FMNL2/FMNL3 formins are linked with oncogenic pathways and predict melanoma outcome

Characterization of Expression and Function of the Formins FHOD1, INF2, and DAAM1 in HER2-Positive Breast Cancer

PURPOSE

Human epidermal growth factor receptor 2 (HER2)-targeted therapies, such as trastuzumab, benefit patients with HER2-positive metastatic breast cancer; however, owing to traditional pathway activation or alternative signaling, resistance persists. Given the crucial role of the formin family in shaping the actin cytoskeleton during cancer progression, these proteins may function downstream of the HER2 signaling pathway. Our aim was to uncover the potential correlations between formins and HER2 expression using a combination of public databases, immunohistochemistry, and functional in vitro assays.

METHODS

Using online databases, we identified a negative prognostic correlation between specific formins mRNA expression in HER2-positive cancers. To validate these findings at the protein level, immunohistochemistry was performed on HER2 subtype breast cancer tumors to establish the links between staining patterns and clinical characteristics. We then knocked down individual or combined formins in MDA-MB-453 and SK-BR-3 cells and investigated their effects on wound healing, transwell migration, and proliferation. Furthermore, we investigated the effects of erb-b2 receptor tyrosine kinase 2 (ERBB2)/HER2 small interfering RNA (siRNA)-mediated knockdown on the PI3K/Akt and MEK/ERK1 pathways as well as on selected formins.

RESULTS

Our results revealed that correlations between INF2, FHOD1, and DAAM1 mRNA expression and ERBB2 in HER2-subtype breast cancer were associated with worse outcomes. Using immunohistochemistry, we found that high FHOD1 protein expression was linked to higher histological grades and was negatively correlated with estrogen and progesterone receptor positivity. Upon formins knockdown, we observed effects on wound healing and transwell migration, with a minimal impact on proliferation, which was evident through single and combined knockdowns in both cell lines. Notably, siRNA-mediated knockdown of HER2 affected FHOD1 and INF2 expression, along with the phosphorylated Akt/MAPK states.

CONCLUSION

Our study highlights the roles of FHOD1 and INF2 as downstream effectors of the HER2/Akt and HER2/MAPK pathways, suggesting that they are potential therapeutic targets in HER2-positive breast cancer.

Vesicle-Associated Actin Assembly by Formins Promotes TGFβ-Induced ANGPTL4 Trafficking, Secretion and Cell Invasion

Vesicle trafficking has emerged as an important process driving tumor progression through various mechanisms. Transforming growth factor beta (TGFβ)-mediated secretion of Angiopoietin-like 4 (ANGPTL4) is important for cancer development. Here, Formin-like 2 (FMNL2) is identified to be necessary for ANGPTL4 trafficking and secretion in response to TGFβ. Protein kinase C (PKC)-dependent phosphorylation of FMNL2 downstream of TGFβ stimulation is required for cancer cell invasion as well as ANGPTL4 vesicle trafficking and secretion. Moreover, using super resolution microscopy, ANGPTL4 trafficking is actin-dependent with FMNL2 directly polymerizing actin at ANGPTL4-containing vesicles, which are associated with Rab8a and myosin Vb. This work uncovers a formin-controlled mechanism that transiently polymerizes actin directly at intracellular vesicles to facilitate their mobility. This mechanism may be important for the regulation of cancer cell metastasis and tumor progression.

Aggregation tests identify new gene associations with breast cancer in populations with diverse ancestry

BACKGROUND

Low-frequency variants play an important role in breast cancer (BC) susceptibility. Gene-based methods can increase power by combining multiple variants in the same gene and help identify target genes.

METHODS

We evaluated the potential of gene-based aggregation in the Breast Cancer Association Consortium cohorts including 83,471 cases and 59,199 controls. Low-frequency variants were aggregated for individual genes' coding and regulatory regions. Association results in European ancestry samples were compared to single-marker association results in the same cohort. Gene-based associations were also combined in meta-analysis across individuals with European, Asian, African, and Latin American and Hispanic ancestry.

RESULTS

In European ancestry samples, 14 genes were significantly associated (q < 0.05) with BC. Of those, two genes, FMNL3 (P = 6.11 × 10-6) and AC058822.1 (P = 1.47 × 10-4), represent new associations. High FMNL3 expression has previously been linked to poor prognosis in several other cancers. Meta-analysis of samples with diverse ancestry discovered further associations including established candidate genes ESR1 and CBLB. Furthermore, literature review and database query found further support for a biologically plausible link with cancer for genes CBLB, FMNL3, FGFR2, LSP1, MAP3K1, and SRGAP2C.

