Final Report Summary - AP-1-FUN (AP-1 (Fos/Jun) Functions in Physiology and Disease)
The dimeric transcription factor AP-1 (Activator Protein-1) is conserved throughout evolution and contains members of the Fos and Jun families. AP-1 regulates a wide range of cellular processes in response to various physiological and environmental stress stimuli. AP-1 activity is closely linked to cellular proliferation, apoptosis, differentiation and transformation. The aim of our research program was to gain a better understanding of the molecular mechanisms regulating health and disease in specific organs like bone, liver and skin. We discovered novel molecules which enable a cross-talk between different organs within the body. This will facilitate the development of novel therapies for human conditions such as inflammatory diseases, fibrosis and cancer.
During the course of this project, we have defined the importance of the AP-1 member c-Fos and its phosphorylation in bone physiology, cytokine response and skin cancer. Furthermore, the analysis of human osteosarcoma cell lines pointed to the relevance of Fos and a Fos target gene, TGFBI in bone cancers.
Using newly generated state of the art mouse models we show, how another Fos protein, Fra-2 limits bone loss (osteoporosis) by targeting osteocalcin and collagen gene expression. We demonstrate that Fra-2 is an important regulator of bone physiology in mouse and human cells.
Using experimental models for liver cancer and conditional genetic AP-1 inactivation, we discovered a novel pathway involving c-Jun, c-Fos, Survivin and SIRT6, and showed its relevance in human patient early liver tumor samples. Furthermore, ectopic expression of Fos and its binding partners in adult hepatocytes leads to liver inflammation, fibrosis, hepatocyte and bile duct hyperproliferation with loss of liver architecture and predisposition to liver cancer. Conversely, deletion of c-Fos in hepatocytes protects from chemical-induced liver cancer. Interestingly, additional deletion of Fos in immune cells abrogates this protective effect, implying an intricate genetic network regulating liver cancer formation dependent on AP-1.
In an elegant series of experiments we were able to show that specific AP-1 dimers activate a genetic program leading to high fat diet-induced fatty liver disease (HFLD), whereas other dimers composed of Fra-Jun proteins were able to prevent and even revert HFLD. The transcriptional target of these dimers is the master regulator of lipid metabolism, the PPARg pathway. We also found that while Fra-1 has little impact on hepatic fibrosis, it modulates the detoxification function of the liver and is protective during paracetamol overdose.
We have also characterized in several mouse models the effects a growing tumour has on the whole organism leading to a deleterious clinical syndrome termed cancer-associated cachexia. We identified that burning the fat reservoirs is an early event in cancer cachexia, a highly relevant finding for the clinic.
Characterization of inflammatory skin disease was carried out in mice lacking or ectopically expressing AP-1 components in the epidermis. We discovered a cross-talk between skin inflammation and bone loss through the expression of the JunB-dependent cytokine IL-17A. Moreover, we discovered a link between epidermal c-Fos/AP-1 and the Notch pathway, established a mouse model with inducible c-Fos expression for inflammation-dependent skin cancers and discovered how AP-1 epigenetically modulates epidermal differentiation in homeostasis and skin cancer.
We have also employed our established psoriasis-like mouse model to discover new therapeutically-relevant pathways and performed pre-clinical studies. We showed how systemic anti-VEGF treatment reduces skin inflammation. Furthermore, we have shown that an AP-1-dependent TIMP-3-TACE-TNF pathway is functional to establish the inflammatory skin disease and investigated the specific roles of AP-1 targets such as S100A8/A9, the complement component C3 and miR21 in skin inflammation.
During the course of this project, we have defined the importance of the AP-1 member c-Fos and its phosphorylation in bone physiology, cytokine response and skin cancer. Furthermore, the analysis of human osteosarcoma cell lines pointed to the relevance of Fos and a Fos target gene, TGFBI in bone cancers.
Using newly generated state of the art mouse models we show, how another Fos protein, Fra-2 limits bone loss (osteoporosis) by targeting osteocalcin and collagen gene expression. We demonstrate that Fra-2 is an important regulator of bone physiology in mouse and human cells.
Using experimental models for liver cancer and conditional genetic AP-1 inactivation, we discovered a novel pathway involving c-Jun, c-Fos, Survivin and SIRT6, and showed its relevance in human patient early liver tumor samples. Furthermore, ectopic expression of Fos and its binding partners in adult hepatocytes leads to liver inflammation, fibrosis, hepatocyte and bile duct hyperproliferation with loss of liver architecture and predisposition to liver cancer. Conversely, deletion of c-Fos in hepatocytes protects from chemical-induced liver cancer. Interestingly, additional deletion of Fos in immune cells abrogates this protective effect, implying an intricate genetic network regulating liver cancer formation dependent on AP-1.
In an elegant series of experiments we were able to show that specific AP-1 dimers activate a genetic program leading to high fat diet-induced fatty liver disease (HFLD), whereas other dimers composed of Fra-Jun proteins were able to prevent and even revert HFLD. The transcriptional target of these dimers is the master regulator of lipid metabolism, the PPARg pathway. We also found that while Fra-1 has little impact on hepatic fibrosis, it modulates the detoxification function of the liver and is protective during paracetamol overdose.
We have also characterized in several mouse models the effects a growing tumour has on the whole organism leading to a deleterious clinical syndrome termed cancer-associated cachexia. We identified that burning the fat reservoirs is an early event in cancer cachexia, a highly relevant finding for the clinic.
Characterization of inflammatory skin disease was carried out in mice lacking or ectopically expressing AP-1 components in the epidermis. We discovered a cross-talk between skin inflammation and bone loss through the expression of the JunB-dependent cytokine IL-17A. Moreover, we discovered a link between epidermal c-Fos/AP-1 and the Notch pathway, established a mouse model with inducible c-Fos expression for inflammation-dependent skin cancers and discovered how AP-1 epigenetically modulates epidermal differentiation in homeostasis and skin cancer.
We have also employed our established psoriasis-like mouse model to discover new therapeutically-relevant pathways and performed pre-clinical studies. We showed how systemic anti-VEGF treatment reduces skin inflammation. Furthermore, we have shown that an AP-1-dependent TIMP-3-TACE-TNF pathway is functional to establish the inflammatory skin disease and investigated the specific roles of AP-1 targets such as S100A8/A9, the complement component C3 and miR21 in skin inflammation.