis by affecting chondrocyte differentiation.
Development 12/2004; 131(22):5717-25. · 6.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Because JunB is an essential gene for placentation, it was conditionally deleted in the embryo proper. JunBDelta/Delta mice are born viable, but develop severe low turnover osteopenia caused by apparent cell-autonomous osteoblast and osteoclast defects before a chronic myeloid leukemia-like disease. Although JunB was reported to be a negative regulator of cell proliferation, junBDelta/Delta osteoclast precursors and osteoblasts show reduced proliferation along with a differentiation defect in vivo and in vitro. Mutant osteoblasts express elevated p16(INK4a) levels, but exhibit decreased cyclin D1 and cyclin A expression. Runx2 is transiently increased during osteoblast differentiation in vitro, whereas mature osteoblast markers such as osteocalcin and bone sialoprotein are strongly reduced. To support a cell-autonomous function of JunB in osteoclasts, junB was inactivated specifically in the macrophage-osteoclast lineage. Mutant mice develop an osteopetrosis-like phenotype with increased bone mass and reduced numbers of osteoclasts. Thus, these data reveal a novel function of JunB as a positive regulator controlling primarily osteoblast as well as osteoclast activity.
The Journal of Cell Biology 03/2004; 164(4):613-23. · 10.82 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To investigate the function of c-Jun during skin development and skin tumor formation, we conditionally inactivated c-jun in the epidermis. Mice lacking c-jun in keratinocytes (c-jun(Deltaep)) develop normal skin but express reduced levels of EGFR in the eyelids, leading to open eyes at birth, as observed in EGFR null mice. Primary keratinocytes from c-jun(Deltaep) mice proliferate poorly, show increased differentiation, and form prominent cortical actin bundles, most likely because of decreased expression of EGFR and its ligand HB-EGF. In the absence of c-Jun, tumor-prone K5-SOS-F transgenic mice develop smaller papillomas, with reduced expression of EGFR in basal keratinocytes. Thus, using three experimental systems, we show that EGFR and HB-EGF are regulated by c-Jun, which controls eyelid development, keratinocyte proliferation, and skin tumor formation.