CONCLUSIONS

Using extended gene-based aggregation tests including coding and regulatory variation, we report identification of plausible target genes for previously identified single-marker associations with BC as well as the discovery of novel genes implicated in BC development. Including multi ancestral cohorts in this study enabled the identification of otherwise missed disease associations as ESR1 (P = 1.31 × 10-5), demonstrating the importance of diversifying study cohorts.

Small Extracellular Vesicles and Their Involvement in Cancer Resistance: An Up-to-Date Review

In recent years, tremendous progress has been made in understanding the roles of extracellular vesicles (EVs) in cancer. Thanks to advancements in molecular biology, it has been found that the fraction of EVs called exosomes or small EVs (sEVs) modulates the sensitivity of cancer cells to chemotherapeutic agents by delivering molecularly active non-coding RNAs (ncRNAs). An in-depth analysis shows that two main molecular mechanisms are involved in exosomal modified chemoresistance: (1) translational repression of anti-oncogenes by exosomal microRNAs (miRs) and (2) lack of translational repression of oncogenes by sponging of miRs through long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs). At the cellular level, these processes increase the proliferation and survival of cancer cells and improve their ability to metastasize and resist apoptosis. In addition, studies in animal models have shown enhancing tumor size under the influence of exosomal ncRNAs. Ultimately, exosomal ncRNAs are responsible for clinically significant chemotherapy failures in patients with different types of cancer. Preliminary data have also revealed that exosomal ncRNAs can overcome chemotherapeutic agent resistance, but the results are thoroughly fragmented. This review presents how exosomes modulate the response of cancer cells to chemotherapeutic agents. Understanding how exosomes interfere with chemoresistance may become a milestone in developing new therapeutic options, but more data are still required.

Cooperative assembly of filopodia by the formin FMNL2 and I-BAR domain protein IRTKS

Filopodia are long finger-like actin-based structures that project out from the plasma membrane as cells navigate and explore their extracellular environment. The initiation of filopodia formation requires release of tension at the plasma membrane followed by the coordinated assembly of long unbranched actin filaments. Filopodia growth is maintained by a tip complex that promotes actin polymerization and protects the growing barbed ends of the actin fibers from capping proteins. Filopodia growth also depends on additional F-actin bundling proteins to stiffen the actin filaments as well as extension of the membrane sheath projecting from the cell periphery. These activities can be provided by a number of actin-binding and membrane-binding proteins including formins such as formin-like 2 (FMNL2) and FMNL3, and Inverse-Bin-Amphiphysin-Rvs (I-BAR) proteins such as IRTKS and IRSp53, but the specific requirement for these proteins in filopodia assembly is not clear. We report here that IRTKS and IRSp53 are FMNL2-binding proteins. Coexpression of FMNL2 with either I-BAR protein promotes cooperative filopodia assembly. We find IRTKS, but not IRSp53, is required for FMNL2-induced filopodia assembly, and FMNL2 and IRTKS are mutually dependent cofactors in this process. Our results suggest that the primary function for FMNL2 during filopodia assembly is binding to the plasma membrane and that regulation of actin dynamics by its formin homology 2 domain is secondary. From these results, we conclude that FMNL2 initiates filopodia assembly via an unexpected novel mechanism, by bending the plasma membrane to recruit IRTKS and thereby nucleate filopodia assembly.

Combined analyses of RNA-sequence and Hi-C along with GWAS loci—A novel approach to dissect keloid disorder genetic mechanism

Keloid disorder is a tumour-like disease with invasive growth and a high recurrence rate. Genetic contribution is well expected due to the presence of autosomal dominant inheritance and various genetic mutations in keloid lesions. However, GWAS failed to reveal functional variants in exon regions but single nucleotide polymorphisms in the non-coding regions, suggesting the necessity of innovative genetic investigation. This study employed combined GWAS, RNA-sequence and Hi-C analyses to dissect keloid disorder genetic mechanisms using paired keloid tissues and normal skins. Differentially expressed genes, miRNAs and lncRNAs mined by RNA-sequence were identified to construct a network. From which, 8 significant pathways involved in keloid disorder pathogenesis were enriched and 6 of them were verified. Furthermore, topologically associated domains at susceptible loci were located via the Hi-C database and ten differentially expressed RNAs were identified. Among them, the functions of six molecules for cell proliferation, cell cycle and apoptosis were particularly examined and confirmed by overexpressing and knocking-down assays. This study firstly revealed unknown key biomarkers and pathways in keloid lesions using RNA-sequence and previously reported mutation loci, indicating a feasible approach to reveal the genetic contribution to keloid disorder and possibly to other diseases that are failed by GWAS analysis alone.

