KIF3A tail domain phosphorylation is not required for ciliogenesis in mouse embryonic fibroblasts

Primary cilia are essential signaling organelles that protrude from most cells in the body. Heterodimeric kinesin-2 (KIF3A/KIF3B/KAP3) powers several intracellular transport processes, including intraflagellar transport (IFT), essential for ciliogenesis. A long-standing question is how a motor protein is differentially regulated for specific cargos. Since phosphorylation of the KIF3A tail domain was suggested to regulate the activity of kinesin-2 for ciliogenesis, similarly as for the cytosolic cargo N-Cadherin, we set out to map the phosphosites involved in this regulation. Using well-characterized Kif3a-/-; Kif3b-/- mouse embryonic fibroblasts, we performed ciliogenesis rescue assays with a library of phosphomimetic mutants comprising all predicted phosphosites in the KIF3A tail domain. In contrast to previous reports, we found that KIF3A tail domain phosphorylation is dispensable for ciliogenesis in mammals. Thus, mammalian kinesin-2 is differently regulated for IFT than currently thought, consistent with the idea of differential regulation for ciliary and cytosolic cargo.

Phosphoregulation of Kinesins Involved in Long-Range Intracellular Transport

Kinesins, the microtubule-dependent mechanochemical enzymes, power a variety of intracellular movements. Regulation of Kinesin activity and Kinesin-Cargo interactions determine the direction, timing and flux of various intracellular transports. This review examines how phosphorylation of Kinesin subunits and adaptors influence the traffic driven by Kinesin-1, -2, and -3 family motors. Each family of Kinesins are phosphorylated by a partially overlapping set of serine/threonine kinases, and each event produces a unique outcome. For example, phosphorylation of the motor domain inhibits motility, and that of the stalk and tail domains induces cargo loading and unloading effects according to the residue and context. Also, the association of accessory subunits with cargo and adaptor proteins with the motor, respectively, is disrupted by phosphorylation. In some instances, phosphorylation by the same kinase on different Kinesins elicited opposite outcomes. We discuss how this diverse range of effects could manage the logistics of Kinesin-dependent, long-range intracellular transport.

METTL3-mediated m6A modification of KIF3C-mRNA promotes prostate cancer progression and is negatively regulated by miR-320d

The occurrence of distant metastasis is one of the leading causes of death in patients with prostate cancer (PCa). It is confirmed that kinesin protein is associated with a variety of malignancies, and the KIF3 family is related to cancer, but the relationship between KIF3C and prostate cancer is not clear. Our experiments have confirmed that KIF3C is highly expressed in prostate cancer tissues and cell lines. Further, functional tests have proven that KIF3C can promote the growth migration and invasion of PCa. We used Starbase 3.0 to discover that methyltransferase like 3 (METTL3) interacts with KIF3C. Our hypothesis and experiments concluded that METTL3 induced m6A modification on KIF3C, promoting the stabilization of KIF3C-mRNA by IGF2 binding protein 1 (IGF2BP1). The prediction that miR-320d inhibits KIF3C expression by targeting METTL3 using the miRmap website, was later confirmed experimentally. Further, a recovery experiment was used to confirm that miR-320d inhibited the progression of prostate cancer. KIF3C was overexpressed in prostate cancer, promoting its growth migration and invasion was induced by miR-320d/METTL3 in an m6A dependent process.

