Hepatocellular carcinoma (HCC) is a highly metastatic cancer with very poor prognosis. AMP activated kinase (AMPK) constitutes a candidate to inhibit HCC progression. First, AMPK is downregulated in ...HCC. Second, glucose starvation induces apoptosis in HCC cells via AMPK. Correspondingly, metformin activates AMPK and inhibits HCC cell proliferation. Nevertheless, the effect of AMPK activation on HCC cell invasiveness remains elusive. Here, migration/invasion was studied in HCC cells exposed to metformin and glucose starvation. Cell viability, proliferation and differentiation, as well as AMPK and PKA activation were analyzed. In addition, invasiveness in mutants of the AMPKα activation loop was assessed. Metformin decreased cell migration, invasion and epithelial-mesenchymal transition, and interference with AMPKα expression avoided metformin actions. Those antitumor effects were potentiated by glucose deprivation. Metformin activated AMPK at the same time that inhibited PKA, and both effects were enhanced by glucose starvation. Given that AMPKα(S173) phosphorylation by PKA decreases AMPK activation, we hypothesized that the reduction of PKA inhibitory effect by metformin could explain the increased antitumor effects observed. Supporting this, in AMPK activating conditions, cell migration/invasion was further impaired in AMPKα(S173C) mutant cells. Metformin emerges as a strong inhibitor of migration/invasion in HCC cells, and glucose restriction potentiates this effect.
The elimination of transformed and viral infected cells by natural killer (NK) cells requires a specialized junction between NK and target cells, denominated immunological synapse (IS). After initial ...recognition, the IS enables the directed secretion of lytic granules content into the susceptible target cell. The lymphocyte function‐associated antigen (LFA)‐1 regulates NK effector function by enabling NK‐IS assembly and maturation. The pathways underlying LFA‐1 accumulation at the IS in NK cells remained uncharacterized. A kinase anchoring protein 350 (AKAP350) is a centrosome/Golgi‐associated protein, which, in T cells, participates in LFA‐1 activation by mechanisms that have not been elucidated. We first evaluated AKAP350 participation in NK cytolytic activity. Our results showed that the decrease in AKAP350 levels by RNA interference (AKAP350KD) inhibited NK‐YTS cytolytic activity, without affecting conjugate formation. The impairment of NK effector function in AKAP350KD cells correlated with decreased LFA‐1 clustering and defective IS maturation. AKAP350KD cells that were exclusively activated via LFA‐1 showed impaired LFA‐1 organization and deficient lytic granule translocation as well. In NK AKAP350KD cells, activation signaling through Vav1 was preserved up to 10 min of interaction with target cells, but significantly decreased afterwards. Experiments in YTS and in ex vivo NK cells identified an intracellular pool of LFA‐1, which partially associated with the Golgi apparatus and, upon NK activation, redistributed to the IS in an AKAP350‐dependent manner. The analysis of Golgi organization indicated that the decrease in AKAP350 expression led to the disruption of the Golgi integrity in NK cells. Alteration of Golgi function by BFA treatment or AKAP350 delocalization from this organelle also led to impaired LFA‐1 localization at the IS. Therefore, this study characterizes AKAP350 participation in the modulation of NK effector function, revealing the existence of a Golgi‐dependent trafficking pathway for LFA‐1, which is relevant for LFA‐1 organization at NK‐lytic IS.
The signaling pathways that govern survival response in hepatic cancer cells subjected to nutritional restriction have not been clarified yet. In this study we showed that liver cancer cells ...undergoing glucose deprivation both arrested in G0/G1 and died mainly by apoptosis. Treatment with the AMPK activator AICAR phenocopied the effect of glucose deprivation on cell survival, whereas AMPK silencing in HepG2/C3A, HuH-7 or SK-Hep-1 cells blocked the cell cycle arrest and the increase in apoptotic death induced by glucose starvation. Both AMPK and PKA were promptly activated after glucose withdrawal. PKA signaling had a dual role during glucose starvation: whereas it elicited an early decreased in cell viability, it later improved this parameter. We detected AMPK phosphorylation (AMPKα(Ser173)) by PKA, which was increased in glucose starved cells and was associated with diminution of AMPK activation. To better explore this inhibitory effect, we constructed a hepatocarcinoma derived cell line which stably expressed an AMPK mutant lacking that PKA phosphorylation site: AMPKα1(S173C). Expression of this mutant significantly decreased viability in cells undergoing glucose starvation. Furthermore, after 36 h of glucose deprivation, the index of AMPKα1(S173C) apoptotic cells doubled the apoptotic index observed in control cells. Two main remarks arise: 1. AMPK is the central signaling kinase in the scenario of cell cycle arrest and death induced by glucose starvation in hepatic cancer cells; 2. PKA phosphorylation of Ser173 comes out as a strong control point that limits the antitumor effects of AMPK in this situation.
