PIAS1-mediated sumoylation of focal adhesion kinase activates its autophosphorylation

A comparative analysis of paxillin and Hic-5 proximity interactomes

Focal adhesions serve as structural and signaling hubs, facilitating bidirectional communication at the cell-extracellular matrix interface. Paxillin and the related Hic-5 (TGFβ1i1) are adaptor/scaffold proteins that recruit numerous structural and regulatory proteins to focal adhesions, where they perform both overlapping and discrete functions. In this study, paxillin and Hic-5 were expressed in U2OS osteosarcoma cells as biotin ligase (BioID2) fusion proteins and used as bait proteins for proximity-dependent biotinylation in order to directly compare their respective interactomes. The fusion proteins localized to both focal adhesions and the centrosome, resulting in biotinylation of components of each of these structures. Biotinylated proteins were purified and analyzed by mass spectrometry. The list of proximity interactors for paxillin and Hic-5 comprised numerous shared core focal adhesion proteins that likely contribute to their similar functions in cell adhesion and migration, as well as proteins unique to paxillin and Hic-5 that have been previously localized to focal adhesions, the centrosome, or the nucleus. Western blotting confirmed biotinylation and enrichment of FAK and vinculin, known interactors of Hic-5 and paxillin, as well as several potentially unique proximity interactors of Hic-5 and paxillin, including septin 7 and ponsin, respectively. Further investigation into the functional relationship between the unique interactors and Hic-5 or paxillin may yield novel insights into their distinct roles in cell migration.

FERM domain-containing proteins are active components of the cell nucleus

The FERM domain is a conserved and widespread protein module that appeared in the common ancestor of amoebae, fungi, and animals, and is therefore now found in a wide variety of species. The primary function of the FERM domain is localizing to the plasma membrane through binding lipids and proteins of the membrane; thus, for a long time, FERM domain-containing proteins (FDCPs) were considered exclusively cytoskeletal. Although their role in the cytoplasm has been extensively studied, the recent discovery of the presence and importance of cytoskeletal proteins in the nucleus suggests that FDCPs might also play an important role in nuclear function. In this review, we collected data on their nuclear localization, transport, and possible functions, which are still scattered throughout the literature, with special regard to the role of the FERM domain in these processes. With this, we would like to draw attention to the exciting, new dimension of the role of FDCPs, their nuclear activity, which could be an interesting novel direction for future research.

SUMOylation of Rho-associated protein kinase 2 induces goblet cell metaplasia in allergic airways

Allergic asthma is characterized by goblet cell metaplasia and subsequent mucus hypersecretion that contribute to the morbidity and mortality of this disease. Here, we explore the potential role and underlying mechanism of protein SUMOylation-mediated goblet cell metaplasia. The components of SUMOylaion machinery are specifically expressed in healthy human bronchial epithelia and robustly upregulated in bronchial epithelia of patients or mouse models with allergic asthma. Intratracheal suppression of SUMOylation by 2-D08 robustly attenuates not only allergen-induced airway inflammation, goblet cell metaplasia, and hyperreactivity, but IL-13-induced goblet cell metaplasia. Phosphoproteomics and biochemical analyses reveal SUMOylation on K1007 activates ROCK2, a master regulator of goblet cell metaplasia, by facilitating its binding to and activation by RhoA, and an E3 ligase PIAS1 is responsible for SUMOylation on K1007. As a result, knockdown of PIAS1 in bronchial epithelia inactivates ROCK2 to attenuate IL-13-induced goblet cell metaplasia, and bronchial epithelial knock-in of ROCK2(K1007R) consistently inactivates ROCK2 to alleviate not only allergen-induced airway inflammation, goblet cell metaplasia, and hyperreactivity, but IL-13-induced goblet cell metaplasia. Together, SUMOylation-mediated ROCK2 activation is an integral component of Rho/ROCK signaling in regulating the pathological conditions of asthma and thus SUMOylation is an additional target for the therapeutic intervention of this disease.

Functional Diversity of Neuronal Cell Adhesion and Recognition Molecule L1CAM through Proteolytic Cleavage

The neuronal cell adhesion and recognition molecule L1 does not only 'keep cells together' by way of homophilic and heterophilic interactions, but can also promote cell motility when cleaved into fragments by several proteases. It has largely been thought that such fragments are signs of degradation. Now, it is clear that proteolysis contributes to the pronounced functional diversity of L1, which we have reviewed in this work. L1 fragments generated at the plasma membrane are released into the extracellular space, whereas other membrane-bound fragments are internalised and enter the nucleus, thus conveying extracellular signals to the cell interior. Post-translational modifications on L1 determine the sequence of cleavage by proteases and the subcellular localisation of the generated fragments. Inside the neuronal cells, L1 fragments interact with various binding partners to facilitate morphogenic events, as well as regenerative processes. The stimulation of L1 proteolysis via injection of L1 peptides or proteases active on L1 or L1 mimetics is a promising tool for therapy of injured nervous systems. The collective findings gathered over the years not only shed light on the great functional diversity of L1 and its fragments, but also provide novel mechanistic insights into the adhesion molecule proteolysis that is active in the developing and diseased nervous system.

Cancer-Associated Dysregulation of Sumo Regulators: Proteases and Ligases

SUMOylation is a post-translational modification that has emerged in recent decades as a mechanism involved in controlling diverse physiological processes and that is essential in vertebrates. The SUMO pathway is regulated by several enzymes, proteases and ligases being the main actors involved in the control of sumoylation of specific targets. Dysregulation of the expression, localization and function of these enzymes produces physiological changes that can lead to the appearance of different types of cancer, depending on the enzymes and target proteins involved. Among the most studied proteases and ligases, those of the SENP and PIAS families stand out, respectively. While the proteases involved in this pathway have specific SUMO activity, the ligases may have additional functions unrelated to sumoylation, which makes it more difficult to study their SUMO-associated role in cancer process. In this review we update the knowledge and advances in relation to the impact of dysregulation of SUMO proteases and ligases in cancer initiation and progression.

FAK in Cancer: From Mechanisms to Therapeutic Strategies

Focal adhesion kinase (FAK), a non-receptor tyrosine kinase, is overexpressed and activated in many cancer types. FAK regulates diverse cellular processes, including growth factor signaling, cell cycle progression, cell survival, cell motility, angiogenesis, and the establishment of immunosuppressive tumor microenvironments through kinase-dependent and kinase-independent scaffolding functions in the cytoplasm and nucleus. Mounting evidence has indicated that targeting FAK, either alone or in combination with other agents, may represent a promising therapeutic strategy for various cancers. In this review, we summarize the mechanisms underlying FAK-mediated signaling networks during tumor development. We also summarize the recent progress of FAK-targeted small-molecule compounds for anticancer activity from preclinical and clinical evidence.

