Novel proteins interacting with the leucine-rich repeat domain of human flightless-I identified by the yeast two-hybrid system

Copy number variations of LRRFIP1 gene and the relationship with growth traits in four Chinese sheep

CNVs (copy number variations) are the novel and common structural variants that could cover entire genes found in plenty of species. CNV may influence economically important traits or disease susceptibility in livestock species. Based on the whole genome resequencing results, we found that there was a CNV region on the LRRFIP1 gene. Then we used qPCR to detect the copy number type distribution in 553 individuals of four sheep breeds and used them for association analysis. The results showed that: (1) In the CKS, the sheep with gain type had a larger heart girth (p = 0.049). (2) For the HS, the CNV could significantly affect rump breadth (p = 0.037) and circumference of the cannon (p = 0.035). And the sheep with median type showed better performance in rump breadth and circumference of cannon. (3) At the STHS, the CNV was significantly correlated with chest width (p = 0.000) with loss type as the most favorable CNV type. Meanwhile, the best was the loss type, and the lowest was the median. (4) This CNV had no significant effect on the LTHS. So, the CNV of LRRFIP1 was related to the growth traits of these three sheep breeds and it may be used as a molecular marker for sheep.

ZAKα/P38 kinase signaling pathway regulates hematopoiesis by activating the NLRP1 inflammasome

Chronic inflammatory diseases are associated with hematopoietic lineage bias, including neutrophilia and anemia. We have recently identified that the canonical inflammasome mediates the cleavage of the master erythroid transcription factor GATA1 in hematopoietic stem and progenitor cells (HSPCs). We report here that genetic inhibition of Nlrp1 resulted in reduced number of neutrophils and increased erythrocyte counts in zebrafish larvae. We also found that the NLRP1 inflammasome in human cells was inhibited by LRRFIP1 and FLII, independently of DPP9, and both inhibitors regulated hematopoiesis. Mechanistically, erythroid differentiation resulted in ribosomal stress-induced activation of the ZAKα/P38 kinase axis which, in turn, phosphorylated and promoted the assembly of NLRP1 in both zebrafish and human. Finally, inhibition of Zaka with the FDA/EMA-approved drug Nilotinib alleviated neutrophilia in a zebrafish model of neutrophilic inflammation and promoted erythroid differentiation and GATA1 accumulation in K562 cells. In conclusion, our results reveal that the NLRP1 inflammasome regulates hematopoiesis and pave the way to develop novel therapeutic strategies for the treatment of hematopoietic alterations associated with chronic inflammatory and rare diseases.

ESRP1-regulated isoform switching of LRRFIP2 determines metastasis of gastric cancer

Although accumulating evidence indicates that alternative splicing is aberrantly altered in many cancers, the functional mechanism remains to be elucidated. Here, we show that epithelial and mesenchymal isoform switches of leucine-rich repeat Fli-I-interacting protein 2 (LRRFIP2) regulated by epithelial splicing regulatory protein 1 (ESRP1) correlate with metastatic potential of gastric cancer cells. We found that expression of the splicing variants of LRRFIP2 was closely correlated with that of ESRP1. Surprisingly, ectopic expression of the mesenchymal isoform of LRRFIP2 (variant 3) dramatically increased liver metastasis of gastric cancer cells, whereas deletion of exon 7 of LRRFIP2 by the CRISPR/Cas9 system caused an isoform switch, leading to marked suppression of liver metastasis. Mechanistically, the epithelial LRRFIP2 isoform (variant 2) inhibited the oncogenic function of coactivator-associated arginine methyltransferase 1 (CARM1) through interaction. Taken together, our data reveals a mechanism of LRRFIP2 isoform switches in gastric cancer with important implication for cancer metastasis.

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

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

Comparative Proteomics Unveils LRRFIP1 as a New Player in the DAPK1 Interactome of Neurons Exposed to Oxygen and Glucose Deprivation

Death-associated protein kinase 1 (DAPK1) is a pleiotropic hub of a number of networked distributed intracellular processes. Among them, DAPK1 is known to interact with the excitotoxicity driver NMDA receptor (NMDAR), and in sudden pathophysiological conditions of the brain, e.g., stroke, several lines of evidence link DAPK1 with the transduction of glutamate-induced events that determine neuronal fate. In turn, DAPK1 expression and activity are known to be affected by the redox status of the cell. To delineate specific and differential neuronal DAPK1 interactors in stroke-like conditions in vitro, we exposed primary cultures of rat cortical neurons to oxygen/glucose deprivation (OGD), a condition that increases reactive oxygen species (ROS) and lipid peroxides. OGD or control samples were co-immunoprecipitated separately, trypsin-digested, and proteins in the interactome identified by high-resolution LC-MS/MS. Data were processed and curated using bioinformatics tools. OGD increased total DAPK1 protein levels, cleavage into shorter isoforms, and dephosphorylation to render the active DAPK1 form. The DAPK1 interactome comprises some 600 proteins, mostly involving binding, catalytic and structural molecular functions. OGD up-regulated 190 and down-regulated 192 candidate DAPK1-interacting proteins. Some differentially up-regulated interactors related to NMDAR were validated by WB. In addition, a novel differential DAPK1 partner, LRRFIP1, was further confirmed by reverse Co-IP. Furthermore, LRRFIP1 levels were increased by pro-oxidant conditions such as ODG or the ferroptosis inducer erastin. The present study identifies novel partners of DAPK1, such as LRRFIP1, which are suitable as targets for neuroprotection.

The Activities of the Gelsolin Homology Domains of Flightless-I in Actin Dynamics

Flightless-I is a unique member of the gelsolin superfamily alloying six gelsolin homology domains and leucine-rich repeats. Flightless-I is an established regulator of the actin cytoskeleton, however, its biochemical activities in actin dynamics are still largely elusive. To better understand the biological functioning of Flightless-I we studied the actin activities of Drosophila Flightless-I by in vitro bulk fluorescence spectroscopy and single filament fluorescence microscopy, as well as in vivo genetic approaches. Flightless-I was found to interact with actin and affects actin dynamics in a calcium-independent fashion in vitro. Our work identifies the first three gelsolin homology domains (1–3) of Flightless-I as the main actin-binding site; neither the other three gelsolin homology domains (4–6) nor the leucine-rich repeats bind actin. Flightless-I inhibits polymerization by high-affinity (∼nM) filament barbed end capping, moderately facilitates nucleation by low-affinity (∼μM) monomer binding, and does not sever actin filaments. Our work reveals that in the presence of profilin Flightless-I is only able to cap actin filament barbed ends but fails to promote actin assembly. In line with the in vitro data, while gelsolin homology domains 4–6 have no effect on in vivo actin polymerization, overexpression of gelsolin homology domains 1–3 prevents the formation of various types of actin cables in the developing Drosophila egg chambers. We also show that the gelsolin homology domains 4–6 of Flightless-I interact with the C-terminus of Drosophila Disheveled-associated activator of morphogenesis formin and negatively regulates its actin assembly activity.