POPX2 phosphatase enhances topographical contact guidance for cell morphology and migration

Topography mediated contact guidance affects multiple cell behaviors such as establishment of cellular morphology and migration. The direction of cell migration is associated with the establishment of cell polarity, which also affects the primary cilia in migrating cells. POPX2, a partner of PIX2, is involved in pathways essential to primary cilium formation, while over-expression of POPX2 has been reported to cause a loss of cell polarity during migration. This study aims to examine how topographical cues direct morphological changes, and how topography affects the process of cellular migration and primary cilium architecture, in the context of POPX2 over-expression. Thus, the effect of anisotropic topography, 2 μm grating pattern on tissue-culture polystyrene, was used as a contact guidance cue to investigate the migration and cell polarity of POPX2 overexpressing cells, in comparison to control NIH3T3 fibroblast cells. We report that POPX2 overexpressing NIH3T3 cells were more sensitive to surface topographical cues as the cells became more elongated. In addition, these cues also affected focal adhesion alignment of POPX2 overexpressing cells. Cell migration was further studied using wound closure assays, in which the 2 μm gratings were designed to be either perpendicular or parallel to wound-induced cell migration direction, which would be agonistic or antagonistic to cell migration, respectively. We observed that both POPX2 overexpressing cells' migration direction and migration rate were more significantly influenced by gratings direction compared to control NIH3T3 cells. The migration paths of POPX2 overexpressing cells become more direct in the presence of anisotropic topographical cues. Further, cilia and centrosome alignment, which is important in cell migration, was also affected by the direction of gratings during this migration process. Collectively, enhancement of NIH3T3 cell sensitivity towards surface topography through POPX2 overexpression might reflect one of the mechanisms that combine biochemical and mechanical cues for directional cell migration.

Intraflagellar transport trains and motors: Insights from structure

Intraflagellar transport (IFT) sculpts the proteome of cilia and flagella; the antenna-like organelles found on the surface of virtually all human cell types. By delivering proteins to the growing ciliary tip, recycling turnover products, and selectively transporting signalling molecules, IFT has critical roles in cilia biogenesis, quality control, and signal transduction. IFT involves long polymeric arrays, termed IFT trains, which move to and from the ciliary tip under the power of the microtubule-based motor proteins kinesin-II and dynein-2. Recent top-down and bottom-up structural biology approaches are converging on the molecular architecture of the IFT train machinery. Here we review these studies, with a focus on how kinesin-II and dynein-2 assemble, attach to IFT trains, and undergo precise regulation to mediate bidirectional transport.

Partners in crime: POPX2 phosphatase and its interacting proteins in cancer

Protein phosphorylation and dephosphorylation govern intracellular signal transduction and cellular functions. Kinases and phosphatases are involved in the regulation and development of many diseases such as Alzheimer’s, diabetes, and cancer. While the functions and roles of many kinases, as well as their substrates, are well understood, phosphatases are comparatively less well studied. Recent studies have shown that rather than acting on fewer and more distinct substrates like the kinases, phosphatases can recognize specific phosphorylation sites on many different proteins, making the study of phosphatases and their substrates challenging. One approach to understand the biological functions of phosphatases is through understanding their protein–protein interaction network. POPX2 (Partner of PIX 2; also known as PPM1F or CaMKP) is a serine/threonine phosphatase that belongs to the PP2C family. It has been implicated in cancer cell motility and invasiveness. This review aims to summarize the different binding partners of POPX2 phosphatase and explore the various functions of POPX2 through its interactome in the cell. In particular, we focus on the impact of POPX2 on cancer progression. Acting via its different substrates and interacting proteins, POPX2’s involvement in metastasis is multifaceted and varied according to the stages of metastasis.

Interaction of the Hippo Pathway and Phosphatases in Tumorigenesis

The Hippo pathway is an emerging tumor suppressor signaling pathway involved in a wide range of cellular processes. Dysregulation of different components of the Hippo signaling pathway is associated with a number of diseases including cancer. Therefore, identification of the Hippo pathway regulators and the underlying mechanism of its regulation may be useful to uncover new therapeutics for cancer therapy. The Hippo signaling pathway includes a set of kinases that phosphorylate different proteins in order to phosphorylate and inactivate its main downstream effectors, YAP and TAZ. Thus, modulating phosphorylation and dephosphorylation of the Hippo components by kinases and phosphatases play critical roles in the regulation of the signaling pathway. While information regarding kinase regulation of the Hippo pathway is abundant, the role of phosphatases in regulating this pathway is just beginning to be understood. In this review, we summarize the most recent reports on the interaction of phosphatases and the Hippo pathway in tumorigenesis. We have also introduced challenges in clarifying the role of phosphatases in the Hippo pathway and future direction of crosstalk between phosphatases and the Hippo pathway.