Keloid disorder is a benign skin tumour characterized by uncontrolled fibroproliferative tissue growth, which only occurs in human beings with severe reoccurrence post-therapy. It affects several hundred million people with difficulty to control its growth and relapse. It has been long thought that exonic gene mutations must play an important role, but large-scaled GWAS analyses only revealed 3 single nucleotide polymorphisms in the non-coding regions as previously reported. For the first time, this study demonstrated that the true genetic mechanism is likely to be the dysfunctional epigenetic regulation caused by mutations in regulatory elements at the non-coding region as revealed by the combined analyses of GWAS, RNA-sequence and Hi-C data. This approach may lead to the breakthrough of keloid disorder genetic/epigenetic mechanism, if further large-scaled analyses are performed along with human keloid tissue Hi-C data.

FMNL2 suppresses cell migration and invasion of breast cancer: a reduction of cytoplasmic p27 via RhoA/LIMK/Cofilin pathway

Formin-like protein 2 (FMNL2) belongs to a highly conserved family of cytoskeletal remodeling proteins that have been reported to be implicated in various actin-dependent physiological and cancer-associated processes. In this study, we mainly investigated the effects of FMNL2 on breast cancer cell migration and invasion, and the underlying mechanisms involved. We found that FMNL2 reduced cell migration and invasion of breast cancer in vitro and in vivo. Further, FMNL2 disrupted actin cytoskeleton rearrangement and hampered the RhoA/LIMK/Cofilin pathway in breast cancer cells. Critically, both Rho inhibitor ZOL and LIMK inhibitor BMS3 significantly abrogated these migration-promoting effects in FMNL2-silencing MDA-MB-231 and BT549 cells. RhoA/LIMK/Cofilin pathway was involved in FMNL2 silencing-induced actin cytoskeleton rearrangement in MDA-MB-231 and BT549 cells. More importantly, cytoplasmic p27 promoted FMNL2-mediated cell migration and invasion through RhoA/LIMK/Cofilin pathway in MCF7 and MDA-MB-231 cells. In addition, the expression and prognosis of FMNL2 were associated with ER in breast cancer. Furthermore, ERα overexpression reduced the protein levels of FMNL2 in breast cancer cells, which were reversed by MG132. In conclusion, FMNL2 suppressed cell migration and invasion of breast cancer by inhibiting RhoA/LIMK/Cofilin pathway through a reduction of cytoplasmic p27. This finding implies that the interference of FMNL2-mediated RhoA/LIMK/Cofilin pathway involving the cytoplasmic p27 may be a promising strategy for ameliorating breast cancer metastasis and prognosis.

Formins in Human Disease

Almost 25 years have passed since a mutation of a formin gene, DIAPH1, was identified as being responsible for a human inherited disorder: a form of sensorineural hearing loss. Since then, our knowledge of the links between formins and disease has deepened considerably. Mutations of DIAPH1 and six other formin genes (DAAM2, DIAPH2, DIAPH3, FMN2, INF2 and FHOD3) have been identified as the genetic cause of a variety of inherited human disorders, including intellectual disability, renal disease, peripheral neuropathy, thrombocytopenia, primary ovarian insufficiency, hearing loss and cardiomyopathy. In addition, alterations in formin genes have been associated with a variety of pathological conditions, including developmental defects affecting the heart, nervous system and kidney, aging-related diseases, and cancer. This review summarizes the most recent discoveries about the involvement of formin alterations in monogenic disorders and other human pathological conditions, especially cancer, with which they have been associated. In vitro results and experiments in modified animal models are discussed. Finally, we outline the directions for future research in this field.