Disturbed flow-induced FAK K152 SUMOylation initiates the formation of pro-inflammation positive feedback loop by inducing reactive oxygen species production in endothelial cells

Focal adhesion kinase (FAK) activation plays a crucial role in vascular diseases. In endothelial cells, FAK activation is involved in the activation of pro-inflammatory signaling and the progression of atherosclerosis. Disturbed flow (D-flow) induces endothelial activation and senescence, but the exact role of FAK in D-flow-induced endothelial activation and senescence remains unclear. The objective of this study is to investigate the role of FAK SUMOylation in D-flow-induced endothelial activation and senescence. The results showed that D-flow induced reactive oxygen species (ROS) production via NADPH oxidase activation and activated a redox-sensitive kinase p90RSK, leading to FAK activation by upregulating FAK K152 SUMOylation and the subsequent Vav2 phosphorylation, which in turn formed a positive feedback loop by upregulating ROS production. This feedback loop played a crucial role in regulating endothelial activation and senescence. D-flow-induced endothelial activation and senescence were significantly inhibited by mutating a FAK SUMOylation site lysine152 to arginine. Collectively, we concluded that FAK K152 SUMOylation plays a key role in D-flow-induced endothelial activation and senescence by forming a positive feedback loop through ROS production.

Therapeutic Potential of Targeting the SUMO Pathway in Cancer

SUMOylation is a dynamic and reversible post-translational modification, characterized more than 20 years ago, that regulates protein function at multiple levels. Key oncoproteins and tumor suppressors are SUMO substrates. In addition to alterations in SUMO pathway activity due to conditions typically present in cancer, such as hypoxia, the SUMO machinery components are deregulated at the genomic level in cancer. The delicate balance between SUMOylation and deSUMOylation is regulated by SENP enzymes possessing SUMO-deconjugation activity. Dysregulation of SUMO machinery components can disrupt the balance of SUMOylation, contributing to the tumorigenesis and drug resistance of various cancers in a context-dependent manner. Many molecular mechanisms relevant to the pathogenesis of specific cancers involve SUMO, highlighting the potential relevance of SUMO machinery components as therapeutic targets. Recent advances in the development of inhibitors targeting SUMOylation and deSUMOylation permit evaluation of the therapeutic potential of targeting the SUMO pathway in cancer. Finally, the first drug inhibiting SUMO pathway, TAK-981, is currently also being evaluated in clinical trials in cancer patients. Intriguingly, the inhibition of SUMOylation may also have the potential to activate the anti-tumor immune response. Here, we comprehensively and systematically review the recent developments in understanding the role of SUMOylation in cancer and specifically focus on elaborating the scientific rationale of targeting the SUMO pathway in different cancers.

Novel insights into the impact of the SUMOylation pathway in hematological malignancies (Review)

The small ubiquitin-like modifier (SUMO) system serves an important role in the regulation of protein stability and function. SUMOylation sustains the homeostatic equilibrium of protein function in normal tissues and numerous types of tumor. Accumulating evidence has revealed that SUMO enzymes participate in carcinogenesis via a series of complex cellular or extracellular processes. The present review outlines the physiological characteristics of the SUMOylation pathway and provides examples of SUMOylation participation in different cancer types, including in hematological malignancies (leukemia, lymphoma and myeloma). It has been indicated that the SUMO pathway may influence chromosomal instability, cell cycle progression, apoptosis and chemical drug resistance. The present review also discussed the possible relationship between SUMOylation and carcinogenic mechanisms, and evaluated their potential as biomarkers and therapeutic targets in the diagnosis and treatment of hematological malignancies. Developing and investigating inhibitors of SUMO conjugation in the future may offer promising potential as novel therapeutic strategies.

Wrestling and Wrapping: A Perspective on SUMO Proteins in Schwann Cells

Schwann cell development and peripheral nerve myelination are finely orchestrated multistep processes; some of the underlying mechanisms are well described and others remain unknown. Many posttranslational modifications (PTMs) like phosphorylation and ubiquitination have been reported to play a role during the normal development of the peripheral nervous system (PNS) and in demyelinating neuropathies. However, a relatively novel PTM, SUMOylation, has not been studied in these contexts. SUMOylation involves the covalent attachment of one or more small ubiquitin-like modifier (SUMO) proteins to a substrate, which affects the function, cellular localization, and further PTMs of the conjugated protein. SUMOylation also regulates other proteins indirectly by facilitating non-covalent protein–protein interaction via SUMO interaction motifs (SIM). This pathway has important consequences on diverse cellular processes, and dysregulation of this pathway has been reported in several diseases including neurological and degenerative conditions. In this article, we revise the scarce literature on SUMOylation in Schwann cells and the PNS, we propose putative substrate proteins, and we speculate on potential mechanisms underlying the possible involvement of this PTM in peripheral myelination and neuropathies.

Transcriptome response comparison between vector and non-vector aphids after feeding on virus-infected wheat plants

BACKGROUND

Plant viruses maintain intricate interactions with their vector and non-vector insects and can impact the fitness of insects. However, the details of their molecular and cellular mechanisms have not been studied well. We compared the transcriptome-level responses in vector and non-vector aphids (Schizaphis graminum and Rhopalosiphum padi, respectively) after feeding on wheat plants with viral infections (Barley Yellow Dwarf Virus (BYDV) and Wheat dwarf virus (WDV), respectively). We conducted differentially expressed gene (DEG) annotation analyses and observed DEGs related to immune pathway, growth, development, and reproduction. And we conducted cloning and bioinformatic analyses of the key DEG involved in immune.

RESULTS

For all differentially expressed gene analyses, the numbers of DEGs related to immune, growth, development, reproduction and cuticle were higher in vector aphids than in non-vector aphids. STAT5B (signal transducer and activator of transcription 5B), which is involved in the JAK-STAT pathway, was upregulated in R. padi exposed to WDV. The cloning and bioinformatic results indicated that the RpSTAT5B sequence contains a 2082 bp ORF encoding 693 amino acids. The protein molecular weight is 79.1 kD and pI is 8.13. Analysis indicated that RpSTAT5B is a non-transmembrane protein and a non-secreted protein. Homology and evolutionary analysis indicated that RpSTAT5B was closely related to R. maidis.

CONCLUSIONS

Unigene expression analysis showed that the total number of differentially expressed genes (DEGs) in the vector aphids was higher than that in the non-vector aphids. Functional enrichment analysis showed that the DEGs related to immunity, growth and reproduction in vector aphids were higher than those in non-vector aphids, and the differentially expressed genes related to immune were up-regulated. This study provides a basis for the evaluation of the response mechanisms of vector/non-vector insects to plant viruses.