Metal-dependent Ser/Thr protein phosphatase PPM family: Evolution, structures, diseases and inhibitors

Protein phosphatases and kinases control multiple cellular events including proliferation, differentiation, and stress responses through regulating reversible protein phosphorylation, the most important post-translational modification. Members of metal-dependent protein phosphatase (PPM) family, also known as PP2C phosphatases, are Ser/Thr phosphatases that bind manganese/magnesium ions (Mn²⁺/Mg²⁺) in their active center and function as single subunit enzymes. In mammals, there are 20 isoforms of PPM phosphatases: PPM1A, PPM1B, PPM1D, PPM1E, PPM1F, PPM1G, PPM1H, PPM1J, PPM1K, PPM1L, PPM1M, PPM1N, ILKAP, PDP1, PDP2, PHLPP1, PHLPP2, PP2D1, PPTC7, and TAB1, whereas there are only 8 in yeast. Phylogenetic analysis of the DNA sequences of vertebrate PPM isoforms revealed that they can be divided into 12 different classes: PPM1A/PPM1B/PPM1N, PPM1D, PPM1E/PPM1F, PPM1G, PPM1H/PPM1J/PPM1M, PPM1K, PPM1L, ILKAP, PDP1/PDP2, PP2D1/PHLPP1/PHLPP2, TAB1, and PPTC7. PPM-family members have a conserved catalytic core region, which contains the metal-chelating residues. The different isoforms also have isoform specific regions within their catalytic core domain and terminal domains, and these regions may be involved in substrate recognition and/or functional regulation of the phosphatases. The twenty mammalian PPM phosphatases are involved in regulating diverse cellular functions, such as cell cycle control, cell differentiation, immune responses, and cell metabolism. Mutation, overexpression, or deletion of the PPM phosphatase gene results in abnormal cellular responses, which lead to various human diseases. This review focuses on the structures and biological functions of the PPM-phosphatase family and their associated diseases. The development of specific inhibitors against the PPM phosphatase family as a therapeutic strategy will also be discussed.

MicroRNAs Involved in Metastasis of Hepatocellular Carcinoma: Target Candidates, Functionality and Efficacy in Animal Models and Prognostic Relevance

Hepatocellular carcinoma (HCC) is responsible for the second-leading cancer-related death toll worldwide. Although sorafenib and levantinib as frontline therapy and regorafenib, cabazantinib and ramicurimab have now been approved for second-line therapy, the therapeutic benefit is in the range of only a few months with respect to prolongation of survival. Aggressiveness of HCC is mediated by metastasis. Intrahepatic metastases and distant metastasis to the lungs, lymph nodes, bones, omentum, adrenal gland and brain have been observed. Therefore, the identification of metastasis-related new targets and treatment modalities is of paramount importance. In this review, we focus on metastasis-related microRNAs (miRs) as therapeutic targets for HCC. We describe miRs which mediate or repress HCC metastasis in mouse xenograft models. We discuss 18 metastasis-promoting miRs and 35 metastasis-inhibiting miRs according to the criteria as outlined. Six of the metastasis-promoting miRs (miR-29a, -219-5p, -331-3p, 425-5p, -487a and -1247-3p) are associated with unfavourable clinical prognosis. Another set of six down-regulated miRs (miR-101, -129-3p, -137, -149, -503, and -630) correlate with a worse clinical prognosis. We discuss the corresponding metastasis-related targets as well as their potential as therapeutic modalities for treatment of HCC-related metastasis. A subset of up-regulated miRs -29a, -219-5p and -425-5p and down-regulated miRs -129-3p and -630 were evaluated in orthotopic metastasis-related models which are suitable to mimic HCC-related metastasis. Those miRNAs may represent prioritized targets emerging from our survey.