A Transcriptome-Wide Isoform Landscape of Melanocytic Nevi and Primary Melanomas Identifies Gene Isoforms Associated with Malignancy

Genetic splice variants have become of central interest in recent years, as they play an important role in different cancers. Little is known about splice variants in melanoma. Here, we analyzed a genome-wide transcriptomic dataset of benign melanocytic nevi and primary melanomas (n = 80) for the expression of specific splice variants. Using kallisto, a map for differentially expressed splice variants in melanoma vs. benign melanocytic nevi was generated. Among the top genes with differentially expressed splice variants were Ras-related in brain 6B (RAB6B), a member of the RAS family of GTPases, Macrophage Scavenger Receptor 1 (MSR1), Collagen Type XI Alpha 2 Chain (COLL11A2), and LY6/PLAUR Domain Containing 1 (LYPD1). The Gene Ontology terms of differentially expressed splice variants showed no enrichment for functional gene sets of melanoma vs. nevus lesions, but between type 1 (pigmentation type) and type 2 (immune response type) melanocytic lesions. A number of genes such as Checkpoint Kinase 1 (CHEK1) showed an association of mutational patterns and occurrence of splice variants in melanoma. Moreover, mutations in genes of the splicing machinery were common in both benign nevi and melanomas, suggesting a common mechanism starting early in melanoma development. Mutations in some of these genes of the splicing machinery, such as Serine and Arginine Rich Splicing Factor A3 and B3 (SF3A3, SF3B3), were significantly enriched in melanomas as compared to benign nevi. Taken together, a map of splice variants in melanoma is presented that shows a multitude of differentially expressed splice genes between benign nevi and primary melanomas. The underlying mechanisms may involve mutations in genes of the splicing machinery.

Formin-like protein 2 promotes cell proliferation by a p27-related mechanism in human breast cancer cells

Background

Breast cancer is the leading cause of cancer-related deaths in females worldwide. Formin-like protein 2 (FMNL2) is a member of formin family that governs cytokinesis, cell polarity, morphogenesis and cell division. To our knowledge, the function of FMNL2 in breast cancer proliferation still remains uncovered.

Methods

Tumor immune estimation resource (TIMER) analysis was used to detect the correlation between FMNL2 and Ki67 in breast cancer tissues. Quantitative real-time transcription polymerase chain reaction (qRT-PCR) and western blotting were performed to analyze the expression in human breast cancer cells. Moreover, RNA interference (RNAi) and plasmids were performed to silence and overexpress FMNL2 and p27. The CCK8, MTT, cell counting, colony formation, and 5-ethynyl-2-deoxyuridine (EdU) incorporation assays were used to detect cell proliferation, respectively. Flow cytometry analysis was used to detect cell cycle distribution. Further, the distribution of p27 was examined using immunofluorescence.

Results

We found that FMNL2 expression was positively associated with Ki67 among collected breast cancer tissues and in TCGA database. Compared to lower proliferative cells MCF7 and T47D, FMNL2 was overexpressed in highly proliferative breast cancer cells MDA-MB-231, BT549 and SUM159, accompanied by reduced levels of p27 and p21, and elevated CyclinD1 and Ki67 expression. FMNL2 silencing significantly inhibited the cell proliferation of MDA-MB-231 and BT549 cells. Meanwhile, FMNL2 overexpression distinctly promoted the cell proliferation of MCF7 cells. Furthermore, FMNL2 suppressed the nuclear levels of p27 and promoted p27 proteasomal degradation in human breast cancer cells. The ubiquitination of p27 was inhibited by FMNL2 silencing in BT549 cells. Besides, p27 silencing markedly elevated Ki67 expression and cell viability, which could be blocked by additionally FMNL2 silencing in MDA-MB-231 and BT549 cells. Furthermore, overexpression of p27WT significantly reversed the increased levels of FMNL2 and Ki67, cell viability and cell cycle progression induced by FMNL2 overexpression in MCF7 cells. More importantly, compared to p27WT group, those effects could be significantly reversed by p27△NLS overexpression.

Conclusions

These results demonstrated that FMNL2 promoted cell proliferation partially by reducing p27 nuclear localization and p27 protein stability in human breast cancer cells, suggesting the pivotal role of FMNL2 in breast cancer progression.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08533-w.

Characterization of a L136P mutation in Formin-like 2 (FMNL2) from a patient with chronic inflammatory bowel disease

Diaphanous related formins are highly conserved proteins regulated by Rho-GTPases that act as actin nucleation and assembly factors. Here we report the functional characterization of a non-inherited heterozygous FMNL2 p.L136P mutation carried by a patient who presented with severe very early onset inflammatory bowel disease (IBD). We found that the FMNL2 L136P protein displayed subcellular mislocalization and deregulated protein autoinhibition indicating gain-of-function mechanism. Expression of FMNL2 L136P impaired cell spreading as well as filopodia formation. THP-1 macrophages expressing FMNL2 L136P revealed dysregulated podosome formation and a defect in matrix degradation. Our data indicate that the L136P mutation affects cellular actin dynamics in fibroblasts and immune cells such as macrophages.