The implication of the SUMOylation pathway in breast cancer pathogenesis and treatment

Breast cancer is the most commonly diagnosed malignancy in woman worldwide, and is the second most common cause of death in developed countries. The transformation of a normal cell into a malignant derivate requires the acquisition of diverse genomic and proteomic changes, including enzymatic post-translational modifications (PTMs) on key proteins encompassing critical cell signaling events. PTMs occur on proteins after translation, and regulate several aspects of proteins activity, including their localization, activation and turnover. Deregulation of PTMs can potentially lead to tumorigenesis, and several de-regulated PTM pathways contribute to abnormal cell proliferation during breast tumorigenesis. SUMOylation is a PTM that plays a pivotal role in numerous aspects of cell physiology, including cell cycle regulation, protein trafficking and turnover, and DNA damage repair. Consistently with this, the deregulation of the SUMO pathway is observed in different human pathologies, including breast cancer. In this review we will describe the role of SUMOylation in breast tumorigenesis and its implication for breast cancer therapy.

Quantitative SUMO proteomics identifies PIAS1 substrates involved in cell migration and motility

The protein inhibitor of activated STAT1 (PIAS1) is an E3 SUMO ligase that plays important roles in various cellular pathways. Increasing evidence shows that PIAS1 is overexpressed in various human malignancies, including prostate and lung cancers. Here we used quantitative SUMO proteomics to identify potential substrates of PIAS1 in a system-wide manner. We identified 983 SUMO sites on 544 proteins, of which 62 proteins were assigned as putative PIAS1 substrates. In particular, vimentin (VIM), a type III intermediate filament protein involved in cytoskeleton organization and cell motility, was SUMOylated by PIAS1 at Lys-439 and Lys-445 residues. VIM SUMOylation was necessary for its dynamic disassembly and cells expressing a non-SUMOylatable VIM mutant showed a reduced level of migration. Our approach not only enables the identification of E3 SUMO ligase substrates but also yields valuable biological insights into the unsuspected role of PIAS1 and VIM SUMOylation on cell motility.

PIAS1 is an E3 SUMO ligase involved in various cellular processes. Here, the authors use quantitative proteomics to identify potential PIAS1 substrates in human cells and elucidate the biological consequences of PIAS1-mediated SUMOylation of vimentin.

The roles of nuclear focal adhesion kinase (FAK) on Cancer: a focused review

FAK is a tyrosine kinase overexpressed in cancer cells and plays an important role in the progression of tumors to a malignant phenotype. Except for its typical role as a cytoplasmic kinase downstream of integrin and growth factor receptor signaling, related studies have shown new aspects of the roles of FAK in the nucleus. FAK can promote p53 degradation through ubiquitination, leading to cancer cell growth and proliferation. FAK can also regulate GATA4 and IL-33 expression, resulting in reduced inflammatory responses and immune escape. These findings establish a new model of FAK from the cytoplasm to the nucleus. Activated FAK binds to transcription factors and regulates gene expression. Inactive FAK synergizes with different E3 ligases to promote the turnover of transcription factors by enhancing ubiquitination. In the tumor microenvironment, nuclear FAK can regulate the formation of new blood vessels, affecting the tumor blood supply. This article reviews the roles of nuclear FAK in regulating gene expression. In addition, the use of FAK inhibitors to target nuclear FAK functions will also be emphasized.

Talin is a substrate for SUMOylation in migrating cancer cells

Focal adhesions (FAs) play an important role in cancer cell migration and metastasis by linking the actin cytoskeleton to the extracellular matrix, allowing the cell to generate traction. SUMOylation is a post-translational modification of proteins on lysine residues that can affect protein localisation, turnover and protein-protein interactions. In this study, we demonstrate that talin, a key component of FAs, can be post-translationally modified by SUMOylation in MDA-MB-231 breast cancer cells and U2OS osteosarcoma cells. Furthermore we demonstrate that SUMOylation regulates the dynamic activities of FAs including their number, size and turnover rate. Inhibiting SUMOylation significantly reduced the speed of cell migration. The identification of talin as a SUMO target provides insight into the mechanisms regulating focal adhesion formation and turnover and potentially identifies a novel mechanism underlying cell migration.

Targeting Focal Adhesion Kinase Using Inhibitors of Protein-Protein Interactions

Focal adhesion kinase (FAK) is a cytoplasmic non-receptor protein tyrosine kinase that is overexpressed and activated in many human cancers. FAK transmits signals to a wide range of targets through both kinase-dependant and independent mechanism thereby playing essential roles in cell survival, proliferation, migration and invasion. In the past years, small molecules that inhibit FAK kinase function have been developed and show reduced cancer progression and metastasis in several preclinical models. Clinical trials have been conducted and these molecules display limited adverse effect in patients. FAK contain multiple functional domains and thus exhibit both important scaffolding functions. In this review, we describe the major FAK interactions relevant in cancer signalling and discuss how such knowledge provide rational for the development of Protein-Protein Interactions (PPI) inhibitors.

Dynamics of p14ARF and Focal Adhesion Kinase-Mediated Autophagy in Cancer

It has been widely shown that the focal adhesion kinase (FAK) is involved in nearly every aspect of cancer, from invasion to metastasis to epithelial–mesenchymal transition and maintenance of cancer stem cells. FAK has been shown to interact with p14ARF (alternative reading frame)—a well-established tumor suppressor—and functions in the negative regulation of cancer through both p53-dependent and -independent pathways. Interestingly, both FAK and ARF (human and mouse counterpart) proteins, as well as p53, are involved in autophagy—a process of “self-digestion”—whose main function is the recycling of cellular components and quality control of proteins and organelles. In the last years, an unexpected role of p14ARF in the survival of cancer cells has been underlined in different cellular contexts, suggesting a novel pro-oncogenic function of this protein. In this review, the mechanisms whereby ARF and FAK control autophagy are presented, as well as the role of autophagy in cell migration and spreading. Integrated investigation of these cell functions is extremely important to understand the mechanism of the basis of cell transformation and migration and thus cancer development.

Endogenous Control Mechanisms of FAK and PYK2 and Their Relevance to Cancer Development

Focal adhesion kinase (FAK) and its close paralogue, proline-rich tyrosine kinase 2 (PYK2), are key regulators of aggressive spreading and metastasis of cancer cells. While targeted small-molecule inhibitors of FAK and PYK2 have been found to have promising antitumor activity, their clinical long-term efficacy may be undermined by the strong capacity of cancer cells to evade anti-kinase drugs. In healthy cells, the expression and/or function of FAK and PYK2 is tightly controlled via modulation of gene expression, competing alternatively spliced forms, non-coding RNAs, and proteins that directly or indirectly affect kinase activation or protein stability. The molecular factors involved in this control are frequently deregulated in cancer cells. Here, we review the endogenous mechanisms controlling FAK and PYK2, and with particular focus on how these mechanisms could inspire or improve anticancer therapies.

