Inhibition of protein kinase C-dependent protein phosphorylation correlates with increased polarity and locomotion in Walker 256 carcinosarcoma cells

An ezrin-rich, rigid uropod-like structure directs movement of amoeboid blebbing cells

Melanoma cells can switch between an elongated mesenchymal-type and a rounded amoeboid-type migration mode. The rounded 'amoeboid' form of cell movement is driven by actomyosin contractility resulting in membrane blebbing. Unlike elongated A375 melanoma cells, rounded A375 cells do not display any obvious morphological front-back polarisation, although polarisation is thought to be a prerequisite for cell movement. We show that blebbing A375 cells are polarised, with ezrin (a linker between the plasma membrane and actin cytoskeleton), F-actin, myosin light chain, plasma membrane, phosphatidylinositol (4,5)-bisphosphate and β1-integrin accumulating at the cell rear in a uropod-like structure. This structure does not have the typical protruding shape of classical leukocyte uropods, but, as for those structures, it is regulated by protein kinase C. We show that the ezrin-rich uropod-like structure (ERULS) is an inherent feature of polarised A375 cells and not a consequence of cell migration, and is necessary for cell invasion. Furthermore, we demonstrate that membrane blebbing is reduced at this site, leading to a model in which the rigid ezrin-containing structure determines the direction of a moving cell through localised inhibition of membrane blebbing.

Ezrin/moesin in motile Walker 256 carcinosarcoma cells: Signal-dependent relocalization and role in migration

Rat Walker 256 carcinosarcoma cells spontaneously develop front-tail polarity and migrate in the absence of added stimuli. Constitutive activation of phosphatidylinositol-3 kinase (PI 3-kinase), Rac, Rho and Rho kinase are essential for these processes. Ezrin and moesin are putative targets of these signaling pathways leading to spontaneous migration. To test this hypothesis, we used specific siRNA probes that resulted in a downregulation of ezrin and moesin by about 70% and in a similar reduction in the fraction of migrating cells. Spontaneous polarization however was not affected, indicating a more subtle role of ezrin and moesin in migration. We provide furthermore evidence that endogenous ezrin and moesin colocalize with F-actin at the contracted tail of polarized cells, similar to ectopically expressed green fluorescent protein-tagged ezrin. Our results suggest that myosin light chain and ezrin are markers of front and tail, respectively, even in the absence of morphological polarization. We further show that endogenous ezrin and moesin are phosphorylated and that activities of PI-3 kinase, Rho and Rac, but not of Rho-kinase, are required for this C-terminal phosphorylation. Activation of protein kinase C in contrast suppressed phosphorylation of ezrin and moesin. Inhibition of ezrin phosphorylation prevented its membrane association.

Walker 256 tumor growth in rats with hereditary defect of vasopressin synthesis

Stable deceleration of Walker 256 tumor growth was detected in Brattleboro rats with vasopressin synthesis defect in comparison with normal WAG rats. In contrast to continuous tumor growth typical of rats, the growth of this tumor in Brattleboro rats was negligible and was observed during the first 15-18 days after transplantation, after which the tumor regressed and disappeared. The effect was age-dependent and was more pronounced in old animals. Repeated injection of Walker 256 cells does not lead to tumor development, which attested to direct involvement of the immune system in the detected phenomenon.

The Rho/Rho-kinase and the phosphatidylinositol 3-kinase pathways are essential for spontaneous locomotion of Walker 256 carcinosarcoma cells

Signal transduction pathways controlling spontaneous locomotion of Walker carcinosarcoma cells are not well understood. We have therefore investigated the role of signalling proteins in development of polarity and locomotion of these cells. Treatment of the cells with 100 ng/ml pertussis toxin had no significant effect on the percentage of polarized cells. In contrast, 2 different phosphatidylinositol 3-kinase inhibitors (wortmannin and LY-294002) markedly reduced the proportion of polarized cells. Spontaneous locomotion of the cells was also significantly inhibited by these two inhibitors. In agreement with these data, we observed localization of the p85alpha subunit of phosphatidylinositol 3-kinase predominantly in the membrane fraction of Walker carcinosarcoma cells, indicating constitutive activation of this enzyme. We also investigated a role of Rho family proteins. Spontaneous development of polarity was almost completely suppressed by electroporation of the cells in the presence of 4 microg/ml C(3) exoenzyme, which specifically ADP-ribosylates and inactivates Rho. Two downstream targets of Rho, the Rho-activated kinases I and II, were also detected predominantly in the particulate membrane fraction, suggesting constitutive activation. A specific Rho-kinase inhibitor (Y-27632) blocked spontaneous polarization and migration in a concentration-dependent manner. Our results indicate that constitutive activation of the Rho/Rho-kinase pathway and of phosphatidylinositol 3-kinase plays an essential part in spontaneous development of polarity and cell locomotion of these cells.

Protein kinase C isoforms involved in regulation of cell shape and locomotion of human fibrosarcoma HT1080 cells