Proximity Labeling To Map Host-Pathogen Interactions at the Membrane of a Bacterium-Containing Vacuole in Chlamydia trachomatis-Infected Human Cells

Many intracellular bacteria, including the obligate intracellular pathogen Chlamydia trachomatis, grow within a membrane-bound bacterium-containing vacuole (BCV). Secreted cytosolic effectors modulate host activity, but an understanding of the host-pathogen interactions that occur at the BCV membrane is limited by the difficulty in purifying membrane fractions from infected host cells.

Many intracellular bacteria, including the obligate intracellular pathogen Chlamydia trachomatis, grow within a membrane-bound bacterium-containing vacuole (BCV). Secreted cytosolic effectors modulate host activity, but an understanding of the host-pathogen interactions that occur at the BCV membrane is limited by the difficulty in purifying membrane fractions from infected host cells. We used the ascorbate peroxidase (APEX2) proximity labeling system, which labels proximal proteins with biotin in vivo, to study the protein-protein interactions that occur at the chlamydial vacuolar, or inclusion, membrane. An in vivo understanding of the secreted chlamydial inclusion membrane protein (Inc) interactions (e.g., Inc-Inc and Inc-eukaryotic protein) and how these contribute to overall host-chlamydia interactions at this unique membrane is lacking. We hypothesize some Incs organize the inclusion membrane, whereas other Incs bind eukaryotic proteins to promote chlamydia-host interactions. To study this, Incs fused to APEX2 were expressed in C. trachomatis L2. Affinity purification-mass spectrometry (AP-MS) identified biotinylated proteins, which were analyzed for statistical significance using significance analysis of the interactome (SAINT). Broadly supporting both Inc-Inc and Inc-host interactions, our Inc-APEX2 constructs labeled Incs as well as known and previously unreported eukaryotic proteins localizing to the inclusion. We demonstrate, using bacterial two-hybrid and coimmunoprecipitation assays, that endogenous LRRFIP1 (LRRF1) is recruited to the inclusion by the Inc CT226. We further demonstrate interactions between CT226 and the Incs used in our study to reveal a model for inclusion membrane organization. Combined, our data highlight the utility of APEX2 to capture the complex in vivo protein-protein interactions at the chlamydial inclusion.

LRRFIP1 expression triggers platelet agglutination by enhancing αIIbβ3 expression

Platelets primarily participate in hemostasis and antimicrobial host defense. The present study aimed to investigate the effects of leucine-rich repeat flightless-interacting protein-1 (LRRFIP1) on platelet agglutination. The bacterial strain of LRRFIP1 was used to synthesize the recombinant protein and a mouse model of LRRFIP1 gene knockout was established. Platelets were isolated from the mice and divided into the different trial groups according to their treatment with collagen, thrombin receptor SFLLRN, anti-wild-type (w)LRRFIP1monoclonal antibodies and the model of LRRFIP1 gene knockout. The platelets were prepared and platelet agglutination was examined using platelet aggregation apparatus. The active αIIbβ3 integrin was examined by flow cytometry. The results revealed that the combined wLRRFIP1 protein was successfully expressed. wLRRFIP1 treatment significantly triggered platelet agglutination of collagen, thrombin and monoclonal antibody treated platelets. wLRRFIP1 knockout significantly decreased αIIbβ3 levels compared with the wild-type. Platelet agglutination was also significantly inhibited in the LRRFIP1^−/−mouse model compared with the wild-type. LRRFIP1 knockout significantly decreased the αIIbβ3 levels in platelets undergoing convulxin treatment. In conclusion, LRRFIP1 treatment triggered platelet agglutination and LRRFIP1 gene knockout inhibited platelet agglutination. In addition, LRRFIP1 gene knockout significantly decreased the levels of αIIbβ3. This suggests that LRRFIP1 my be applied to patients in a clinical setting to trigger platelet agglutination in inflammatory diseases and atherothrombotic diseases.

Nuclear actin interactome analysis links actin to KAT14 histone acetyl transferase and mRNA splicing

In addition to its essential functions within the cytoskeleton, actin also localizes to the cell nucleus, where it is linked to many important nuclear processes from gene expression to maintenance of genomic integrity. However, the molecular mechanisms by which actin operates in the nucleus remain poorly understood. Here, we have used two complementary mass spectrometry (MS) techniques, AP-MS and BioID, to identify binding partners for nuclear actin. Common high-confidence interactions highlight the role of actin in chromatin-remodeling complexes and identify the histone-modifying complex human Ada-Two-A-containing (hATAC) as a novel actin-containing nuclear complex. Actin binds directly to the hATAC subunit KAT14, and modulates its histone acetyl transferase activity in vitro and in cells. Transient interactions detected through BioID link actin to several steps of transcription as well as to RNA processing. Alterations in nuclear actin levels disturb alternative splicing in minigene assays, likely by affecting the transcription elongation rate. This interactome analysis thus identifies both novel direct binding partners and functional roles for nuclear actin, as well as forms a platform for further mechanistic studies on how actin operates during essential nuclear processes.This article has an associated First Person interview with the first author of the paper.

Multidisciplinary Roles of LRRFIP1/GCF2 in Human Biological Systems and Diseases

Leucine Rich Repeat of Flightless-1 Interacting Protein 1/GC-binding factor 2 (LRRFIP1/GCF2) cDNA was cloned for a transcriptional repressor GCF2, which bound sequence-specifically to a GC-rich element of epidermal growth factor receptor (EGFR) gene and repressed its promotor. LRRFIP1/GCF2 was also cloned as a double stranded RNA (dsRNA)-binding protein to trans-activation responsive region (TAR) RNA of Human Immunodeficiency Virus-1 (HIV-1), termed as TAR RNA interacting protein (TRIP), and as a binding protein to the Leucine Rich Repeat (LRR) of Flightless-1(Fli-1), termed as Flightless-1 LRR associated protein 1 (FLAP1) and LRR domain of Flightless-1 interacting Protein 1 (LRRFIP1). Subsequent functional studies have revealed that LRRFIP1/GCF2 played multiple roles in the regulation of diverse biological systems and processes, such as in immune response to microorganisms and auto-immunity, remodeling of cytoskeletal system, signal transduction pathways, and transcriptional regulations of genes. Dysregulations of LRRFIP1/GCF2 have been implicated in the causes of several experimental and clinico-pathological states and the responses to them, such as autoimmune diseases, excitotoxicity after stroke, thrombosis formation, inflammation and obesity, the wound healing process, and in cancers. LRRFIP1/GCF2 is a bioregulator in multidisciplinary systems of the human body and its dysregulation can cause diverse human diseases.