POPX2 is a novel LATS phosphatase that regulates the Hippo pathway

The Hippo pathway regulates cell proliferation, survival, apoptosis and differentiation. During carcinogenesis, members of the Hippo pathway are mutated to avoid anoikis and promote anchorage independent growth. Although many regulators of the Hippo pathway have been reported, negative regulators of the hippo kinases are not well studied. Through an interactome screen, we found that POPX2 phosphatase interacts with several of the Hippo pathway core kinases, including LATS1 which is the direct kinase regulating the transcription co-activators, YAP and TAZ. Phosphorylated YAP/TAZ are retained in the cytoplasm and prevented from translocation into the nucleus to activate transcription of target genes. We found that POPX2 could dephosphorylate LATS1 on Threonine-1079, leading to inactivation of LATS1 kinase. As a result, YAP/TAZ are not phosphorylated and are able to translocate into the nucleus to activate target genes involved in cell proliferation. Furthermore, POPX2 knock-out using CRISPR in the highly metastatic MDA-MB-231 breast cancer cells results in decreased cell proliferation and impairment of anchorage independent growth. We propose that POPX2 act as a suppressor of the Hippo pathway through LATS1 dephosphorylation and inactivation.

Identification of novel loci for pediatric cholestatic liver disease defined by KIF12, PPM1F, USP53, LSR, and WDR83OS pathogenic variants

PURPOSE

Genetic testing in pediatric cholestasis can be very informative but genetic causes have not been fully characterized.

METHODS

Exome sequencing and positional mapping in seven families with cholestatic liver disease and negative clinical testing for known disease genes.

RESULTS

KIF12, which encodes a microtubule motor protein with a tentative role in cell polarity, was found to harbor three homozygous likely deleterious variants in three families with sclerosing cholangitis. KIF12 expression is dependent on HNF-1β, deficiency which is known to cause bile duct dysmorphogenesis associated with loss of KIF12 expression. In another extended family, we mapped an apparently novel syndrome of sclerosing cholangitis, short stature, hypothyroidism, and abnormal tongue pigmentation in two cousins to a homozygous variant in PPM1F (POPX2), a regulator of kinesin-mediated ciliary transport. In the fifth family, a syndrome of normal gamma glutamyltransferase (GGT) cholestasis and hearing loss was found to segregate with a homozygous truncating variant in USP53, which encodes an interactor with TJP2. In the sixth family, we mapped a novel syndrome of transient neonatal cholestasis, intellectual disability, and short stature to a homozygous variant in LSR, an important regulator of liver development. In the last family of three affected siblings, a novel syndrome of intractable itching, hypercholanemia, short stature, and intellectual disability was mapped to a single locus that contains a homozygous truncating variant in WDR83OS (C19orf56), known to interact with ATP13A2 and BSEP.

CONCLUSION

Our results expand the genetic heterogeneity of pediatric cholestatic liver disease and highlight the vulnerability of bile homeostasis to a wide range of molecular perturbations.

miR-149 in Human Cancer: A Systemic Review

MicroRNAs (miRNAs) are small noncoding RNAs that regulate post-transcriptional gene expression via binding to the 3'-untranslated region (3'-UTR) of targeted mRNAs. They are reported to play important roles in tumorigenesis and progression of various cancers. Among them, miR-149 was confirmed to be aberrantly regulated in various tumors. In this review, we provide a complex overview of miR-149, particularly summarize the critical roles of it in cancers and expect to lay the foundation for future works on this important microRNA.

