A common cofilin activity cycle in invasive tumor cells and inflammatory cells

Inhibition of iron-induced cofilin activation and inflammation in microglia by a novel cofilin inhibitor

Neuroinflammatory conditions linked to iron dysregulation pose significant challenges in neurodegenerative diseases. Iron-loaded microglia are observed in the brains of patients with various neuroinflammatory conditions, yet how iron overload affects microglial function and contributes to various neuroinflammatory processes is poorly understood. This in vitro study elucidates the relationship between excess iron, cofilin activation, and microglial function, shedding light on potential therapeutic avenues. Iron overload was induced in Human Microglial Clone 3 cells using ferrous sulfate, and the expressions of ferritin heavy chain, ferritin light chain, divalent metal transporter 1, cofilin, p-cofilin, nuclear factor-κB (NF-κB), and various inflammatory cytokines were analyzed using real-time quantitative polymerase chain reaction, immunocytochemistry, Western blotting, and enzyme-linked immunosorbent assay. Results revealed a notable increase in cofilin, NF-κB, and inflammatory cytokine expression levels following excess iron exposure. Moreover, treatment with deferoxamine (DFX), a known iron chelator, and a novel cofilin inhibitor (CI) synthesized in our laboratory demonstrate a mitigating effect on iron-induced cofilin expression. Furthermore, both DFX and CI exhibit promising outcomes in mitigating the inflammatory consequences of excess iron, including the expression of pro-inflammatory cytokines and NF-κB activation. These findings suggest that both DFX and CI can potentially alleviate microglia-induced neuroinflammation by targeting both iron dysregulation and cofilin-mediated pathways. Overall, this study provides valuable insights into iron-induced cofilin activation and microglial activation, offering avenues for potential targeted therapies for neuroinflammatory conditions associated with iron and cofilin dysregulation in neurodegenerative diseases.

The role of actin cytoskeleton CFL1 and ADF/cofilin superfamily in inflammatory response

Actin remodeling proteins are important in immune diseases and regulate cell cytoskeletal responses. These responses play a pivotal role in maintaining the delicate balance of biological events, protecting against acute or chronic inflammation in a range of diseases. Cofilin (CFL) and actin depolymerization factor (ADF) are potent actin-binding proteins that cut and depolymerize actin filaments to generate actin cytoskeleton dynamics. Although the molecular mechanism by which actin induces actin cytoskeletal reconstitution has been studied for decades, the regulation of actin in the inflammatory process has only recently become apparent. In this paper, the functions of the actin cytoskeleton and ADF/cofilin superfamily members are briefly introduced, and then focus on the role of CFL1 in inflammatory response.

Biomolecules Involved in Both Metastasis and Placenta Accreta Spectrum-Does the Common Pathophysiological Pathway Exist?

The process of epithelial-to-mesenchymal transition (EMT) is crucial in the implantation of the blastocyst and subsequent placental development. The trophoblast, consisting of villous and extravillous zones, plays different roles in these processes. Pathological states, such as placenta accreta spectrum (PAS), can arise due to dysfunction of the trophoblast or defective decidualization, leading to maternal and fetal morbidity and mortality. Studies have drawn parallels between placentation and carcinogenesis, with both processes involving EMT and the establishment of a microenvironment that facilitates invasion and infiltration. This article presents a review of molecular biomarkers involved in both the microenvironment of tumors and placental cells, including placental growth factor (PlGF), vascular endothelial growth factor (VEGF), E-cadherin (CDH1), laminin γ2 (LAMC2), the zinc finger E-box-binding homeobox (ZEB) proteins, αVβ3 integrin, transforming growth factor β (TGF-β), β-catenin, cofilin-1 (CFL-1), and interleukin-35 (IL-35). Understanding the similarities and differences in these processes may provide insights into the development of therapeutic options for both PAS and metastatic cancer.

Subtype-specific kinase dependency regulates growth and metastasis of poor-prognosis mesenchymal colorectal cancer

BACKGROUND

Colorectal cancer (CRC) can be divided into four consensus molecular subtypes (CMS), each with distinct biological features. CMS4 is associated with epithelial-mesenchymal transition and stromal infiltration (Guinney et al., Nat Med 21:1350-6, 2015; Linnekamp et al., Cell Death Differ 25:616-33, 2018), whereas clinically it is characterized by lower responses to adjuvant therapy, higher incidence of metastatic spreading and hence dismal prognosis (Buikhuisen et al., Oncogenesis 9:66, 2020).

METHODS

To understand the biology of the mesenchymal subtype and unveil specific vulnerabilities, a large CRISPR-Cas9 drop-out screen was performed on 14 subtyped CRC cell lines to uncover essential kinases in all CMSs. Dependency of CMS4 cells on p21-activated kinase 2 (PAK2) was validated in independent 2D and 3D in vitro cultures and in vivo models assessing primary and metastatic outgrowth in liver and peritoneum. TIRF microscopy was used to uncover actin cytoskeleton dynamics and focal adhesion localization upon PAK2 loss. Subsequent functional assays were performed to determine altered growth and invasion patterns.

RESULTS

PAK2 was identified as a key kinase uniquely required for growth of the mesenchymal subtype CMS4, both in vitro and in vivo. PAK2 plays an important role in cellular attachment and cytoskeletal rearrangements (Coniglio et al., Mol Cell Biol 28:4162-72, 2008; Grebenova et al., Sci Rep 9:17171, 2019). In agreement, deletion or inhibition of PAK2 impaired actin cytoskeleton dynamics in CMS4 cells and, as a consequence, significantly reduced invasive capacity, while it was dispensable for CMS2 cells. Clinical relevance of these findings was supported by the observation that deletion of PAK2 from CMS4 cells prevented metastatic spreading in vivo. Moreover, growth in a model for peritoneal metastasis was hampered when CMS4 tumor cells were deficient for PAK2.

CONCLUSION

Our data reveal a unique dependency of mesenchymal CRC and provide a rationale for PAK2 inhibition to target this aggressive subgroup of colorectal cancer.

Mechanisms and roles of podosomes and invadopodia

Cell invasion into the surrounding extracellular matrix or across tissue boundaries and endothelial barriers occurs in both physiological and pathological scenarios such as immune surveillance or cancer metastasis. Podosomes and invadopodia, collectively called 'invadosomes', are actin-based structures that drive the proteolytic invasion of cells, by forming highly regulated platforms for the localized release of lytic enzymes that degrade the matrix. Recent advances in high-resolution microscopy techniques, in vivo imaging and high-throughput analyses have led to considerable progress in understanding mechanisms of invadosomes, revealing the intricate inner architecture of these structures, as well as their growing repertoire of functions that extends well beyond matrix degradation. In this Review, we discuss the known functions, architecture and regulatory mechanisms of podosomes and invadopodia. In particular, we describe the molecular mechanisms of localized actin turnover and microtubule-based cargo delivery, with a special focus on matrix-lytic enzymes that enable proteolytic invasion. Finally, we point out topics that should become important in the invadosome field in the future.

Translationally controlled tumor protein: the mediator promoting cancer invasion and migration and its potential clinical prospects

Translationally controlled tumor protein (TCTP) is a highly conserved multifunctional protein localized in the cytoplasm and nucleus of eukaryotic cells. It is secreted through exosomes and its degradation is associated with the ubiquitin-proteasome system (UPS), heat shock protein 27 (Hsp27), and chaperone-mediated autophagy (CMA). Its structure contains three α‍-helices and eleven β‍-strands, and features a helical hairpin as its hallmark. TCTP shows a remarkable similarity to the methionine-R-sulfoxide reductase B (MsrB) and mammalian suppressor of Sec4 (Mss4/Dss4) protein families, which exerts guanine nucleotide exchange factor (GEF) activity on small guanosine triphosphatase (GTPase) proteins, suggesting that some functions of TCTP may at least depend on its GEF action. Indeed, TCTP exerts GEF activity on Ras homolog enriched in brain (Rheb) to boost the growth and proliferation of Drosophila cells. TCTP also enhances the expression of cell division control protein 42 homolog (Cdc42) to promote cancer cell invasion and migration. Moreover, TCTP regulates cytoskeleton organization by interacting with actin microfilament (MF) and microtubule (MT) proteins and inducing the epithelial-mesenchymal transition (EMT) process. In essence, TCTP promotes cancer cell movement. It is usually highly expressed in cancerous tissues and thus reduces patient survival; meanwhile, drugs can target TCTP to reduce this effect. In this review, we summarize the mechanisms of TCTP in promoting cancer invasion and migration, and describe the current inhibitory strategy to target TCTP in cancerous diseases.