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

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

The alternatively spliced LRRFIP1 Isoform-1 is a key regulator of the Wnt/β-catenin transcription pathway

The GC-rich Binding Factor 2/Leucine Rich Repeat in the Flightless 1 Interaction Protein 1 gene (GCF2/LRRFIP1) is predicted to be alternatively spliced in five different isoforms. Although important peptide sequence differences are expected to result from this alternative splicing, to date, only the gene transcription regulator properties of LRRFIP1-Iso5 were unveiled. Based on molecular, cellular and biochemical data, we show here that the five isoforms define two molecular entities with different expression profiles in human tissues, subcellular localizations, oligomerization properties and transcription enhancer properties of the canonical Wnt pathway. We demonstrated that LRRFIP1-Iso3, -4 and -5, which share over 80% sequence identity, are primarily located in the cell cytoplasm and form homo and hetero-multimers between each other. In contrast, LRRFIP1-Iso1 and -2 are primarily located in the cell nucleus in part thanks to their shared C-terminal domain. Furthermore, we showed that LRRFIP1-Iso1 is preferentially expressed in the myocardium and skeletal muscle. Using the in vitro Topflash reporter assay we revealed that among LRRFIP1 isoforms, LRRFIP1-Iso1 is the strongest enhancer of the β-catenin Wnt canonical transcription pathway thanks to a specific N-terminal domain harboring two critical tryptophan residues (W76, 82). In addition, we showed that the Wnt enhancer properties of LRRFIP1-Iso1 depend on its homo-dimerisation which is governed by its specific coiled coil domain. Together our study identified LRRFIP1-Iso1 as a critical regulator of the Wnt canonical pathway with a potential role in myocyte differentiation and myogenesis.

Flightless I interacts with NMMIIA to promote cell extension formation, which enables collagen remodeling

The role of the actin-capping protein flightless I in collagen remodeling by mouse fibroblasts is examined. Flightless and nonmuscle myosin IIA cooperate to enable collagen phagocytosis.

We examined the role of the actin-capping protein flightless I (FliI) in collagen remodeling by mouse fibroblasts. FliI-overexpressing cells exhibited reduced spreading on collagen but formed elongated protrusions that stained for myosin10 and fascin and penetrated pores of collagen-coated membranes. Inhibition of Cdc42 blocked formation of cell protrusions. In FliI-knockdown cells, transfection with constitutively active Cdc42 did not enable protrusion formation. FliI-overexpressing cells displayed increased uptake and degradation of exogenous collagen and strongly compacted collagen fibrils, which was blocked by blebbistatin. Mass spectrometry analysis of FliI immunoprecipitates showed that FliI associated with nonmuscle myosin IIA (NMMIIA), which was confirmed by immunoprecipitation. GFP-FliI colocalized with NMMIIA at cell protrusions. Purified FliI containing gelsolin-like domains (GLDs) 1–6 capped actin filaments efficiently, whereas FliI GLD 2–6 did not. Binding assays showed strong interaction of purified FliI protein (GLD 1–6) with the rod domain of NMMIIA (k_D = 0.146 μM), whereas FliI GLD 2–6 showed lower binding affinity (k_D = 0.8584 μM). Cells expressing FliI GLD 2–6 exhibited fewer cell extensions, did not colocalize with NMMIIA, and showed reduced collagen uptake compared with cells expressing FliI GLD 1–6. We conclude that FliI interacts with NMMIIA to promote cell extension formation, which enables collagen remodeling in fibroblasts.

Circulating tumor cells exhibit a biologically aggressive cancer phenotype accompanied by selective resistance to chemotherapy

With prostate cancer (PCa), circulating tumor cells (CTCs) and disseminated tumor cells (DTCs) portend a poor clinical prognosis. Their unknown biology precludes rational therapeutic design. We demonstrate that CTC and DTC cell lines, established from mice bearing human PCa orthotopic implants, exhibit increased cellular invasion in vitro, increased metastasis in mice, and express increased epithelial to mesenchymal transition biomarkers. Further, they are selectively resistant to growth inhibition by mitoxantrone-like agents. These findings demonstrate that CTC formation is accompanied by phenotypic progression without obligate reversion. Their increased metastatic potential, selective therapeutic resistance, and differential expression of potential therapeutic targets provide a rational basis to test further interventions.

LRRFIP2 negatively regulates NLRP3 inflammasome activation in macrophages by promoting Flightless-I-mediated caspase-1 inhibition

The NLRP3 inflammasome is the most characterized inflammasome activated by cellular infection or stress, which is responsible for the maturation of proinflammatory cytokines IL-1β and IL-18. The precise molecular mechanism for negative regulation of NLRP3 inflammasome activation needs to be further defined. Here we identify leucine-rich repeat Fli-I-interacting protein 2 (LRRFIP2) as an NLRP3-associated protein and an inhibitor for NLRP3 inflammasome activation. LRRFIP2 binds to NLRP3 via its N terminus upon NLRP3 inflammasome activation, and also interacts with Flightless-I, a pseudosubstrate of caspase-1, via its Coil motif. Knockdown of Flightless-I significantly promotes NLRP3 inflammasome activation. LRRFIP2 enhances the interaction between Flightless-I and caspase-1, facilitating the inhibitory effect of Flightless-I on caspase-1 activation. Furthermore, silencing of Flightless-I abrogates the inhibitory effect of LRRFIP2 on NLRP3 inflammasome. These data demonstrate that LRRFIP2 inhibits NLRP3 inflammasome activation by recruiting the caspase-1 inhibitor Flightless-I, thus outlining a new mechanism for negative regulation of NLRP3 inflammasome.

Inflammasomes promote the maturation of inflammatory cytokines in response to signals associated with damage and infection, but it remains unclear how these signals are attenuated. Here, the authors show that the NLRP3 inflammasome is inhibited by LRRFIP2 through recruitment of the protein Flightless I.

