Cytoskeletal protein Flightless I inhibits apoptosis, enhances tumor cell invasion and promotes cutaneous squamous cell carcinoma progression

Deferiprone and Gallium-Protoporphyrin Chitogel as an antimicrobial treatment: Preclinical studies demonstrating antimicrobial activity for S. aureus infected cutaneous wounds

Staphylococcus aureus (S. aureus) is one of the most common wound pathogens with increased resistance towards currently available antimicrobials. S. aureus biofilms lead to increase wound chronicity and delayed healing. Chitosan-dextran hydrogel (Chitogel) loaded with the hydroxypyridinone-derived iron chelator Deferiprone (Def) and the heme analogue Gallium-Protoporphyrin (GaPP) have previously been shown to have antimicrobial effects in clinical sinusitis. In this study, the efficacy of Chitogel loaded with Def, GaPP and a combination of Def and GaPP, were investigated in an S. aureus biofilm infected wound murine model over 10 days of treatment. Bacterial wound burden was monitored daily showing a significant decrease in bacterial bioburden on days 6 and 8 when treated with Def-GaPP Chitogel (log10 1.0 and 1.2 reduction vs control, respectively). The current study demonstrates that the combination of Def-GaPP delivered in a Chitogel in vivo is not only effective in reducing S. aureus biofilm infection, but also improves cutaneous healing via effects on reduced inflammation, promotion of anti-inflammatory macrophage phenotype and marked early collagen deposition in the wound bed. This delivery platform presents a promising alternative non-toxic, antibacterial, wound-promoting treatment as a novel approach for the management of S. aureus wound infections that warrants further clinical investigation.

Investigating Cutaneous Squamous Cell Carcinoma in vitro and in vivo: Novel 3D Tools and Animal Models

Cutaneous Squamous Cell Carcinoma (cSCC) represents the second most common type of skin cancer, which incidence is continuously increasing worldwide. Given its high frequency, cSCC represents a major public health problem. Therefore, to provide the best patients’ care, it is necessary having a detailed understanding of the molecular processes underlying cSCC development, progression, and invasion. Extensive efforts have been made in developing new models allowing to study the molecular pathogenesis of solid tumors, including cSCC tumors. Traditionally, in vitro studies were performed with cells grown in a two-dimensional context, which, however, does not represent the complexity of tumor in vivo. In the recent years, new in vitro models have been developed aiming to mimic the three-dimensionality (3D) of the tumor, allowing the evaluation of tumor cell-cell and tumor-microenvironment interaction in an in vivo-like setting. These models include spheroids, organotypic cultures, skin reconstructs and organoids. Although 3D models demonstrate high potential to enhance the overall knowledge in cancer research, they lack systemic components which may be solved only by using animal models. Zebrafish is emerging as an alternative xenotransplant model in cancer research, offering a high-throughput approach for drug screening and real-time in vivo imaging to study cell invasion. Moreover, several categories of mouse models were developed for pre-clinical purpose, including xeno- and syngeneic transplantation models, autochthonous models of chemically or UV-induced skin squamous carcinogenesis, and genetically engineered mouse models (GEMMs) of cSCC. These models have been instrumental in examining the molecular mechanisms of cSCC and drug response in an in vivo setting. The present review proposes an overview of in vitro, particularly 3D, and in vivo models and their application in cutaneous SCC research.

Increased Expression of Flightless I in Cutaneous Squamous Cell Carcinoma Affects Wnt/β-Catenin Signaling Pathway