Inositol Polyphosphate-5-Phosphatase K (Inpp5k) Enhances Sprouting of Corticospinal Tract Axons after CNS Trauma

Failure of CNS neurons to mount a significant growth response after trauma contributes to chronic functional deficits after spinal cord injury. Activator and repressor screening of embryonic cortical neurons and retinal ganglion cells in vitro and transcriptional profiling of developing CNS neurons harvested in vivo have identified several candidates that stimulate robust axon growth in vitro and in vivo Building on these studies, we sought to identify novel axon growth activators induced in the complex adult CNS environment in vivo We transcriptionally profiled intact sprouting adult corticospinal neurons (CSNs) after contralateral pyramidotomy (PyX) in nogo receptor-1 knock-out mice and found that intact CSNs were enriched in genes in the 3-phosphoinositide degradation pathway, including six 5-phosphatases. We explored whether inositol polyphosphate-5-phosphatase K (Inpp5k) could enhance corticospinal tract (CST) axon growth in preclinical models of acute and chronic CNS trauma. Overexpression of Inpp5k in intact adult CSNs in male and female mice enhanced the sprouting of intact CST terminals after PyX and cortical stroke and sprouting of CST axons after acute and chronic severe thoracic spinal contusion. We show that Inpp5k stimulates axon growth in part by elevating the density of active cofilin in labile growth cones, thus stimulating actin polymerization and enhancing microtubule protrusion into distal filopodia. We identify Inpp5k as a novel CST growth activator capable of driving compensatory axon growth in multiple complex CNS injury environments and underscores the veracity of using in vivo transcriptional screening to identify the next generation of cell-autonomous factors capable of repairing the damaged CNS.SIGNIFICANCE STATEMENT Neurologic recovery is limited after spinal cord injury as CNS neurons are incapable of self-repair post-trauma. In vitro screening strategies exploit the intrinsically high growth capacity of embryonic CNS neurons to identify novel axon growth activators. While promising candidates have been shown to stimulate axon growth in vivo, concomitant functional recovery remains incomplete. We identified Inpp5k as a novel axon growth activator using transcriptional profiling of intact adult corticospinal tract (CST) neurons that had initiated a growth response after pyramidotomy in plasticity sensitized nogo receptor-1-null mice. Here, we show that Inpp5k overexpression can stimulate CST axon growth after pyramidotomy, stroke, and acute and chronic contusion injuries. These data support in vivo screening approaches to identify novel axon growth activators.

Cytoskeletal dynamics regulates stromal invasion behavior of distinct liver cancer subtypes

Drug treatment against liver cancer has limited efficacy due to heterogeneous response among liver cancer subtypes. In addition, the functional biophysical phenotypes which arise from this heterogeneity and contribute to aggressive invasive behavior remain poorly understood. This study interrogated how heterogeneity in liver cancer subtypes contributes to differences in invasive phenotypes and drug response. Utilizing histological analysis, quantitative 2D invasion metrics, reconstituted 3D hydrogels, and bioinformatics, our study linked cytoskeletal dynamics to differential invasion profiles and drug resistance in liver cancer subtypes. We investigated cytoskeletal regulation in 2D and 3D culture environments using two liver cancer cell lines, SNU-475 and HepG2, chosen for their distinct cytoskeletal features and invasion profiles. For SNU-475 cells, a model for aggressive liver cancer, many cytoskeletal inhibitors abrogated 2D migration but only some suppressed 3D migration. For HepG2 cells, cytoskeletal inhibition did not significantly affect 3D migration but did affect proliferative capabilities and spheroid core growth. This study highlights cytoskeleton driven phenotypic variation, their consequences and coexistence within the same tumor, as well as efficacy of targeting biophysical phenotypes that may be masked in traditional screens against tumor growth.

Targeting LIMK1 with luteolin inhibits the growth of lung cancer in vitro and in vivo

Lung cancer is the leading cause of cancer‐related deaths. LIM domain kinase (LIMK) 1 is a member of serine/threonine kinase family and highly expressed in various cancers. Luteolin, a polyphenolic plant flavonoid, has been reported to suppress tumour proliferation through inducing apoptosis and autophagy via MAPK activation in glioma. However, the mechanism of luteolin on suppressing lung cancer growth is still unclear. We found that luteolin targeted LIMK1 from the in silico screening and significantly inhibited the LIMK1 kinase activity, which was confirmed with pull‐down binding assay and computational docking models. Treatment with luteolin inhibited lung cancer cells anchorage‐independent colony growth and induced apoptosis and cell cycle arrest at G1 phase. Luteolin also decreased the expression of cyclin D1 and increased the levels of cleaved caspase‐3 by down‐regulating LIMK1 signalling related targets, including p‐LIMK and p‐cofilin. Furthermore, luteolin suppressed the lung cancer patient‐derived xenograft tumour growth by decreasing Ki‐67, p‐LIMK and p‐cofilin expression in vivo. Taken together, these results provide insight into the mechanism that underlies the anticancer effects of luteolin on lung cancer, which involved in down‐regulation of LIMK1 and its interaction with cofilin. It also provides valuable evidence for translation towards lung cancer clinical trials with luteolin.

Actin Remodeling Defects Leading to Autoinflammation and Immune Dysregulation

A growing number of monogenic immune-mediated diseases have been related to genes involved in pathways of actin cytoskeleton remodeling. Increasing evidences associate cytoskeleton defects to autoinflammatory diseases and primary immunodeficiencies. We reviewed the pathways of actin cytoskeleton remodeling in order to identify inflammatory and immunological manifestations associated to pathological variants. We list more than twenty monogenic diseases, ranging from pure autoinflammatory conditions as familial Mediterranean fever, mevalonate kinase deficiency and PAPA syndrome, to classic and novel primary immunodeficiencies as Wiskott-Aldrich syndrome and DOCK8 deficiency, characterized by the presence of concomitant inflammatory and autoimmune manifestations, such as vasculitis and cytopenia, to severe and recurrent infections. We classify these disorders according to the role of the mutant gene in actin cytoskeleton remodeling, and in particular as disorders of transcription, elongation, branching and activation of actin. This expanding field of rare immune disorders offers a new perspective to all immunologists to better understand the physiological and pathological role of actin cytoskeleton in cells of innate and adaptive immunity.

Actin Remodeling Defects Leading to Autoinflammation and Immune Dysregulation

A growing number of monogenic immune-mediated diseases have been related to genes involved in pathways of actin cytoskeleton remodeling. Increasing evidences associate cytoskeleton defects to autoinflammatory diseases and primary immunodeficiencies. We reviewed the pathways of actin cytoskeleton remodeling in order to identify inflammatory and immunological manifestations associated to pathological variants. We list more than twenty monogenic diseases, ranging from pure autoinflammatory conditions as familial Mediterranean fever, mevalonate kinase deficiency and PAPA syndrome, to classic and novel primary immunodeficiencies as Wiskott-Aldrich syndrome and DOCK8 deficiency, characterized by the presence of concomitant inflammatory and autoimmune manifestations, such as vasculitis and cytopenia, to severe and recurrent infections. We classify these disorders according to the role of the mutant gene in actin cytoskeleton remodeling, and in particular as disorders of transcription, elongation, branching and activation of actin. This expanding field of rare immune disorders offers a new perspective to all immunologists to better understand the physiological and pathological role of actin cytoskeleton in cells of innate and adaptive immunity.

Coactosin Phosphorylation Controls Entamoeba histolytica Cell Membrane Protrusions and Cell Motility

