PKC mediates 12(S)-HETE-induced cytoskeletal rearrangement in B16a melanoma cells

Enantioselectivity in some physiological and pathophysiological roles of hydroxyeicosatetraenoic acids

The phenomenon of chirality has been shown to greatly impact drug activities and effects. Different enantiomers may exhibit different effects in a certain biological condition or disease state. Cytochrome P450 (CYP) enzymes metabolize arachidonic acid (AA) into a large variety of metabolites with a wide range of activities. Hydroxylation of AA by CYP hydroxylases produces hydroxyeicosatetraenoic acids (HETEs), which are classified into mid-chain (5, 8, 9, 11, 12, and 15-HETE), subterminal (16-, 17-, 18- and 19-HETE) and terminal (20-HETE) HETEs. Except for 20-HETE, these metabolites exist as a racemic mixture of R and S enantiomers in the physiological system. The two enantiomers could have different degrees of activity or sometimes opposing effects. In this review article, we aimed to discuss the role of mid-chain and subterminal HETEs in different organs, importantly the heart and the kidneys. Moreover, we summarized their effects in some conditions such as neutrophil migration, inflammation, angiogenesis, and tumorigenesis, with a focus on the reported enantiospecific effects. We also reported some studies using genetically modified models to investigate the roles of HETEs in different conditions.

Synchronous Comparative Evaluation of Fibronectin Continuity and Cellular Growth Kinetics in Malignant Cutaneous Melanoma

Cellular fibronectin mediates the adhesion of cells with the extracellular matrix and thus probably regulates tumor invasion. Evaluation of proliferating cell nuclear antigen expression and counting of silver nuclear organizer regions potentially assess proliferative fraction and biologic aggressiveness in several malignancies. We investigated the above markers’ prognostic value in 60 malignant melanomas of the skin. Deep Clark levels were statistically associated with discontinuous fibronectin staining pattern (SPII) ( P < .05) as well as with high proliferating cell nuclear antigen and silver nuclear organizer regions indexes ( P < .01 and P < .05, respectively). Fibronectin staining pattern (SPII) was frequently observed in thick melanomas ( P < .05). High proliferating cell nuclear antigen immunoreactivity positively correlated with mitotic activity ( P < .05), the presence of vertical growth phase ( P < .05), and increased silver nuclear organizer regions counts ( P < .05). Patients with continuous fibronectin staining pattern (SPI) and low proliferating cell nuclear antigen scores were unlikely to develop metastatic disease ( P < .01). Therefore, the simultaneous comparative assessment of these factors is very promising in predicting melanomas clinical evolution.

Convergence of eicosanoid and integrin biology: 12-lipoxygenase seeks a partner

Background

Integrins and enzymes of the eicosanoid pathway are both well-established contributors to cancer. However, this is the first report of the interdependence of the two signaling systems. In a screen for proteins that interacted with, and thereby potentially regulated, the human platelet-type 12-lipoxygenase (12-LOX, ALOX12), we identified the integrin β4 (ITGB4).

Methods

Using a cultured mammalian cell model, we have demonstrated that ITGB4 stimulation leads to recruitment of 12-LOX from the cytosol to the membrane where it physically interacts with the integrin to become enzymatically active to produce 12(S)-HETE, a known bioactive lipid metabolite that regulates numerous cancer phenotypes.

Results

The net effect of the interaction was the prevention of cell death in response to starvation. Additionally, regulation of β4-mediated, EGF-stimulated invasion was shown to be dependent on 12-LOX, and downstream Erk signaling in response to ITGB4 activation also required 12-LOX.

Conclusions

This is the first report of an enzyme of the eicosanoid pathway being recruited to and regulated by activated β4 integrin. Integrin β4 has recently been shown to induce expansion of prostate tumor progenitors and there is a strong correlation between stage/grade of prostate cancer and 12-LOX expression. The 12-LOX enzymatic product, 12(S)-HETE, regulates angiogenesis and cell migration in many cancer types. Therefore, disruption of integrin β4-12LOX interaction could reduce the pro-inflammatory oncogenic activity of 12-LOX. This report on the consequences of 12-LOX and ITGB4 interaction sets a precedent for the linkage of integrin and eicosanoid biology through direct protein-protein association.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-015-0382-5) contains supplementary material, which is available to authorized users.

