FERMT1 promoter mutations in patients with Kindler syndrome

Structure, signal transduction, activation, and inhibition of integrin αIIbβ3

Integrins are heterodimeric receptors comprising α and β subunits. They are expressed on the cell surface and play key roles in cell adhesion, migration, and growth. Several types of integrins are expressed on the platelets, including αvβ3, αIIbβ3, α2β1, α5β1, and α6β1. Among these, physically αIIbβ3 is exclusively expressed on the platelet surface and their precursor cells, megakaryocytes. αIIbβ3 adopts at least three conformations: i) bent-closed, ii) extended-closed, and iii) extended-open. The transition from conformation i) to iii) occurs when αIIbβ3 is activated by stimulants. Conformation iii) possesses a high ligand affinity, which triggers integrin clustering and platelet aggregation. Platelets are indispensable for maintaining vascular system integrity and preventing bleeding. However, excessive platelet activation can result in myocardial infarction (MI) and stroke. Therefore, finding a novel strategy to stop bleeding without accelerating the risk of thrombosis is important. Regulation of αIIbβ3 activation is vital for this strategy. There are a large number of molecules that facilitate or inhibit αIIbβ3 activation. The interference of these molecules can accurately control the balance between hemostasis and thrombosis. This review describes the structure and signal transduction of αIIbβ3, summarizes the molecules that directly or indirectly affect integrin αIIbβ3 activation, and discusses some novel antiαIIbβ3 drugs. This will advance our understanding of the activation of αIIbβ3 and its essential role in platelet function and tumor development.

Examination of FERMT1 expression in placental chorionic villi and its role in HTR8-SVneo cell invasion

Transmembrane integrin receptors mediate cell-extracellular matrix as well as cell-cell adhesion. As placental trophoblast cells undergo differentiation they display changes in integrin expression or switching, but the mechanism(s) of integrin activation that supports this differentiation is still unknown. The Fermitin family of adapter proteins (FERMT 1-3) are integrin activators that mediate integrin-mediated signaling. In this study, we examined the spatiotemporal pattern of expression of FERMT1 in human chorionic villi throughout gestation and its role in HTR8-SVneo substrate adhesion and invasion. Placental villous tissue was obtained from patients undergoing elective terminations at weeks 8-14, as well as from term deliveries at weeks 37-40 and analyzed by immunofluorescence. Additionally, HTR8-SVneo trophoblast cells were transfected with FERMT1-specific siRNA or non-targeting siRNA (control) and used in cell-substrate adhesion as well as invasion assays. FERMT1 was primarily localized to membrane-associated regions at the base or around the periphery of the villous cytotrophoblast and proximal as well as distal cell column trophoblast. FERMT1 was also localized to endothelial cells of blood vessels in chorionic villi. siRNA-mediated depletion of FERMT1 in HTR8-SVneo cells did not markedly alter HTR8-SVneo cell-substrate adhesion but did significantly decrease invasion (P < 0.05) compared to control cells. These novel findings identify the presence of the integrin activator FERMT1 in trophoblast cells and that FERMT1 can regulate HTR8-SVneo cell invasion. FERMT1 may directly influence integrin activation and the subsequent integrin-mediated signaling and differentiation that underlies the acquisition of the invasive trophoblast phenotype in vivo.

Multifunctional Roles of the Actin-Binding Protein Flightless I in Inflammation, Cancer and Wound Healing

Flightless I is an actin-binding member of the gelsolin family of actin-remodeling proteins that inhibits actin polymerization but does not possess actin severing ability. Flightless I functions as a regulator of many cellular processes including proliferation, differentiation, apoptosis, and migration all of which are important for many physiological processes including wound repair, cancer progression and inflammation. More than simply facilitating cytoskeletal rearrangements, Flightless I has other important roles in the regulation of gene transcription within the nucleus where it interacts with nuclear hormone receptors to modulate cellular activities. In conjunction with key binding partners Leucine rich repeat in the Flightless I interaction proteins (LRRFIP)1/2, Flightless I acts both synergistically and competitively to regulate a wide range of cellular signaling including interacting with two of the most important inflammatory pathways, the NLRP3 inflammasome and the MyD88-TLR4 pathways. In this review we outline the current knowledge about this important cytoskeletal protein and describe its many functions across a range of health conditions and pathologies. We provide perspectives for future development of Flightless I as a potential target for clinical translation and insights into potential therapeutic approaches to manipulate Flightless I functions.

Assessment of the risk and characterization of non-melanoma skin cancer in Kindler syndrome: study of a series of 91 patients

BACKGROUND

Kindler Syndrome (KS) is a rare genodermatosis characterized by skin fragility, skin atrophy, premature aging and poikiloderma. It is caused by mutations in the FERMT1 gene, which encodes kindlin-1, a protein involved in integrin signalling and the formation of focal adhesions. Several reports have shown the presence of non-melanoma skin cancers in KS patients but a systematic study evaluating the risk of these tumors at different ages and their potential outcome has not yet been published. We have here addressed this condition in a retrospective study of 91 adult KS patients, characterizing frequency, metastatic potential and body distribution of squamous cell carcinoma (SCC) in these patients. SCC developed in 13 of the 91 patients.