Invasion of the colon wall by Entamoeba histolytica during amoebic dysentery entails migration of trophozoites through tissue layers that are rich in extracellular matrix. Transcriptional silencing of the E. histolytica surface metalloprotease EhMSP-1 produces hyperadherent less-motile trophozoites that are deficient in forming invadosomes. Reversible protein phosphorylation is often implicated in regulation of cell motility and invadosome formation. To identify such intermediaries of the EhMSP-1-silenced phenotype, here we compared the phosphoproteomes of EhMSP-1-silenced and vector control trophozoites by using quantitative tandem mass spectrometry-based proteomics. Six proteins were found to be differentially phosphorylated in EhMSP-1-silenced and control cells, including EhCoactosin, a member of the ADF/cofilin family of actin-binding proteins, which was more frequently phosphorylated at serine 147. Regulated overexpression of wild-type, phosphomimetic, and nonphosphorylatable EhCoactosin variants was used to test if phosphorylation functions in control of E. histolytica actin dynamics. Each of the overexpressed proteins colocalized with F-actin during E. histolytica phagocytosis. Nonetheless, trophozoites overexpressing an EhCoactosin phosphomimetic mutant formed more and poorly coordinated cell membrane protrusions compared to those in control or cells expressing a nonphosphorylatable mutant, while trophozoites overexpressing nonphosphorylatable EhCoactosin were significantly more motile within a model of mammalian extracellular matrix. Therefore, although EhCoactosin's actin-binding ability appeared unaffected by phosphorylation, EhCoactosin phosphorylation helps to regulate amoebic motility. These data help to understand the mechanisms underlying altered adherence and motility in EhMSP-1-silenced trophozoites and lay the groundwork for identifying kinases and phosphatases critical for control of amoebic invasiveness.IMPORTANCE Invasive amoebiasis, caused by the intestinal parasite Entamoeba histolytica, causes life-threatening diarrhea and liver abscesses, but, for unknown reasons, only approximately 10% of E. histolytica infections become symptomatic. A key requirement of invasion is the ability of the parasite to migrate through tissue layers. Here, we systematically looked for differences in protein phosphorylation between control parasites and a previously identified hyperadherent E. histolytica cell line that has reduced motility. We identified EhCoactosin, an actin-binding protein not previously known to be phosphoregulated, as one of the differentially phosphorylated proteins in E. histolytica and demonstrated that EhCoactosin phosphorylation functions in control of cell membrane dynamics and amoebic motility. This and the additional differentially phosphorylated proteins reported lay the groundwork for identifying kinases and phosphatases that regulate tissue invasiveness.

Long-Range and Directional Allostery of Actin Filaments Plays Important Roles in Various Cellular Activities

A wide variety of uniquely localized actin-binding proteins (ABPs) are involved in various cellular activities, such as cytokinesis, migration, adhesion, morphogenesis, and intracellular transport. In a micrometer-scale space such as the inside of cells, protein molecules diffuse throughout the cell interior within seconds. In this condition, how can ABPs selectively bind to particular actin filaments when there is an abundance of actin filaments in the cytoplasm? In recent years, several ABPs have been reported to induce cooperative conformational changes to actin filaments allowing structural changes to propagate along the filament cables uni- or bidirectionally, thereby regulating the subsequent binding of ABPs. Such propagation of ABP-induced cooperative conformational changes in actin filaments may be advantageous for the elaborate regulation of cellular activities driven by actin-based machineries in the intracellular space, which is dominated by diffusion. In this review, we focus on long-range allosteric regulation driven by cooperative conformational changes of actin filaments that are evoked by binding of ABPs, and discuss roles of allostery of actin filaments in narrow intracellular spaces.

Cytoskeleton and Nucleotide Signaling in Glioma C6 Cells

This chapter describes signaling pathways, stimulated by the P2Y₂ nucleotide receptor (P2Y₂R), that regulate cellular processes dependent on actin cytoskeleton dynamics in glioma C6 cells. P2Y₂R coupled with G-proteins, in response to ATP or UTP, regulates the level of iphosphatidylinositol-4,5-bisphosphate (PIP₂) which modulates a variety of actin binding proteins and is involved in calcium response and activates Rac1 and RhoA proteins. The RhoA/ROCK signaling pathway plays an important role in contractile force generation needed for the assembly of stress fibers, focal adhesions and for tail retraction during cell migration. Blocking of this pathway by a specific Rho-kinase inhibitor induces changes in F-actin organization and cell shape and decreases the level of phosphorylated myosin II and cofilin. In glioma C6 cells these changes are reversed after UTP stimulation of P2Y₂R. Signaling pathways responsible for this compensation are calcium signaling which regulates MLC kinase activation via calmodulin, and the Rac1/PAK/LIMK cascade. Stimulation of the Rac1 mediated pathway via G_o proteins needs additional interaction between α_vβ₅ integrins and P2Y₂Rs. Calcium free medium, or growing of the cells in suspension, prevents Gα_o activation by P2Y₂ receptors. Rac1 activation is necessary for cofilin phosphorylation as well as integrin activation needed for focal complexes formation and stabilization of lamellipodium. Inhibition of positive Rac1 regulation prevents glioma C6 cells from recovery of control cell like morphology.

Cofilin is a mediator of RET-promoted medullary thyroid carcinoma cell migration, invasion and proliferation

Medullary thyroid carcinoma (MTC) is a rare neuroendocrine tumor that originates from parafollicular thyroid C cells and accounts for 5% of thyroid cancers. In inherited cases of MTC, and in about 40% of sporadic cases, activating mutations of the receptor tyrosine kinase proto-oncogene RET are found. Constitutively active RET triggers signaling pathways involved in cell proliferation, survival and motility, but the mechanisms underlying malignant transformation of C-cells have been only partially elucidated. Cofilin is a key regulator of actin cytoskeleton dynamics. A crucial role of cofilin in tumor development, progression, invasion and metastasis has been demonstrated in different human cancers, but no data are available in MTC. Interestingly, RET activation upregulates cofilin gene expression. The aim of this study was to investigate cofilin contribution in invasiveness and growth of MTC cells, and its relevance in the context of mutant RET signaling. We found that cofilin transfection in human MTC cell line TT significantly increased migration (178 ± 44%, p < 0.001), invasion (165 ± 28%, p < 0.01) and proliferation (146 ± 18%, p < 0.001), accompanied by an increase of ERK1/2 phosphorylation (2.23-fold) and cyclin D1 levels (1.43-fold). Accordingly, all these responses were significantly reduced after genetic silencing of cofilin (-55 ± 10% migration, p < 0.001, -41 ± 8% invasion, p < 0.001, -17 ± 3% proliferation, p < 0.001). These results have been confirmed in primary cells cultures obtained from human MTCs. The inhibition of constitutively active RET in TT cells by both the RET pharmacological inhibitor RPI-1 and the transfection of dominant negative RET mutant (RETΔTK) resulted in a reduction of cofilin expression (-37 ± 8%, p < 0.001 and -31 ± 16%, p < 0.01, respectively). Furthermore, RPI-1 inhibitory effects on TT cell migration (-57 ± 13%, p < 0.01), but not on cell proliferation, were completely abolished in cells transfected with cofilin. In conclusion, these data indicate that an unbalanced cofilin expression, induced by oncogenic RET, contributes to promote MTC invasiveness and growth, suggesting the possibility of targeting cofilin pathway for more effective treatment of MTC.

Nonconserved miR-608 suppresses prostate cancer progression through RAC2/PAK4/LIMK1 and BCL2L1/caspase-3 pathways by targeting the 3'-UTRs of RAC2/BCL2L1 and the coding region of PAK4

The aim of this study is to investigate the functions and mechanisms of miR-608 in prostate cancer (PCa). CISH and qRT-PCR analysis demonstrated that miR-608 was low expressed in PCa tissues and cells, which was partly attributed to the methylation of CpG island adjacent to the transcription start site (TSS) of miR-608 gene. Intracellular miR-608 overexpression inhibited in vivo PCa tumor growth, and suppressed PCa cell proliferation, G2/M transition, and migration in vitro, which was independent of EMT-associated mechanisms. Then RAC2, a GTPase previously deemed hematopoiesis-specific but now discovered to exist and play important roles in PCa, was verified by western blot and dual-luciferase reporter assays to mediate the effects of miR-608 through RAC2/PAK4/LIMK1/cofilin pathway. MiR-608 also promoted the apoptosis of PCa cells through BCL2L1/caspase-3 pathway by targeting the 3'-UTR of BCL2L1. Moreover, PAK4, the downstream effector of RAC2, was found to be targeted by miR-608 at the mRNA coding sequence (CDS) instead of the canonical 3'-UTR. Knocking down RAC2, PAK4, or BCL2L1 with siRNAs reproduced the antiproliferative, mitosis-obstructive, antimigratory and proapoptotic effects of miR-608 in PCa cells, which could be attenuated by downregulating miR-608. In conclusion, miR-608 suppresses PCa progression, and its activation provides a new therapeutic option for PCa.

The modulation of actin dynamics via atypical Protein Kinase-C activated Cofilin regulates metastasis of colorectal cancer cells

Colorectal cancer (CRC) is the third most common cancer in the United States. The exact mechanism of CRC cells metastasis is poorly understood. Actin polymerization is thought to be an initial step in the cancer cell motility cycle which drives the formation of cell protrusions and defines the direction of migration. Cofilin, a significant actin-regulating molecule, regulates the migration of cancer cells by the formation of lamellipodia and filopodia, however, little is known about the upstream regulation of cofilin. In this study, the effect of atypical Protein Kinase C (atypical PKC) on Cofilin activity in CRC was studied. This study demonstrates that the atypical PKC inhibition impedes the metastasis of CRC cells by increasing phospho-Cofilin (S3) and changing actin organization.

