Mechanismus regulace aktivace ligandů EGF receptoru prostřednictvím intramembránové pseudoproteasy iRhom a metaloproteasy ADAM17

Signalling through the EGF receptor is subject to a complex and multilayered regulation. One such mode of regulation is through control of ligand production which plays an important role in fine- tuning EGF receptor activation. In mammals, the production of soluble, biologically active forms of EGF receptor ligands relies on ADAM metalloproteases, predominantly ADAM10 and ADAM17. Recently, a pseudoprotease from the rhomboid-like family of intramembrane proteases, iRhom, emerged as a key positive regulator of ADAM17. However, Drosophila iRhom has also been implicated in the negative regulation of EGF receptor signalling by promoting the degradation of precursors of its ligands. Cell culture based assays suggest that mammalian iRhoms might also be involved in a similar process. In this thesis, the effect of mammalian iRhom overexpression on the levels of EGF receptor ligands has been investigated. Contrary to previous findings, the data presented in this thesis suggest that the observed effect might not be entirely iRhom specific, for the inactive mutants of rhomboid proteases also diminish the levels of EGF receptor ligands. Nor do we find the effect to be specific to EGF receptor ligands, as unrelated transmembrane proteins were also depleted by iRhom overexpression. The coexpression of ADAM17 was...Signalisace skrz receptor pro epidermální růstový faktor (EGF receptor, EGFR) podléhá propracované a mnohovrstevné regulaci. Jedním ze způsobů vylaďování signalisace zprostředkované tímto receptorem je kontrola produkce jeho ligandů. U savců za uvolňování solubilních, biologicky aktivních forem ligandů EGF receptoru zodpovídají především metaloproteasy ADAM10 a ADAM17. Pseudoprotease iRhom z rodiny rhomboid-like proteinů byla nedávno připsána úloha klíčového positivního regulátora ADAM17. U drosofily však je iRhom spjat s negativní regulací EGF receptoru, a to prostřednictvím degradace prekursorů jeho ligandů. Experimenty prováděné v savčích buněčných kulturách ovšem naznačují, že podobná funkce by mohla být zachována i u savčích iRhomů. V této diplomové práci byl studován vliv overexprese iRhomu na expresní úroveň ligandů EGF receptoru. Na rozdíl od dřívějších publikací však nebylo potvrzeno, že by pozorovaný efekt bylo možno vysvětlit výlučně přítomností iRhomu, neboť neaktivní mutanti rhomboidních proteas jej působili rovněž. Také nebylo prokázáno, že by iRhom takto ovlivňoval pouze ligandy EGF receptoru - strukturně podobné, avšak ligandům EGF receptoru nepříbuzné proteiny v přítomnosti iRhomu taktéž podléhaly depleci. Koexprese ADAM17 mizení ligandů EGF receptoru zamezila, avšak pouze v...Katedra buněčné biologieDepartment of Cell BiologyPřírodovědecká fakultaFaculty of Scienc

Mechanism of regulation of EGFR receptor ligand activation via the intramembrane pseudoprotease iRhom and cell surface metalloprotease ADAM17

Signalling through the EGF receptor is subject to a complex and multilayered regulation. One such mode of regulation is through control of ligand production which plays an important role in fine- tuning EGF receptor activation. In mammals, the production of soluble, biologically active forms of EGF receptor ligands relies on ADAM metalloproteases, predominantly ADAM10 and ADAM17. Recently, a pseudoprotease from the rhomboid-like family of intramembrane proteases, iRhom, emerged as a key positive regulator of ADAM17. However, Drosophila iRhom has also been implicated in the negative regulation of EGF receptor signalling by promoting the degradation of precursors of its ligands. Cell culture based assays suggest that mammalian iRhoms might also be involved in a similar process. In this thesis, the effect of mammalian iRhom overexpression on the levels of EGF receptor ligands has been investigated. Contrary to previous findings, the data presented in this thesis suggest that the observed effect might not be entirely iRhom specific, for the inactive mutants of rhomboid proteases also diminish the levels of EGF receptor ligands. Nor do we find the effect to be specific to EGF receptor ligands, as unrelated transmembrane proteins were also depleted by iRhom overexpression. The coexpression of ADAM17 was..