The myosin Va head domain binds to the neurofilament-L rod and modulates endoplasmic reticulum (ER) content and distribution within axons

The neurofilament light subunit (NF-L) binds to myosin Va (Myo Va) in neurons but the sites of interaction and functional significance are not clear. We show by deletion analysis that motor domain of Myo Va binds to the NF-L rod domain that forms the NF backbone. Loss of NF-L and Myo Va binding from axons significantly reduces the axonal content of ER, and redistributes ER to the periphery of axon. Our data are consistent with a novel function for NFs as a scaffold in axons for maintaining the content and proper distribution of vesicular organelles, mediated in part by Myo Va. Based on observations that the Myo Va motor domain binds to intermediate filament (IF) proteins of several classes, Myo Va interactions with IFs may serve similar roles in organizing organelle topography in different cell types.

Oleic acid promotes migration on MDA-MB-231 breast cancer cells through an arachidonic acid-dependent pathway

An association between dietary fatty, obesity and an increased risk of developing breast cancer has been suggested. In breast cancer cells, free fatty acids (FFAs) mediate biological effects including cell proliferation and ERK1/2 activation. However, the contribution of FFAs to tumor progression and metastasis through the regulation of cell migration has not been studied. We demonstrated here that stimulation on MDA-MB-231 breast cancer cells with oleic acid (OA) promotes an increase in focal adhesion kinase (FAK) phosphorylation, as revealed by site-specific antibodies that recognize the phosphorylation state of FAK at tyrosine-397 (Tyr-397), Tyr-577 and in vitro kinase assays. OA also promotes the migration of MDA-MB-231 cells. Treatment with Gi/Go proteins, phospholipase C (PLC), lipoxygenases (LOXs) and Src inhibitor prevents FAK phosphorylation and cell migration. In summary, our findings delineate a new signal transduction pathway, where OA mediates the production of arachidonic acid (AA), and then AA metabolites mediate FAK phosphorylation and cell migration in MDA-MB-231 breast cancer cells.

New aspects of the role of hydroxyeicosatetraenoic acids in cell growth and cancer development

Lipoxygenase (LOX) pathway leads to the formation of leukotrienes and also catalyses the conversion of arachidonic acid (AA) to hydroperoxyeicosatetraenoic acids that are then reduced to hydroxyeicosatetraenoic acids (HETE) by glutathione peroxidase. There are four mammalian LOXs that produce 5-, 8-, 12- and 15-HETE, respectively. Cytochrome P-450 isozymes are also capable of metabolising AA to HETEs either by bis-allylic oxidation (lipoxygenase-like reaction) to generate 5-, 8-, 9-, 11-, 12- and 15-HETE; or by varpi/varpi-1 hydroxylation to yield 16-, 17-, 18-, 19- and 20-HETEs. It is now widely recognised that HETEs have important physiological and pathological functions that modulate ion transport, renal and pulmonary functions, vascular tone and reactivity, and inflammatory and growth responses. They can be released during the action of growth factors and cytokines, reaching physiological concentrations higher than that of prostanoids and modulating the functions of these factors. Their effects can occur through receptor or non-receptor mechanisms. Recent reviews have summarised the effects of HETEs in vascular homeostasis or lung and renal physiology. The present review focuses on the emerging effects of HETEs on cell signalling and physiological cell growth. It also discusses current observations regarding the role of HETEs in apoptosis, angiogenesis, the proliferation of cancer cells and metastasis, which constitute a potential area for successful therapeutic intervention.

Overexpression of ROCK in human breast cancer cells: evidence that ROCK activity mediates intracellular membrane traffic of lysosomes

Small GTPase Rho and its downstream effectors, ROCK family of Rho-associated serine-threonine kinases, are thought to participate in cell morphology, motility, and tumor progression through regulating the rearrangement of actin cytoskeleton. Here we present evidence that transfection of human breast cancer cells with cDNA encoding a dominant active mutant of ROCK causes dispersal of lysosomal vesicles throughout the cytoplasm without perturbing the machinery of the endocytic pathway. The intracellular distribution of lysosomes and endocytosed transferrin, an early endosomal marker, were further assessed by confocal immunofluorescence microscopy. In the active ROCK transfected cells the lysosomal proteins, cathepsin D, LIMPII, and LAMP1, were found throughout the cytoplasm in dispersed small vesicles, which were accessible to the endocytosed Texas Red-labeled transferrin. 3D-image analysis of lysosomal distribution in the active ROCK transfectants revealed abundant punctate signals in the peripheral region of the basal plasma membrane. Cells expressing vector alone did not exhibit these alterations. Wortmannin, a phosphatidylinositol 3-kinase inhibitor, induced LIMPII-positive/ transferrin negative large vacuoles in the perinuclear region, and disappearence of the dispersed small vesicular structures. To our knowledge, this is the first evidence that increasing ROCK expression contributes to selective cellular dispersion of lysosomes in invasive breast cancer cells.