RESULTS

The youngest case arose in a 29-year-old patient; however, the cumulative risk of SCC increased to 66.7% in patients over 60 years of age. The highly aggressive nature of SCCs in KS was confirmed showing that 53.8% of the patients bearing SCCs develop metastatic disease. Our data also showed there are no specific mutations that correlate directly with the development of SCC; however, the mutational distribution along the gene appears to be different in patients bearing SCC from SCC-free patients. The body distribution of the tumor appearance was also unique and different from other bullous diseases, being concentrated in the hands and around the oral cavity, which are areas of high inflammation in this disease.

CONCLUSIONS

This study characterizes SCCs in the largest series of KS patients reported so far, showing the high frequency and aggressiveness of these tumors. It also describes their particular body distribution and their relationship with mutations in the FERMT-1 gene. These data reinforce the need for close monitoring of premalignant or malignant lesions in KS patients.

Advances in understanding the molecular basis of skin fragility

Skin fragility refers to a large group of conditions in which the ability of the skin to provide protection against trivial mechanical trauma is diminished, resulting in the formation of blisters, erosions, wounds, or scars. Acquired and physiological skin fragility is common; genetic disorders are rare but give insight into the molecular mechanisms ensuring skin stability. The paradigm is represented by inherited epidermolysis bullosa. This review is focused on recent advances in understanding the molecular basis of genetic skin fragility, including emerging concepts, controversies, unanswered questions, and opinions of the author. In spite of the advanced knowledge on the genetic causes of skin fragility, the molecular pathology is still expanding. Open questions in understanding the molecular basis of genetic skin fragility are the following: what are the causes of phenotypes which remain genetically unsolved, and what are the molecular modifiers which might explain phenotypic differences among individuals with similar mutations?  New mutational mechanisms and new genes have recently been discovered and are briefly described here. Comprehensive next-generation sequencing-based genetic testing improved mutation detection and facilitated the identification of the genetic basis of unclear and new phenotypes. Characterization of the biochemical and cell biological consequences of the genetic variants is challenging and laborious but may represent the basis for personalized therapeutic approaches. Molecular modifiers of skin fragility have been uncovered in particular animal and genetic models but not in larger cohorts of patients. This scientific progress is the basis for revisions of the epidermolysis bullosa classification and for innovative therapeutic approaches designed for this intractable condition.

KIND1 Loss Sensitizes Keratinocytes to UV-Induced Inflammatory Response and DNA Damage

Loss of function of KIND1, a cytoskeletal protein involved in β1-integrin function, causes Kindler syndrome, a genetic disease characterized by skin fragility, photosensitivity, and increased risk of squamous cell carcinoma. Dysregulation of β1-integrin underlies Kindler syndrome skin fragility. However, the mechanisms underlying squamous cell carcinoma susceptibility are unclear. Here, we demonstrate that gene silencing of KIND1 decreased keratinocyte proliferation and increased apoptosis in vitro and in skin grafts regenerated on mice, which was correlated with reduced cyclinB1. In addition, KIND1 loss sensitized keratinocytes to cytokine and UV-induced NF-κB and c-Jun N-terminal kinase activation and upregulation of CXCL10 and tumor necrosis factor-α. Moreover, KIND1 loss impaired DNA repair, as indicated by the increased detection of γH2AX and cyclobutane pyrimidine dimers 24 hours after UVB radiation. Genetic or pharmacological c-Jun N-terminal kinase inhibition and NF-κB inhibition markedly reduced cyclobutane pyrimidine dimers-positive cells. Further, we show that KIND1 was regulated by JunB at the transcriptional level and, like JunB, it was downregulated in human squamous cell carcinoma cells. Together, these results indicate that KIND1 is important not only for keratinocyte proliferation but also for the suppression of UV-induced inflammation and DNA damage. These latter findings support a tumor suppressor function for KIND1, and identify c-Jun N-terminal kinase and NF-κB as potential therapeutic targets for prevention of squamous cell carcinoma in patients with Kindler syndrome.

Kindlin-1 Regulates Keratinocyte Electrotaxis

Kindler syndrome (KS) is an autosomal recessive blistering skin disease resulting from pathogenic mutations in FERMT1. This gene encodes kindlin-1, a focal adhesion protein involved in activation of the integrin family of extracellular matrix receptors. Most cases of KS show a marked reduction or complete absence of the kindlin-1 protein in keratinocytes, resulting in defective cell adhesion and migration. Electric fields also act as intrinsic regulators of adhesion and migration in the skin, but the molecular mechanisms by which this occurs are poorly understood. Here we show that keratinocytes derived from KS patients are unable to undergo electrotaxis, and this defect is restored by overexpression of wild-type kindlin-1 but not a W612A mutation that prevents kindlin-integrin binding. Moreover, deletion of the pleckstrin homology domain of kindlin-1 also failed to rescue electrotaxis in KS cells, indicating that both integrin and lipid binding are required for this function. Kindlin-1 was also required for the maintenance of lamellipodial protrusions during electrotaxis via electric field-activated β1 integrin. Indeed, inhibition of β1 integrins also leads to loss of electrotaxis in keratinocytes. Our data suggest that loss of kindlin-1 function may therefore result in epithelial insensitivity to electric fields and contribute to KS disease pathology.