Cutaneous squamous cell carcinoma (cSCC) accounts for 25% of cutaneous malignancies diagnosed in Caucasian populations. Surgical removal in combination with radiation and chemotherapy are effective treatments for cSCC. Nevertheless, the aggressive metastatic forms of cSCC still have a relatively poor patient outcome. Studies have linked actin cytoskeletal dynamics and the Wnt/β-catenin signaling pathway as important modulators of cSCC pathogenesis. Previous studies have also shown that the actin-remodeling protein Flightless (Flii) is a negative regulator of cSCC. The aim of this study was to investigate if the functional effects of Flii on cSCC involve the Wnt/β-catenin signaling pathway. Flii knockdown was performed using siRNA in a human late stage aggressive metastatic cSCC cell line (MET-1) alongside analysis of Flii genetic murine models of 3-methylcholanthrene induced cSCC. Flii was increased in a MET-1 cSCC cell line and reducing Flii expression led to fewer PCNA positive cells and a concomitant reduction in cellular proliferation and symmetrical division. Knockdown of Flii led to decreased β-catenin and a decrease in the expression of the downstream effector of β-catenin signaling protein SOX9. 3-Methylcholanthrene (MCA)-induced cSCC in Flii overexpressing mice showed increased markers of cancer metastasis including talin and keratin-14 and a significant increase in SOX9 alongside a reduction in Flii associated protein (Flap-1). Taken together, this study demonstrates a role for Flii in regulating proteins involved in cSCC proliferation and tumor progression and suggests a potential role for Flii in aggressive metastatic cSCC.

Overexpression of Flii during Murine Embryonic Development Increases Symmetrical Division of Epidermal Progenitor Cells

Epidermal progenitor cells divide symmetrically and asymmetrically to form stratified epidermis and hair follicles during late embryonic development. Flightless I (Flii), an actin remodelling protein, is implicated in Wnt/β-cat and integrin signalling pathways that govern cell division. This study investigated the effect of altering Flii on the divisional orientation of epidermal progenitor cells (EpSCs) in the basal layer during late murine embryonic development and early adolescence. The effect of altering Flii expression on asymmetric vs. symmetric division was assessed in vitro in adult human primary keratinocytes and in vivo at late embryonic development stages (E16, E17 and E19) as well as adolescence (P21 day-old) in mice with altered Flii expression (Flii knockdown: Flii^+/−, wild type: WT, transgenic Flii overexpressing: Flii^Tg/Tg) using Western blot and immunohistochemistry. Flii^+/− embryonic skin showed increased asymmetrical cell division of EpSCs with an increase in epidermal stratification and elevated talin, activated-Itgb1 and Par3 expression. Flii^Tg/Tg led to increased symmetrical cell division of EpSCs with increased cell proliferation rate, an elevated epidermal SOX9, Flap1 and β-cat expression, a thinner epidermis, but increased hair follicle number and depth. Flii promotes symmetric division of epidermal progenitor cells during murine embryonic development.

Multifunctional ultrasmall AgNP hydrogel accelerates healing of S. aureus infected wounds

The increasing emergence of antibiotic resistance coupled with the limited effectiveness of current treatments highlights the need for the development of new treatment modalities. Silver nanoparticles (AgNPs) are a promising alternative with broad-spectrum antibacterial activity. However, the clinical translation of AgNPs have been hampered primarily due to the delivery of unsafe levels of silver ions (Ag⁺) resulting in cellular toxicity and their susceptibility to aggregation resulting in loss of efficacy. Here, we describe a safe and effective, thermo-responsive AgNP hydrogel that provides antibacterial effects in conjunction with wound promoting properties. Using a murine model of wound infection, we demonstrate that the applied AgNP hydrogel to the wound (12 µg silver) not only provides superior bactericidal activity but also reduces inflammation leading to accelerated wound closure when compared to industry-standard silver sulfadiazine (302 µg silver). The AgNP hydrogel-treatment significantly accelerated wound closure at day 4 post-infection (56 closure) compared to both blank hydrogel or Ag SD (74% and 91% closure respectively) with a concurrent increase in PCNA-positive proliferating cells corresponding with a significant 32% improvement in wound re-epithelization compared to the blank hydrogel. Treatment of infected wounds with AgNP hydrogel also decreased neutrophil infiltration, increased anti-inflammatory Ym-1 positive M2 macrophages, and reduced the number of caspase-1 positive apoptotic cells. Therefore, this novel multifunctional AgNP thermo-responsive hydrogel is potentially a safe and effective treatment at much lower concentration for the treatment of wound infections. STATEMENT OF SIGNIFICANCE: In this study, we describe the development of a multifunctional thermo-responsive hydrogel of ultrasmall silver nanoparticles (AgNPs) for controlled and optimized delivery of silver to infected wounds. The in vivo biological effects of the developed hydrogel showed significant S. aureus elimination from infected mouse wounds compared to a commercial antibacterial formulation. The developed AgNP hydrogel optimally regulates inflammatory responses to promote wound healing as indicated by increased cell proliferation and wound re-epithelization. Additionally, AgNP hydrogel shows significant potential in regulating neutrophil infiltration while increasing levels of anti-inflammatory M2 macrophages and reduces the number of apoptotic cells. Therefore, the multifunctional properties of the developed AgNP thermo-responsive hydrogel offers great clinical potential to control bacterial infections and promote wound healing.