A role for small GTPase RhoA in regulating intracellular membrane traffic of lysosomes in invasive rat hepatoma cells

Small GTPase RhoA regulates signal transduction from receptors in the membrane to a variety of cellular events related to cell morphology, motility, cytoskeletal dynamics, cytokinesis, and tumour progression, but it is unclear how RhoA regulates intracellular membrane dynamics of lysosomes. We showed previously by confocal immunofluorescence microscopy that the transfection of dominant active RhoA in MM1 cells causes the dispersal translocation of lysosomes stained for cathepsin D throughout the cytoplasm. Y-27632, a selective inhibitor of p160ROCK, impeded the cellular redistribution of lysosomes and promoted reclustering of lysosomes toward the perinuclear region. Here we have further investigated whether the acidic lysosomal vesicles dispersed throughout the cytoplasm are applied to the early endosomes in the endocytic pathway, and we demonstrate that the dispersed lysosomes were accessible to endocytosed molecule such as dextran, and their acidity was not changed, as determined by increased accumulation of the acidotropic probe LysoTracker Red. Brefeldin A did not induce the tabulation of these dispersed lysosomes, but it caused early endosomes to form an extensive tubular network. The dispersed lysosomes associated with cathepsin D and LIMPII were not colocalized with early endosomes, and these vesicles were not inaccessible to the endocytosed anti-transferrin receptor antibody. Moreover, wortmannin, an inhibitor of phosphatidylinositol 3-kinase, induced a dramatic change in LIMPII-containing structures in which LIMPII-positive swollen large vacuoles were increased and small punctate structures disappeared in the cytoplasm. These swollen vacuoles were not doubly positive for LIMPII and transferrin receptor, and were not inaccessible to the internalized anti-transferrin receptor antibody. Therefore, our novel findings presented in this paper indicate that RhoA activity causes a selective translocation of lysosomes without perturbing the machinery of endocytic pathway.

Modulation of cell-substrate adhesion by arachidonic acid: lipoxygenase regulates cell spreading and ERK1/2-inducible cyclooxygenase regulates cell migration in NIH-3T3 fibroblasts

Adhesion of cells to an extracellular matrix is characterized by several discrete morphological and functional stages beginning with cell-substrate attachment, followed by cell spreading, migration, and immobilization. We find that although arachidonic acid release is rate-limiting in the overall process of adhesion, its oxidation by lipoxygenase and cyclooxygenases regulates, respectively, the cell spreading and cell migration stages. During the adhesion of NIH-3T3 cells to fibronectin, two functionally and kinetically distinct phases of arachidonic acid release take place. An initial transient arachidonate release occurs during cell attachment to fibronectin, and is sufficient to signal the cell spreading stage after its oxidation by 5-lipoxygenase to leukotrienes. A later sustained arachidonate release occurs during and after spreading, and signals the subsequent migration stage through its oxidation to prostaglandins by newly synthesized cyclooxygenase-2. In signaling migration, constitutively expressed cyclooxygenase-1 appears to contribute approximately 25% of prostaglandins synthesized compared with the inducible cyclooxygenase-2. Both the second sustained arachidonate release, and cyclooxygenase-2 protein induction and synthesis, appear to be regulated by the mitogen-activated protein kinase extracellular signal-regulated kinase (ERK)1/2. The initial cell attachment-induced transient arachidonic acid release that signals spreading through lipoxygenase oxidation is not sensitive to ERK1/2 inhibition by PD98059, whereas PD98059 produces both a reduction in the larger second arachidonate release and a blockade of induced cyclooxygenase-2 protein expression with concomitant reduction of prostaglandin synthesis. The second arachidonate release, and cyclooxygenase-2 expression and activity, both appear to be required for cell migration but not for the preceding stages of attachment and spreading. These data suggest a bifurcation in the arachidonic acid adhesion-signaling pathway, wherein lipoxygenase oxidation generates leukotriene metabolites regulating the spreading stage of cell adhesion, whereas ERK 1/2-induced cyclooxygenase synthesis results in oxidation of a later release, generating prostaglandin metabolites regulating the later migration stage.