Evolution of regulatory mechanisms of EGF receptor activation

Signalling through EGF receptor is crucial both for ontogenesis and for maintaining homeostasis in adult organisms. It is involved in controlling cellular behaviours such as proliferation, migration or differentiation. This thesis provides an insight into evolution of the regulatory mechanisms of EGF receptor activation by discussing their principles in C. elegans, D. melanogaster and H. sapiens sapiens, on the basis of which conclusions about their evolutionary tendencies are made. Attention is focused on the roles of the rhomboid family of proteins, whose activity is tightly associated with EGF receptor signalling. Dysregulation of the EGF receptor unnegligibly contributes to the development of various diseases, mainly many types of cancer, but also schizophrenia, psoriasis and cardiovascular disorders. Experimental results obtained on this field of research therefore have the potential to be applied in drug design

Semaphorin 4B is an ADAM17-cleaved adipokine that inhibits adipocyte differentiation and thermogenesis

Objective: The metalloprotease ADAM17 (also called TACE) plays fundamental roles in homeostasis by shedding key signaling molecules from the cell surface. Although its importance for the immune system and epithelial tissues is well-documented, little is known about the role of ADAM17 in metabolic homeostasis. The purpose of this study was to determine the impact of ADAM17 expression, specifically in adipose tissues, on metabolic homeostasis. Methods: We used histopathology, molecular, proteomic, transcriptomic, in vivo integrative physiological and ex vivo biochemical approaches to determine the impact of adipose tissue-specific deletion of ADAM17 upon adipocyte and whole organism metabolic physiology. Results: ADAM17adipoq-creΔ/Δ mice exhibited a hypermetabolic phenotype characterized by elevated energy consumption and increased levels of adipocyte thermogenic gene expression. On a high fat diet, these mice were more thermogenic, while exhibiting elevated expression levels of genes associated with lipid oxidation and lipolysis. This hypermetabolic phenotype protected mutant mice from obesogenic challenge, limiting weight gain, hepatosteatosis and insulin resistance. Activation of beta-adrenoceptors by the neurotransmitter norepinephrine, a key regulator of adipocyte physiology, triggered the shedding of ADAM17 substrates, and regulated ADAM17 expression at the mRNA and protein levels, hence identifying a functional connection between thermogenic licensing and the regulation of ADAM17. Proteomic studies identified Semaphorin 4B (SEMA4B), as a novel ADAM17-shed adipokine, whose expression is regulated by physiological thermogenic cues, that acts to inhibit adipocyte differentiation and dampen thermogenic responses in adipocytes. Transcriptomic data showed that cleaved SEMA4B acts in an autocrine manner in brown adipocytes to repress the expression of genes involved in adipogenesis, thermogenesis, and lipid uptake, storage and catabolism. Conclusions: Our findings identify a novel ADAM17-dependent axis, regulated by beta-adrenoceptors and mediated by the ADAM17-cleaved form of SEMA4B, that modulates energy balance in adipocytes by inhibiting adipocyte differentiation, thermogenesis and lipid catabolism

iRhom2/ADAM17 deletion protects from obesity associated to increased adipocyte thermogenesis and differentiation and reduced adipocyte Semaphorin 4B shedding

Objectives: The metalloprotease ADAM17 (also called TACE) plays fundamental roles during development, and to promote homeostasis and multiple inflammatory diseases and cancer by shedding key signaling molecules from the cell surface. Its importance in inflammation and growth control is well documented, while little is known about the role of ADAM17 and its regulator iRhom2 in metabolic homeostasis. The purpose of this study was to determine the impact of the sheddase ADAM17/TACE and of its modulator iRhom2 in the pathophysiology of obesity and in adipocyte homeostasis. Materials and Methods: We challenged controls versus iRhom2 global KO or adipocyte specific ADAM17 KO mice to positive energy balance by chronic exposure to a high fat diet, and then compared their metabolic phenotypes. We also carried out ex vivo assays with primary and immortalized mouse brown and beige adipocytes to establish the autonomy of the effect of loss of iRhom2 and ADAM17 on differentiation, thermogenesis and respiration. In addition, we used proteomic and transcriptomic analyses to identify and characterize a novel ADAM17 substrate involved. Results: iRhom2 global KO and adipocyte-specific ADAM17 KO mice exhibited a hypermetabolic phenotype characterized by elevated energy consumption and increased levels of adipocyte thermogenic gene expression and browning. This protected mutant mice from obesogenic challenge, limiting weight gain, hepatosteatosis and insulin resistance. Proteomic studies identified Semaphorin 4B (SEMA4B), as a novel ADAM17-shed adipokine, whose expression is regulated by physiological thermogenic cues, that acts to inhibit adipocyte differentiation and dampen thermogenic responses in adipocytes. Conclusion: Our findings identify a novel iRhom2/ADAM17-dependent axis, regulated by beta-adrenoceptors and mediated by the ADAM17-cleaved form of SEMA4B, that modulates energy balance in adipocytes by inhibiting adipocyte differentiation, thermogenesis and lipid catabolism. Keywords: iRhom2, ADAM17/TACE; Semaphorin4B; Thermogenesis; Obesity