POPX2 phosphatase regulates apoptosis through the TAK1-IKK-NF-κB pathway

Chemoresistance is one of the leading causes that contributes to tumor relapse and poor patient outcome after several rounds of drug therapy. The causes of chemoresistance are multi-factorial. Ultimately, it is the balance of pro- and anti-apoptotic activities in the cells. We have previously reported links between POPX2 serine/threonine phosphatase with cell motility and invasiveness of breast cancer cells. Here, we show that POPX2 plays a role in the regulation of apoptosis. The effect of POPX2 on apoptosis centers on the inactivation of TGF-β activated kinase (TAK1). TAK1 is essential for several important biological functions including innate immunity, development and cell survival. We find that POPX2 interacts directly with TAK1 and is able to dephosphorylate TAK1. Cells with lower levels of POPX2 exhibit higher TAK1 activity in response to etoposide (VP-16) treatment. This subsequently leads to increased translocation of NF-κB from the cytosol to the nucleus. Consequently, NF-κB-mediated transcription of anti-apoptotic proteins is upregulated to promote cell survival. On the other hand, cells with higher levels of POPX2 are more vulnerable to apoptosis induced by etoposide. Our data demonstrate that POPX2 is a negative regulator of TAK1 signaling pathway and modulates apoptosis through the regulation of TAK1 activity. As inhibition of TAK1 has been proposed to reduce chemoresistance and increase sensitivity to chemotherapy in certain types of cancer, modulation of POPX2 levels may provide an additional avenue and consideration in fine-tuning therapeutic response.

Analyses of PDE-regulated phosphoproteomes reveal unique and specific cAMP-signaling modules in T cells

Specific functions for different cyclic nucleotide phosphodiesterases (PDEs) have not yet been identified in most cell types. Conventional approaches to study PDE function typically rely on measurements of global cAMP, general increases in cAMP-dependent protein kinase (PKA), or the activity of exchange protein activated by cAMP (EPAC). Although newer approaches using subcellularly targeted FRET reporter sensors have helped define more compartmentalized regulation of cAMP, PKA, and EPAC, they have limited ability to link this regulation to downstream effector molecules and biological functions. To address this problem, we have begun to use an unbiased mass spectrometry-based approach coupled with treatment using PDE isozyme-selective inhibitors to characterize the phosphoproteomes of the functional pools of cAMP/PKA/EPAC that are regulated by specific cAMP-PDEs (the PDE-regulated phosphoproteomes). In Jurkat cells we find multiple, distinct PDE-regulated phosphoproteomes that can be defined by their responses to different PDE inhibitors. We also find that little phosphorylation occurs unless at least two different PDEs are concurrently inhibited in these cells. Moreover, bioinformatics analyses of these phosphoproteomes provide insight into the unique functional roles, mechanisms of action, and synergistic relationships among the different PDEs that coordinate cAMP-signaling cascades in these cells. The data strongly suggest that the phosphorylation of many different substrates contributes to cAMP-dependent regulation of these cells. The findings further suggest that the approach of using selective, inhibitor-dependent phosphoproteome analysis can provide a generalized methodology for understanding the roles of different PDEs in the regulation of cyclic nucleotide signaling.

iCellFusion

Temporal, multimodal microscopy imaging of live cells is becoming widely used in studies of cellular processes. In general, temporal sequences of images with functional and morphological data from live cells are acquired using multiple image sensors. The images from the different sources usually differ in resolution and have non-coincident fields of view, making the merging process complex. We present a new tool – iCellFusion – that performs data fusion of images from Phase-Contrast Microscopy and Fluorescence Microscopy in order to correlate the information on cell morphology, lineage and functionality. Prior to image fusion, iCellFusion performs automatic or computer-aided cell segmentation and establishes cell lineages. We exemplify its usage on time-lapse, multimodal microscopy images of bacteria producing fluorescent spots. We expect iCellFusion to assist research in Cell and Molecular Biology and the healthcare sector, where live-cell imaging is an increasingly important technique to detect and study diseases at the cellular level.