Study of cofilin 1 gene expression in colorectal cancer

Background

Colorectal cancer (CRC) is one of the most prevalent malignancies worldwide. Cofilin is a key regulatory protein in the dynamics of actin filaments. Previous studies have shown cofilin 1's major role in cell migration process and its role in tumor cell migration and invasion. Therefore, cofilin 1 may have the potential as a novel diagnostic tumor marker in various cancers. In this study, differential expression of CFL1 in CRC tissues in comparison with adjacent non-tumor tissues was investigated and the diagnostic value of this protein in CRC was evaluated.

Methods

Synthesized cDNA from extracted RNAs of 30 patients were subjected to qRT-PCR to quantify relative expression of cofilin 1. The relationship between cofilin 1 expression and clinicopathological features of patients were studied too.

Results

The study showed significant upregulation of cofilin 1 in CRC tissue samples compared to adjacent non-tumor tissue samples (P<0.05). The receiver operating characteristic curve analysis showed higher area under the curve (0.85). There was no significant correlation between cofilin 1 expression levels and clinicopathological features of patients.

Conclusions

According to the obtained results, cofilin 1 can serve as a candidate for clinically useful diagnostic biomarker or therapeutic target for CRC.

Changes in Vasodilator-Stimulated Phosphoprotein Phosphorylation, Profilin-1, and Cofilin-1 in Accreta and Protection by DHA

Accreta and gestational trophoblastic disease (ie, choriocarcinoma) are placental pathologies characterized by hyperproliferative and invasive trophoblasts. Cellular proliferation, migration, and invasion are heavily controlled by actin-binding protein (ABP)-mediated actin dynamics. The ABP vasodilator-stimulated phosphoprotein (VASP) carries key regulatory role. Profilin-1, cofilin-1, and VASP phosphorylated at Ser157 (pVASP-S157) and Ser239 (pVASP-S239) are ABPs that regulate actin polymerization and stabilization and facilitate cell metastases. Docosahexaenoic acid (DHA) inhibits cancer cell migration and proliferation. We hypothesized that analogous to malignant cells, ABPs regulate these processes in extravillous trophoblasts (EVTs), which exhibit aberrant expression in placenta accreta. Placental-myometrial junction biopsies of histologically confirmed placenta accreta had significantly increased immunostaining levels of cofilin-1, VASP, pVASP-S239, and F-actin. Treatment of choriocarcinoma-derived trophoblast (BeWo) cells with DHA (30 µM) for 24 hours significantly suppressed proliferation, migration, and pVASP-S239 levels and altered protein profiles consistent with increased apoptosis. We concluded that in accreta changes in the ABP expression profile were a response to restore homeostasis by counteracting the hyperproliferative and invasive phenotype of the EVT. The observed association between VASP phosphorylation, apoptosis, and trophoblast proliferation and migration suggest that DHA may offer a therapeutic solution for conditions where EVT is hyperinvasive.

PKD regulates actin polymerization, neutrophil deformability, and transendothelial migration in response to fMLP and trauma

Neutrophils are important mediators of the innate immune defense and of the host response to a physical trauma. Because aberrant infiltration of injured sites by neutrophils was shown to cause adverse effects after trauma, we investigated how neutrophil infiltration could be modulated at the cellular level. Our data indicate that protein kinase D (PKD) is a vital regulator of neutrophil transmigration. PKD phosphorylates the Cofilin-phosphatase Slingshot-2L (SSH-2L). SSH-2L in turn dynamically regulates Cofilin activity and actin polymerization in response to a chemotactic stimulus for neutrophils, for example, fMLP. Here, we show that inhibition of PKD by two specific small molecule inhibitors results in broad, unrestricted activation of Cofilin and strongly increases the F-actin content of neutrophils even under basal conditions. This phenotype correlates with a significantly impaired neutrophil deformability as determined by optical stretcher analysis. Consequently, inhibition of PKD impaired chemotaxis as shown by reduced extravasation of neutrophils. Consequently, we demonstrate that transendothelial passage of both, neutrophil-like NB4 cells and primary PMNs recovered from a hemorrhagic shock trauma model was significantly reduced. Thus, inhibition of PKD may represent a promising modulator of the neutrophil response to trauma.

Proteomic Analysis of Normal and Cancer Cervical Cell Lines Reveals Deregulation of Cytoskeleton-associated Proteins

BACKGROUND

Both HPV-positive and -negative cervical cancers are primarily associated with features of cell cycle and cytoskeletal disruption; however, the actual biological processes affected remain elusive. To this end, we systematically characterized the intracellular proteomic profiles of four distinct and informative cervical cell lines.

MATERIALS AND METHODS

Cell extracts from a normal cervical (HCK1T) and three cervical cancer cell lines, one HPV-negative (C33A), and two HPV-positive, SiHa (HPV16+) and HeLa (HPV18+), were analyzed by 2-dimensional electrophoresis and differentially expressed proteins were identified by MALDI-TOF mass spectrometry, while differential expression was confirmed by western blot analysis.

RESULTS

In total, 113 proteins were found differentially expressed between the normal and the cervical cancer lines. Bioinformatics analysis revealed the actin cytoskeleton signaling pathway to be significantly affected, while up-regulation of cofilin-1, an actin depolymerizing factor, was documented and further validated by western blotting. Furthermore, two-way comparisons among the four cell lines, revealed a set of 18 informative differentially expressed proteins.

CONCLUSION

These novel identified proteins provide the impetus for further functional studies to dissect the mechanisms operating in the two distinct pathways of cervical carcinogenesis.

A novel pathway activated by somatostatin receptor type 2 (SST2): Inhibition of pituitary tumor cell migration and invasion through cytoskeleton protein recruitment

The pharmacological therapy of GH-secreting pituitary tumors is based on somatostatin (SS) analogs that reduce GH secretion and cell proliferation by binding mainly SS receptors type 2 (SST2). Antimigratory effects of SS have been demonstrated in different cell models, but no data on pituitary tumors are available. Aims of our study were to evaluate SST2 effects on migration and invasion of human and rat tumoral somatotrophs, and to elucidate the molecular mechanism involved focusing on the role of cofilin and filamin A (FLNA). Our data revealed that SST2 agonist BIM23120 significantly reduced GH3 cells migration (-22% ± 3.6%, p < 0.001) and invasion on collagen IV (-31.3% ± 12.2%, p < 0.01), both these effects being reproduced by octreotide and pasireotide. Similar results were obtained in primary cultured cells from human GH-secreting tumors. These inhibitory actions were accompanied by a marked increase in RhoA/ROCK-dependent cofilin phosphorylation (about 2.7-fold in GH3 and 2.1-fold in human primary cells). Accordingly, the anti-invasive effect of the SS analog was mimicked by the overexpression in GH3 cells of the S3D phosphomimetic cofilin mutant, and abolished by both phosphodeficient S3A cofilin and a specific ROCK inhibitor that prevented cofilin phosphorylation. Moreover, FLNA silencing and FLNA dominant-negative mutants FLNA19-20 and FLNA21-24 transfection demonstrated that FLNA plays a scaffold function for SST2-mediated cofilin phosphorylation. Accordingly, cofilin recruitment to agonist-activated SST2 was completely lost in FLNA silenced cells. In conclusion, we demonstrated that SST2 inhibits rat and human tumoral somatotrophs migration and invasion through a molecular mechanism that involves FLNA-dependent cofilin recruitment and phosphorylation.

Parallel mRNA, proteomics and miRNA expression analysis in cell line models of the intestine

AIM

To identify miRNA-regulated proteins differentially expressed between Caco2 and HT-29: two principal cell line models of the intestine.

METHODS

Exponentially growing Caco-2 and HT-29 cells were harvested and prepared for mRNA, miRNA and proteomic profiling. mRNA microarray profiling analysis was carried out using the Affymetrix GeneChip Human Gene 1.0 ST array. miRNA microarray profiling analysis was carried out using the Affymetrix Genechip miRNA 3.0 array. Quantitative Label-free LC-MS/MS proteomic analysis was performed using a Dionex Ultimate 3000 RSLCnano system coupled to a hybrid linear ion trap/Orbitrap mass spectrometer. Peptide identities were validated in Proteome Discoverer 2.1 and were subsequently imported into Progenesis QI software for further analysis. Hierarchical cluster analysis for all three parallel datasets (miRNA, proteomics, mRNA) was conducted in the R software environment using the Euclidean distance measure and Ward's clustering algorithm. The prediction of miRNA and oppositely correlated protein/mRNA interactions was performed using TargetScan 6.1. GO biological process, molecular function and cellular component enrichment analysis was carried out for the DE miRNA, protein and mRNA lists via the Pathway Studio 11.3 Web interface using their Mammalian database.