Expression of Formin-like 2 and cortactin in gallbladder adenocarcinoma and their clinical significance

OBJECTIVE

To investigate the expressions of Formin-like 2 (FMNL2) and Cortactin (CTTN) in gallbladder adenocarcinoma (GBAC) and their associations with the clinicopathological characteristics of the patients.

METHODS

The expressions of FMNL2 and CTTN were detected with immunohistochemistry (Max Vision) in 105 GBAC tissues and 40 normal gallbladder tissues.

RESULTS

The positive expression rates of FMNL2 and CTTN in normal gallbladder tissues were 25% and 20%, different from the positive expression rates of 84.76% and 86.67% in GBAC tissues (P < 0.001). The positive expression rate of FMNL2 and CTTN in GBAC correlated with tumor differentiation, tumor-node-metastasis (TNM), lymph node metastasis (LNM), and distant metastasis. FMNL2 expression was positively correlated with CTTN expression. Kaplan-Meier analysis showed that the overall survival time of patients with positive expressions group of FMNL2 and CTTN was significantly shorter than that of the negative expression group. Cox multivariate analysis showed that TNM, LNM, distant metastasis, and positive expression of FMNL2 and CTTN were independent factors influencing the prognosis of patients with GBAC (P < 0.05).

CONCLUSION

The positive expression of FMNL2 and CTTN in GBAC is significantly increased, which may be related to the occurrence and development of GBAC. The combined detection of FMNL2 and CTTN may provide a scientific theoretical basis for the early diagnosis of GBAC, the development of new antitumor drugs, and the search for new targets of biotherapy.

Systematic Characterization of the Expression and Prognostic Values of Formin-Like Gene Family in Gastric Cancer

Formin-like genes (FMNLs) are members of formins family and have been implicated to the development and progression of multiple cancers. This research aims to analyze the expression profiles, prognostic values, and immune infiltrating associations of FMNLs in gastric cancer (GC) using multiple online bioinformatics website, including Oncomine, UALCAN, Kaplan-Meier Plotter, TIMER, GeneMANIA, DAVID, and LinkedOmics databases. The mRNA levels of FMNL1/2/3 were higher in GC tissues than normal. Meanwhile, FMNLs expressions tend to be upregulated in advanced and poorly differentiated GC. Prognostic value analysis suggested that high transcription levels of FMNL1/3 were associated with poor overall survival in GC patients. Correlation analysis between FMNLs expressions and immune infiltrating GC revealed that the expressions of FMNLs were significantly associated with immune infiltrating. Protein-protein interaction network and enrichment analysis of FMNLs in GC showed that FMNLs coexpressed genes mainly participated in organizing actin cytoskeleton through affecting small G proteins activity. Moreover, Gene Set Enrichment Analysis (GSEA) analysis uncovered FMNLs and their coexpressed genes was tightly associated with immune-related cellular functions. These findings demonstrate that FMNLs might play significant immunomodulatory roles in tumor immunity and could be novel therapeutic targets and potential prognostic biomarkers in GC.

FMNL2 regulates dynamics of fascin in filopodia

Filopodia are peripheral F-actin-rich structures that enable cell sensing of the microenvironment. Fascin is an F-actin-bundling protein that plays a key role in stabilizing filopodia to support efficient adhesion and migration. Fascin is also highly up-regulated in human cancers, where it increases invasive cell behavior and correlates with poor patient prognosis. Previous studies have shown that fascin phosphorylation can regulate F-actin bundling, and that this modification can contribute to subcellular fascin localization and function. However, the factors that regulate fascin dynamics within filopodia remain poorly understood. In the current study, we used advanced live-cell imaging techniques and a fascin biosensor to demonstrate that fascin phosphorylation, localization, and binding to F-actin are highly dynamic and dependent on local cytoskeletal architecture in cells in both 2D and 3D environments. Fascin dynamics within filopodia are under the control of formins, and in particular FMNL2, that binds directly to dephosphorylated fascin. Our data provide new insight into control of fascin dynamics at the nanoscale and into the mechanisms governing rapid cytoskeletal adaptation to environmental changes. This filopodia-driven exploration stage may represent an essential regulatory step in the transition from static to migrating cancer cells.