Flightless I is a catabolic factor of chondrocytes that promotes hypertrophy and cartilage degeneration in osteoarthritis

Synovial macrophages that are activated by cartilage fragments initiate synovitis, a condition that promotes hypertrophic changes in chondrocytes leading to cartilage degeneration in OA. In this study, we analyzed the molecular response of chondrocytes under condition of this type of stimulation to identify a molecular therapeutic target. Stimulated macrophages promoted hypertrophic changes in chondrocytes resulting in production of matrix-degrading enzymes of cartilage. Among the top-upregulated genes, FliI was found to be released from activated chondrocytes and exerted autocrine/paracrine effects on chondrocytes leading to an increase in expression of catabolic and hypertrophic factors. Silencing FliI in stimulated cells significantly reduced expression of catabolic and hypertrophic factors in cocultured chondrocytes. Our further results demonstrated that the FliI-TLR4-ERK1/2 axis is involved in the hypertrophic signaling of chondrocytes and catabolism of cartilage. Our findings provide a new insight into the pathogenesis of OA and identify a potentially new molecular target for diagnostics and therapeutics.

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Activated macrophages promote the secretion of FliI from chondrocytes

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FliI acts as a DAMP-triggering molecule in cartilage

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FliI promotes chondrocyte hypertrophy and cartilage catabolism

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FliI represents attractive target for therapeutic intervention

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.

Increasing the level of cytoskeletal protein Flightless I reduces adhesion formation in a murine digital flexor tendon model

Background

Surgical repair of tendons is common, but function is often limited due to the formation of flexor tendon adhesions which reduce the mobility and use of the affected digit and hand. The severity of adhesion formation is dependent on numerous cellular processes many of which involve the actin cytoskeleton. Flightless I (Flii) is a highly conserved cytoskeletal protein, which has previously been identified as a potential target for improved healing of tendon injuries. Using human in vitro cell studies in conjunction with a murine model of partial laceration of the digital flexor tendon, we investigated the effect of modulating Flii levels on tenocyte function and formation of adhesions.

Methods

Human tenocyte proliferation and migration was determined using WST-1 and scratch wound assays following Flii knockdown by siRNA in vitro. Additionally, mice with normal and increased levels of Flii were subjected to a partial laceration of the digital flexor tendon in conjunction with a full tenotomy to immobilise the paw. Resulting adhesions were assessed using histology and immunohistochemistry for collagen I, III, TGF-β1and -β3

Results

Flii knockdown significantly reduced human tenocyte proliferation and migration in vitro. Increasing the expression of Flii significantly reduced digital tendon adhesion formation in vivo which was confirmed through significantly smaller adhesion scores based on collagen fibre orientation, thickness, proximity to other fibres and crimping. Reduced adhesion formation was accompanied with significantly decreased deposition of type I collagen and increased expression of TGF-β1 in vivo.

Conclusions

These findings suggest that increasing the level of Flii in an injured tendon may be beneficial for decreasing tendon adhesion formation.

Attenuation of Flightless I Increases Human Pericyte Proliferation, Migration and Angiogenic Functions and Improves Healing in Murine Diabetic Wounds

