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K Jalink

Publications and source records attributed to K Jalink.

29 records · Page 2Linked to original sources
PubMed1993

Lysophosphatidic acid is a chemoattractant for Dictyostelium discoideum amoebae.

The naturally occurring phospholipid lysophosphatidic acid (LPA) can induce a number of physiological responses in vertebrate cells, including platelet aggregation, smooth muscle contraction, and fibroblast proliferation. LPA is thought to activate a specific G-protein-coupled receptor, thereby triggering classic second messenger pathways such as stimulation of phospholipase C and inhibition of adenylate cyclase. Here we report that 1-oleoyl-LPA, at submicromolar concentrations, evokes a chemotactic response in amoebae of the cellular slime mold Dictyostelium discoideum. LPA-induced chemotaxis is specific in that other lysophospholipids, phosphatidic acid, and monoacylglycerol have no effect. We show that the response to LPA is not secondary to the accumulation of extracellular cAMP, a well-established chemoattractant for nutrient-starved D. discoideum. Compared with cAMP-induced chemotaxis, LPA-induced chemotaxis has a somewhat lower efficiency and is not accompanied by the characteristic cellular elongation and orientation along the gradient. These results indicate that LPA has a previously unsuspected role as a chemoattractant for D. discoideum and imply that its biological function as a "first messenger" is not restricted to vertebrate cells.

Animals↗
PubMed1993

Lysophosphatidic acid induces neuronal shape changes via a novel, receptor-mediated signaling pathway: similarity to thrombin action.

Lysophosphatidic acid (LPA) is a mitogenic phospholipid produced by certain activated cells and present in serum. LPA stimulates phospholipase C and inhibits adenylate cyclase in its target cells, apparently by activating a specific G-protein-coupled receptor. Here, we demonstrate that LPA causes transient rounding of N1E-115 and NG108-15 neuronal cells accompanied by growth cone collapse and retraction of neurites. The effect of LPA is concentration dependent, being half-maximal at 10-20 nM, and reversibly blocked by suramin, an LPA receptor antagonist. The morphological response to LPA is indistinguishable from that evoked by thrombin or a thrombin receptor-activating peptide (TRP) (K. Jalink and W. H. Moolenaar, J. Cell Biol., 118: 411-419, 1992); yet, LPA and thrombin appear to act through distinct receptors. LPA-induced shape changes, like those induced by thrombin and TRP, are driven by contraction of the cortical actin cytoskeleton and not attributable to prior phospholipid hydrolysis and Ca2+ mobilization nor to other classic second messenger systems. Instead, LPA- and TRP-induced shape changes are accompanied by a small but significant increase in p60src protein tyrosine kinase activity. Treatment of cells with pervanadate selectively inhibits LPA- and TRP-induced shape changes as well as p60src activation. These results indicate that, in N1E-115 and NG108-15 cells, LPA and TRP trigger neurite retraction and cell rounding through a novel, receptor-mediated signaling pathway, and they suggest that p60src may play a role in this pathway.

Actins↗
PubMed1992

Mitogenic action of lysophosphatidic acid and phosphatidic acid on fibroblasts. Dependence on acyl-chain length and inhibition by suramin.