Formin-like 1 (FMNL1) Is Associated with Glioblastoma Multiforme Mesenchymal Subtype and Independently Predicts Poor Prognosis

Glioblastoma multiforme (GBM), the most common primary malignant brain tumor in adults, is characterized by rapid proliferation, aggressive migration, and invasion into normal brain tissue. Formin proteins have been implicated in these processes. However, the role of formin-like 1 (FMNL1) in cancer remains unclear. We studied FMNL1 expression in glioblastoma samples using immunohistochemistry. We sought to analyze the correlation between FMNL1 expression, clinicopathologic variables, and patient survival. Migration and invasion assays were used to verify the effect of FMNL1 on glioblastoma cell lines. Microarray data were downloaded from The Cancer Genome Atlas and analyzed using gene set enrichment analysis (GSEA). FMNL1 was an independent predictor of poor prognosis in a cohort of 217 glioblastoma multiforme cases (p < 0.001). FMNL1 expression was significantly higher in the mesenchymal subtype. FMNL1 upregulation and downregulation were associated with mesenchymal and proneural markers in the GSEA, respectively. These data highlight the important role of FMNL1 in the neural-to-mesenchymal transition. Conversely, FMNL1 downregulation suppressed glioblastoma multiforme cell migration and invasion via DIAPH1 and GOLGA2, respectively. FMNL1 downregulation also suppressed actin fiber assembly, induced morphological changes, and diminished filamentous actin. FMNL1 is a promising therapeutic target and a useful biomarker for GBM progression.

BRAF immunohistochemistry predicts sentinel lymph node involvement in intermediate thickness melanomas

Background

Sentinel node biopsy (SNB) is an important step in melanoma staging and prognostication. It is commonly performed for patients with intermediate thickness melanomas, based on clinicopathological features. However, only 20–25% of patients eventually demonstrate nodal involvement. The aim of this study was to evaluate whether tissue biomarkers with links to melanoma biology, together with clinicopathological parameters, could aid in the prediction of sentinel node involvement and improve selection of patients for SNB. In addition, we examined the role of these clinical or biological markers in disease outcome.

Methods

We collected a case-control cohort of 140 intermediate thickness (Breslow 0,9–4,0mm) melanoma patients with or without SNB involvement matched for age, gender, Breslow thickness and location. From this cohort, we tested the predictive value of common clinicopathological parameters (ulceration, mitotic count and tumor regression) and FMNL-2, ezrin and BRAF V600E immunoreactivity, for sentinel node involvement and survival. We further analyzed the correlations in the superficial spreading melanoma subtype.

Results

Based on our case control analysis, of the markers, BRAF V600E status (p = 0.010) and mitotic count (p = 0.036) correlated with SNB involvement. SNB status was a strong independent prognosticator for recurrence free survival (RFS p<0.001), melanoma specific survival (MSS p = 0.000) and overall survival (OS p = 0.029). In the superficially spreading melanoma subgroup, BRAF V600E positivity indicated poorer RFS (p = 0.039) and OS (p = 0.012). By combining the Breslow thickness, mitotic count and BRAF immunohistochemistry, we identified a group of superficially spreading melanomas with an excellent survival probability independent of SNB status.

Conclusions

These results demonstrate that BRAF immunohistochemistry could serve as a useful addition to a marker panel for selecting intermediate thickness melanoma patients for SNB.

Formin-like 3 regulates RhoC/FAK pathway and actin assembly to promote cell invasion in colorectal carcinoma

AIM

To clarify the underlying mechanism of formin-like 3 (FMNL3) in the promotion of colorectal carcinoma (CRC) cell invasion.

METHODS

The in vitro biological function analyses of FMNL3 were performed by gain- and loss-of function approaches. Changes in the F-actin cytoskeleton were detected by the technologies of phalloidin-TRITC labeling and confocal microscopy. The signaling pathway mediated by FMNL3 was explored by western blot, gelatin zymograph assay, co-immunoprecipitation (co-IP), immunofluorescence co-localization, and glutathione S-transferase (GST) pull-down assay.

RESULTS

The in vitro experimental results showed that FMNL3 significantly promoted the proliferation, invasion, and migration of CRC cells (P < 0.05 and P < 0.01). Moreover, FMNL3 regulated the remodeling of actin-based protrusions such as filopodia and lamellipodia in a RhoC-dependent manner. The western blot and gelatin zymograph assay results indicated that FMNL3 was involved in the RhoC/ focal adhesion kinase (FAK) pathway and acted as an effector of RhoC to activate the downstream signaling of p-FAK as well as p-MAPK and p-AKT. This resulted in the increased expression of matrix metalloproteinase 2 (MMP2), matrix metalloproteinase 9 (MMP9) and vascular endothelial growth factor (VEGF), and the subsequent promotion of CRC cell invasion. The results of TAE226, U0126 or Ly294002 treatment confirmed an essential role of FMNL3 in activation of the RhoC/FAK pathway and the subsequent promotion of CRC invasion. Co-IP, co-localization and GST pull-down assays showed the direct interaction of FMNL3 with RhoC in vivo and in vitro.