Characterization of Gcf2/Lrrfip1 in experimental cerebral ischemia and its role as a modulator of Akt, mTOR and β-catenin signaling pathways

Leucine-rich repeat in Flightless-1 interaction protein 1 (Lrrfip1) is an up-regulated protein after cerebral ischemia whose precise role in the brain both in healthy and ischemic conditions is unclear. Different Lrrfip1 isoforms with distinct roles have been reported in human and mouse species. The present study aimed to analyze the Lrrfip1 transcriptional variants expressed in rat cortex, to characterize their expression patterns and subcellular location after ischemia, and to define their putative role in the brain. Five transcripts were identified and three of them (Lrrfip1, CRA_g and CRA_a' (Fli-I leucine-rich repeat associated protein 1 - Flap-1)) were analyzed by quantitative real-time polymerase chain reaction (qPCR). All the transcripts were up-regulated and showed differential expression patterns after in vivo and in vitro ischemia models. The main isoform, Lrrfip1, was found to be up-regulated from the acute to the late phases of ischemia in the cytoplasm of neurons and astrocytes of the peri-infarct area. This study demonstrates that Lrrfip1 activates β-catenin, Akt, and mammalian target of rapamycin (mTOR) proteins in astrocytes and positively regulates the expression of the excitatory amino acid transporter subtype 2 (GLT-1). Our findings point to Lrrfip1 as a key brain protein that regulates pro-survival pathways and proteins and encourages further studies to elucidate its role in cerebral ischemia as a potential target to prevent brain damage and promote functional recovery after stroke.

Diet-induced over-expression of flightless-I protein and its relation to flightlessness in Mediterranean fruit fly, Ceratitis capitata

The Mediterranean fruit fly (medfly), Ceratitis capitata is among the most economically important pests worldwide. Understanding nutritional requirement helps rearing healthy medfly for biocontrol of its population in fields. Flight ability is a high priority criterion. Two groups of medfly larvae were reared with two identical component diets except one with fatty acids (diet A) and another without it (diet B). Adults from larvae reared on diet B demonstrated 20±8% of normal flight ability, whereas those from larvae reared on diet A displayed full flight ability of 97±1%. Proteomes were profiled to compare two groups of medfly pupae using shotgun proteomics to study dietary effects on flight ability. When proteins detected in pupae A were compared with those in pupae B, 233 and 239 proteins were, respectively, under- and over-expressed in pupae B, while 167 proteins were overlapped in both pupae A and B. Differential protein profiles indicate that nutritional deficiency induced over-expression of flightless-I protein (fli-I) in medfly. All proteins were subjected to Ingenuity Pathway Analysis (IPA) to create 13 biological networks and 17 pathways of interacting protein clusters in human ortholog. Fli-I, leucine-rich repeat (LRR)-containing G protein-coupled receptor 2, LRR protein soc-2 and protein wings apart-like were over-expressed in pupae B. Inositol-1,4,5-trisphosphate receptor, protocadherin-like wing polarity protein stan and several Wnt pathway proteins were under-expressed in pupae B. These results suggest down-regulation of the Wnt/wingless signaling pathway, which consequently may result in flightlessness in pupae B. The fli-I gene is known to be located within the Smith-Magenis syndrome (SMS) region on chromosome 17, and thus, we speculate that nutritional deficiency might induce over-expression of fli-I (or fli-I gene) and be associated with human SMS. However, more evidence would be needed to confirm our speculation.

Identification and function of leucine-rich repeat flightless-I-interacting protein 2 (LRRFIP2) in Litopenaeus vannamei

Leucine-rich repeat flightless-I-interacting protein 2 (LRRFIP2) is a myeloid differentiation factor 88-interacting protein with a positive regulatory function in toll-like receptor signaling. In this study, seven LRRFIP2 protein variants (LvLRRFIP2A-G) were identified in Litopenaeus vannamei. All the seven LvLRRFIP2 protein variants encode proteins with a DUF2051 domain. LvLRRFIP2s were upregulated in hemocytes after challenged with lipopolysaccharide, poly I:C, CpG-ODN2006, Vibrio parahaemolyticus, Staphylococcus aureus, and white spot syndrome virus (WSSV). Dual-luciferase reporter assays in Drosophila Schneider 2 cells revealed that LvLRRFIP2 activates the promoters of Drosophila and shrimp AMP genes. The knockdown of LvLRRFIP2 by RNA interference resulted in higher cumulative mortality of L. vannamei upon V. parahaemolyticus but not S. aureus and WSSV infections. The expression of L. vannamei AMP genes were reduced by dsLvLRRFIP2 interference. These results indicate that LvLRRFIP2 has an important function in antibacterials via the regulation of AMP gene expression.

The influence of Flightless I on Toll-like-receptor-mediated inflammation in a murine model of diabetic wound healing

Impaired wound healing and ulceration represent a serious complication of both type 1 and type 2 diabetes. Cytoskeletal protein Flightless I (Flii) is an important inhibitor of wound repair, and reduced Flii gene expression in fibroblasts increased migration, proliferation, and adhesion. As such it has the ability to influence all phases of wound healing including inflammation, remodelling and angiogenesis. Flii has the potential to modulate inflammation through its interaction with MyD88 which it an adaptor protein for TLR4. To assess the effect of Flii on the inflammatory response of diabetic wounds, we used a murine model of streptozocin-induced diabetes and Flii genetic mice. Increased levels of Flii were detected in Flii transgenic murine wounds resulting in impaired healing which was exacerbated when diabetes was induced. When Flii levels were reduced in diabetic wounds of Flii-deficient mice, healing was improved and decreased levels of TLR4 were observed. In contrast, increasing the level of Flii in diabetic mouse wounds led to increased TLR4 and NF- κ B production. Treatment of murine diabetic wounds with neutralising antibodies to Flii led to an improvement in healing with decreased expression of TLR4. Decreasing the level of Flii in diabetic wounds may therefore reduce the inflammatory response and improve healing.