Src SUMOylation Inhibits Tumor Growth Via Decreasing FAK Y925 Phosphorylation

Src, a non-receptor tyrosine kinase protein, plays a critical role in cell proliferation and tumorigenesis. SUMOylation, a reversible ubiquitination-like post-translational modification, is vital for tumor progression. Here, we report that the Src protein can be SUMOylated at lysine 318 both in vitro and in vivo. Hypoxia can induce a decrease of Src SUMOylation along with an increase of Y419 phosphorylation, a phosphorylation event required for Src activation. On the other hand, treatment with hydrogen peroxide can enhance Src SUMOylation. Significantly, ectopic expression of SUMO-defective mutation, Src K318R, promotes tumor growth more potently than that of wild-type Src, as determined by migration assay, soft agar assay, and tumor xenograft experiments. Consistently, Src SUMOylation leads to a decrease of Y925 phosphorylation of focal adhesion kinase (FAK), an established regulatory event of cell migration. Our results suggest that SUMOylation of Src at lysine 318 negatively modulate its oncogenic function by, at least partially, inhibiting Src-FAK complex activity.

SUMOylation regulates nuclear accumulation and signaling activity of the soluble intracellular domain of the ErbB4 receptor tyrosine kinase

Erb-B2 receptor tyrosine kinase 4 (ErbB4) is a kinase that can signal via a proteolytically released intracellular domain (ICD) in addition to classical receptor tyrosine kinase-activated signaling cascades. Previously, we have demonstrated that ErbB4 ICD is posttranslationally modified by the small ubiquitin-like modifier (SUMO) and functionally interacts with the PIAS3 SUMO E3 ligase. However, direct evidence of SUMO modification in ErbB4 signaling has remained elusive. Here, we report that the conserved lysine residue 714 in the ErbB4 ICD undergoes SUMO modification, which was reversed by sentrin-specific proteases (SENPs) 1, 2, and 5. Although ErbB4 kinase activity was not necessary for the SUMOylation, the SUMOylated ErbB4 ICD was tyrosine phosphorylated to a higher extent than unmodified ErbB4 ICD. Mutation of the SUMOylation site compromised neither ErbB4-induced phosphorylation of the canonical signaling pathway effectors Erk1/2, Akt, or STAT5 nor ErbB4 stability. In contrast, SUMOylation was required for nuclear accumulation of the ErbB4 ICD. We also found that Lys-714 was located within a leucine-rich stretch, which resembles a nuclear export signal, and could be inactivated by site-directed mutagenesis. Furthermore, SUMOylation modulated the interaction of ErbB4 with chromosomal region maintenance 1 (CRM1), the major nuclear export receptor for proteins. Finally, the SUMO acceptor lysine was functionally required for ErbB4 ICD-mediated inhibition of mammary epithelial cell differentiation in a three-dimensional cell culture model. Our findings indicate that a SUMOylation-mediated mechanism regulates nuclear localization and function of the ICD of ErbB4 receptor tyrosine kinase.

p14ARF interacts with the focal adhesion kinase and protects cells from anoikis

The ARF protein functions as an important sensor of hyper-proliferative stimuli restricting cell proliferation through both p53-dependent and -independent pathways. Although to date the majority of studies on ARF have focused on its anti-proliferative role, few studies have addressed whether ARF may also have pro-survival functions. Here we show for the first time that during the process of adhesion and spreading ARF re-localizes to sites of active actin polymerization and to focal adhesion points where it interacts with the phosphorylated focal adhesion kinase. In line with its recruitment to focal adhesions, we observe that hampering ARF function in cancer cells leads to gross defects in cytoskeleton organization resulting in apoptosis through a mechanism dependent on the Death-Associated Protein Kinase. Our data uncover a novel function for p14ARF in protecting cells from anoikis that may reflect its role in anchorage independence, a hallmark of malignant tumor cells.

A single structurally conserved SUMOylation site in CRMP2 controls NaV1.7 function

The neuronal collapsin response mediator protein 2 (CRMP2) undergoes several posttranslational modifications that codify its functions. Most recently, CRMP2 SUMOylation (addition of small ubiquitin like modifier (SUMO)) was identified as a key regulatory step within a modification program that codes for CRMP2 interaction with, and trafficking of, voltage-gated sodium channel NaV1.7. In this paper, we illustrate the utility of combining sequence alignment within protein families with structural analysis to identify, from several putative SUMOylation sites, those that are most likely to be biologically relevant. Co-opting this principle to CRMP2, we demonstrate that, of 3 sites predicted to be SUMOylated in CRMP2, only the lysine 374 site is a SUMOylation client. A reduction in NaV1.7 currents was the corollary of the loss of CRMP2 SUMOylation at this site. A 1.78-Å-resolution crystal structure of mouse CRMP2 was solved using X-ray crystallography, revealing lysine 374 as buried within the CRMP2 tetramer interface but exposed in the monomer. Since CRMP2 SUMOylation is dependent on phosphorylation, we postulate that this state forces CRMP2 toward a monomer, exposing the SUMO site and consequently, resulting in constitutive regulation of NaV1.7.

Focal Adhesion Kinase Regulates the DNA Damage Response and Its Inhibition Radiosensitizes Mutant KRAS Lung Cancer

PURPOSE

Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related deaths worldwide due to the limited availability of effective therapeutic options. For instance, there are no effective strategies for NSCLCs that harbor mutant KRAS, the most commonly mutated oncogene in NSCLC. Thus, our purpose was to make progress toward the generation of a novel therapeutic strategy for NSCLC.

EXPERIMENTAL DESIGN

We characterized the effects of suppressing focal adhesion kinase (FAK) by RNA interference (RNAi), CRISPR/CAS9 gene editing or pharmacologic approaches in NSCLC cells and in tumor xenografts. In addition, we tested the effects of suppressing FAK in association with ionizing radiation (IR), a standard-of-care treatment modality.

RESULTS

FAK is a critical requirement of mutant KRAS NSCLC cells. With functional experiments, we also found that, in mutant KRAS NSCLC cells, FAK inhibition resulted in persistent DNA damage and susceptibility to exposure to IR. Accordingly, administration of IR to FAK-null tumor xenografts causes a profound antitumor effect in vivo CONCLUSIONS: FAK is a novel regulator of DNA damage repair in mutant KRAS NSCLC and its pharmacologic inhibition leads to radiosensitizing effects that could be beneficial in cancer therapy. Our results provide a framework for the rationale clinical testing of FAK inhibitors in NSCLC patients. Clin Cancer Res; 22(23); 5851-63. ©2016 AACR.

PIAS1-FAK Interaction Promotes the Survival and Progression of Non-Small Cell Lung Cancer

The sequence of genomic alterations acquired by cancer cells during tumor progression and metastasis is poorly understood. Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that integrates cytoskeleton remodeling, mitogenic signaling and cell survival. FAK has previously been reported to undergo nuclear localization during cell migration, cell differentiation and apoptosis. However, the mechanism behind FAK nuclear accumulation and its contribution to tumor progression has remained elusive. We report that amplification of FAK and the SUMO E3 ligase PIAS1 gene loci frequently co-occur in non-small cell lung cancer (NSCLC) cells, and that both gene products are enriched in a subset of primary NSCLCs. We demonstrate that endogenous FAK and PIAS1 proteins interact in the cytoplasm and the cell nucleus of NSCLC cells. Ectopic expression of PIAS1 promotes proteolytic cleavage of the FAK C-terminus, focal adhesion maturation and FAK nuclear localization. Silencing of PIAS1 deregulates focal adhesion turnover, increases susceptibility to apoptosis in vitro and impairs tumor xenograft formation in vivo. Nuclear FAK in turn stimulates gene transcription favoring DNA repair, cell metabolism and cytoskeleton regulation. Consistently, ablation of FAK by CRISPR/Cas9 editing, results in basal DNA damage, susceptibility to ionizing radiation and impaired oxidative phosphorylation. Our findings provide insight into a mechanism regulating FAK cytoplasm-nuclear distribution and demonstrate that FAK activity in the nucleus promotes NSCLC survival and progression by increasing cell-ECM interaction and DNA repair regulation.