CONCLUSION

FMNL3 regulates the RhoC/FAK signaling pathway and RhoC-dependent remodeling of actin-based protrusions to promote CRC invasion.

Filopodia and focal adhesions: An integrated system driving branching morphogenesis in neuronal pathfinding and angiogenesis

Single cell branching during development in vertebrates is typified by neuronal branching to form neurites and vascular branches formed by sprouting angiogenesis. Neurons and endothelial tip cells possess subcellular protrusions that share many common features from the morphological to the molecular level. Both systems utilize filopodia as their cellular protrusion organelles and depend on specific integrin-mediated adhesions to the local extracellular matrix for guidance in their pathfinding. We discuss the similar molecular machineries involved in these two types of cell branch formation and use their analogy to propose a new mechanism for angiogenic filopodia function, namely as adhesion assembly sites. In support of this model we provide primary data of angiogenesis in zebrafish in vivo showing that the actin assembly factor VASP participates in both filopodia formation and adhesion assembly at the base of the filopodia, enabling forward progress of the tip cell. The use of filopodia and their associated adhesions provide a common mechanism for neuronal and endothelial pathfinding during development in response to extracellular matrix cues.

Silencing Formin-like 2 inhibits growth and metastasis of gastric cancer cells through suppressing internalization of integrins

Background

Formin-like 2 (FMNL2) is a member of Formin family which governs cytokinesis, cellular polarity and morphogenesis. Dysregulation of FMNL2 has been discovered in cancers and is closely related to cancers. However, the role of FMNL2 in gastric cancer remains unclear. In this study, we aimed to investigate the role of FMNL2 in gastric cancer cells.

Methods

A FMNL2-specific shRNA was employed to decrease the endogenous expression of FMNL2. Then the degree of proliferation, apoptosis, migration and invasion of gastric cancer cells was assessed by MTT assay, flow cytometry, wound healing assay and transwell assay, respectively. The expression and distribution of FMNL2 and protein kinase C (PKC) α was detected by immunofluorescence. The internalization of integrins was detected by enzyme-linked immunosorbent assay.

Results

Our results showed that silencing FMNL2 suppressed proliferation, migration and invasion, and induced apoptosis of gastric cancer cells. The integrin internalization induced by PKC was declined by FMNL2 silencing.

Conclusions

Our study reveals that silencing FMNL2 suppresses growth and metastasis of gastric cancer cells. Modulation on integrin internalization may be implicated in the role of FMNL2 in growth and migration of gastric cancer cells. Our study indicates that FMNL2 may become a potential therapeutic target for gastric cancer.

A Rac1-FMNL2 signaling module affects cell-cell contact formation independent of Cdc42 and membrane protrusions

De novo formation of epithelial cell-cell contacts relies on actin-based protrusions as well as tightly controlled turnover of junctional actin once cells encounter each other and adhesion complexes assemble. The specific contributions of individual actin regulators on either protrusion formation or junctional actin turnover remain largely unexplored. Based on our previous findings of Formin-like 2 (FMNL2)-mediated control of junctional actin dynamics, we investigated its potential role in membrane protrusions and impact on newly forming epithelial contacts. CRISPR/Cas9-mediated loss of FMNL2 in human MCF10A cells combined with optogenetic control of Rac1 activity confirmed its critical function in the establishment of intercellular contacts. While lamellipodial protrusion rates remained unaffected, FMNL2 knockout cells were characterized by impaired filopodia formation similar to depletion of the Rho GTPase Cdc42. Silencing of Cdc42, however, failed to affect FMNL2-mediated contact formation. Hence, we propose a cell-cell contact-specific and Rac1-mediated function of FMNL2 entirely independent of Cdc42. Consistent with this, direct visualizations of native epithelial junction formation revealed a striking and specifically Rac1- and not Cdc42-dependent recruitment of FMNL2 to newly forming junctions as well as established cell-cell contacts within epithelial sheets.

FMNL2 destabilises COMMD10 to activate NF-κB pathway in invasion and metastasis of colorectal cancer

BACKGROUND

Diaphanous-related formins (DRFs), actin necleator, have been known to participate in the progression of cancer cells. We previously reported that FMNL2 (Formin-like2), a member of DRFs, was a positive regulator in colorectal cancer (CRC) metastasis, yet proteins and pathways required for the function of this pro-invasive DRFs remain to be identified.