Pericytes are peri-vascular mural cells which have an important role in the homeostatic regulation of inflammatory and angiogenic processes. Flightless I (Flii) is a cytoskeletal protein involved in regulating cellular functions, but its involvement in pericyte activities during wound healing is unknown. Exacerbated inflammation and reduced angiogenesis are hallmarks of impaired diabetic healing responses, and strategies aimed at regulating these processes are vital for improving healing outcomes. To determine the effect of altering Flii expression on pericyte function, in vitro and in vivo studies were performed to assess the effect on healing, inflammation and angiogenesis in diabetic wounds. Here, we demonstrated that human diabetic wounds display upregulated expression of the Flii protein in conjunction with a depletion in the number of platelet derived growth factor receptor β (PDGFRβ) +/ neural glial antigen 2 (NG2) + pericytes present in the dermis. Human pericytes were found to be positive for Flii and attenuating its expression in vitro through siRNA knockdown led to enhanced proliferation, migration and angiogenic functions. Genetic knockdown of Flii in a streptozotocin-induced murine model of diabetes led to increased numbers of pericytes within the wound. This was associated with dampened inflammation, an increased rate of angiogenic repair and improved wound healing. Our findings show that Flii expression directly impacts pericyte functions, including proliferation, motility and angiogenic responses. This suggests that Flii regulation of pericyte function may be in part responsible for the changes in pericyte-related processes observed in diabetic wounds.

Flightless-1 inhibits ER stress-induced apoptosis in colorectal cancer cells by regulating Ca2+ homeostasis

The endoplasmic reticulum (ER) stress response is an adaptive mechanism that is activated upon disruption of ER homeostasis and protects the cells against certain harmful environmental stimuli. However, critical and prolonged cell stress triggers cell death. In this study, we demonstrate that Flightless-1 (FliI) regulates ER stress-induced apoptosis in colon cancer cells by modulating Ca²⁺ homeostasis. FliI was highly expressed in both colon cell lines and colorectal cancer mouse models. In a mouse xenograft model using CT26 mouse colorectal cancer cells, tumor formation was slowed due to elevated levels of apoptosis in FliI-knockdown (FliI-KD) cells. FliI-KD cells treated with ER stress inducers, thapsigargin (TG), and tunicamycin exhibited activation of the unfolded protein response (UPR) and induction of UPR-related gene expression, which eventually triggered apoptosis. FliI-KD increased the intracellular Ca²⁺ concentration, and this upregulation was caused by accelerated ER-to-cytosolic efflux of Ca²⁺. The increase in intracellular Ca²⁺ concentration was significantly blocked by dantrolene and tetracaine, inhibitors of ryanodine receptors (RyRs). Dantrolene inhibited TG-induced ER stress and decreased the rate of apoptosis in FliI-KD CT26 cells. Finally, we found that knockdown of FliI decreased the levels of sorcin and ER Ca²⁺ and that TG-induced ER stress was recovered by overexpression of sorcin in FliI-KD cells. Taken together, these results suggest that FliI regulates sorcin expression, which modulates Ca²⁺ homeostasis in the ER through RyRs. Our findings reveal a novel mechanism by which FliI influences Ca²⁺ homeostasis and cell survival during ER stress.

A cytoskeletal protein that helps tumors avoid cell death offers a promising new drug target for fighting cancer. A team led by Jang Hyun Choi and Sun Sil Choi of the Ulsan National Institute of Science and Technology, South Korea, detailed how a protein called Flightless I (FliI) that normally regulates the remodeling of structural filaments in the cell can, in colorectal cancer cells, serve as a tumor promoter through its action on calcium levels. Typically, cells respond to chronic stress by altering calcium signaling to promote their own death. In tumors, however, FliI maintains normal calcium levels to enhance cell survival even in the face of chemotherapy and other stressful stimuli. Suppressing FliI activity could thus help sensitize cancer cells to other stress- and death-inducing drug regimens.

Proteomics Analysis for Identification of Potential Cell Signaling Pathways and Protein Targets of Actions of Atractylodin and β-Eudesmol Against Cholangiocarcinoma

OBJECTIVE

The study aimed to identify potential cell signaling pathways and protein targets of actions of atractylodin and β-eudesmol in cholangiocarcinoma, the two active compounds isolated from Atracylodes lancea using proteomics approach.

METHOD

The cholangiocarcinoma cell line, CL-6, was treated with each compound for 3 and 6 hours, and the proteins from both intra- and extracellular components were extracted. LC-MS/MS was applied following the separation of the extract proteins by SDS-PAGE and digestion with trypsin. Signaling pathways and protein expression were analyzed by MASCOT and STITCH software.

RESULTS

A total of 4,323 and 4,318 proteins were identified from intra- and extracellular components, respectively. Six and 4 intracellular proteins were linked with the signaling pathways (apoptosis, cell cycle control, and PI3K-AKT) of atractylodin and β-eudesmol, respectively. Four and 3 extracellular proteins were linked with the signaling pathways (NF-κB and PI3K-AKT) of atractylodin and β-eudesmol, respectively.