Background and aims
Non‐alcoholic fatty liver (NAFLD) and its more serious form non‐alcoholic steatohepatitis increase risk of hepatocellular carcinoma (HCC). Lipid metabolic alterations and its role ...in HCC development remain unclear. SPARC (Secreted Protein, Acidic and Rich in Cysteine) is involved in lipid metabolism, NAFLD and diabetes, but the effects on hepatic lipid metabolism and HCC development is unknown. The aim of this study was to evaluate the role of SPARC in HCC development in the context of NAFLD.
Methods
Primary hepatocyte cultures from knockout (SPARC−/−) or wild‐type (SPARC+/+) mice, and HepG2 cells were used to assess the effects of free fatty acids on lipid accumulation, expression of lipogenic genes and de novo triglyceride (TG) synthesis. A NAFLD‐HCC model was stabilized on SPARC−/− or SPARC+/+ mice. Correlations among SPARC, lipid metabolism‐related gene expression patterns and clinical prognosis were studied using HCC gene expression dataset.
Results
SPARC−/− mice increases hepatic lipid deposits over time. Hepatocytes from SPARC−/− mice or inhibition of SPARC by an antisense adenovirus in HepG2 cells resulted in increased TG deposit, expression of lipid‐related genes and nuclear translocation of SREBP1c. Human HCC database analysis revealed that SPARC negatively correlated with genes involved in lipid metabolism, and with poor survival. In NAFLD‐HCC murine model, the absence of SPARC accelerates HCC development. RNA‐seq study revealed that pathways related to lipid metabolism, cellular detoxification and proliferation were upregulated in SPARC−/− tumour‐bearing mice.
Conclusions
The absence of SPARC is associated with an altered hepatic lipid metabolism, and an accelerated NAFLD‐related HCC development.
A-kinase anchoring protein 350 (AKAP350) is a centrosomal/Golgi scaffold protein, critical for the regulation of microtubule dynamics. AKAP350 recruits end-binding protein 1 (EB1) to the centrosome ...in mitotic cells, ensuring proper spindle orientation in epithelial cells. AKAP350 also interacts with p150glued, the main component of the dynactin complex. In the present work, we found that AKAP350 localized p150glued to the spindle poles, facilitating p150glued/EB1 interaction at these structures. Our results further showed that the decrease in AKAP350 expression reduced p150glued localization at astral microtubules and impaired the elongation of astral microtubules during anaphase. Overall, this study provides mechanistic data on how microtubule regulatory proteins gather to define microtubule dynamics in mitotic cells.
•AKAP350 knock down (AKAP350KD) reduces p150glued localization at the spindle poles.•P150glued/EB1 interaction at the spindle poles is diminished in AKAP350KD cells.•P150glued overexpression does not rescue EB1 spindle pole-levels in AKAP350KD cells.•AKAP350 knock down delays astral microtubule-elongation during anaphase.
CDC42 interacting protein 4 (CIP4) is a CDC42 effector that coordinates membrane deformation and actin polymerization. The correlation of CIP4 overexpression with metastatic capacity has been ...characterized in several types of cancer. However, little information exists on how CIP4 function is regulated. CIP4 interacts with A-kinase (PKA) anchoring protein 350 (AKAP350) and CIP4 is also a PKA substrate. Here, we identified CIP4 T225 as the major CIP4 PKA phosphorylation site. In vitro and in vivo experiments using hepatocellular carcinoma (HCC) and breast cancer cells showed that expression of a CIP4(T225E) phosphomimetic mutant increased cancer cell metastatic capacity and that, conversely, expression of a CIP4(T225A) non-phosphorylatable mutant reduced invasive properties. PKA inhibition decreased to CIP4(T225A) cell-levels control but not CIP4(T225E) cell migratory and invasive efficiency. Concomitantly, our studies indicate that CIP4 T225 phosphorylation promotes the formation of functional invadopodia and enhances CIP4 localization at these structures. Our findings further provide mechanistic data indicating that CIP4 T225 phosphorylation facilitates CIP4 interaction with CDC42. Altogether this study identifies a signaling pathway that involves CIP4 phosphorylation by PKA during the acquisition of a metastatic phenotype in cancer cells.
•AKAP350 enables CIP4 phosphorylation by PKA, which occurs at the CIP4 T225 residue.•CIP4 T225 is a relevant substrate in PKA regulation of breast cancer cell invasiveness.•CIP4 T225 phosphorylation regulates CIP4/CDC42 interaction and invadopodia formation.•CIP4(T225E) phosphomimetic mutant enhances HCC and breast cancer cell invasiveness.