Cytoskeletal regulation of dermal regeneration

Wound healing results in the repair of injured tissues however fibrosis and scar formation are, more often than not the unfortunate consequence of this process. The ability of lower order vertebrates and invertebrates to regenerate limbs and tissues has been all but lost in mammals; however, there are some instances where glimpses of mammalian regenerative capacity do exist. Here we describe the unlocked potential that exists in mammals that may help us understand the process of regeneration post-injury and highlight the potential role of the actin cytoskeleton in this process. The precise function and regulation of the cytoskeleton is critical to the success of the healing process and its manipulation may therefore facilitate regenerative healing. The gelsolin family of actin remodelling proteins in particular has been shown to have important functions in wound healing and family member Flightless I (Flii) is involved in both regeneration and repair. Understanding the interactions between different cytoskeletal proteins and their dynamic control of processes including cellular adhesion, contraction and motility may assist the development of therapeutics that will stimulate regeneration rather than repair.

Topically applied flightless I neutralizing antibodies improve healing of blistered skin in a murine model of epidermolysis bullosa acquisita

Epidermolysis bullosa (EB) is a chronic inheritable disease that leads to severe blistering and fibrosis. Previous studies have shown that the actin cytoskeletal protein flightless I (Flii) impairs wound healing associated with EB. Using a mouse model of EB acquisita (EBA), the effect of "mopping up" Flii using Flii-neutralizing antibodies (FnAbs) before, during, and after blister formation was determined. FnAbs, incorporated into a cream vehicle and applied topically to the skin, penetrated into the basal epidermis and upper papillary dermis but were not detected in serum or other organs and did not alter neutrophil or macrophage infiltration into the blistered skin. Histological assessment of blister severity showed that treatment of early-stage blisters with FnAb cream reduced their severity and improved their rate of healing. Treatment of established blisters with FnAb cream also improved healing and restored the skin's tensile strength toward that of normal skin. Repeated application of FnAbs to EBA skin before the onset of blistering reduced the severity of skin blistering. Independent of when the FnAbs were applied, skin barrier function and wound healing were improved and skin fragility was reduced, suggesting that FnAbs could potentially improve healing of patients with EB.

Crystal structure of the dimeric coiled-coil domain of the cytosolic nucleic acid sensor LRRFIP1

LRRFIP1 binds cytoplasmic double-stranded DNA and RNA and interacts with FLI, the mammalian homolog of Drosophila flightless I, through a highly conserved 87-amino acid domain. Upon binding nucleic acid ligands, LRRFIP1 recruits and activates β-catenin, leading to the IRF3-dependent production of type I interferon. However, the molecular mechanism of LRRFIP1 signaling is not well understood. Here we show that the FLI-interacting domain of LRRFIP1 forms a classic parallel, homodimeric coiled coil with 10 heptad repeats and 22 helical turns. The coiled coil domain is also a dimer in solution. However, a longer LRRFIP1 construct spanning the coiled coil and DNA binding domains assembles into higher order oligomers in solution. The structure of LRRFIP1-CC constitutes a valuable tool for probing the mechanism of LRRFIP1 signaling and for structural studies of larger LRRFIP1 constructs.

Flii neutralizing antibodies improve wound healing in porcine preclinical studies

Wound healing is an important area of widely unmet medical need, with millions of procedures carried out worldwide which could potentially benefit from a product to improve the wound repair process. Our studies investigating the actin-remodeling protein Flightless I (Flii) show it to be an important regulator of wound healing. Flii-deficient mice have enhanced wound healing in comparison to Flii overexpressing mice which have impaired wound healing. For the first time, we show that a Flightless I neutralizing monoclonal antibody (FnAb) therapy is effective in a large animal model of wound repair. Porcine 5 cm incisional and 6.25 cm(2) excisional wounds were treated with FnAb at the time of wounding and for two subsequent days. The wounds were dressed in Tegaderm dressings and left to heal by secondary intention for 7 and 35 days, respectively. At the relevant end points, the wounds were excised and processed for histological analysis. Parameters of wound area, collagen deposition, and scar appearance were analyzed. The results show that treatment with FnAb accelerates reepithelialization and improves the macroscopic appearance of early scars. FnAbs have the potential to enhance wound repair and reduce scar formation.

Decreased expression of Flightless I, a gelsolin family member and developmental regulator, in early-gestation fetal wounds improves healing

Up until late in the third trimester of gestation and through to adulthood, the healing response acts more to regenerate than to repair a wound. The mechanisms underlying this "scar-free" healing remain unknown although the actin cytoskeleton has a major role. Flightless I (Flii), an actin-remodelling protein and essential developmental regulator, negatively affects wound repair but its effect on scar-free fetal healing is unknown. Using fetal skin explants from E17 (regenerate) and E19 (repair) rats, the function of Flii in fetal wound repair was determined. Expression of Flii increased between E17 and E19 days of gestation and wounding transiently increased Flii expression in E17 but not E19 wounds. However, both confocal and immunofluorescent analysis showed E17 keratinocytes immediately adjacent to the wounds downregulated Flii. As a nuclear coactivator and inhibitor of proliferation and migration, the absence of Flii in cells at the edge of the wound could be instrumental in allowing these cells to proliferate and migrate into the wound deficit. In contrast, Flii was strongly expressed within the cytoplasm and nucleus of keratinocytes within epidermal cells at the leading edge of E19 wounded fetal skin explants. This increase in Flii expression in E19 wounds could affect the way these cells migrate into the wound space and contribute to impaired wound healing. Neutralising Flii protein improved healing of early- but not late-gestation wounds. Flii did not colocalise with actin cables formed around E17 wounds suggesting an independent mechanism of action distinct from its actin-binding function in scar-free wound repair.

GC-binding factor 2 interacts with dishevelled and regulates Wnt signaling pathways in human carcinoma cell lines

GC-binding factor 2 (GCF2), a transcriptional repressor that decreases the activity of several genes is capable of binding directly to the GC-rich sequence of the EGFR promoter and repressing the transcriptional activity of EGFR. In addition to its function as a transcriptional repressor, GCF2 can directly interact with other proteins such as flightless-1 (Fli-1). Many previous findings pertaining to the function of Fli-1 have suggested a role for fli-1 in providing a direct link between molecules involved in signal transduction pathways and the actin cytoskeleton. We hypothesized that GCF2, together with Fli-1, plays a role in regulating cytoskeleton function, cell migration, and/or morphology. In our study, we observed that GCF2 is crucial for the activation of RhoA, a small GTPase that plays a key role in the regulation of the actin cytoskeleton. RhoA was markedly inactivated as a result of the decreased expression of GCF2. Co-immunoprecipitations were subsequently performed to further investigate the mechanism for the repressive function. We identified dishevelled (Dvl), which is the key mediator for the Wnt pathway, as a binding partner with GCF2. These results strongly suggest that GCF2 plays a role in the Wnt-noncanonical planar cell polarity (PCP) signaling pathway. Consequently, GCF2 may regulate the cytoskeleton or migration via Dvls and RhoA.