CONCLUSION

In conclusion, a total of 17 proteins associated with four cell signaling pathways that could be potential molecular targets of anticholangiocarcinoma action of atractylodin and β-eudesmol were identified through the application of proteomics approach.

Flightless I exacerbation of inflammatory responses contributes to increased colonic damage in a mouse model of dextran sulphate sodium-induced ulcerative colitis

Ulcerative colitis (UC) is a chronic inflammatory bowel disease characterized by cytokine driven inflammation that disrupts the mucosa and impedes intestinal structure and functions. Flightless I (Flii) is an immuno-modulatory protein is a member of the gelsolin family of actin-remodelling proteins that regulates cellular and inflammatory processes critical in tissue repair. Here we investigated its involvement in UC and show that Flii is significantly elevated in colonic tissues of patients with inflammatory bowel disease. Using an acute murine model of colitis, we characterised the contribution of Flii to UC using mice with low (Flii+/-), normal (Flii+/+) and high Flii (FliiTg/Tg). High levels of Flii resulted in significantly elevated disease severity index scores, increased rectal bleeding and degree of colon shortening whereas, low Flii expression decreased disease severity, reduced tissue inflammation and improved clinical indicators of UC. Mice with high levels of Flii had significantly increased histological disease severity and elevated mucosal damage with significantly increased inflammatory cell infiltrate and significantly higher levels of TNF-α, IFN-γ, IL-5 and IL-13 pro-inflammatory cytokines. Additionally, Flii overexpression resulted in decreased β-catenin levels, inhibited Wnt/β-catenin signalling and impaired regeneration of colonic crypts. These studies suggest that high levels of Flii, as is observed in patients with UC, may adversely affect mucosal healing via mechanisms involving Th1 and Th2 mediated tissue inflammation and Wnt/β-catenin signalling pathway.

The Society for Immunotherapy of Cancer consensus statement on immunotherapy for the treatment of squamous cell carcinoma of the head and neck (HNSCC)

Head and neck cancers, including those of the lip and oral cavity, nasal cavity, paranasal sinuses, oropharynx, larynx and nasopharynx represent nearly 700,000 new cases and 380,000 deaths worldwide per annum, and account for over 10,000 annual deaths in the United States alone. Improvement in outcomes are needed for patients with recurrent and or metastatic squamous cell carcinoma of the head and neck (HNSCC). In 2016, the US Food and Drug Administration (FDA) granted the first immunotherapeutic approvals - the anti-PD-1 immune checkpoint inhibitors nivolumab and pembrolizumab - for the treatment of patients with recurrent squamous cell carcinoma of the head and neck (HNSCC) that is refractory to platinum-based regimens. The European Commission followed in 2017 with approval of nivolumab for treatment of the same patient population, and shortly thereafter with approval of pembrolizumab monotherapy for the treatment of recurrent or metastatic HNSCC in adults whose tumors express PD-L1 with a ≥ 50% tumor proportion score and have progressed on or after platinum-containing chemotherapy. Then in 2019, the FDA granted approval for PD-1 inhibition as first-line treatment for patients with metastatic or unresectable, recurrent HNSCC, approving pembrolizumab in combination with platinum and fluorouracil for all patients with HNSCC and pembrolizumab as a single agent for patients with HNSCC whose tumors express a PD-L1 combined positive score ≥ 1. These approvals marked the first new therapies for these patients since 2006, as well as the first immunotherapeutic approvals in this disease. In light of the introduction of these novel therapies for the treatment of patients with head and neck cancer, The Society for Immunotherapy of Cancer (SITC) formed an expert committee tasked with generating consensus recommendations for emerging immunotherapies, including appropriate patient selection, therapy sequence, response monitoring, adverse event management, and biomarker testing. These consensus guidelines serve as a foundation to assist clinicians' understanding of the role of immunotherapies in this disease setting, and to standardize utilization across the field for patient benefit. Due to country-specific variances in approvals, availability and regulations regarding the discussed agents, this panel focused solely on FDA-approved drugs for the treatment of patients in the U.S.

