Acute and chronic effects of a light-activated FGF receptor in keratinocytes in vitro and in mice

A F420-dependent Single Domain Chemogenetic Tool for Protein De-dimerization

Protein-protein interactions (PPIs) mediate many fundamental cellular processes. Control of PPIs through optically or chemically responsive protein domains has had a profound impact on basic research and some clinical applications. Most chemogenetic methods induce the association, i.e., dimerization or oligomerization, of target proteins, whilst the few available dissociation approaches either break large oligomeric protein clusters or heteromeric complexes. Here, we have exploited the controlled dissociation of a homodimeric oxidoreductase from mycobacteria (MSMEG_2027) by its native cofactor, F420, which is not present in mammals, as a bioorthogonal monomerization switch. Using X-ray crystallography, we found that in the absence of F420 MSMEG_2027 forms a unique domain-swapped dimer that occludes the cofactor binding site. Rearrangement of the N-terminal helix upon F420 binding results in the dissolution of the dimer. We then showed that MSMEG_2027 can be fused to proteins of interest in human cells and applied it as a tool to induce and release MAPK/ERK signalling downstream of a chimeric fibroblast growth factor receptor 1 (FGFR1) tyrosine kinase. This F420-dependent chemogenetic de-homodimerization tool is stoichiometric and based on a single domain and thus represents a novel mechanism to investigate protein complexes in situ.

Dose-dependent effects of Nrf2 on the epidermis in chronic skin inflammation

Atopic dermatitis (AD) is a chronic inflammatory skin disease, characterized by an impaired epidermal barrier and immunological alterations. The activity of the cytoprotective NRF2 transcription factor is reduced in the epidermis of AD patients. To determine the functional relevance of this deficiency, we used mice lacking fibroblast growth factor receptors 1 and 2 in keratinocytes (K5-R1/R2 mice), which exhibit several AD-like symptoms. Proteomics analysis of their epidermis revealed reduced Nrf2 activity. This was accompanied by an increase in DNA damage and in the number of senescent cells. Genetic deletion of Nrf2 in keratinocytes of these mice further promoted DNA damage and senescence, but time-limited pharmacological activation of Nrf2 in the skin had a mild protective effect. Surprisingly, long-term genetic activation of Nrf2 in keratinocytes of K5-R1/R2 mice caused strong hyperkeratosis, keratinocyte hyperproliferation, epidermal thickening, increased keratinocyte apoptosis and DNA damage, and altered immune cell composition. These results reveal a complex role of Nrf2 in the epidermis and show the necessity to optimize the duration and intensity of NRF2 activation for the treatment of epidermal alterations in patients with AD.

Serine protease 35 regulates the fibroblast matrisome in response to hyperosmotic stress

Hyperosmotic stress occurs in several diseases, but its long-term effects are largely unknown. We used sorbitol-treated human fibroblasts in 3D culture to study the consequences of hyperosmotic stress in the skin. Sorbitol regulated many genes, which help cells cope with the stress condition. The most robustly regulated gene encodes serine protease 35 (PRSS35). Its regulation by hyperosmotic stress was dependent on the kinases p38 and JNK and the transcription factors NFAT5 and ATF2. We identified different collagens and collagen-associated proteins as putative PRSS35 binding partners. This is functionally important because PRSS35 affected the extracellular matrix proteome, which limited cell proliferation. The in vivo relevance of these findings is reflected by the coexpression of PRSS35 and its binding partners in human skin wounds, where hyperosmotic stress occurs as a consequence of excessive water loss. These results identify PRSS35 as a key regulator of the matrisome under hyperosmotic stress conditions.

New developments in the biology of fibroblast growth factors

The fibroblast growth factor (FGF) family is composed of 18 secreted signaling proteins consisting of canonical FGFs and endocrine FGFs that activate four receptor tyrosine kinases (FGFRs 1-4) and four intracellular proteins (intracellular FGFs or iFGFs) that primarily function to regulate the activity of voltage-gated sodium channels and other molecules. The canonical FGFs, endocrine FGFs, and iFGFs have been reviewed extensively by us and others. In this review, we briefly summarize past reviews and then focus on new developments in the FGF field since our last review in 2015. Some of the highlights in the past 6 years include the use of optogenetic tools, viral vectors, and inducible transgenes to experimentally modulate FGF signaling, the clinical use of small molecule FGFR inhibitors, an expanded understanding of endocrine FGF signaling, functions for FGF signaling in stem cell pluripotency and differentiation, roles for FGF signaling in tissue homeostasis and regeneration, a continuing elaboration of mechanisms of FGF signaling in development, and an expanding appreciation of roles for FGF signaling in neuropsychiatric diseases. This article is categorized under: Cardiovascular Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology Congenital Diseases > Stem Cells and Development Cancer > Stem Cells and Development.

Light-activated receptor tyrosine kinases: Designs and applications

Receptor tyrosine kinases (RTKs) are a large and essential membrane receptor family. The molecular mechanisms and physiological consequences of RTK activation depend on, for example, ligand identity, subcellular localization, and developmental or disease stage. In the past few years, genetically-encoded light-activated RTKs (Opto-RTKs) have been developed to dissect these complexities by providing reversible and spatio-temporal control over cell signaling. These methods have very recently matured to include highly-sensitive multi-color actuators. The new ability to regulate RTK activity with high precision has been recently harnessed to gain mechanistic insights in subcellular, tissue, and animal models. Because of their sophisticated engineering, Opto-RTKs may only mirror some aspects of natural activation mechanisms but nevertheless offer unique opportunities to study RTK signaling and physiology.