Characterization of LRRFIP1

LRRFIP1 has been identified as a regulator of toll-like receptor (TLR) pathway signaling; however, little is known about its own regulation and function. This study was undertaken to characterize the biochemical properties and its regulation. Over-expression of full length LRRFIP1 led to enhanced responses to lipopolysaccharide (LPS). We examined its expression in monocytic cell lines because they express a broad range of TLRs. We found that its level of expression was not altered by LPS or phorbol myristate acetate (PMA) but that it was up-regulated by nicotine, influenza infection, and serum starvation. Phosphorylation was examined because of the bioinformatically predicted serine phosphorylation sites. Serine phosphorylation was detected and was altered by both poly I:C and nicotine. Finally, we examined the regulation of intracellular localization in response to dsRNA and found that LRRFIP1 colocalized with labeled dsRNA in monocyte lysosomal structures but not with lysosomes lacking dsRNA. These data suggest that LRRFIP1 is phosphorylated in response to immunologic stimuli and it is directed to lysosomal structures.

Transcription profiling in human platelets reveals LRRFIP1 as a novel protein regulating platelet function

Within the healthy population, there is substantial, heritable, and interindividual variability in the platelet response. We explored whether a proportion of this variability could be accounted for by interindividual variation in gene expression. Through a correlative analysis of genome-wide platelet RNA expression data from 37 subjects representing the normal range of platelet responsiveness within a cohort of 500 subjects, we identified 63 genes in which transcript levels correlated with variation in the platelet response to adenosine diphosphate and/or the collagen-mimetic peptide, cross-linked collagen-related peptide. Many of these encode proteins with no reported function in platelets. An association study of 6 of the 63 genes in 4235 cases and 6379 controls showed a putative association with myocardial infarction for COMMD7 (COMM domain-containing protein 7) and a major deviation from the null hypo thesis for LRRFIP1 [leucine-rich repeat (in FLII) interacting protein 1]. Morpholino-based silencing in Danio rerio identified a modest role for commd7 and a significant effect for lrrfip1 as positive regulators of thrombus formation. Proteomic analysis of human platelet LRRFIP1-interacting proteins indicated that LRRFIP1 functions as a component of the platelet cytoskeleton, where it interacts with the actin-remodeling proteins Flightless-1 and Drebrin. Taken together, these data reveal novel proteins regulating the platelet response.

Modulation of TLR signaling by multiple MyD88-interacting partners including leucine-rich repeat Fli-I-interacting proteins

Emerging evidences suggest TLR-mediated signaling is tightly regulated by a specific chain of intracellular protein-protein interactions, some of which are yet to be identified. Previously we utilized a dual-tagging quantitative proteomics approach to uncover MyD88 interactions in LPS-stimulated cells and described the function of Fliih, a leucine-rich repeat (LRR) protein that negatively regulates NF-kappaB activity. Here we characterize two distinct LRR-binding MyD88 interactors, LRRFIP2 and Flap-1, and found that both are positive regulators of NF-kappaB activity. Upon LPS stimulation, LRRFIP2 was also found to positively regulate cytokine production in macrophages, suggesting a functional role in TLR4-mediated inflammatory response. Furthermore, we observed that immediately following LPS stimulation both LRRFIP2 and Flap-1 compete with Fliih for interacting with MyD88 to activate the signaling. By using a novel multiplex quantitative proteomic approach, we found that at endogenous levels these positive and negative regulators interact with MyD88 in a timely and orderly manner to differentially mediate the NF-kappaB activity through the course of signaling from initiation to prolongation, and to repression. Based on these data, we describe a mechanistic model in which selective modulation of TLR signaling is achieved by temporal and dynamic interactions of MyD88 with its regulators.

Flightless I regulates hemidesmosome formation and integrin-mediated cellular adhesion and migration during wound repair

Flightless I (Flii), a highly conserved member of the gelsolin family of actin-remodelling proteins associates with actin structures and is involved in cellular motility and adhesion. Our previous studies have shown that Flii is an important negative regulator of wound repair. Here, we show that Flii affects hemidesmosome formation and integrin-mediated keratinocyte adhesion and migration. Impaired hemidesmosome formation and sparse arrangements of keratin cytoskeleton tonofilaments and actin cytoskeleton anchoring fibrils were observed in Flii(Tg/+) and Flii(Tg/Tg) mice with their skin being significantly more fragile than Flii(+/-) and WT mice. Flii(+/-) primary keratinocytes showed increased adhesion on laminin and collagen I than WT and Flii(Tg/Tg) primary keratinocytes. Decreased expression of CD151 and laminin-binding integrins alpha3, beta1, alpha6 and beta4 were observed in Flii overexpressing wounds, which could contribute to the impaired wound re-epithelialization observed in these mice. Flii interacts with proteins directly linked to the cytoplasmic domain of integrin receptors suggesting that it may be a mechanical link between ligand-bound integrin receptors and the actin cytoskeleton driving adhesion-signaling pathways. Therefore Flii may regulate wound repair through its effect on hemidesmosome formation and integrin-mediated cellular adhesion and migration.

[Screening and identification of differentially expressed genes in Beijing fatty and broiler breast muscles]

mRNA differential display reverse-transcripton PCR(DDRT-PCR) was applied to identify differentially expressed genes in Arbor Acres broiler(AA) and Beijing fatty chicken breast muscles in order to find the mechanism which induces the differential gene expression at the molecular level. A total of 7 ESTs were found using reverse Northern dot blot, and all of them were compared with the nucleotide sequences in GenBank database using BLAST. S1 was highly similar to HMGN3; S3 was highly similar to ChEST294a8 with unknown functions; S4 and S5 were highly similar to PGM; S6 and S2 had highly similar nucleotide sequences with unknown functions in nucleotide databases; S7 had no significant similarity with existing genes or ESTs and was regarded as a new EST. The new EST was submitted to GenBank(Accession number: EU594549). This lays a foundation for further study on the mechanism of differential gene expression in Beijing fatty and AA breast muscles.