How to awaken your nanomachines: Site-specific activation of focal adhesion kinases through ligand interactions

The focal adhesion kinase (FAK) and the related protein-tyrosine kinase 2-beta (Pyk2) are highly versatile multidomain scaffolds central to cell adhesion, migration, and survival. Due to their key role in cancer metastasis, understanding and inhibiting their functions are important for the development of targeted therapy. Because FAK and Pyk2 are involved in many different cellular functions, designing drugs with partial and function-specific inhibitory effects would be desirable. Here, we summarise recent progress in understanding the structural mechanism of how the tug-of-war between intramolecular and intermolecular interactions allows these protein 'nanomachines' to become activated in a site-specific manner.

Conformational dynamics of the focal adhesion targeting domain control specific functions of focal adhesion kinase in cells

Focal adhesion (FA) kinase (FAK) regulates cell survival and motility by transducing signals from membrane receptors. The C-terminal FA targeting (FAT) domain of FAK fulfils multiple functions, including recruitment to FAs through paxillin binding. Phosphorylation of FAT on Tyr(925) facilitates FA disassembly and connects to the MAPK pathway through Grb2 association, but requires dissociation of the first helix (H1) of the four-helix bundle of FAT. We investigated the importance of H1 opening in cells by comparing the properties of FAK molecules containing wild-type or mutated FAT with impaired or facilitated H1 openings. These mutations did not alter the activation of FAK, but selectively affected its cellular functions, including self-association, Tyr(925) phosphorylation, paxillin binding, and FA targeting and turnover. Phosphorylation of Tyr(861), located between the kinase and FAT domains, was also enhanced by the mutation that opened the FAT bundle. Similarly phosphorylation of Ser(910) by ERK in response to bombesin was increased by FAT opening. Although FAK molecules with the mutation favoring FAT opening were poorly recruited at FAs, they efficiently restored FA turnover and cell shape in FAK-deficient cells. In contrast, the mutation preventing H1 opening markedly impaired FAK function. Our data support the biological importance of conformational dynamics of the FAT domain and its functional interactions with other parts of the molecule.

Non-nuclear function of sumoylated proteins

Post-translational modification by the SUMO moiety is now regarded as one of the key regulatory modifications in eukaryotic cells. Up to now, plenty of sumoylated proteins have been found to be involved in nuclear processes such as chromatin organization, transcription and DNA repair as well as in other cellular functions. Since the number of data concerning sumoylated proteins and their function outside the nucleus has grown rapidly, in this review we summarized the results describing the non-nuclear role of SUMO substrates. In particular, we focused on the role of sumoylation in the regulation of channel activity, receptor function, G-protein signaling, activity of enzymes, cytoskeletal organization, exocytosis, autophagy and mitochondrial dynamics.

Sumoylated hnRNPA2B1 controls the sorting of miRNAs into exosomes through binding to specific motifs

Exosomes are released by most cells to the extracellular environment and are involved in cell-to-cell communication. Exosomes contain specific repertoires of mRNAs, microRNAs (miRNAs) and other non-coding RNAs that can be functionally transferred to recipient cells. However, the mechanisms that control the specific loading of RNA species into exosomes remain unknown. Here we describe sequence motifs present in miRNAs that control their localization into exosomes. The protein heterogeneous nuclear ribonucleoprotein A2B1 (hnRNPA2B1) specifically binds exosomal miRNAs through the recognition of these motifs and controls their loading into exosomes. Moreover, hnRNPA2B1 in exosomes is sumoylated, and sumoylation controls the binding of hnRNPA2B1 to miRNAs. The loading of miRNAs into exosomes can be modulated by mutagenesis of the identified motifs or changes in hnRNPA2B1 expression levels. These findings identify hnRNPA2B1 as a key player in miRNA sorting into exosomes and provide potential tools for the packaging of selected regulatory RNAs into exosomes and their use in biomedical applications.

Cells secrete micro-RNAs by packaging them into exosomes; however, the mechanisms by which this packaging occurs are unclear. Here, the authors identify a sequence motif that confers exosomal targeting to micro-RNAs and identify a ribonucleoprotein complex that plays a role in this process.

The CacyBP/SIP protein is sumoylated in neuroblastoma NB2a cells

The Calcyclin binding protein and Siah-1 interacting protein (CacyBP/SIP) protein is highly expressed in mammalian brain as well as in neuroblastoma NB2a cells and pheochromocytoma PC12 cells. This protein interacts with several targets such as cytoskeletal proteins or ERK1/2 kinase and seems to be involved in many cellular processes. In this work we examined a post-translational modification of CacyBP/SIP which might have an effect on its function. Since theoretical analysis of the amino acid sequence of CacyBP/SIP indicated several lysine residues which could potentially be sumoylated we checked experimentally whether this protein might be modified by SUMO attachment. We have shown that indeed CacyBP/SIP bound the E2 SUMO ligase, Ubc9, in neuroblastoma NB2a cell extract and was sumoylated in these cells. By fractionation of NB2a cell extract we have found that, contrary to the majority of SUMO-modified proteins, sumoylated CacyBP/SIP is present in the cytoplasmic and not in the nuclear fraction. We have also established that lysine 16 is the residue which undergoes sumoylation in the CacyBP/SIP protein.

Targeting FAK in human cancer: from finding to first clinical trials

It is twenty years since Focal Adhesion Kinase (FAK) was found to be overexpressed in many types of human cancer. FAK plays an important role in adhesion, spreading, motility, invasion, metastasis, survival, angiogenesis, and recently has been found to play an important role as well in epithelial to mesenchymal transition (EMT), cancer stem cells and tumor microenvironment. FAK has kinase-dependent and kinase independent scaffolding, cytoplasmic and nuclear functions. Several years ago FAK was proposed as a potential therapeutic target; the first clinical trials were just reported, and they supported further studies of FAK as a promising therapeutic target. This review discusses the main functions of FAK in cancer, and specifically focuses on recent novel findings on the role of FAK in cancer stem cells, microenvironment, epithelial-to-mesenchymal transition, invasion, metastasis, and also highlight new approaches of targeting FAK and critically discuss challenges that lie ahead for its targeted therapeutics. The review provides a summary of translational approaches of FAK-targeted and combination therapies and outline perspectives and future directions of FAK research.