Phosphatase POPX2 Exhibits Dual Regulatory Functions in Cancer Metastasis

Cancer metastasis is a complex mechanism involving multiple processes. Previously, our integrative proteome, transcriptome, and phosphoproteome study reported that the levels of serine/threonine phosphatase POPX2 were positively correlated with cancer cell motility through modulating MAPK signaling. Surprisingly, here we found that POPX2 knockdown cells induced more numerous and larger tumor nodules in lungs in longer term animal studies. Interestingly, our analysis of DNA microarray data from cancer patient samples that are available in public databases shows that low POPX2 expression is linked to distant metastasis and poor survival rate. These observations suggest that lower levels of POPX2 may favor tumor progression in later stages of metastasis. We hypothesize that POPX2 may do so by modulation of angiogenesis. Secretome analysis of POPX2-knockdown MDA-MB-231 cells using LC-MS/MS-based SILAC quantitative proteomics and cytokine array show that silencing of POPX2 leads to increased secretion of exosomes, which may, in turn, induce multiple pro-angiogenic cytokines. This study, combined with our previous findings, suggests that a single ubiquitously expressed phosphatase POPX2 influences cancer metastasis via modulating multiple biological processes including MAPK signaling and exosome cytokine secretion.

miR-149 represses metastasis of hepatocellular carcinoma by targeting actin-regulatory proteins PPM1F

microRNAs have been implicated in hepatocellular carcinoma (HCC) metastasis, which is predominant cause of high mortality in these patients. Although an increasing body of evidence indicates that miR-149 plays an important role in the growth and metastasis of multiple types of cancers, its role in the progression of HCC remains unknown. Here, we demonstrated that miR-149 was significantly down-regulated in HCC, which was correlated with distant metastasis and TNM stage with statistical significance. A survival analysis showed that decreased miR-149 expression was correlated with a poor prognosis of HCC as well. We found that over-expression of miR-149 suppressed migration and invasion of HCC cells in vitro. In addition, we identified PPM1F (protein phosphatase, Mg(2+)/Mn(2+)-dependent, 1F) as a direct target of miR-149 whose expression was negatively correlated with the expression of miR-149 in HCC tissues. The re-expression of PPM1F rescued the miR-149-mediated inhibition of cell migration and invasion. miR-149 regulated formation of stress fibers to inhibit migration, and re-expression of PPM1F reverted the miR-149-mediated loss of stress fibers. Moreover, we demonstrated that over-expression of miR-149 reduced pMLC2, a downstream effector of PPM1F, in MHCC-97H cells. In vivo studies confirm inhibition of HCC metastasis by miR-149. Taken together, our findings indicates that miR-149 is a potential prognostic biomarker of HCC and that the miR-149/PPM1F regulatory axis represents a novel therapeutic target for HCC treatment.

Ca(2+)/calmodulin-dependent protein kinase phosphatase (CaMKP/PPM1F) interacts with neurofilament L and inhibits its filament association

Ca(2+)/calmodulin-dependent protein kinase phosphatase (CaMKP/PPM1F) is a Ser/Thr phosphatase that belongs to the PPM family. Growing evidence suggests that PPM phosphatases including CaMKP act as a complex with other proteins to regulate cellular functions. In this study, using the two-dimensional far-western blotting technique with digoxigenin-labeled CaMKP as a probe, in conjunction with peptide mass fingerprinting analysis, we identified neurofilament L (NFL) as a CaMKP-binding protein in a Triton-insoluble fraction of rat brain. We confirmed binding of fluorescein-labeled CaMKP (F-CaMKP) to NFL in solution by fluorescence polarization. The analysis showed that the dissociation constant of F-CaMKP for NFL is 73 ± 17 nM (n = 3). Co-immunoprecipitation assay using a cytosolic fraction of NGF-differentiated PC12 cells showed that endogenous CaMKP and NFL form a complex in cells. Furthermore, the effect of CaMKP on self-assembly of NFL was examined. Electron microscopy revealed that CaMKP markedly prevented NFL from forming large filamentous aggregates, suggesting that CaMKP-binding to NFL inhibits its filament association. These findings may provide new insights into a novel mechanism for regulating network formation of neurofilaments during neuronal differentiation.