RESULTS

Differential expression (DE) profiling comparing the intestinal cell lines HT-29 and Caco-2 identified 1795 Genes, 168 Proteins and 160 miRNAs as DE between the two cell lines. At the gene level, 1084 genes were upregulated and 711 were downregulated in the Caco-2 cell line relative to the HT-29 cell line. At the protein level, 57 proteins were found to be upregulated and 111 downregulated in the Caco-2 cell line relative to the HT-29 cell line. Finally, at the miRNAs level, 104 were upregulated and 56 downregulated in the Caco-2 cell line relative to the HT-29 cell line. Gene ontology (GO) analysis of the DE mRNA identified cell adhesion, migration and ECM organization, cellular lipid and cholesterol metabolic processes, small molecule transport and a range of responses to external stimuli, while similar analysis of the DE protein list identified gene expression/transcription, epigenetic mechanisms, DNA replication, differentiation and translation ontology categories. The DE protein and gene lists were found to share 15 biological processes including for example epithelial cell differentiation [P value ≤ 1.81613E-08 (protein list); P ≤ 0.000434311 (gene list)] and actin filament bundle assembly [P value ≤ 0.001582797 (protein list); P ≤ 0.002733714 (gene list)]. Analysis was conducted on the three data streams acquired in parallel to identify targets undergoing potential miRNA translational repression identified 34 proteins, whose respective mRNAs were detected but no change in expression was observed. Of these 34 proteins, 27 proteins downregulated in the Caco-2 cell line relative to the HT-29 cell line and predicted to be targeted by 19 unique anti-correlated/upregulated microRNAs and 7 proteins upregulated in the Caco-2 cell line relative to the HT-29 cell line and predicted to be targeted by 15 unique anti-correlated/downregulated microRNAs.

CONCLUSION

This first study providing "tri-omics" analysis of the principal intestinal cell line models Caco-2 and HT-29 has identified 34 proteins potentially undergoing miRNA translational repression.

Shigella depends on SepA to destabilize the intestinal epithelial integrity via cofilin activation

Shigella is unique among enteric pathogens, as it invades colonic epithelia through the basolateral pole. Therefore, it has evolved the ability to breach the intestinal epithelial barrier to deploy an arsenal of effector proteins, which permits bacterial invasion and leads to a severe inflammatory response. However, the mechanisms used by Shigella to regulate epithelial barrier permeability remain unknown. To address this question, we used both an intestinal polarized model and a human ex-vivo model to further characterize the early events of host-bacteria interactions. Our results showed that secreted Serine Protease A (SepA), which belongs to the serine protease autotransporter of Enterobacteriaceae family, is responsible for critically disrupting the intestinal epithelial barrier. Such disruption facilitates bacterial transit to the basolateral pole of the epithelium, ultimately fostering the hallmarks of the disease pathology. SepA was found to cause a decrease in active LIM Kinase 1 (LIMK1) levels, a negative inhibitor of actin-remodeling proteins, namely cofilin. Correspondingly, we observed increased activation of cofilin, a major actin-polymerization factor known to control opening of tight junctions at the epithelial barrier. Furthermore, we resolved the crystal structure of SepA to elucidate its role on actin-dynamics and barrier disruption. The serine protease activity of SepA was found to be required for the regulatory effects on LIMK1 and cofilin, resulting in the disruption of the epithelial barrier during infection. Altogether, we demonstrate that SepA is indispensable for barrier disruption, ultimately facilitating Shigella transit to the basolateral pole where it effectively invades the epithelium.

NKCC1 Regulates Migration Ability of Glioblastoma Cells by Modulation of Actin Dynamics and Interacting with Cofilin

Glioblastoma (GBM) is the most aggressive primary brain tumor in adults. The mechanisms that confer GBM cells their invasive behavior are poorly understood. The electroneutral Na⁺-K⁺-2Cl^- co-transporter 1 (NKCC1) is an important cell volume regulator that participates in cell migration. We have shown that inhibition of NKCC1 in GBM cells leads to decreased cell migration, in vitro and in vivo. We now report on the role of NKCC1 on cytoskeletal dynamics. We show that GBM cells display a significant decrease in F-actin content upon NKCC1 knockdown (NKCC1-KD). To determine the potential actin-regulatory mechanisms affected by NKCC1 inhibition, we studied NKCC1 protein interactions. We found that NKCC1 interacts with the actin-regulating protein Cofilin-1 and can regulate its membrane localization. Finally, we analyzed whether NKCC1 could regulate the activity of the small Rho-GTPases RhoA and Rac1. We observed that the active forms of RhoA and Rac1 were decreased in NKCC1-KD cells. In summary, we report that NKCC1 regulates GBM cell migration by modulating the cytoskeleton through multiple targets including F-actin regulation through Cofilin-1 and RhoGTPase activity. Due to its essential role in cell migration NKCC1 may serve as a specific therapeutic target to decrease cell invasion in patients with primary brain cancer.

Differential expression of cytoskeletal regulatory factors in the adolescent prefrontal cortex: Implications for cortical development

The prevalence of depression, anxiety, schizophrenia, and drug and alcohol use disorders peaks during adolescence. Further, up to 50% of "adult" mental health disorders emerge in adolescence. During adolescence, the prefrontal cortex (PFC) undergoes dramatic structural reorganization, in which dendritic spines and synapses are refined, pruned, and stabilized. Understanding the molecular mechanisms that underlie these processes should help to identify factors that influence the development of psychiatric illness. Here we briefly discuss the anatomical connections of the medial and orbital prefrontal cortex (mPFC and OFC, respectively). We then present original findings suggesting that dendritic spines on deep-layer excitatory neurons in the mouse mPFC and OFC prune at different adolescent ages, with later pruning in the OFC. In parallel, we used Western blotting to define levels of several cytoskeletal regulatory proteins during early, mid-, and late adolescence, focusing on tropomyosin-related kinase receptor B (TrkB) and β1-integrin-containing receptors and select signaling partners. We identified regional differences in the levels of several proteins in early and midadolescence that then converged in early adulthood. We also observed age-related differences in TrkB levels, both full-length and truncated isoforms, Rho-kinase 2, and synaptophysin in both PFC subregions. Finally, we identified changes in protein levels in the dorsal and ventral hippocampus that were distinct from those in the PFC. We conclude with a general review of the manner in which TrkB- and β1-integrin-mediated signaling influences neuronal structure in the postnatal brain. Elucidating the role of cytoskeletal regulatory factors throughout adolescence may identify critical mechanisms of PFC development. © 2016 Wiley Periodicals, Inc.

Cofilin Activation Is Temporally Associated with the Cessation of Growth in the Developing Hippocampus

Dendritic extension and synaptogenesis proceed at high rates in rat hippocampus during early postnatal life but markedly slow during the third week of development. The reasons for the latter, fundamental event are poorly understood. Here, we report that levels of phosphorylated (inactive) cofilin, an actin depolymerizing factor, decrease by 90% from postnatal days (pnds) 10 to 21. During the same period, levels of total and phosphorylated Arp2, which nucleates actin branches, increase. A search for elements that could explain the switch from inactive to active cofilin identified reductions in β1 integrin, TrkB, and LIM domain kinase 2b, upstream proteins that promote cofilin phosphorylation. Moreover, levels of slingshot 3, which dephosphorylates cofilin, increase during the period in which growth slows. Consistent with the cofilin results, in situ phalloidin labeling of F-actin demonstrated that spines and dendrites contained high levels of dynamic actin filaments during Week 2, but these fell dramatically by pnd 21. The results suggest that the change from inactive to constitutively active cofilin leads to a loss of dynamic actin filaments needed for process extension and thus the termination of spine formation and synaptogenesis. The relevance of these events to the emergence of memory-related synaptic plasticity is described.