Dysfunction of the ubiquitin proteasome and ubiquitin-like systems in schizophrenia

Protein expression abnormalities have been implicated in the pathophysiology of schizophrenia, but the underlying cause of these changes is not known. We sought to investigate ubiquitin and ubiquitin-like (UBL) systems (SUMOylation, NEDD8ylation, and Ufmylation) as putative mechanisms underlying protein expression abnormalities seen in schizophrenia. For this, we performed western blot analysis of total ubiquitination, free ubiquitin, K48- and K63-linked ubiquitination, and E1 activases, E2 conjugases, and E3 ligases involved in ubiquitination and UBL post-translational modifications in postmortem brain tissue samples from persons with schizophrenia (n=13) and comparison subjects (n=13). We studied the superior temporal gyrus (STG) of subjects from the Mount Sinai Medical Center brain collection that were matched for age, tissue pH, and sex. We found an overall reduction of protein ubiquitination, free ubiquitin, K48-linked ubiquitination, and increased K63 polyubiquitination in schizophrenia. Ubiquitin E1 activase UBA (ubiquitin activating enzyme)-6 and E3 ligase Nedd (neural precursor cell-expressed developmentally downregulated)-4 were decreased in this illness, as were E3 ligases involved in Ufmylation (UFL1) and SUMOylation (protein inhibitor of activated STAT 3, PIAS3). NEDD8ylation was also dysregulated in schizophrenia, with decreased levels of the E1 activase UBA3 and the E3 ligase Rnf7. This study of ubiquitin and UBL systems in schizophrenia found abnormalities of ubiquitination, Ufmylation, SUMOylation, and NEDD8ylation in the STG in this disorder. These results suggest a novel approach to the understanding of schizophrenia pathophysiology, where a disruption in homeostatic adaptation of the cell underlies discreet changes seen at the protein level in this illness.

Modification of Akt by SUMO conjugation regulates alternative splicing and cell cycle

Akt/PKB is a key signaling molecule in higher eukaryotes and a crucial protein kinase in human health and disease. Phosphorylation, acetylation, and ubiquitylation have been reported as important regulatory post-translational modifications of this kinase. We describe here that Akt is modified by SUMO conjugation, and show that lysine residues 276 and 301 are the major SUMO attachment sites within this protein. We found that phosphorylation and SUMOylation of Akt appear as independent events. However, decreasing Akt SUMOylation levels severely affects the role of this kinase as a regulator of fibronectin and Bcl-x alternative splicing. Moreover, we observed that the Akt mutant (Akt E17K) found in several human tumors displays increased levels of SUMOylation and also an enhanced capacity to regulate fibronectin splicing patterns. This splicing regulatory activity is completely abolished by decreasing Akt E17K SUMO conjugation levels. Additionally, we found that SUMOylation controls Akt regulatory function at G₁/S transition during cell cycle progression. These findings reveal SUMO conjugation as a novel level of regulation for Akt activity, opening new areas of exploration related to the molecular mechanisms involved in the diverse cellular functions of this kinase.

Akt SUMOylation regulates cell proliferation and tumorigenesis

Proto-oncogene Akt plays essential roles in cell proliferation and tumorigenesis. Full activation of Akt is regulated by phosphorylation, ubiquitination, and acetylation. Here we report that SUMOylation of Akt is a novel mechanism for its activation. Systematically analyzing the role of lysine residues in Akt activation revealed that K276, which is located in a SUMOylation consensus motif, is essential for Akt activation. Ectopic or endogenous Akt1 could be modified by SUMOylation. RNA interference-mediated silencing of UBC9 reduced Akt SUMOylation, which was promoted by SUMO E3 ligase PIAS1 and reversed by the SUMO-specific protease SENP1. Although multiple sites on Akt could be SUMOylated, K276 was identified as a major SUMO acceptor site. K276R or E278A mutation reduced SUMOylation of Akt but had little effect on its ubiquitination. Strikingly, these mutations also completely abolished Akt kinase activity. In support of these results, we found that expression of PIAS1 and SUMO1 increased Akt activity, whereas expression of SENP1 reduced Akt1 activity. Interestingly, the cancer-derived mutant E17K in Akt1 that occurs in various cancers was more efficiently SUMOylated than wild-type Akt. Moreover, SUMOylation loss dramatically reduced Akt1 E17K-mediated cell proliferation, cell migration, and tumorigenesis. Collectively, our findings establish that Akt SUMOylation provides a novel regulatory mechanism for activating Akt function.

Sumoylation in neurodegenerative diseases

The yeast SUMO (small ubiquitin-like modifier) orthologue SMT3 was initially discovered in a genetic suppressors screen for the centromeric protein Mif2 (Meluh and Koshland in Mol Bio Cell 6:793-807, 1). Later, it turned out that the homologous mammalian proteins SUMO1 to SUMO4 are reversible protein modifiers that can form isopeptide bonds with lysine residues of respective target proteins (Mahajan et al. in Cell 88:97-107, 2). This was the discovery of a post-translational modification called sumoylation, which enzymatically resembles ubiquitination. However, very soon it became clear that SUMO attachments served a far more diverse role than ubiquitination. Meanwhile, numerous cellular processes are known to be subject to the impact of SUMO modification, including transcription, protein targeting, protein solubility, apoptosis or activity of various enzymes. In many instances, SUMO proteins create new protein interaction surfaces or block existing interaction domains (Geiss-Friedlander and Melchior in Nat Rev in Mol Cell Biol 8:947-956, 3). For the past few years, sumoylation attracted increasing attention as a versatile regulator of toxic protein properties in neurodegenerative diseases. In this review, we summarize the growing knowledge about the involvement of sumoylation in neurodegeneration, and discuss the underlying molecular principles affected by this multifaceted and intriguing post-translational modification.

Effect of posttranslational modifications on enzyme function and assembly

The detailed examination of enzyme molecules by mass spectrometry and other techniques continues to identify hundreds of distinct PTMs. Recently, global analyses of enzymes using methods of contemporary proteomics revealed widespread distribution of PTMs on many key enzymes distributed in all cellular compartments. Critically, patterns of multiple enzymatic and nonenzymatic PTMs within a single enzyme are now functionally evaluated providing a holistic picture of a macromolecule interacting with low molecular mass compounds, some of them being substrates, enzyme regulators, or activated precursors for enzymatic and nonenzymatic PTMs. Multiple PTMs within a single enzyme molecule and their mutual interplays are critical for the regulation of catalytic activity. Full understanding of this regulation will require detailed structural investigation of enzymes, their structural analogs, and their complexes. Further, proteomics is now integrated with molecular genetics, transcriptomics, and other areas leading to systems biology strategies. These allow the functional interrogation of complex enzymatic networks in their natural environment. In the future, one might envisage the use of robust high throughput analytical techniques that will be able to detect multiple PTMs on a global scale of individual proteomes from a number of carefully selected cells and cellular compartments. This article is part of a Special Issue entitled: Posttranslational Protein modifications in biology and Medicine.