Associations of PKC isoforms with the cytoskeleton of B16F10 melanoma cells

Although PKC plays a major role in regulating the morphology and function of the cytoskeleton, little is known about in situ associations of specific isoforms with the cytoskeleton. We demonstrate that seven PKC isoforms are expressed in B16F10 melanoma cells and show different levels of induction by serum. Using cell cytoskeleton preparations (CSKs), confocal microscopy, and immunocytochemistry, all isoforms show specific patterns of localization to focal contact-like structures (alpha, delta), very small cytoplasmic granules/vesicles (all isoforms), dense ordered arrays of small granules in the perinuclear region (alpha, delta), granules/vesicles associated with a homogeneous framework in the cytoplasm adjacent to the nucleus (gamma), or irregular-shaped patches of granules at or near the nuclear perimeter (eta, theta). In addition, several isoforms are present as cytoplasmic granules/ vesicles in linear or curvilinear arrays (alpha, delta, epsilon, theta). When isoform localization is examined using 3.7% formaldehyde or methanol:acetone, the patterns of localization in CSKs are often difficult or impossible to detect, and many are described here for the first time. Double-labeling experiments with CSK demonstrate that PKC actin co-localizes with punctate alpha-rich particles above the nucleus, granules of epsilon throughout the cytoplasm, and with theta in irregular-shaped aggregates associated with the nucleus. Vimentin co-localizes with perinuclear granules of delta and beta(2), and alpha-tubulin co-localizes with theta in structures at or near the nuclear surface and in microtubules associated with the microtubule organizing center (MTOC). In summary, the present study demonstrates that seven PKC isoforms are endogenously expressed in B16F10 melanoma cells. These isoforms show various levels of induction by serum and specific patterns of association with various components of the detergent-resistant cell cytoskeleton.

Expression, subcellular localization and putative function of platelet-type 12-lipoxygenase in human prostate cancer cell lines of different metastatic potential

The involvement of 12-lipoxygenase (12-LOX) expression and function in tumor metastasis has been demonstrated in several murine tumor cell lines. In addition, 12-LOX expression was detected in human prostatic tumors and correlated to the clinical stage of disease. Here we provide data that human prostate cancer cell lines express the platelet-type isoform of 12-LOX at both the mRNA and protein levels, and immunohistochemistry revealed 12-LOX expression in human prostate tumors. The enzyme was localized to the plasma membrane, cytoplasmic organelles and nucleus in non-metastatic cells (PC-3 nm) and to the cytoskeleton and nucleus in metastatic cells (DU-145). After orthotopic/intraprostatic injection of tumor cells into SCID mice, the metastatic prostate carcinoma cells (DU-145) expressed 12-LOX at a significantly higher level compared with the non-metastatic counterparts, PC-3nm. The functional involvement of 12-LOX in the metastatic process was demonstrated when DU-145 cells were pretreated in vitro with the 12-LOX inhibitors N-benzyl-N-hydroxy-5-phenylpentamide (BHPP) or baicalein, the use of which significantly inhibited lung colonization. These data suggest a potential involvement of 12-LOX in the progression of human prostate cancer.

Cell-cell interactions during transendothelial migration of tumor cells

A key event in cancer metastasis is the transendothelial migration of tumor cells. This process involves multiple adhesive interactions between tumor cells and the endothelium. After adhering to the surface of endothelial cells, tumor cells must penetrate the endothelial junction, which contains high concentrations of the cell adhesion molecules VE-cadherin and PECAM-1. Studies using an in vitro model system, consisting of melanoma cells which are seeded onto a monolayer of endothelial cells cultured on Matrigel, have revealed reorganization of the cytoskeleton and dynamic changes in the cell shape of both tumor and endothelial cells. The initial stages of transmigration are characterized by numerous membrane blebs protruding from the basolateral surfaces of the melanoma cells. Contact regions also show an abundance of microfilaments arising from the underlying endothelial cells. These adhesive interactions lead to the redistribution of both VE-cadherin and PECAM-1 and, consequently, a localized dissolution of the endothelial junction. The penetration of the endothelial junction is initiated by melanoma pseudopods. Despite the disappearance of VE-cadherin from the retracting endothelial junction, heterotypic contacts between the tumor cell and its surrounding endothelial cells show a high concentration of pan-cadherin staining, suggesting that transmigration of melanoma cells might yet be facilitated by interactions with another member of the cadherin family. Upon adhesion to the Matrigel, melanoma cells begin to spread and invade the matrix material, while the endothelial cells extend processes over the melanoma cells to reform the monolayer. Interestingly, the leading margins of these endothelial processes contain a high concentration ofN-cadherin. VE-cadherin and PECAM-1 reappear only when the advancing endothelial processes meet to reform the endothelial junction. Together, these observations suggest that endothelial cells actively participate in the transmigration of tumor cells and specific cadherins are involved in different steps of this complex process.