Mechanism of Activity-Dependent Cargo Loading via the Phosphorylation of KIF3A by PKA and CaMKIIa

A regulated mechanism of cargo loading is crucial for intracellular transport. N-cadherin, a synaptic adhesion molecule that is critical for neuronal function, must be precisely transported to dendritic spines in response to synaptic activity and plasticity. However, the mechanism of activity-dependent cargo loading remains unclear. To elucidate this mechanism, we investigated the activity-dependent transport of N-cadherin via its transporter, KIF3A. First, by comparing KIF3A-bound cargo vesicles with unbound KIF3A, we identified critical KIF3A phosphorylation sites and specific kinases, PKA and CaMKIIa, using quantitative phosphoanalyses. Next, mutagenesis and kinase inhibitor experiments revealed that N-cadherin transport was enhanced via phosphorylation of the KIF3A C terminus, thereby increasing cargo-loading activity. Furthermore, N-cadherin transport was enhanced during homeostatic upregulation of synaptic strength, triggered by chronic inactivation by TTX. We propose the first model of activity-dependent cargo loading, in which phosphorylation of the KIF3A C terminus upregulates the loading and transport of N-cadherin in homeostatic synaptic plasticity.

Regulation of Ca(2+)/calmodulin-dependent protein kinase phosphatase (CaMKP/PPM1F) by protocadherin-γC5 (Pcdh-γC5)

Ca(2+)/calmodulin-dependent protein kinase phosphatase (CaMKP/PPM1F) is a Ser/Thr protein phosphatase that belongs to the PPM family. It is important to identify an endogenous regulator of CaMKP. Using an Escherichia coli two-hybrid screening method, we identified the C-terminal cytoplasmic fragment of protocadherin γ subfamily C5 (Pcdh-γC5), which was generated by intracellular processing, as a CaMKP-binding protein. Dephosphorylation of phosphorylated Ca(2+)/calmodulin-dependent protein kinase I (CaMKI) by CaMKP was significantly activated by the C-terminal cytoplasmic fragment, Pcdh-γC5(715-944), both in vitro and in cells, suggesting that the C-terminal fragment functions as an endogenous activator of CaMKP. The nuclear translocation of the fragment was blocked by its binding to cytoplasmic CaMKP to form a ternary complex with CaMKI. Taken together, these results strongly suggest that the C-terminal cytoplasmic fragment of Pcdh-γC5 acts as a scaffold for CaMKP and CaMKI to regulate CaMKP activity. These findings may provide new insights into the reversible regulation of CaMKP in cells.

POPX2 phosphatase regulates cell polarity and centrosome placement

Proper centrosome positioning is critical for many cellular functions, such as cell migration and maintenance of polarity. During wound healing, fibroblasts orient their centrosomes such that they face the wound edge. The centrosome orientation determines the direction of cells' migration so that they can close the wound effectively. In this study, we investigated the regulation of centrosome polarization and have identified the phosphatase POPX2 as an important regulator of centrosome orientation. We found that POPX2 inhibits centrosome centration, but not rearward nuclear movement, by regulating multiple proteins that function in centrosome positioning. High POPX2 levels result in reduced motility of the kinesin-2 motor, which, in turn, inhibits the transport of N-cadherin to the cell periphery and cell junctions. Loss of N-cadherin localization to the cell membrane affects the localization of focal adhesions and perturbs CDC42-Par6/PKCζ signaling. In addition, overexpression of POPX2 also results in a loss of Par3 localization to the cell periphery and reduced levels of LIC2 (dynein light intermediate chain 2), leading to defects in microtubule tethering and dynamics at cell-cell contacts. Therefore, POPX2 functions as a regulator of signaling pathways to modulate the positioning of centrosome in fibroblast during wound healing.