METHODS

The relationship between FMNL2 and COMMD10 was examined using Co-IP, GST pull-down, immunofluorescence and in vitro ubiquitination assay. The in vitro and in vivo function of COMMD10 in CRC was evaluated using CCK-8 proliferation assay, plate colony formation, cell cycle, apoptosis and animal models. The inhibition of NF-κB signalling by COMMD10 was detected using dual-luciferase reporter assay and western blotting. Co-IP, GST pull-down and nuclear protein extraction assay were performed to evaluate the effect on p65 by COMMD10. Real-time PCR and western blotting were performed to detect expressions of FMNL2, COMMD10 and p65 in paired tissues.

RESULTS

FMNL2 targets COMMD10 for ubiquitin-mediated proteasome degradation in CRC cells. COMMD10 targets p65 NF-κB (nuclear factor-κB) subunit and reduces its nuclear translocation, thereby leading to the inactivation of NF-κB pathway and suppression of CRC invasion and metastasis. Inhibition of NF-κB signalling by COMMD10 is necessary for FMNL2-mediated CRC cell behaviours. Downregulation of COMMD10 predicts poor prognosis of CRC patients. The expressions of FMNL2, COMMD10 and p65 are highly linked in CRC tissues.

CONCLUSIONS

These data demonstrate that the FMNL2/COMMD10/p65 axis acts as a critical regulator in the maintenance of metastatic phenotypes and is strongly associated with negative clinical outcomes.

Long non-coding RNA TUG1 promotes progression of oral squamous cell carcinoma through upregulating FMNL2 by sponging miR-219

Oral squamous cell carcinoma (OSCC) is a prevalent oral disease with a high morbidity and mortality rate. Several long non-coding RNAs (lncRNAs) were identified as important regulators of carcinogenesis. However, the pathogenic implications of TUG1 in OSCC are still unclear. In the present study, the expression of TUG1 was increased in OSCC cells. Knockdown of TUG1 inhibited cell proliferation, migration, and invasion, and induced cell cycle arrest at G0/G1 phase, whereas overexpression of TUG1 exerted the opposite effect on OSCC cells. A reciprocal repressive interaction between TUG1 and miR-219 was found, and miR-219 inhibition abolished the tumor-suppressive effect of TUG1 knockdown on cell growth and motility. Furthermore, bioinformatics analysis and luciferase reporter assay showed that FMNL2 was a direct target of miR-219. Restoration of FMNL2 abrogated the miR-219-induced inhibition of cell proliferation, cell cycle progression, migration, and invasion. Besides, overexpression of TUG1 promoted tumor growth and metastasis in vivo. Clinically, the expression of TUG1 and FMNL2 were increased, but miR-219 was decreased in primary tumors compared to non-tumor tissues. Both the upregulated TUG1, and FMNL2 and the downregulated miR-219 was associated with advanced stage of OSCC and poor overall survival. Notably, multivariate analyses confirmed that FMNL2 was an independent risk factor for OSCC. In conclusion, our data revealed that TUG1 confers oncogenic function in OSCC and TUG1/miR-219/FMNL2 axis may be a novel therapeutic strategy in this disease.

FHOD1 formin is upregulated in melanomas and modifies proliferation and tumor growth

The functional properties of actin-regulating formin proteins are diverse and in many cases cell-type specific. FHOD1, a formin expressed predominantly in cells of mesenchymal lineage, bundles actin filaments and participates in maintenance of cell shape, migration and cellular protrusions. FHOD1 participates in cancer-associated epithelial to mesenchymal transition (EMT) in oral squamous cell carcinoma and breast cancer. The role of FHOD1 in melanomas has not been characterized. Here, we show that FHOD1 expression is typically strong in cutaneous melanomas and cultured melanoma cells while the expression is low or absent in benign nevi. By using shRNA to knockdown FHOD1 in melanoma cells, we discovered that FHOD1 depleted cells are larger, rounder and have smaller focal adhesions and inferior migratory capacity as compared to control cells. Importantly, we found FHOD1 depleted cells to have reduced colony-forming capacity and attenuated tumor growth in vivo, a finding best explained by the reduced proliferation rate caused by cell cycle arrest. Unexpectedly, FHOD1 depletion did not prevent invasive growth at the tumor margins. These results suggest that FHOD1 participates in key cellular processes that are dysregulated in malignancy, but may not be essential for melanoma cell invasion.