Role of protein kinase C and phosphatases in 12(S)-HETE-induced tumor cell cytoskeletal reorganization

Adherent B16 amelanotic melanoma (B16a) cells exposed to fatty acid 12(S)-HETE, a lipoxygenase metabolite of arachidonic acid, demonstrated a gradual dissolution of stress fibers and bundling-together of vimentin. The 12(S)-HETE effects on tumor cell cytoskeleton appeared 5 min after treatment, became prominent approximately 15 min following stimulation, and generally disappeared by 30 min. Simultaneous treatment of cells with 12(S)-HETE and okadaic acid (OA) prevented disappearance of the 12(S)-HETE effects by 30 min. Quantitative double immunoblotting of actin and vimentin indicated that actin, but not vimentin, underwent a time-related depolymerization. On the other hand, enhanced phosphorylation of vimentin but not of actin was observed after 12(S)-HETE treatment. 12(S)-HETE-enhanced vimentin phosphorylation was abolished by protein kinase C (PKC) inhibitor calphostin C, thus suggesting the involvement of PKC.

Malignant transformation alters intracellular trafficking of lysosomal cathepsin D in human breast epithelial cells

Increased expression and alteration of intracellular trafficking of lysosomal cathepsins have been reported in malignant tumors, or in cells transformed by the transfection with the ras oncogene. In the present study, immortal MCF-10A human breast epithelial cells were transformed with the mutated ras oncogene. Both cell lines were investigated for changes in the intracellular localization of lysosomal cathepsin D and lamp-1 (lysosome-associated membrane protein) employing specific antibodies and confocal immunofluorescence microscopy. The results revealed that staining for cathepsin D along with for lamp-1 was mostly localized in the perinuclear region of MCF-10A cells. In contrast, the staining for these proteins was found to be widely distributed throughout the cytoplasm and at the cell periphery in MCF-10AneoT cells. The organization of microtubules, but not actin, appeared to differ between MCF-10A cells and their oncogenic ras transfectants. When the microtubules were depolymerized by treatment of MCF-10A cells with nocodazole, vesicles containing the lysosomal cathepsin D were dispersed in the cytoplasm and translocation of these vesicles to the cell periphery was observed. The intracellular localization of cathepsin D in the nocodazole-treated MCF-10A cells seemed to be similar to that observed in the oncogenic ras transfectants of these cells. When taxol, which inhibits microtubule depolymerization, was added to the culture medium of neoT cells, a polymerized microtubule network was observed, and the reclustering of cathepsin D and lamp-1 occurred in an unidirectional manner towards the perinuclear region. These findings support a model in which cytoskeletal microtubule organization is closely related to the trafficking of lysosomes/endosomes, and in which oncogenic ras interferes with such organization in human breast epithelial cells.

Arachidonate initiated protein kinase C activation regulates HeLa cell spreading on a gelatin substrate by inducing F-actin formation and exocytotic upregulation of beta 1 integrin