Cofilin Mediates LPS-Induced Microglial Cell Activation and Associated Neurotoxicity Through Activation of NF-κB and JAK-STAT Pathway

Microglial cells are activated in response to different types of injuries or stress in the CNS. Such activation is necessary to get rid of the injurious agents and restore tissue homeostasis. However, excessive activation of microglial cells is harmful and contributes to secondary injury. Pertinently, microglial cell activity was targeted in many preclinical and clinical studies but such strategy failed in clinical trials. The main reason behind the failed attempts is the complexity of the injury mechanisms which needs either a combination therapy or targeting a process that is involved in multiple pathways. Cofilin is a cytoskeleton-associated protein involved in actin dynamics. In our previous study, we demonstrated the role of cofilin in mediating neuronal apoptosis during OGD conditions. Previous studies on microglia have shown the involvement of cofilin in ROS formation and phagocytosis. However, additional studies are needed to delineate the role of cofilin in microglial cell activation. Therefore, in the current study, we investigated the role of cofilin in LPS-induced microglial cell activation using cofilin siRNA knockdown paradigms. The viability of differentiated PC12 cells was used as a measure of the neurotoxic potential of conditioned medium derived from cofilin siRNA-transfected and LPS-activated microglial cells. Cofilin knockdown significantly inhibited LPS-induced microglial cell activation through NF-κB and JAK-STAT pathways. The release of proinflammatory mediators (NO, TNF-α, iNOS, and COX2) as well as microglial proliferation and migration rates were significantly reduced by cofilin knockdown. Furthermore, differentiated PC12 cells were protected from the neurotoxicity induced by conditioned medium derived from cofilin-transfected and LPS-activated microglial cells. In conclusion, we demonstrated that cofilin is involved in the cascade of microglial cell activation and further validates our previous study on cofilin's role in mediating neuronal apoptosis. Together, our results suggest that cofilin could present a common target in neurons and microglial cells and might prove to be a promising therapy for different brain injury mechanisms including stroke.

Mitochondrial dysfunction and mitochondrial dynamics-The cancer connection

Mitochondrial dysfunction is a hallmark of many diseases. The retrograde signaling initiated by dysfunctional mitochondria can bring about global changes in gene expression that alters cell morphology and function. Typically, this is attributed to disruption of important mitochondrial functions, such as ATP production, integration of metabolism, calcium homeostasis and regulation of apoptosis. Recent studies showed that in addition to these factors, mitochondrial dynamics might play an important role in stress signaling. Normal mitochondria are highly dynamic organelles whose size, shape and network are controlled by cell physiology. Defective mitochondrial dynamics play important roles in human diseases. Mitochondrial DNA defects and defective mitochondrial function have been reported in many cancers. Recent studies show that increased mitochondrial fission is a pro-tumorigenic phenotype. In this paper, we have explored the current understanding of the role of mitochondrial dynamics in pathologies. We present new data on mitochondrial dynamics and dysfunction to illustrate a causal link between mitochondrial DNA defects, excessive fission, mitochondrial retrograde signaling and cancer progression. This article is part of a Special Issue entitled Mitochondria in Cancer, edited by Giuseppe Gasparre, Rodrigue Rossignol and Pierre Sonveaux.

Evidence that phospholipase C is involved in the antitumour action of NSC768313, a new thieno[2,3-b]pyridine derivative

BACKGROUND

The thieno[2,3-b]pyridines were discovered by virtual high throughput screening as potential inhibitors of phospholipase C (PLC) isoforms and showed potent growth inhibitory effects in National Cancer Institute's human tumour cell line panel (NCI60). The mechanism of the anti-proliferative activity of thieno[2,3-b]pyridines is explored here.

OBJECTIVES

We aimed to investigate the basis for the anti-proliferative activity of these thieno[2,3-b]pyridines and to determine whether the cellular inhibition was related to their inhibition of PLC.

METHODS

Four breast cancer cell lines were used to assess the anti-proliferative effects (IC50 values) of six representative thieno[2,3-b]pyridines. The most potent compound (derivative 3; NSC768313), was further studied in MDA-MB-231 cells. DNA damage was examined by γH2AX expression level, and cell cycle arrest by flow cytometry. Cell morphology was examined by tubulin antibody staining. The growth inhibitory effect of combination treatment with derivative 3 and paclitaxel (tubulin inhibitor), doxorubicin (topoisomerase II inhibitor) or camptothecin (topoisomerase I inhibitor) was evaluated. A preliminary mouse toxicity assay was used to evaluate the pharmacological properties.

RESULTS

Addition of the thieno[2,3-b]pyridine derivative 3 to the MDA-MB-231 cells induced G2/M growth inhibition, cell cycle arrest in G2-phase, membrane blebbing and the formation of multinucleated cells. It did not induce DNA damage, mitotic arrest or changes in calcium ion flux. Combination of derivative 3 with paclitaxel showed a high degree of synergy, while combinations with doxorubicin and camptothecin showed only additive effects. A mouse pharmacokinetic study of derivative 3 showed that after intraperitoneal injection of a single does (10 mg/Kg), the Cmax was 0.087 μmol/L and the half-life was 4.11 h.

CONCLUSIONS

The results are consistent with a mechanism in which thieno[2,3-b]pyridine derivatives interact with PLC isoforms (possibly PLC-δ), which in turn affect the cellular dynamics of tubulin-β, inducing cell cycle arrest in G2-phase. We conclude that these compounds have novelty because of their PLC target and may have utility in combination with mitotic poisons for cancer treatment.

Potential crosstalk between cofilin-1 and EGFR pathways in cisplatin resistance of non-small-cell lung cancer

Current challenge in oncology is to establish the concept of personalized medicine in clinical practice. In this context, non-small-cell lung cancer (NSCLC) presents clinical, histological and molecular heterogeneity, being one of the most genomically diverse of all cancers. Recent advances added Epidermal Growth Factor Receptor (EGFR) as a predictive biomarker for patients with advanced NSCLC. In tumors with activating EGFR mutations, tyrosine kinase inhibitors (TKI) are indicated as first-line treatment, although restricted to a very small target population. In this context, cofilin-1 (a cytosolic protein involved with actin dynamics) has been widely studied as a biomarker of an aggressive phenotype in tumors, and overexpression of cofilin-1 is associated with cisplatin resistance and poor prognosis in NSCLC. Here, we gather information about the predictive potential of cofilin-1 and reviewed the crosstalk between cofilin-1/EGFR pathways. We aimed to highlight new perspectives of how these interactions might affect cisplatin resistance in NSCLC. We propose that cofilin-1 quantification in clinical samples in combination with presence/absence of EGFR mutation could be used to select patients that would benefit from TKI's treatment. This information is of paramount importance and could result in a possibility of guiding more effective treatments to NSCLC patients.

Cofilin contributes to phagocytosis of IgG-opsonized particles but not non-opsonized particles in RAW264 macrophages

Cofilin is an actin-binding protein that severs actin filaments. It plays a key role in regulating actin cytoskeletal remodeling, thereby contributing to diverse cellular functions. However, the involvement of cofilin in phagocytosis remains to be elucidated. We examined the spatiotemporal localization of cofilin during phagocytosis of IgG-opsonized erythrocytes, IgG-opsonized latex beads and non-opsonized latex beads. Live-cell imaging showed that GFP-cofilin accumulates in the sites of IgG-opsonized particle binding and in phagocytic cups. Moreover, immunofluorescence microscopy revealed that endogenous cofilin localizes to phagocytic cups engulfing IgG-opsonized particles, but not non-opsonized latex beads. Scanning electron microscopy demonstrated a notable difference in morphology between phagocytic structures in IgG-dependent and IgG-independent phagocytosis. In phagocytosis of IgG-opsonized particles, sheet-like pseudopodia extended along the surface of IgG-opsonized particles to form phagocytic cups. In contrast, in opsonin-independent phagocytosis, long finger-like filopodia captured non-opsonized latex beads. Importantly, non-opsonized beads sank into the cells without extending phagocytic cups. Our analysis of cofilin mutant expression demonstrates that phagocytosis of IgG-opsonized particles is enhanced in cells expressing wild-type cofilin or active mutant cofilin-S3A, whereas the uptake of non-opsonized latex beads is not. These data suggest that cofilin promotes actin cytoskeletal remodeling to form phagocytic cups by accelerating actin turnover and thereby facilitating phagosome formation. In contrast, cofilin is not involved in opsonin-independent phagocytosis of latex beads.

Ceramide signals for initiation of yeast mating-specific cell cycle arrest

Sphingolipids are major constituents of membranes. A number of S. cerevisiae sphingolipid intermediates such as long chains sphingoid bases (LCBs) and ceramides act as signaling molecules regulating cell cycle progression, adaptability to heat stress, and survival in response to starvation. Here we show that S. cerevisiae haploid cells must synthesize ceramide in order to induce mating specific cell cycle arrest. Cells devoid of sphingolipid biosynthesis or defective in ceramide synthesis are sterile and harbor defects in pheromone-induced MAP kinase-dependent transcription. Analyses of G1/S cyclin levels indicate that mutant cells cannot reduce Cln1/2 levels in response to pheromone. FACS analysis indicates a lack of ability to arrest. The addition of LCBs to sphingolipid deficient cells restores MAP kinase-dependent transcription, reduces cyclin levels, and allows for mating, as does the addition of a cell permeable ceramide to cells blocked at ceramide synthesis. Pharmacological studies using the inositolphosphorylceramide synthase inhibitor aureobasidin A indicate that the ability to synthesize and accumulate ceramide alone is sufficient for cell cycle arrest and mating. Studies indicate that ceramide also has a role in PI(4,5)P2 polarization during mating, an event necessary for initiating cell cycle arrest and mating itself. Moreover, our studies suggest a third role for ceramide in localizing the mating-specific Ste5 scaffold to the plasma membrane. Thus, ceramide plays a role 1) in pheromone-induced cell cycle arrest, 2) in activation of MAP kinase-dependent transcription, and 3) in PtdIns(4,5)P2 polarization. All three events are required for differentiation during yeast mating.