Herpes Simplex Virus 1 US3 Phosphorylates Cellular KIF3A To Downregulate CD1d Expression

Herpes simplex virus 1 (HSV-1) causes one of the most prevalent herpesviral infections in humans and is the leading etiological agent of viral encephalitis and eye infections. Our understanding of how HSV-1 interacts with the host at the cellular and organismal levels is still limited. We and others previously reported that, upon infection, HSV-1 rapidly and efficiently downregulates CD1d cell surface expression and suppresses the function of NKT cells, a group of innate T cells with critical immunoregulatory function. The viral protein kinase US3 plays a major role in this immune evasion mechanism, and its kinase activity is required for this function. In this study, we investigated the cellular substrate(s) phosphorylated by US3 and how it mediates US3 suppression of CD1d recycling. We identified the type II kinesin motor protein KIF3A as a critical kinesin factor in the cell surface expression of CD1d. Interestingly, KIF3A is phosphorylated by US3 both in vitro and in infected cells. Mass spectrometry analysis of purified KIF3A showed that it is phosphorylated predominantly at serine 687 by US3. Ablation of this phosphorylation abolished US3-mediated downregulation of CD1d expression, suggesting that phosphorylation of KIF3A is the primary mechanism of HSV-1 suppression of CD1d expression by US3 protein. Understanding of the precise mechanism of viral modulation of CD1d expression will help to develop more efficient vaccines in the future to boost host NKT cell-mediated immune responses against herpesviruses.

IMPORTANCE

Herpes simplex virus 1 (HSV-1) is among the most common human pathogens. Little is known regarding the exact mechanism by which this virus evades the human immune system, particularly the innate immune system. We previously reported that HSV-1 employs its protein kinase US3 to modulate the expression of the key antigen-presenting molecule CD1d to evade the antiviral function of NKT cells. Here we identified the key cellular motor protein KIF3A as a cellular substrate phosphorylated by US3, and this phosphorylation event mediates US3-induced immune evasion.

The heterotrimeric kinesin-2 complex interacts with and regulates GLI protein function

GLI transport to the primary cilium and nucleus is required for proper Hedgehog (HH) signaling; however, the mechanisms that mediate these trafficking events are poorly understood. Kinesin-2 motor proteins regulate ciliary transport of cargo, yet their role in GLI protein function remains unexplored. To examine a role for the heterotrimeric KIF3A-KIF3B-KAP3 kinesin-2 motor complex in regulating GLI activity, we performed a series of structure-function analyses using biochemical, cell signaling and in vivo approaches that define novel specific interactions between GLI proteins and two components of this complex, KAP3 and KIF3A. We find that all three mammalian GLI proteins interact with KAP3 and we map specific interaction sites in both proteins. Furthermore, we find that GLI proteins interact selectively with KIF3A, but not KIF3B, and that GLI interacts synergistically with KAP3 and KIF3A. Using a combination of cell signaling assays and chicken in ovo electroporation, we demonstrate that KAP3 interactions restrict GLI activator function but not GLI repressor function. These data suggest that GLI interactions with KIF3A-KIF3B-KAP3 complexes are essential for proper GLI transcriptional activity.

Signaling to the microtubule cytoskeleton: an unconventional role for CaMKII

Synaptic plasticity is a hallmark of the nervous system and is thought to be integral to higher brain functions such as learning and memory. Calcium, acting as a second messenger, and the calcium/calmodulin dependent kinase CaMKII are key regulators of neuronal plasticity. Given the importance of the actin and microtubule (MT) cytoskeleton in dendritic spine morphology, composition and plasticity, it is not surprising that many regulators of these cytoskeletal elements are downstream of the CaMKII pathway. In this review, we discuss the emerging role of calcium and CaMKII in the regulation of MTs and cargo unloading during synaptic plasticity.