A Unique Panel of Patient-Derived Cutaneous Squamous Cell Carcinoma Cell Lines Provides a Preclinical Pathway for Therapeutic Testing

BACKGROUND

Cutaneous squamous cell carcinoma (cSCC) incidence continues to rise with increasing morbidity and mortality, with limited treatment options for advanced disease. Future improvements in targeted therapy will rely on advances in genomic/transcriptomic understanding and the use of model systems for basic research. We describe here the panel of 16 primary and metastatic cSCC cell lines developed and characterised over the past three decades in our laboratory in order to provide such a resource for future preclinical research and drug screening.

METHODS

Primary keratinocytes were isolated from cSCC tumours and metastases, and cell lines were established. These were characterised using short tandem repeat (STR) profiling and genotyped by whole exome sequencing. Multiple in vitro assays were performed to document their morphology, growth characteristics, migration and invasion characteristics, and in vivo xenograft growth.

RESULTS

STR profiles of the cSCC lines allow the confirmation of their unique identity. Phylogenetic trees derived from exome sequence analysis of the matched primary and metastatic lines provide insight into the genetic basis of disease progression. The results of in vivo and in vitro analyses allow researchers to select suitable cell lines for specific experimentation.

CONCLUSIONS

There are few well-characterised cSCC lines available for widespread preclinical experimentation and drug screening. The described cSCC cell line panel provides a critical tool for in vitro and in vivo experimentation.

Flightless I Alters the Inflammatory Response and Autoantibody Profile in an OVA-Induced Atopic Dermatitis Skin-Like Disease

Atopic dermatitis (AD) is a chronic pruritic inflammatory skin disease characterized by excessive inflammation and disrupted skin barrier function. Although the etiology of AD is not completely understood, clinical and basic studies suggest increasing involvement of autoantibodies against intracellular proteins. An actin remodeling protein, Flightless I (Flii), has been shown to promote development of inflammatory mediated skin conditions and impairment of skin barrier development and function. Here, we sought to determine the effect of altering Flii expression on the development of AD and its contribution to autoimmune aspects of inflammatory skin conditions. Ovalbumin (OVA)-induced AD skin-like disease was induced in Flii heterozygous (Flii^+/−), wild-type (Flii^+/+), and Flii transgenic (Flii^Tg/Tg) mice by epicutaneous exposure to OVA for 3 weeks; each week was separated by 2-week resting period. Reduced Flii expression resulted in decreased disease severity and tissue inflammation as determined by histology, lymphocytic, and mast cell infiltrate and increased anti-inflammatory IL-10 cytokine levels and a marked IFN-γ Th₁ response. In contrast, Flii over-expression lead to a Th₂ skewed response characterized by increased pro-inflammatory TNF-α cytokine production, Th₂ chemokine levels, and Th₂ cell numbers. Sera from OVA-induced AD skin-like disease Flii^+/− mice showed a decreased level of autoreactivity while sera from Flii^Tg/Tg mice counterparts showed an altered autoantibody profile with strong nuclear localization favoring development of a more severe disease. These findings demonstrate autoimmune responses in this model of OVA-induced AD-like skin disease and suggest that Flii is a novel target, whose manipulation could be a potential approach for the treatment of patients with AD.

Flightless-I Blocks p62-Mediated Recognition of LC3 to Impede Selective Autophagy and Promote Breast Cancer Progression