Lysophosphatidic acid (LPA) is a naturally occurring phospholipid with growth-factor-like activities [van Corven, Groenink, Jalink, Eichholtz & Moolenaar (1989) Cell 45, 45-54]. We have examined various structural analogues of LPA for their ability to stimulate DNA synthesis in quiescent fibroblasts. When the acyl-chain length is varied, the rank order of mitogenic potency is: 1-oleoyl LPA congruent to 1-palmitoyl LPA greater than 1-myristoyl LPA greater than 1-lauroyl LPA greater than 1-decanoyl LPA; the last compound shows almost no activity over the concentration range tested (1-100 microM). An ether-linked LPA (1-O-hexadecylglycerol 3-phosphate) has much decreased mitogenic activity as compared with the ester-linked analogue at concentrations less than 25 microM, and becomes cytotoxic at higher concentrations. Hexadecylphosphate, which lacks a glycerol backbone, has negligible activity. On a molar basis, diacyl phosphatidic acid (PA) is about equally potent as the corresponding LPA analogue, showing similar acyl-chain-length dependence; the data argue against the possibility that the mitogenic action of PA is due to contaminating traces of LPA. Although the short-chain analogues of LPA and PA fail to antagonize the action of long-chain (L)PAs, the polyanionic drug suramin inhibits LPA- and PA-induced, DNA synthesis in a reversible and dose-dependent manner, at concentrations [IC50 (concn. giving 50% inhibition) approximately 70 microM] that do not affect epidermal-growth-factor-induced DNA synthesis. Suramin appears to act in the early G0/G1 phase of the cell cycle, blocking immediate responses to LPA such as phosphoinositide hydrolysis. We conclude that both LPA and PA can function as growth-promoting phospholipids, with the fatty acid chain length being a major determinant of mitogenic potency.

Animals↗
PubMed1992

Identification of a putative membrane receptor for the bioactive phospholipid, lysophosphatidic acid.

Lysophosphatidic acid (LPA) is a naturally occurring phospholipid with hormone- and growth factor-like activities. Exogenous LPA stimulates GTP-dependent phosphoinositide hydrolysis and inhibits adenylate cyclase in its target cells, but the site of action of LPA is unknown. We now report the identification by photoaffinity labeling of a putative LPA membrane receptor in various LPA-responsive cell types. A 32P-labeled LPA analogue containing a photoreactive fatty acid, [32P]diazirine-LPA, labels a membrane protein of apparent molecular mass of 38-40 kDa in various cell types, including neuronal cells, brain homogenates, carcinoma cells, leukemic cells and normal fibroblasts. Labeling of the 38-40 kDa protein is competitively inhibited by unlabeled 1-oleoyl-LPA (IC50 approximately 10 nM), but not by other phospholipids. Specific labeling is not detected in rat liver membranes or in human neutrophils, which are physiologically unresponsive to LPA. Suramin, an inhibitor of both early and late events in the action of LPA, completely inhibits the binding of photoreactive LPA. We suggest that the 38-40 kDa protein represents a specific LPA cell surface receptor mediating at least part of the multiple cellular responses to LPA.

Affinity Labels↗
PubMed1992

Thrombin receptor activation causes rapid neural cell rounding and neurite retraction independent of classic second messengers.

The protease thrombin is a potent activator of various cell types. Thrombin cleaves and thereby activates its own seven-transmembrane-domain receptor which couples to G proteins. Thrombin also can inhibit neuronal differentiation, supposedly by degrading components of the extracellular matrix. Here we report that active thrombin induces immediate cell rounding and neurite retraction in differentiating N1E-115 and NG108-15 neural cells in serum-free culture. Serum (0.5-5% vol/vol) evokes similar responses, but the cell-rounding and neurite-retracting activity of serum is not attributable to thrombin. Neural cell rounding is transient, subsiding after 10-15 min, and subject to homologous desensitization, whereas retracted neurites rapidly degenerate. Thrombin action is inhibited by cytochalasin, but not colchicine. A novel 14-amino acid peptide agonist of the thrombin receptor fully mimics thrombin's morphoregulatory activity, indicating that thrombin-induced shape changes are receptor-mediated and not secondary to extracellular matrix degradation. Although thrombin receptors couple to phosphoinositide hydrolysis and Ca2+ mobilization, thrombin-induced shape changes appear to depend neither on the Ca2+/protein kinase C- nor the cyclic nucleotide-mediated signal transduction pathways; however, the morphological response to thrombin is blocked by pervanadate, an inhibitor of tyrosine phosphatases, and by broad-specificity kinase inhibitors. Our results suggest that the thrombin receptor communicates to an as-yet-uncharacterized effector to reorganize the actin cytoskeleton and to reverse the differentiated phenotype of neural cells.

Alkaloids↗
PubMed1990

Lysophosphatidic acid, but not phosphatidic acid, is a potent Ca2(+)-mobilizing stimulus for fibroblasts. Evidence for an extracellular site of action.