Tools for protein posttranslational modifications analysis: FAK, a case study

Recent advances in mass spectrometry have resulted in an exponential increase in annotation of posttranslational modifications (PTMs). Just in the Swiss-Prot Knowledgebase, there are 89,931 of a total of 27 characterized PTM types reported experimentally. A single protein can be dynamically modified during its lifetime for regulation of its function. Considering a PTM can occur at different levels and the number of different PTMs described, the number of possibilities for a single protein is unthinkable. Narrowing the study to a single PTM can be rather unmerited considering that most proteins are heavily modified. Currently crosstalk between PTMs is plentifully reported in the literature. The example of amino acids serine and threonine on one hand and lysine on the other hand, as targets of different modifications, demand a more global analysis approach of a protein. Besides the direct competition for the same amino acid, a PTM can directly or indirectly influence other PTMs in the same protein molecule by for example steric hindrance due to close proximity between the modifications or creation of a binding site such as an SH2 binding domain for protein recruitment and further modifications. Given the complexity of PTMs a number of tools have been developed to archive, analyze, and visualize modifications. VISUALPROT is presented here to demonstrate the usefulness of visualizing all annotated protein features such as amino acid content, domains, amino acid modification sites and single amino acid polymorphisms in a single image. VISUALPROT application is demonstrated for the protein focal adhesion kinase (FAK) as an example. FAK is a highly phosphorylated cytoplasmatic tyrosine kinase comprising different domains and regions. FAK is crucial for integrating signals from integrins and receptor tyrosine kinases in processes such as cell survival, proliferation, and motility.

NMDA receptor signaling mediates the expression of protein inhibitor of activated STAT1 (PIAS1) in rat hippocampus

Protein inhibitor of activated STAT1 (PIAS1) was shown to play an important role in inflammation and innate immune response, but how PIAS1 is regulated is not known. We have recently demonstrated that PIAS1 enhances spatial learning and memory performance in rats. In this study, we examined the signaling pathway and neural mechanism that regulate PIAS1 expression in the brain by using pharmacological and molecular approaches. Our results revealed that pias1 gene expression is rapidly induced upon NMDA receptor activation in rat hippocampus, but this effect is blocked by transfection of sub-threshold concentrations of ERK1 siRNA/ERK2 siRNA or CREB siRNA. Pias1 gene expression is similarly induced by overexpression of the ERK1/ERK2 plasmids in rat hippocampus, and this effect is also blocked by sub-threshold concentration of CREB siRNA transfection. On the other hand, transfection of ERK1 siRNA/ERK2 siRNA or CREB siRNA at a higher concentration is sufficient to down-regulate PIAS1 expression. Inhibition of PI-3 kinase signaling and CaMKII signaling, which both result in CREB inactivation, similarly decreases PIAS1 expression. But NMDA and MK-801 do not affect the expression of IL-6 and TNFα. NMDA also did not affect the expression of PIAS2, PIAS3 and PIAS4. Further, pias1 mRNA has a similar degradation rate to that of the zif268 gene. These results together suggest that pias1 may function as an immediate early gene in an activity-dependent manner and PIAS1 expression is regulated by the NMDA-MAPK/ERK-CREB signaling pathway implicated in neuronal plasticity.

DeSUMOylating isopeptidase: a second class of SUMO protease

The modification of proteins by small ubiquitin-like modifier (SUMO) is crucial for the regulation of diverse cellular processes. Protein SUMOylation is reversed by isopeptidases, collectively known as deSUMOylases. Only one family of SUMO-specific proteases has been described so far: the sentrin-specific proteases (SENP). Here, we identify and characterize a new deSUMOylase, which we have named DeSI-1 (DeSumoylating Isopeptidase 1). We describe BZEL—a new transcriptional repressor—as substrate of DeSI-1. DeSI-1 catalyses the deSUMOylation, but not the deubiquitination, of BZEL. Furthermore, the SENP substrates PML and ΔNp63 are not deSUMOylated by DeSI-1, suggesting that SENP and DeSI enzymes recognize different sets of substrates. Together, these data identify a second class of SUMO proteases.

Modularity and functional plasticity of scaffold proteins as p(l)acemakers in cell signaling

Cells coordinate and integrate various functional modules that control their dynamics, intracellular trafficking, metabolism and gene expression. Such capacity is mediated by specific scaffold proteins that tether multiple components of signaling pathways at plasma membrane, Golgi apparatus, mitochondria, endoplasmic reticulum, nucleus and in more specialized subcellular structures such as focal adhesions, cell-cell junctions, endosomes, vesicles and synapses. Scaffold proteins act as "pacemakers" as well as "placemakers" that regulate the temporal, spatial and kinetic aspects of protein complex assembly by modulating the local concentrations, proximity, subcellular dispositions and biochemical properties of the target proteins through the intricate use of their modular protein domains. These regulatory mechanisms allow them to gate the specificity, integration and crosstalk of different signaling modules. In addition to acting as physical platforms for protein assembly, many professional scaffold proteins can also directly modify the properties of their targets while they themselves can be regulated by post-translational modifications and/or mechanical forces. Furthermore, multiple scaffold proteins can form alliances of higher-order regulatory networks. Here, we highlight the emerging themes of scaffold proteins by analyzing their common and distinctive mechanisms of action and regulation, which underlie their functional plasticity in cell signaling. Understanding these mechanisms in the context of space, time and force should have ramifications for human physiology and for developing new therapeutic approaches to control pathological states and diseases.

Regulation of Neuronal Protein Trafficking and Translocation by SUMOylation

Post-translational modifications of proteins are essential for cell function. Covalent modification by SUMO (small ubiquitin-like modifier) plays a role in multiple cell processes, including transcriptional regulation, DNA damage repair, protein localization and trafficking. Factors affecting protein localization and trafficking are particularly crucial in neurons because of their polarization, morphological complexity and functional specialization. SUMOylation has emerged as a major mediator of intranuclear and nucleo-cytoplasmic translocations of proteins involved in critical pathways such as circadian rhythm, apoptosis and protein degradation. In addition, SUMO-regulated re-localization of extranuclear proteins is required to sustain neuronal excitability and synaptic transmission. Thus, SUMOylation is a key arbiter of neuronal viability and function. Here, we provide an overview of recent advances in our understanding of regulation of neuronal protein localization and translocation by SUMO and highlight exciting areas of ongoing research.