p62 is a receptor that facilitates selective autophagy by interacting simultaneously with cargoes and LC3 protein on the autophagosome to maintain cellular homeostasis. However, the regulatory mechanism(s) behind this process and its association with breast cancer remain to be elucidated. Here, we report that Flightless-I (FliI), a novel p62-interacting protein, promotes breast cancer progression by impeding selective autophagy. FliI was highly expressed in clinical breast cancer samples, and heterozygous deletion of FliI retarded the development of mammary tumors in PyVT mice. FliI induced p62-recruited cargoes into Triton X-100 insoluble fractions (TI) to form aggregates, thereby blocking p62 recognition of LC3 and hindering p62-dependent selective autophagy. This function of Flil was reinforced by Akt-mediated phosphorylation at Ser436 and inhibited by phosphorylation of Ulk1 at Ser64. Obstruction of autophagic clearance of p62-recruited cargoes by FliI was associated with the accumulation of oxidative damage on proteins and DNA, which could contribute to the development of cancer. Heterozygous knockout of FliI facilitated selectively autophagic clearance of aggregates, abatement of ROS levels, and protein oxidative damage, ultimately retarding mammary cancer progression. In clinical breast cancer samples, Akt-mediated phosphorylation of FliI at Ser436 negatively correlated with long-term prognosis, while Ulk1-induced FliI phosphorylation at Ser64 positively correlated with clinical outcome. Together, this work demonstrates that FliI functions as a checkpoint protein for selective autophagy in the crosstalk between FliI and p62-recruited cargoes, and its phosphorylation may serve as a prognostic marker for breast cancer.Significance: Flightless-I functions as a checkpoint protein for selective autophagy by interacting with p62 to block its recognition of LC3, leading to tumorigenesis in breast cancer.Cancer Res; 78(17); 4853-64. ©2018 AACR.

Novel Therapeutic Targets in Cutaneous Squamous Cell Carcinoma

Cutaneous squamous cell carcinoma (SCC) is one of the common cancers in Caucasians, accounting for 20–30% of cutaneous malignancies. The risk of metastasis is low in most patients; however, aggressive SCC is associated with very high mortality and morbidity. Although cutaneous SCC can be treated with surgical removal, radiation and chemotherapy singly or in combination, the prognosis of patients with metastatic SCC is poor. Recently, the usage of immune checkpoint blockades has come under consideration. To develop effective therapies that are less toxic than existing ones, it is crucial to achieve a detailed characterization of the molecular mechanisms that are involved in cutaneous SCC pathogenesis and to identify new drug targets. Recent studies have identified novel molecules that are associated with SCC carcinogenesis and progression. This review focuses on recent advances in molecular studies involving SCC tumor development, as well as in new therapeutics that have become available to clinicians.

The flightless I protein interacts with RNA-binding proteins and is involved in the genome-wide mRNA post-transcriptional regulation in lung carcinoma cells

The flightless I protein (FLII) belongs to the gelsolin family. Its function has been associated with actin remodeling, embryonic development, wound repair, and more recently with cancer. The structure of FLII is characterized by the N-terminal leucine-rich repeats (LRR) and C-terminal gesolin related repeated units that are both protein-protein inter-action domains, suggesting that FLII may exert its function by interaction with other proteins. Therefore, systematic study of protein interactions of FLII in cells is important for the understanding of FLII functions. In this study, we found that FLII was downregulated in lung carcinoma cell lines H1299 and A549 as compared with normal HBE (human bronchial epithelial) cell line. The investigation of FLII interactome in H1299 cells revealed that 74 of the total 132 putative FLII interactors are involved in RNA post-transcriptional modification and trafficking. Furthermore, by using high-throughput transcriptome and translatome sequencing combined with cell fractionation, we showed that the overexpression or knockdown of FLII impacts on the overall nuclear export, and translation of mRNAs. IPA analysis revealed that the majority of these target mRNAs encode the proteins whose functions are reminiscent of those previously reported for FLII, suggesting that the post-transcriptional regulation of mRNA might be a major mechanism of action for FLII.

Development of Topical Delivery Systems for Flightless Neutralizing Antibody

Flightless I (Flii) is an actin remodeling protein important for cytoskeletal regulation and cellular processes including migration, proliferation, and adhesion. Previous studies have clearly identified Flii as a novel therapeutical target for improved wound repair and have demonstrated Flii regulation using Flii neutralizing antibodies (FnAb) in different models of wound healing in vivo. Here we describe the development of an optimized topical delivery system that can neutralize Flii activity in the epidermis. Topical delivery of FnAb is an attractive approach as it provides a convenient application, sustained release, localized effect, and reduced dosage. Three successful formulations were developed, and their physical and chemical stability examined. The in vitro release revealed prolonged and sustained release of FnAb in all the tested formulations. Additionally, penetration studies using intact porcine skin showed that FnAb penetrated the epidermis and upper papillary dermis. The penetrated FnAb significantly reduced Flii expression compared to dosed matched IgG controls. This study has successfully developed a topical delivery system for FnAb that could serve as a potential platform for future localized wound treatments.