Progesterone promotes cell migration, invasion and cofilin activation in human astrocytoma cells

Astrocytomas are the most common and aggressive primary brain tumors in humans. Invasiveness of these tumors has been attributed in part to deregulation of cell motility-dependent cytoskeletal dynamics that involves actin-binding proteins such as cofilin. Progesterone (P4) has been found to induce migration and invasion of cells derived from breast cancer and endothelium. However, the role of P4 in migration and invasion of astrocytoma cells as well as its effects on astrocytomas cytoskeleton remodeling is not known. In this work we evaluated these aspects in D54 and U251 cells derived from human astrocytomas from the highest degree of malignancy (grade IV, glioblastoma). Our results showed that in scratch-wound assays P4 increased the number of D54 and U251 cells migrating from 3 to 48 h. Both RU486, a P4 receptor (PR) antagonist, and an oligonucleotide antisense against PR significantly blocked P4 effects. Transwell assays showed that P4 significantly increased the number of invasive cells at 24h. As in the case of migration, this effect was blocked by RU486. Finally, by Western blotting, an increase in the cofilin/p-cofilin ratio at 15 and 30 min and a decrease at 30 and 60 min in U251 and D54 cells, respectively, was observed after P4, P4+RU486 and RU486 treatments. These data suggest that P4 increases human astrocytoma cells migration and invasion through its intracellular receptor, and that cofilin activation by P4 is independent of PR action.

The Novel Functions of the PLC/PKC/PKD Signaling Axis in G Protein-Coupled Receptor-Mediated Chemotaxis of Neutrophils

Chemotaxis, a directional cell migration guided by extracellular chemoattractant gradients, plays an essential role in the recruitment of neutrophils to sites of inflammation. Chemotaxis is mediated by the G protein-coupled receptor (GPCR) signaling pathway. Extracellular stimuli trigger activation of the PLC/PKC/PKD signaling axis, which controls several signaling pathways. Here, we concentrate on the novel functions of PLC/PKC/PKD signaling in GPCR-mediated chemotaxis of neutrophils.

Cofilin phosphorylation is elevated after F-actin disassembly induced by Rac1 depletion

Cytoskeletal reorganization is essential to keratinocyte function. Rac1 regulates cytoskeletal reorganization through signaling pathways such as the cofilin cascade. Cofilin severs actin filaments after activation by dephosphorylation. Rac1 was knocked out in mouse keratinocytes and it was found that actin filaments disassembled. In the epidermis of mice in which Rac1 was knocked out only in keratinocytes, cofilin phosphorylation was aberrantly elevated, corresponding to repression of the phosphatase slingshot1 (SSH1). These effects were independent of the signaling pathways for p21-activated kinase/LIM kinase (Pak/LIMK), protein kinase C, or protein kinase D or generation of reactive oxygen species. Similarly, when actin polymerization was specifically inhibited or Rac1 was knocked down, cofilin phosphorylation was enhanced and SSH1 was repressed. Repression of SSH1 partially blocked actin depolymerization induced by Rac1 depletion. Therefore, aberrant cofilin phosphorylation that induces actin polymerization might be a consequence of actin disassembly induced by the absence of Rac1.

Chronophin coordinates cell leading edge dynamics by controlling active cofilin levels

Cofilin, a critical player of actin dynamics, is spatially and temporally regulated to control the direction and force of membrane extension required for cell locomotion. In carcinoma cells, although the signaling pathways regulating cofilin activity to control cell direction have been established, the molecular machinery required to generate the force of the protrusion remains unclear. We show that the cofilin phosphatase chronophin (CIN) spatiotemporally regulates cofilin activity at the cell edge to generate persistent membrane extension. We show that CIN translocates to the leading edge in a PI3-kinase-, Rac1-, and cofilin-dependent manner after EGF stimulation to activate cofilin, promotes actin free barbed end formation, accelerates actin turnover, and enhances membrane protrusion. In addition, we establish that CIN is crucial for the balance of protrusion/retraction events during cell migration. Thus, CIN coordinates the leading edge dynamics by controlling active cofilin levels to promote MTLn3 cell protrusion.

Synergistic action of dendritic mitochondria and creatine kinase maintains ATP homeostasis and actin dynamics in growing neuronal dendrites

The distribution of mitochondria within mature, differentiated neurons is clearly adapted to their regional physiological needs and can be perturbed under various pathological conditions, but the function of mitochondria in developing neurons has been less well studied. We have studied mitochondrial distribution within developing mouse cerebellar Purkinje cells and have found that active delivery of mitochondria into their dendrites is a prerequisite for proper dendritic outgrowth. Even when mitochondria in the Purkinje cell bodies are functioning normally, interrupting the transport of mitochondria into their dendrites severely disturbs dendritic growth. Additionally, we find that the growth of atrophic dendrites lacking mitochondria can be rescued by activating ATP-phosphocreatine exchange mediated by creatine kinase (CK). Conversely, inhibiting cytosolic CKs decreases dendritic ATP levels and also disrupts dendrite development. Mechanistically, this energy depletion appears to perturb normal actin dynamics and enhance the aggregation of cofilin within growing dendrites, reminiscent of what occurs in neurons overexpressing the dephosphorylated form of cofilin. These results suggest that local ATP synthesis by dendritic mitochondria and ATP-phosphocreatine exchange act synergistically to sustain the cytoskeletal dynamics necessary for dendritic development.

GPCR-mediated PLCβγ/PKCβ/PKD signaling pathway regulates the cofilin phosphatase slingshot 2 in neutrophil chemotaxis

Chemotaxis requires precisely coordinated polymerization and depolymerization of the actin cytoskeleton at leading fronts of migrating cells. However, GPCR activation-controlled F-actin depolymerization remains largely elusive. Here, we reveal a novel signaling pathway, including Gαi, PLC, PKCβ, protein kinase D (PKD), and SSH2, in control of cofilin phosphorylation and actin cytoskeletal reorganization, which is essential for neutrophil chemotaxis. We show that PKD is essential for neutrophil chemotaxis and that GPCR-mediated PKD activation depends on PLC/PKC signaling. More importantly, we discover that GPCR activation recruits/activates PLCγ2 in a PI3K-dependent manner. We further verify that PKCβ specifically interacts with PKD1 and is required for chemotaxis. Finally, we identify slingshot 2 (SSH2), a phosphatase of cofilin (actin depolymerization factor), as a target of PKD1 that regulates cofilin phosphorylation and remodeling of the actin cytoskeleton during neutrophil chemotaxis.

EZH2 regulates cofilin activity and colon cancer cell migration by targeting ITGA2 gene

Reorganization of cytoskeleton via actin remodeling is a basic step of cell locomotion. Although cell migration of normal and cancer cells can be stimulated by a variety of intra- and extra-cellular factors, all paths ultimate on the regulation of cofilin activity. Cofilin is a small actin-binding protein able to bind both forms of actin, globular and filament, and is regulated by phosphorylation at Serine 3. Following phosphorylation at serine 3 cofilin is inactive, therefore cannot bind actin molecules and cytoskeleton remodeling is impaired. The histone methyltransferase EZH2 is frequently over expressed in many tumour types including colorectal cancer (CRC). EZH2 over activity, which results in epigenetic gene-silencing, has been associated with many tumour properties including invasion, angiogenesis and metastasis but little is known about the underneath molecular mechanisms. Herein, we report that EZH2 is able to control cofilin activity and consequently cell locomotion of CRC cell lines through a non-conventional novel axis that involves integrin signaling. Indeed, we show how genetic and pharmacological inhibition (DZNep and GSK343) of EZH2 function produces hyper phosphorylation of cofilin and reduces cell migration. We previously demonstrated by chromatin immuno-precipitation that Integrin alpha 2 (ITGα2) expression is regulated by EZH2. In the present study we provide evidence that in EZH2-silenced cells the signaling activity of the de-repressed ITGα2 is able to increase cofilin phosphorylation, which in turn reduces cell migration. This study also proposes novel mechanisms that might provide new anti-metastatic strategies for CRC treatment based on the inhibition of the epigenetic factor EZH2 and/or its target gene.