HeLa cell spreading on a gelatin substrate requires the activation of protein kinase C (PKC), which occurs as a result of cell-attachment-induced activation of phospholipase A2 (PLA2) to produce arachidonic acid (AA) and metabolism of AA by lipoxyginase (LOX). The present study examines how PKC activation affects the actin- and microtubule-based cytoskeletal machinery to facilitate HeLa cell spreading on gelatin. Cell spreading on gelatin is contingent on PKC induction of both actin polymerization and microtubule-facilitated exocytosis, which is based on the following observations. There is an increase in the relative content of filamentous (F)-actin during HeLa cell spreading, and treating HeLa cells with PKC-activating phorbol esters such as 12-O-tetradecanoyl phorbol 13-acetate (TPA) further increases the relative content of F-actin and the rate and extent to which the cells spread. Conversely, inhibition of PKC by calphostin C blocked both cell spreading and the increase of F-actin content. The increased F-actin content induced by PKC activators also was observed in suspension cells treated with TPA, and the kinetics of F-actin were similar to that for PKC activation. In addition, PKC epsilon, which is the PKC isoform most involved in regulating HeLa cell spreading in response to AA production, is more rapidly translocated to the membrane in response to TPA treatment than is the increase in F-actin. Blocking the activities of either PLA2 or LOX inhibited F-actin formation and cell spreading, both of which were reversed by TPA treatment. This result is consistent with AA and a LOX metabolite of AA as being upstream second messengers of activation of PKC and its regulation of F-actin formation and cell spreading. PKC appears to activate actin polymerization in the entire body of the cell and not just in the region of cell-substrate adhesion because activated PKC was associated not only with the basolateral plasma membrane domain contacting the culture dish but also with the apical plasma membrane domain exposed to the culture medium and with an intracellular membrane fraction. In addition to the facilitation of F-actin formation, activation of PKC induces the exocytotic upregulation of beta 1 integrins from an intracellular domain to the cell surface, possibly in a microtubule-dependent manner because the upregulation is inhibited by Nocodazole. The results support the concept that cell-attachment-induced AA production and its metabolism by LOX results in the activation of PKC, which has a dual role in regulating the cytoskeletal machinery during HeLa cell spreading. One is through the formation of F-actin that induces the structural reorganization of the cells from round to spread, and the other is the exocytotic upregulation of collagen receptors to the cell surface to enhance cell spreading.

Progesterone acts through protein kinase C to remodel the cytoplasm as the amphibian oocyte becomes the fertilization-competent egg

The fertilization-competent Xenopus egg undergoes a contraction of its cortex towards the apex of the pigmented animal hemisphere within 10 min of fertilization. Evidence suggests that protein kinase C (PKC) is involved in the assembly of this contractile network and we show that PKC is rapidly activated as a result of exposure of oocytes to progesterone. Xenopus oocytes contain at least five different isotypes of PKC. Three actin-binding proteins (i.e. vinculin, talin and ankyrin) appear to play an early role in the assembly of the contractile network and one of the proteins (vinculin) becomes phosphorylated shortly after progesterone treatment as the contractile network is assembling. Our results indicated that progesterone acts through a phospholipase to activate PKC and that PKC participates in the remodeling of the cytoplasmic compartment as the oocyte becomes the egg.

Stem cell factor regulates the melanocyte cytoskeleton

Stem cell factor is a growth factor for normal human melanocytes, that acts through the tyrosine kinase receptor c-kit. We have previously demonstrated that stem cell factor increases melanocyte adhesion and migration on fibronectin, and regulates integrin protein expression. In this report, we have characterized the effect of stem cell factor on the organization of the actin cytoskeleton in human melanocytes attached to fibronectin, and have examined the effect of stem cell factor on the phosphorylation of the focal contact protein paxillin and on the expression of the focal contact proteins talin, paxillin, vinculin, and alpha-actinin. Paxillin is a vinculin-binding protein that is a substrate of focal adhesion kinase, a nonreceptor tyrosine kinase, and in its phosphorylated form is believed to stabilize focal contacts. We show that stem cell factor induces a rapid increase in actin stress fiber formation in melanocytes, which can be abrogated by genistein, a tyrosine kinase inhibitor, and that stem cell factor induces phosphorylation of paxillin on tyrosine residues. In contrast, stem cell factor did not regulate expression of any of the four focal contact proteins tested. These findings have implications for the models describing the mechanisms of action of stem cell factor on melanocyte adhesion and migration, and suggest that reorganization of the cytoskeleton is a primary effect of stem cell factor on human melanocytes.

Mononuclear cell conditioned medium enhances bronchial epithelial cell migration but inhibits attachment to fibronectin

The attachment and migration of bronchial epithelial cells are important features in re-epithelialization after tissue injury. We hypothesized that inflammatory cytokines might alter bronchial epithelial cell attachment and migration. To test this hypothesis, we evaluated the effects of mononuclear cell conditioned medium (MNCCM) on attachment and migration of bronchial epithelial cells to fibronectin in vitro. MNCCM was prepared from bovine blood mononuclear cells that were stimulated with concanavalin A. MNCCM stimulated bronchial epithelial cell migration and spreading. Sephadex G-75 column chromatography of MNCCM found two peaks of migration-stimulatory activity. Activity in the higher molecular weight peak was partially inhibited by anti-tumor necrosis factor-alpha antibodies. Activity in the low-molecular-weight peak was lipid-extractable, suggesting the possibility that the activity was an arachidonate metabolite. We evaluated the effects of protein kinase C (PKC) inhibitors on enhancement of bronchial epithelial cell migration by MNCCM under the hypothesis that stimulated bronchial epithelial cell migration by MNCCM was elicited through PKC-dependent signaling pathways. PKC inhibitors, calphostin and H-7, inhibited the effect of MNCCM on bronchial epithelial cell migration. In addition, MNCCM stimulated PKC translocation and activity in these cells. Thus mononuclear cells produce inflammatory cytokines with important effects on bronchial epithelial cell migration and spreading. The stimulatory effect may be mediated in part through PKC signaling pathways.