Display omitted
During ischemic acute kidney injury (AKI), loss of cytoskeletal integrity and disruption of intercellular junctions are rapid events in response to ATP depletion. Angiotensin II type ...2 receptor (AT2R) is overexpressed in injury situations and its stimulation by angiotensin II (AngII) is related to beneficial renal effects. Its role on ischemic AKI has not been deeply studied. The aim of the present study was to investigate whether pretreatment with the AT2R agonist, C21, prevents ischemic renal epithelial cell injury. Studies in a model of 40 min of renal ischemia followed by 24 h of reperfusion (IR) in rats demonstrated that C21 pretreatment attenuated renal dysfunction and induced better preservation of tubular architecture. In addition, we studied the expression of Rho GTPases, RhoA and Cdc42, since they are key proteins in the regulation of the actin cytoskeleton and the stability of epithelial intercellular junctions. IR downregulated RhoA and Cdc42 abundance in rat kidneys. C21 pretreatment prevented RhoA reduction and increased Cdc42 abundance compared to controls. We also used an in vitro model of ATP depletion in MDCK cells grown on filter support. Using immunofluorescence we observed that in MDCK cells, C21 pretreatment prevented the ATP depletion-induced reduction of actin in brush border microvilli and in stress fibers. Moreover, C21 prevented membrane E-cadherin reduction, and RhoA and Cdc42 downregulation. The present study describes for the first time a renoprotective effect of the AT2R agonist, C21, against AKI, and provides evidence supporting that stimulation of AT2R triggers cytoprotective mechanisms against an ischemic event.
The acquisition of a migratory phenotype is central in processes as diverse as embryo differentiation and tumor metastasis. An early event in this phenomenon is the generation of a ...nucleus-centrosome-Golgi back-to-front axis. AKAP350 (also known as AKAP9) is a Golgi and centrosome scaffold protein that is involved in microtubule nucleation. AKAP350 interacts with CIP4 (also known as TRIP10), a cdc42 effector that regulates actin dynamics. The present study aimed to characterize the participation of centrosomal AKAP350 in the acquisition of migratory polarity, and the involvement of CIP4 in the pathway. The decrease in total or in centrosomal AKAP350 led to decreased formation of the nucleus-centrosome-Golgi axis and defective cell migration. CIP4 localized at the centrosome, which was enhanced in migratory cells, but inhibited in cells with decreased centrosomal AKAP350. A decrease in the CIP4 expression or inhibition of the CIP4-AKAP350 interaction also led to defective cell polarization. Centrosome positioning, but not nuclear movement, was affected by loss of CIP4 or AKAP350 function. Our results support a model in which AKAP350 recruits CIP4 to the centrosome, providing a centrosomal scaffold to integrate microtubule and actin dynamics, thus enabling centrosome polarization and ensuring cell migration directionality.
Microtubules regulate brush border formation Tonucci, Facundo M.; Ferretti, Anabela; Almada, Evangelina ...
Journal of cellular physiology,
February 2018, Letnik:
233, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Most epithelial cells contain apical membrane structures associated to bundles of actin filaments, which constitute the brush border. Whereas microtubule participation in the maintenance of the brush ...border identity has been characterized, their contribution to de novo microvilli organization remained elusive. Hereby, using a cell model of individual enterocyte polarization, we found that nocodazole induced microtubule depolymerization prevented the de novo brush border formation. Microtubule participation in brush border actin organization was confirmed in polarized kidney tubule MDCK cells. We also found that centrosome, but not Golgi derived microtubules, were essential for the initial stages of brush border development. During this process, microtubule plus ends acquired an early asymmetric orientation toward the apical membrane, which clearly differs from their predominant basal orientation in mature epithelia. In addition, overexpression of the microtubule plus ends associated protein CLIP170, which regulate actin nucleation in different cell contexts, facilitated brush border formation. In combination, the present results support the participation of centrosomal microtubule plus ends in the activation of the polarized actin organization associated to brush border formation, unveiling a novel mechanism of microtubule regulation of epithelial polarity.
The present work aimed to evaluate the contribution of the microtubule cytoskeleton to de novo microvilli organization in epithelial cells. Our studies demonstrate that microtubules are essential for the polarized actin organization during brush border development, and provide evidence that centrosomal microtubule plus ends are involved in this process.
The organization of epithelial cells to form hollow organs with a single lumen requires the accurate three-dimensional arrangement of cell divisions. Mitotic spindle orientation is defined by ...signaling pathways that provide molecular links between specific spots at the cell cortex and astral microtubules, which have not been fully elucidated. AKAP350 is a centrosomal/Golgi scaffold protein, implicated in the regulation of microtubule dynamics. Using 3D epithelial cell cultures, we found that cells with decreased AKAP350 expression (AKAP350KD) formed polarized cysts with abnormal lumen morphology. Analysis of mitotic cells in AKAP350KD cysts indicated defective spindle alignment. We established that AKAP350 interacts with EB1, a microtubule associated protein that regulates spindle orientation, at the spindle poles. Decrease of AKAP350 expression lead to a significant reduction of EB1 levels at spindle poles and astral microtubules. Conversely, overexpression of EB1 rescued the defective spindle orientation induced by deficient AKAP350 expression. The specific delocalization of the AKAP350/EB1complex from the centrosome decreased EB1 levels at astral microtubules and lead to the formation of 3D-organotypic structures which resembled AKAP350KD cysts. We conclude that AKAP350 recruits EB1 to the spindle poles, ensuring EB1 presence at astral microtubules and proper spindle orientation during epithelial morphogenesis.
PDF