Poly(ADP-ribose) glycohydrolase silencing down-regulates TCTP and Cofilin-1 associated with metastasis in benzo(a)pyrene carcinogenesis

Benzo(a)pyrene (BaP) is a ubiquitously distributed environmental pollutant. BaP is a known carcinogen and can induce malignant transformation of rodent and human cells. Many evidences suggest that inhibitor of poly(ADP-ribose) glycohydrolase (PARG) is potent anticancer drug candidate. However, the effect of PARG on BaP carcinogenesis remains unclear. We explored this question in a PARG-deficient human bronchial epithelial cell line (shPARG cells) treated with various concentration of BaP for 15 weeks. Soft agar assay was used to examine BaP-induced cell malignancy of human bronchial epithelial cells and shPARG cells. Mechanistic investigations were used by 2D-DIGE and mass spectrometry. Western blot analysis and Double immunofluorescence detection were used to confirm some of the results obtained from DIGE experiments. We found that PARG silencing could dramatically inhibit BaP-induced cell malignancy of human bronchial epithelial cells in soft agar assay. Altered levels of expression induced by BaP were observed within shPARG cells for numerous proteins, including proteins required for cell mobility, stress response, DNA repair and cell proliferation pathways. Among these proteins, TCTP and Cofilin-1 involved in malignancy, were validated by western blot analysis and immunofluorescence assay. PARG inhibition contributed to down-regulation of TCTP and Cofilin-1. This is the first experimental demonstration of a link between PARG silencing and reduced cell migration after BaP exposure. We propose that PARG silencing might down-regulate TCTP and Cofilin-1 associated with metastasis in BaP carcinogenesis.

Imaging tumour heterogeneity of the consequences of a PKCα-substrate interaction in breast cancer patients

Breast cancer heterogeneity demands that prognostic models must be biologically driven and recent clinical evidence indicates that future prognostic signatures need evaluation in the context of early compared with late metastatic risk prediction. In pre-clinical studies, we and others have shown that various protein-protein interactions, pertaining to the actin microfilament-associated proteins, ezrin and cofilin, mediate breast cancer cell migration, a prerequisite for cancer metastasis. Moreover, as a direct substrate for protein kinase Cα, ezrin has been shown to be a determinant of cancer metastasis for a variety of tumour types, besides breast cancer; and has been described as a pivotal regulator of metastasis by linking the plasma membrane to the actin cytoskeleton. In the present article, we demonstrate that our tissue imaging-derived parameters that pertain to or are a consequence of the PKC-ezrin interaction can be used for breast cancer prognostication, with inter-cohort reproducibility. The application of fluorescence lifetime imaging microscopy (FLIM) in formalin-fixed paraffin-embedded patient samples to probe protein proximity within the typically <10 nm range to address the oncological challenge of tumour heterogeneity, is discussed.

The actin cytoskeleton as a sensor and mediator of apoptosis

Apoptosis is an important biological process required for the removal of unwanted or damaged cells. Mounting evidence implicates the actin cytoskeleton as both a sensor and mediator of apoptosis. Studies also suggest that actin binding proteins (ABPs) significantly contribute to apoptosis and that actin dynamics play a key role in regulating apoptosis signaling. Changes in the organization of the actin cytoskeleton has been attributed to the process of malignant transformation and it is hypothesized that remodeling of the actin cytoskeleton may enable tumor cells to evade normal apoptotic signaling. This review aims to illuminate the role of the actin cytoskeleton in apoptosis by systematically analyzing how actin and ABPs regulate different apoptosis pathways and to also highlight the potential for developing novel compounds that target tumor-specific actin filaments.

Ionising radiation immediately impairs synaptic plasticity-associated cytoskeletal signalling pathways in HT22 cells and in mouse brain: an in vitro/in vivo comparison study

Patients suffering from brain malignancies are treated with high-dose ionising radiation. However, this may lead to severe learning and memory impairment. Preventive treatments to minimise these side effects have not been possible due to the lack of knowledge of the involved signalling pathways and molecular targets. Mouse hippocampal neuronal HT22 cells were irradiated with acute gamma doses of 0.5 Gy, 1.0 Gy and 4.0 Gy. Changes in the cellular proteome were investigated by isotope-coded protein label technology and tandem mass spectrometry after 4 and 24 hours. To compare the findings with the in vivo response, male NMRI mice were irradiated on postnatal day 10 with a gamma dose of 1.0 Gy, followed by evaluation of the cellular proteome of hippocampus and cortex 24 hours post-irradiation. Analysis of the in vitro proteome showed that signalling pathways related to synaptic actin-remodelling were significantly affected at 1.0 Gy and 4.0 Gy but not at 0.5 Gy after 4 and 24 hours. We observed radiation-induced reduction of the miR-132 and Rac1 levels; miR-132 is known to regulate Rac1 activity by blocking the GTPase-activating protein p250GAP. In the irradiated hippocampus and cortex we observed alterations in the signalling pathways similar to those in vitro. The decreased expression of miR-132 and Rac1 was associated with an increase in hippocampal cofilin and phospho-cofilin. The Rac1-Cofilin pathway is involved in the modulation of synaptic actin filament formation that is necessary for correct spine and synapse morphology to enable processes of learning and memory. We suggest that acute radiation exposure leads to rapid dendritic spine and synapse morphology alterations via aberrant cytoskeletal signalling and processing and that this is associated with the immediate neurocognitive side effects observed in patients treated with ionising radiation.

Neuronal maturation and laminar formation in the chicken optic tectum are accompanied by the transition of phosphorylated cofilin from cytoplasm to nucleus

Laminar formation in the chicken optic tectum requires processes that coordinate proliferation, migration and differentiation of neurons, in which the dynamics of actin filaments are crucial. Cofilin plays pivotal roles in regulating actin arrangement via its phosphorylation on Ser3. Given poor studies on the profile of phosphorylated cofilin (p-cofilin) in the developing tectum, we investigated its expression pattern. As determined by immunofluorescence histochemistry and western blotting, p-cofilin could be detected in most tectal layers except for the neural epithelium. In addition, we found p-cofilin was expressed both in the cytoplasm and the nucleus. During development, the expression of the cytoplasmic p-cofilin was decreasing and the nuclear p-cofilin was gradually increasing, but the total level of p-cofilin was down regulated. Double-labeling experiments revealed that the nuclear p-cofilin could be labeled in mature neurons but undetected in immature neurons. Furthermore, the number of cells co-stained with nuclear p-cofilin and NeuN was up-regulated during lamination and 60% cells were detected to be mature neurons that can express nuclear p-cofilin just at the first appearance of completed laminae. Our results demonstrate that the maturation of neurons is accompanied by this cytoplasm-to-nucleus transition of p-cofilin, and the nuclear p-cofilin can work effectively as a marker in the laminar formation of the chicken optic tectum.

Congenital defects in neutrophil dynamics

Neutrophil granulocytes are key effector cells of the vertebrate immune system. They represent 50-70% of the leukocytes in the human blood and their loss by disease or drug side effect causes devastating bacterial infections. Their high turnover rate, their fine-tuned killing machinery, and their arsenal of toxic vesicles leave them particularly vulnerable to various genetic deficiencies. The aim of this review is to highlight those congenital immunodeficiencies which impede the dynamics of neutrophils, such as migration, cytoskeletal rearrangements, vesicular trafficking, and secretion.

Modeling the synergy of cofilin and Arp2/3 in lamellipodial protrusive activity

Rapid polymerization of actin filament barbed ends generates protrusive forces at the cell edge, leading to cell migration. Two important regulators of free barbed ends, cofilin and Arp2/3, have been shown to work in synergy (net effect greater than additive). To explore this synergy, we model the dynamics of F-actin at the leading edge, motivated by data from EGF-stimulated mammary carcinoma cells. We study how synergy depends on the localized rates and relative timing of cofilin and Arp2/3 activation at the cell edge. The model incorporates diffusion of cofilin, membrane protrusion, F-actin capping, aging, and severing by cofilin and branch nucleation by Arp2/3 (but not G-actin recycling). In a well-mixed system, cofilin and Arp2/3 can each generate a large pulse of barbed ends on their own, but have little synergy; high synergy occurs only at low activation rates, when few barbed ends are produced. In the full spatially distributed model, both synergy and barbed-end production are significant over a range of activation rates. Furthermore, barbed-end production is greatest when Arp2/3 activation is delayed relative to cofilin. Our model supports a direct role for cofilin-mediated actin polymerization in stimulated cell migration, including chemotaxis and cancer invasion.