Protein kinase A regulates Lewis lung carcinoma adherence to extracellular matrix components and spontaneous metastasis

Tumor cell adhesion to and migration through the extracellular matrix (ECM) can influence their capacity to disseminate. Since prior studies with Lewis lung carcinoma (LLC) tumors had shown metastatic clones to have more protein kinase A (PKA) activity than nonmetastatic clones, the present study assessed if PKA regulates the interaction between tumor and the ECM, and how this may be associated with the metastatic capacity of the tumor cells. This was accomplished with the use of metastatic (LLC-LN7) and nonmetastatic (LLC-C8) variants that had been stably transfected to overexpress the PKA Calpha subunit or to have blocked PKA activity. Cells with increased PKA activity were less adherent to vitronectin, laminin, and collagen I, and could more readily migrate through these ECM components than could transfectants with reduced PKA activity. PKA did not regulate adhesion to or migration through fibronectin, and did not appear to be associated with changes in expression of surface integrins. In addition to modulating tumor adhesion and migration in vitro, PKA activation caused an increased formation of metastases from s.c. tumors, but did not regulate formation of experimental metastases by i.v. injected tumor cells. These results suggest that PKA signaling is important for modulating the tumor-ECM interaction and can facilitate tumor transit from the primary tumor site.

Prostaglandin E2-protein kinase A signaling and protein phosphatases-1 and -2A regulate human head and neck squamous cell carcinoma motility, adherence, and cytoskeletal organization

Human head and neck squamous cell carcinoma (HNSCC) cultures were established from cancers of two patients. These cells were used to study if phosphorylation reactions by protein kinase A (PKA) and dephosphorylation reactions by protein phosphatases-1 and -2A (PP-1/2A) regulate tumor motility and adhesion to extracellular matrix components, and if this might be associated with cytoskeletal reorganization. Both cultures were motile and adherent to collagen I, fibronectin, vitronectin and laminin. Motility and adhesiveness was dependent on production of prostaglandin E2 PGE2 and on PKA activation. Blocking PP-1/2A activity with okadaic acid resulted in a PKA-dependent increase in m otility and, in some instances, adhesiveness by the HNSCC cells. The okadaic acid-induced increase in motility and adhesiveness coincided with a reduction in filamentous actin. These data suggest PKA and PP-1/2A have opposing effects in regulating the motility, adherence, and actin polymerization.

Immunomorphological characterization and effects of 12-(S)-HETE on a dynamic intracellular pool of the alpha IIb beta 3-integrin in melanoma cells

In metastatic B16a murine melanoma cells, alpha IIb beta 3 integrin was shown to be one of the key adhesion molecules responsible for matrix adhesion and spreading. Upon stimulation, alpha IIb beta 3 can be upregulated at the cell surface due to translocation of the receptor to the plasma membrane from an intracellular pool. Here we have characterized this integrin pool as a tubulovesicular structure (TVS) corresponding to endosomes. TVS was found to be associated temporarily with microtubules and intermediate filaments especially after protein kinase C (PKC) stimulation with a lipoxygenase metabolite of arachidonic acid, 12-(S)-hydroxyeicosatetraenoic acid [12-(S)-HETE]. After PKC stimulation, the predominantly vesicular TVS became elongated and alpha IIb beta 3 appeared at the apical plasma membrane and microvilli. Disruption of either the microtubules or intermediate filaments prevented the 12-(S)-HETE effect both on vesicular to tubular transition of TVS as well as on surface expression of this integrin. The connection with the Golgi system of the integrin-containing TVS was proved by a Golgi-inhibitor (brefeldin A) pretreatment, which prevented the PKC-stimulation-induced TVS elongation and subsequent receptor-upregulation at the cell surface. After a soluble ligand binding (mAb to the alpha IIb beta 3 complex) the surface receptor endocytosed back to the TVS indicating the presence of a dynamic, cytoskeleton associated integrin pool in melanoma cells.