Flightless-I regulates proinflammatory caspases by selectively modulating intracellular localization and caspase activity

Caspase-1 and caspase-11 are proinflammatory caspases that regulate cytokine production and leukocyte migration during pathogen infection. In an attempt to identify new intracellular regulators of caspase-11, we found that Flightless-I, a member of the gelsolin superfamily of actin-remodeling proteins, interacts and regulates both caspase-11 and caspase-1. Flightless-I targets caspase-11 to the Triton X-100–insoluble cytoskeleton fraction and the cell leading edge. In addition, Flightless-I inhibits caspase-1 activation and caspase-1–mediated interleukine-1β (IL-1β) maturation. The physiological relevance of these findings is supported by the opposing effects of Flightless-I overexpression and knockdown on caspase-1 activity and IL-1β maturation. Our results suggest that Flightless-I may be a bona fide caspase-1 inhibitor that acts through a mechanism similar to that of cytokine response modifier A, a potent caspase-1 inhibitor from the cowpox virus. Our study provides a new mechanism controlling the localization and activation of proinflammatory caspases.

Flightless I deficiency enhances wound repair by increasing cell migration and proliferation

Wound healing disorders are a therapeutic problem of increasing clinical importance involving substantial morbidity, mortality, and rising health costs. Our studies investigating flightless I (FliI), a highly conserved actin-remodelling protein, now reveal that FliI is an important regulator of wound repair whose manipulation may lead to enhanced wound outcomes. We demonstrate that FliI-deficient + /- mice are characterized by improved wound healing with increased epithelial migration and enhanced wound contraction. In contrast, FliI-overexpressing mice have significantly impaired wound healing with larger less contracted wounds and reduced cellular proliferation. We show that FliI is secreted in response to wounding and that topical application of antibodies raised against the leucine-rich repeat domain of the FliI protein (FliL) significantly improves wound repair. These studies reveal that FliI affects wound repair via mechanisms involving cell migration and proliferation and that FliI might represent an effective novel therapeutic factor to improve conditions in which wound healing is impaired.

Mechanism of depolymerization and severing of actin filaments and its significance in cytoskeletal dynamics

The actin cytoskeleton is one of the major structural components of the cell. It often undergoes rapid reorganization and plays crucial roles in a number of dynamic cellular processes, including cell migration, cytokinesis, membrane trafficking, and morphogenesis. Actin monomers are polymerized into filaments under physiological conditions, but spontaneous depolymerization is too slow to maintain the fast actin filament dynamics observed in vivo. Gelsolin, actin-depolymerizing factor (ADF)/cofilin, and several other actin-severing/depolymerizing proteins can enhance disassembly of actin filaments and promote reorganization of the actin cytoskeleton. This review presents advances as well as a historical overview of studies on the biochemical activities and cellular functions of actin-severing/depolymerizing proteins.

Interplay of Fli-I and FLAP1 for regulation of beta-catenin dependent transcription

β-catenin mediates Wnt/wingless signaling and transcriptional activation by lymphocyte enhancer binding factor 1/T cell factor (LEF1/TCF) proteins with the assistance of multiple coregulators, including positive cofactors like p300/CBP and negative cofactors like HDACs. We previously demonstrated that a developmentally essential protein, Flightless-I (Fli-I), serves as a coactivator for nuclear receptor-mediated transcription. To further understand the action mechanism of Fli-I, we investigated the functional roles of Fli-I and Fli-I leucine rich repeat associated protein 1 (FLAP1) in transcriptional activation by β-catenin and LEF1/TCF. β-catenin-dependent transcription was activated by exogenous FLAP1 but inhibited by Fli-I. Reduction of endogenous FLAP1 levels compromised transcriptional activation by LEF1/TCF, β-catenin and the p160 coactivator GRIP1. FLAP1 interacted directly with β-catenin, GRIP1 and p300 and enhanced their activity. Furthermore, FLAP1 was strongly synergistic with p300 in supporting transcriptional activation by β-catenin and LEF1/TCF, but Fli-I disrupted the synergy of FLAP1 with p300 and β-catenin. Thus the opposing effects of Fli-I and FLAP1 may be a key regulatory mechanism for β-catenin and LEF1/TCF-mediated transcription and thus for Wnt signaling, and some mutations of Fli-I may result in developmental defects, such as the flightless phenotype of Drosophila, by causing dysregulation of the Wnt/β-catenin pathway.

GCF2/LRRFIP1 represses tumor necrosis factor alpha expression

Tumor necrosis factor alpha (TNF-alpha) is an important mediator of inflammation, apoptosis, and the development of secondary lymphoid structures. Multiple polymorphic microsatellites have been identified in and around the gene, and there are also multiple single-base pair biallelic polymorphisms in the introns and promoter. The TNF-alpha -308 promoter polymorphism is a G-to-A transition which has been statistically associated with various autoimmune disorders. Some studies have found that it may directly mediate the increased transcription of TNF-alpha in some circumstances. This study characterizes proteins interacting at the polymorphic promoter site. Affinity purification of binding proteins and confirmatory chromatin immunoprecipitation assays were used to identify the proteins. Electrophoretic mobility shift analyses and surface plasmon resonance were used to define binding characteristics. Proteins interacting at this site include GCF2/LRRFIP1 and Ets-1. GCF2/LRRFIP1 appears to act as a repressor and occupies the -308 site in cells that do not make TNF-alpha. Cells competent to produce TNF-alpha have Ets-1 bound to the -308 promoter site. Active transcription is accompanied by NF-kappaB and c-Jun binding to the proximal promoter. Thus, dynamic changes on the TNF-alpha promoter, particularly at the -308 site, accompany the transition from repressed to active transcription. GCF2/LRRFIP1 is the first TNF-alpha repressor identified.

Identification of the Wnt signaling activator leucine-rich repeat in Flightless interaction protein 2 by a genome-wide functional analysis

The Wnt signaling pathway acts ubiquitously in metazoans to control various aspects of embryonic development. Wnt ligands bind their receptors Frizzled and low-density lipoprotein receptor-related protein 5/6 and function through Disheveled (Dvl), Axin, adenomatous polyposis coli, glycogen synthase kinase 3beta, and casein kinase (CK) 1 to stabilize beta-catenin and induce lymphocyte enhancer-binding factor (LEF)/T cell factor (TCF)-dependent transcriptional activities. To identify previously unrecognized Wnt signaling modulators, a genome-wide functional screen was performed using large-scale arrayed cDNA collections. From this screen, both known components and previously uncharacterized regulators of this pathway were identified, including beta-catenin, Dvl1, Dvl3, Fbxw-1, Cul1, CK1epsilon, CK1delta, and gamma-catenin. In particular, a previously unrecognized activator, LRRFIP2 (leucine-rich repeat in Flightless interaction protein 2), was found that interacts with Dvl to increase the cellular levels of beta-catenin and activate beta-catenin/LEF/TCF-dependent transcriptional activity. The function of LRRFIP2 is blocked when a dominant negative Dvl (Xdd1) is coexpressed. Expression of LRRFIP2 in Xenopus embryos induced double axis formation and Wnt target gene expression; a dominant negative form of LRRFIP2 suppresses ectopic Wnt signaling in Xenopus embryos and partially inhibits endogenous dorsal axis formation. These data suggest that LRRFIP2 plays an important role in transducing Wnt signals.