Ubiquitin links to cytoskeletal dynamics, cell adhesion and migration

Post-translational modifications are used by cells to link additional information to proteins. Most modifications are subtle and concern small moieties such as a phosphate group or a lipid. In contrast, protein ubiquitylation entails the covalent attachment of a full-length protein such as ubiquitin. The protein ubiquitylation machinery is remarkably complex, comprising more than 15 Ubls (ubiquitin-like proteins) and several hundreds of ubiquitin-conjugating enzymes. Ubiquitin is best known for its role as a tag that induces protein destruction either by the proteasome or through targeting to lysosomes. However, addition of one or more Ubls also affects vesicular traffic, protein-protein interactions and signal transduction. It is by now well established that ubiquitylation is a component of most, if not all, cellular signalling pathways. Owing to its abundance in controlling cellular functions, ubiquitylation is also of key relevance to human pathologies, including cancer and inflammation. In the present review, we focus on its role in the control of cell adhesion, polarity and directional migration. It will become clear that protein modification by Ubls occurs at every level from the receptors at the plasma membrane down to cytoskeletal components such as actin, with differential consequences for the pathway's final output. Since ubiquitylation is fast as well as reversible, it represents a bona fide signalling event, which is used to fine-tune a cell's responses to receptor agonists.

FERM domain interaction with myosin negatively regulates FAK in cardiomyocyte hypertrophy

Focal adhesion kinase (FAK) regulates cellular processes that affect several aspects of development and disease. The FAK N-terminal FERM (4.1 protein-ezrin-radixin-moesin homology) domain, a compact clover-leaf structure, binds partner proteins and mediates intramolecular regulatory interactions. Combined chemical cross-linking coupled to MS, small-angle X-ray scattering, computational docking and mutational analyses showed that the FAK FERM domain has a molecular cleft (~998 Å(2)) that interacts with sarcomeric myosin, resulting in FAK inhibition. Accordingly, mutations in a unique short amino acid sequence of the FERM myosin cleft, FP-1, impaired the interaction with myosin and enhanced FAK activity in cardiomyocytes. An FP-1 decoy peptide selectively inhibited myosin interaction and increased FAK activity, promoting cardiomyocyte hypertrophy through activation of the AKT-mammalian target of rapamycin pathway. Our findings uncover an inhibitory interaction between the FAK FERM domain and sarcomeric myosin that presents potential opportunities to modulate the cardiac hypertrophic response through changes in FAK activity.

How focal adhesion kinase achieves regulation by linking ligand binding, localization and action

Focal adhesion kinase (FAK) has an astonishing number of ligands and functions, which enable it to contribute to embryonic development and human health. FAK can promote different effects in similar cellular environments or similar effects in different cellular environments. Recent advances in structural and cellular analysis of FAK are starting to reveal the interrelationships between the conformations, localizations, interactions, and functions of FAK. This review focuses on our emerging understanding of how the structural framework of FAK mechanistically allows it to integrate manifold stimuli into environment-specific functions.

SUMOylation-regulated protein phosphorylation, evidence from quantitative phosphoproteomics analyses

Protein modification is critical for the regulation of protein functions. Cross-talks among different types of protein modifications should yield concerted and coordinated regulatory networks for physiological functions. Here we have employed system-wide and quantitative phosphoproteomics analyses to reveal a global cross-talk for SUMOylation-modulated phosphorylation. Furthermore, as specific examples, we have shown that the α subunit of casein kinase II is SUMOylated and that this affects the phosphorylation of its substrates. SUMO-regulated phosphorylation is involved in cell cycle control. Our data demonstrate an interplay between protein SUMOylation and phosphorylation and imply a regulatory role for this SUMOylation-modulated phosphorylation.

Novel role and mechanism of protein inhibitor of activated STAT1 in spatial learning

By using differential display PCR, we have previously identified 98 cDNA fragments from rat dorsal hippocampus, which are expressed differentially between the fast learners and slow learners from water-maze learning task. One cDNA fragment, which showed a higher expression level in fast learners, encodes the rat protein inhibitor of activated STAT1 (pias1) gene. Spatial training induced a significant increase in PIAS1 expression in rat hippocampus. Transient transfection of the wild-type (WT) PIAS1 plasmid to CA1 neurons facilitated, whereas transfection of PIAS1 siRNA impaired spatial learning in rats. Meanwhile, PIAS1WT increased STAT1 sumoylation, decreased STAT1 DNA binding and decreased STAT1 phosphorylation at Tyr-701 associated with spatial learning facilitation. But PIAS1 siRNA transfection produced an opposite effect on these measures associated with spatial learning impairment. Further, transfection of STAT1 sumoylation mutant impaired spatial acquisition, whereas transfection of STAT1 phosphorylation mutant blocked the impairing effect of PIAS1 siRNA on spatial learning. In this study, we first demonstrate the role of PIAS1 in spatial learning. Both posttranslational modifications (increased sumoylation and decreased phosphorylation) mediate the effect of PIAS1 on spatial learning facilitation.

Suppression of TGFβ-induced epithelial-mesenchymal transition like phenotype by a PIAS1 regulated sumoylation pathway in NMuMG epithelial cells

Epithelial-mesenchymal-transition (EMT) is a fundamental cellular process that is critical for normal development and tumor metastasis. The transforming growth factor beta (TGFβ) is a potent inducer of EMT like effects, but the mechanisms that regulate TGFβ-induced EMT remain incompletely understood. Using the widely employed NMuMG mammary epithelial cells as a model to study TGFβ-induced EMT, we report that TGFβ downregulates the levels of the SUMO E3 ligase PIAS1 in cells undergoing EMT. Gain and loss of function analyses indicate that PIAS1 acts in a SUMO ligase dependent manner to suppress the ability of TGFβ to induce EMT in these cells. We also find that TGFβ inhibits sumoylation of the PIAS1 substrate SnoN, a transcriptional regulator that antagonizes TGFβ-induced EMT. Accordingly, loss of function mutations of SnoN sumoylation impair the ability of SnoN to inhibit TGFβ-induced EMT in NMuMG cells. Collectively, our findings suggest that PIAS1 is a novel negative regulator of EMT and reveal that inhibition of the PIAS1-SnoN sumoylation pathway represents a key mechanism by which TGFβ induces EMT, with important implications in normal development and tumor metastasis.

Targets and consequences of protein SUMOylation in neurons

The post-translational modification of proteins is critical for the spatial and temporal regulation of signalling cascades. This is especially important in the CNS where the processes affecting differentiation, growth, targeting and communication between neurones are highly complex and very tightly regulated. In recent years it has emerged that modification of proteins by members of the SUMO (small ubiquitin-related modifier) family of proteins play key roles in neuronal function. SUMOylation involves the covalent conjugation of a member of the SUMO family to lysine residues in target proteins. Multiple nuclear and perinuclear SUMOylation targets have been reported to be involved in nuclear organisation and transcriptional regulation. In addition, a growing number of extranuclear SUMO substrates have been identified that can have important acute effects on neuronal function. The SUMOylation of both intra- and extranuclear proteins have been implicated in a diverse array of processes that have far-reaching implications for neuronal function and pathophysiology. Here we review the current understanding of the targets and consequences of protein SUMOylation in the brain and examine its established and potential involvement in a wide range of neurological and neurodegenerative diseases.