Immunocytochemical localization of eight protein kinase C isozymes overexpressed in NIH 3T3 fibroblasts. Isoform-specific association with microfilaments, Golgi, endoplasmic reticulum, and nuclear and cell membranes

We have used immunocytochemical analyses to characterize the subcellular distribution of protein kinase C (PKC)-alpha, -beta I, -beta II, -gamma, -delta, -epsilon, -zeta, and -eta in NIH 3T3 fibroblasts that overexpress these different PKC isozymes. Immunofluorescence studies and Western blotting with antibodies specific for individual isoforms revealed that before activation the majority of the PKCs are not membrane-bound and are diffusely distributed throughout the cytoplasm. In addition, a fraction of PKC-delta and -eta appears membrane-bound and concentrated in the Golgi apparatus. Activation of each isozyme's kinase activity (with the exception of PKC-zeta) by treatment of these cells with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate results in isozyme-specific alterations of cell morphology, as well as in a rapid, selective redistribution of the different PKC isozymes to distinct subcellular structures. Within minutes after 12-O-tetradecanoylphorbol-13-acetate treatment, PKC-alpha and -epsilon concentrate at cell margins. In addition, PKC-alpha accumulates in the endoplasmic reticulum, PKC-beta II associates with actin-rich microfilaments of the cytoskeleton, PKC-gamma accumulates in Golgi organelles, and PKC-epsilon associates with nuclear membranes. Our results demonstrate that each activated PKC isozyme specifically associates with a particular cellular structure, presumably containing the substrate for that isozyme. These findings support the hypothesis that PKC substrate specificity in vivo is mediated, at least in part, by the restricted subcellular locale for each PKC isozyme and its target protein.

Regulation of Lewis lung carcinoma invasion and metastasis by protein kinase A

Metastatic Lewis lung carcinoma (LLC-LN7) cells have increased protein kinase A (PKA) activity and are more invasive in vitro than are non-metastatic (LLC-C8) cells. To determine whether PKA mediates the in vitro invasiveness and in vivo metastatic capabilities of these tumor cells, the LLC variants were stably transfected to over-express the C alpha subunit of PKA, and thus to have increased PKA activity, or to express a mutant cAMP-resistant PKA R1 alpha subunit which blocks PKA activation. Wild-type LLC-LN7 tumor cells were invasive in vitro and in vivo, recurred after tumor excision and metastasized to the lungs. However, they lost these properties after transfection to express the mutant R1 alpha that blocks PKA activation. The non-invasive, non-recurring and non-metastatic LLC-C8 cells gained the capacity to invade, to recur following tumor excision and to metastasize when transfected to express the PKA C alpha subunit.

12-lipoxygenases and 12(S)-HETE: role in cancer metastasis

Arachidonic acid metabolites have been implicated in multiple steps of carcinogenesis. Their role in tumor cell metastasis, the ultimate challenge for the treatment of cancer patients, are however not well-documented. Arachidonic acid is primarily metabolized through three pathways, i.e., cyclooxygenase, lipoxygenase, and P450-dependent monooxygenase. In this review we focus our attention on one specific lipoxygenase, i.e., 12-lipoxygenase, and its potential role in modulating the metastatic process. In mammalian cells there exist three types of 12-lipoxygenases which differ in tissue distribution, preferential substrates, and profile of their metabolites. Most of these 12-lipoxygenases have been cloned and sequenced, and the molecular and biochemical determinants responsible for catalysis of specific substrates characterized. Solid tumor cells express 12-lipoxygenase mRNA, possess 12-lipoxygenase protein, and biosynthesize 12(S)-HETE [12(S)-hydroxyeicosatetraenoic acid], as revealed by numerous experimental approaches. The ability of tumor cells to generate 12(S)-HETE is positively correlated to their metastatic potential. A large collection of experimental data suggest that 12(S)-HETE is a crucial intracellular signaling molecule that activates protein kinase C and mediates the biological functions of many growth factors and cytokines such as bFGF, PDGF, EGF, and AMF. 12(S)-HETE plays a pivotal role in multiple steps of the metastatic 'cascade' encompassing tumor cell-vasculature interactions, tumor cell motility, proteolysis, invasion, and angiogenesis. The fact that 12-lipoxygenase is expressed in a wide diversity of tumor cell lines and 12(S)-HETE is a key modulatory molecule in metastasis provides the rationale for targeting these molecules in anti-cancer and anti-metastasis therapeutic protocols.