The role of protein kinase C (PKC) isoforms in the regulation of cell shape [switch between fibroblast-like and crescent shape (CS)] and of locomotion of human fibrosarcoma HT1080 cells has been investigated. The PKC activator phorbol myristate acetate (PMA) induced the transition of elongated fibroblast-like cells into CS cells and stimulated locomotion. Both responses to PMA were inhibited by the PKC inhibitor Ro 31-8220. Analysis of the time course showed that stimulation of shape changes (formation of CS cells) and locomotor activity (increase in the proportion and speed of locomoting cells) was maximal in the early phase of the response (up to 2.5 hr) and significantly decreased later (15 to 21 hr). CS formation and stimulated locomotion correlated closely with a marked redistribution from the cytosol to the membrane of PKC isoforms alpha, beta1 and gamma in the early phase (0.5 to 2 hr) following activation with PMA. The subsequent reduction of the proportion of CS cells and of cell locomotion correlated with down-regulation of these isoforms in the second phase (16 to 21 hr). In contrast, the total amount and distribution of PKC beta2 remained almost unchanged with 10(-8) M PMA up to 21 hr. Furthermore, changes in shape and locomotion did not correlate with the responses of PKC delta to PMA. Inhibition of PMA-stimulated locomotion by the more specific inhibitor Gö 6976 is consistent with a role of PKC alpha and beta1 in this response. Ro 31-8220 alone induced a moderate down-regulation of PKC isoforms alpha and delta, but it also inhibited the more pronounced down-regulation of these isoforms by PMA. Our results indicate that activation of PKC isoforms alpha, gamma and beta1, but not beta2 or delta, stimulates locomotion and formation of CS cells in human fibrosarcoma HT1080 cells.

TPA-enhanced motility and invasion in a highly metastatic variant (L-10) of human rectal adenocarcinoma cell line RCM-1: selective role of PKC-alpha and its inhibition by a combination of PDBu-induced PKC downregulation and antisense oligonucleotides treatment

We previously found that 12-O-tetradecanoylphorbol-13-acetate (TPA)-enhanced invasiveness was associated with augmentation of cell motility but not that of metalloproteinase activity in a highly metastatic variant (L-10) of the human colon adenocarcinoma cell line RCM-1 and that this enhancement was possibly mediated by protein kinase C (PKC). In this study, we first intended to determine the specific isoforms of PKC involved in this TPA-enhanced L-10 cell motility that leads to invasion, and then investigated the way to inhibit the enhanced motility and invasion by using antisense oligodeoxynucleotides (ODN) targeting the isoform. An activator of conventional PKC isoforms (cPKC), thymeleatoxin, enhanced L-10 cell motility and invasion like TPA, and an inhibitor of cPKC, Go-6976, efficiently inhibited TPA-enhanced motility and invasion. TPA treatment induced a shift of PKC-alpha, but not other isoforms, from the cytosol to the membrane fraction, indicating the activation of the isoform. During the assay period, only activation but not downregulation of PKC-alpha occurred with the low concentration of TPA used in our assays. Antisense ODNs specific for PKC-alpha efficiently reduced its expression at the protein levels and inhibited L-10 cell motility in the absence of TPA. With TPA treatment, however, the remaining PKC-alpha was sufficient for activation leading to enhanced invasion. Only a combination of depletion of PKC by prolonged stimulation with a high concentration of phorbol 12,13 dibutyrate (PDBu) and treatment with antisense ODNs effectively inhibited L-10 cell invasion even in the presence of TPA. These results suggested that downregulation of PKC isoforms by treatment with antisense ODNs alone is insufficient to suppress the isoform-mediated cellular events in the presence of PKC activators, and thus that some additional treatments are necessary for the successful downregulation of them.

Role of protein kinase C isoforms in locomotion of Walker 256 carcinosarcoma cells

Treatment with low (nanomolar) concentrations of phorbol-12-myristate-13-acetate (PMA) for 5 to 30 min suppresses locomotion of Walker 256 carcinosarcoma cells, suggesting that activation of protein kinase C (PKC) is a stop signal for tumor cell locomotion. We have compared the effects of PMA on cell shape and motility with down-regulation of specific PKC isoforms. Using specific antibodies, we show that Walker carcinosarcoma cells express PKC isoforms alpha, betaI, betaII, gamma, lambda, mu, eta and zeta. Short-term incubation with PMA induced a marked shift of isoforms alpha, betaI, betaII, gamma and eta to the particulate fraction. Long-term incubation with PMA (0.1 microM, 6 hr) resulted in significant reduction of expression of conventional PKCs alpha, betaI, betaII and gamma and of the novel PKC eta to 10% to 26% of controls. Down-regulation of PKC alpha, betaI and betaII by long-term incubation with PMA was reversible after removal of PMA, whereas that of isoforms gamma and eta was not. The motile properties of cells after down-regulation of PKC isoforms were investigated. Concomitant with down-regulation of PKC isoforms, long-term incubation of cells with PMA resulted in recovery of the polar shape and the ability to migrate. Motility and polarized shape of the down-regulated cells were no longer susceptible to short-term treatment with PMA, showing that active PKC is indeed responsible for the inhibitory effects of PMA. Effects of long-term incubation with PMA on cell shape and motility were reversible. Our findings strongly suggest that PKCs alpha, betaI and betaII activated by PMA are involved in stopping Walker carcinosarcoma cell locomotion.

Low concentrations of the phosphatase inhibitor okadaic acid stop tumor cell locomotion

The phosphatase inhibitor okadaic acid exerted a biphasic effect on the shape of spontaneously polarized Walker carcinosarcoma cells. At lower concentrations, the drug suppressed cell polarity (IC50 = 0.14 microM) and the cells reverted to a spherical shape. At higher concentrations (> 0.25 microM), cells developed large blebs (IC50 = 0.4 microM). Furthermore, 0.2 microM okadaic acid completely suppressed spontaneous cell locomotion. Two specific inhibitors of protein kinase C did not prevent the actions of okadaic acid on cell shape, showing that this enzyme is very likely not involved. Another phosphatase inhibitor, calyculin A, also suppressed polarity (IC50 = 60 nM) and produced blebbing cells (IC50 = 70 nM). 1 microM okadaic acid induced a 40- to 70-fold increase in phosphorylation of the intermediate filament protein vimentin in intact cells. Increased phosphorylation of this major phosphoprotein correlated with the generation of blebbing cells, rather than with inhibition of polarity and may thus be involved in generating the marked shape changes. We conclude that constitutive phosphatase activity is required for motility and control of shape in Walker carcinosarcoma cells.