Evolution of the gelsolin family of actin-binding proteins as novel transcriptional coactivators

The gelsolin gene family encodes a number of higher eukaryotic actin-binding proteins that are thought to function in the cytoplasm by severing, capping, nucleating or bundling actin filaments. Recent evidence, however, suggests that several members of the gelsolin family may have adopted unexpected nuclear functions including a role in regulating transcription. In particular, flightless I, supervillin and gelsolin itself have roles as coactivators for nuclear receptors, despite the fact that their divergence appears to predate the evolutionary appearance of nuclear receptors. Flightless I has been shown to bind both actin and the actin-related BAF53a protein, which are subunits of SWI/SNF-like chromatin remodelling complexes. The primary sequences of some actin-related proteins such as BAF53a exhibit conservation of residues that, in actin itself, are known to interact with gelsolin-related proteins. In summary, there is a growing body of evidence supporting a biological role in the nucleus for actin, Arps and actin-binding proteins and, in particular, the gelsolin family of actin-binding proteins.

Fliih, a gelsolin-related cytoskeletal regulator essential for early mammalian embryonic development

The Drosophila melanogaster flightless I gene is required for normal cellularization of the syncytial blastoderm. Highly conserved homologues of flightless I are present in Caenorhabditis elegans, mouse, and human. We have disrupted the mouse homologue Fliih by homologous recombination in embryonic stem cells. Heterozygous Fliih mutant mice develop normally, although the level of Fliih protein is reduced. Cultured homozygous Fliih mutant blastocysts hatch, attach, and form an outgrowing trophoblast cell layer, but egg cylinder formation fails and the embryos degenerate. Similarly, Fliih mutant embryos initiate implantation in vivo but then rapidly degenerate. We have constructed a transgenic mouse carrying the complete human FLII gene and shown that the FLII transgene is capable of rescuing the embryonic lethality of the homozygous targeted Fliih mutation. These results confirm the specific inactivation of the Fliih gene and establish that the human FLII gene and its gene product are functional in the mouse. The Fliih mouse mutant phenotype is much more severe than in the case of the related gelsolin family members gelsolin, villin, and CapG, where the homozygous mutant mice are viable and fertile but display alterations in cytoskeletal actin regulation.

Fliih, the murine homologue of the Drosophila melanogaster flightless I gene: nucleotide sequence, chromosomal mapping and overlap with Llglh

The Drosophila melanogaster flightless I gene is involved in cellularization processes in early embryogenesis and in the structural organization of indirect flight muscle. The encoded protein contains a gelsolin-like actin binding domain and an N-terminal leucine-rich repeat protein-protein interaction domain. We have cloned Fliih, the corresponding chromosomal gene from the mouse, and determined its nucleotide sequence (15.6 kb). The predicted Fliih protein of 1271 amino acids is 95% identical to the human FLII protein. Like the human gene, Fliih has 29 introns, compared with 13 in C. elegans and 3 in D. melanogaster. Fluorescence in situ hybridization was used to map Fliih to Chromosome 11B. Fliih lies adjacent to Llglh, the mouse homologue of the D. melanogaster tumor suppressor gene lethal(2) giant larvae. The sequence of the genomic DNA in this area, combined with cDNA sequences, establishes that the 3' ends of the Fliih and Llglh transcripts overlap. The overlap region contains polyA signals for both genes and is conserved between human and mouse.

The flightless I protein colocalizes with actin- and microtubule-based structures in motile Swiss 3T3 fibroblasts: evidence for the involvement of PI 3-kinase and Ras-related small GTPases

The flightless I protein contains an actin-binding domain with homology to the gelsolin family and is likely to be involved in actin cytoskeletal rearrangements. It has been suggested that this protein is involved in linking the cytoskeletal network with signal transduction pathways. We have developed antibodies directed toward the leucine rich repeat and gelsolin-like domains of the human and mouse homologues of flightless I that specifically recognize expressed and endogenous forms of the protein. We have also constructed a flightless I-enhanced green fluorescent fusion vector and used this to examine the localization of the expressed protein in Swiss 3T3 fibroblasts. The flightless I protein localizes predominantly to the nucleus and translocates to the cytoplasm following serum stimulation. In cells stimulated to migrate, the flightless I protein colocalizes with beta-tubulin- and actin-based structures. Members of the small GTPase family, also implicated in cytoskeletal control, were found to colocalize with flightless I in migrating Swiss 3T3 fibroblasts. LY294002, a specific inhibitor of PI 3-kinase, inhibits the translocation of flightless I to actin-based structures. Our results suggest that PI 3-kinase and the small GTPases, Ras, RhoA and Cdc42 may be part of a common functional pathway involved in Fliih-mediated cytoskeletal regulation. Functionally, we suggest that flightless I may act to prepare actin filaments or provide factors required for cytoskeletal rearrangements necessary for cell migration and/or adhesion.

Mushroom body defect, a gene involved in the control of neuroblast proliferation in Drosophila, encodes a coiled-coil protein

Neurogenesis relies on the establishment of the proper number and precisely controlled proliferation of neuroblasts, the neuronal precursor cells. A role for the mushroom body defect (mud) gene in both of these aspects of neuroblast behavior, as well as possible roles in other aspects of fruit fly biology, is implied by phenotypes associated with mud mutations. We have localized mud by determining the sequence change in one point mutant, identifying a predicted ORF affected by the mutation, and showing that an appropriate segment of the genome rescues mud mutant phenotypes. An analysis of mud cDNAs and a survey of mud transcripts by Northern blotting indicate that the gene is subject to differential splicing and is expressed primarily during embryogenesis but also, at lower levels, during subsequent developmental stages in a sexually dimorphic manner. The gene is predicted to encode a polypeptide without obvious homologs but with two prominent structural features, a long coiled coil that constitutes the central core of the protein and a carboxyl-terminal transmembrane domain.