Lysophosphatidic acid (LPA) is a potent mitogen for quiescent fibroblasts. Among the earliest detectable responses to LPA is GTP-dependent phosphoinositide hydrolysis (van Corven, E. J., Groenink, A., Jalink, K., Eichholtz, T., and Moolenaar, W. H. (1989) Cell 59, 45-54). Here we describe the Ca2(+)-mobilizing properties of LPA in human fibroblasts and present evidence suggesting that previously reported Ca2(+)-mobilizing effects of phosphatidic acid are attributable to contamination with LPA. Addition of LPA (1-oleoyl or 1-palmitoyl) to fibroblasts evokes the formation of inositol 1,4,5-trisphosphate accompanied by an immediate but transient rise in [Ca2+]i which originates primarily from intracellular stores. The Ca2+ response is dose-dependent with a half-maximal effect at LPA concentrations as low as 10 ng/ml, far below the reported half-maximal effect for DNA synthesis (5-10 micrograms/ml). LPA-induced Ca2+ release is also observed in various other cell types, both normal and transformed, but not in Jurkat T cells and neutrophils. The Ca2(+)-mobilizing action of LPA is specific, in that 1,2-dioleoyl-phosphatidic acid (when prepared free of LPA contaminants), other lysophospholipids, monoacylglycerol, and free fatty acids have no effect. Furthermore, LPA, unlike lysophosphatidylcholine, does not cause detectable membrane leakiness, even when added at high concentrations (500 micrograms/ml). The LPA-induced Ca2+ signal is blocked completely by tetradecanoylphorbol acetate, but is not affected by prior stimulation of the cells with Ca2(+)-mobilizing agonists such as bradykinin or histamine. In contrast, pretreating the cells with a low dose of LPA desensitizes the Ca2+ response to subsequent addition of higher doses. This homologous desensitization is not inhibited by staurosporine, nor by down-regulating protein kinase C with tetradecanoylphorbol acetate, suggesting independence of functional protein kinase C activity. Addition of La3+ instantaneously blocks inositol phosphate production and Ca2+ mobilization in response to LPA, but not to bradykinin, most likely due to formation of inactive La3(+)-LPA complexes, suggesting that LPA acts at an extracellular site on the plasma membrane to trigger GTP-dependent phosphoinositide breakdown.

Bradykinin↗
PubMed1990

Morphological and functional properties of rat dorsal root ganglion cells cultured in a chemically defined medium.

A culture procedure for dorsal root ganglion (DRG) cells is presented using a completely defined culture medium without antibiotics, in combination with mechanical dissociation procedures. This culture procedure allows all dorsal root ganglion cell types to be cocultured for periods of at least 106 days. Some of the dorsal root ganglion neurons, which could be identified by their neurofilaments and the presence of fluoride resistant acid phosphatase, regained their original T-cell appearance within two weeks. After one month in culture ganglion-like reaggregates appeared. Schwann cells, satellite cells and fibroblasts were identified using morphological criteria. All neurons tested maintained excitability during, at least, the first 35 days in culture, since in all cases action potentials could be evoked by current pulses. The method has proved to be useful in the study of morphological, cytochemical and electrophysiological aspects of dorsal root ganglion cell differentiation in vitro.

Acid Phosphatase↗
PubMed1989

Lysophosphatidate-induced cell proliferation: identification and dissection of signaling pathways mediated by G proteins.

Lysophosphatidate (LPA), the simplest natural phospholipid, is highly mitogenic for quiescent fibroblasts. LPA-induced cell proliferation is not dependent on other mitogens and is blocked by pertussis toxin. LPA initiates at least three separate signaling cascades: activation of a pertussis toxin-insensitive G protein mediating phosphoinositide hydrolysis with subsequent Ca2+ mobilization and stimulation of protein kinase C; release of arachidonic acid in a GTP-dependent manner, but independent of prior phosphoinositide hydrolysis; and activation of a pertussis toxin-sensitive Gi protein mediating inhibition of adenylate cyclase. The peptide bradykinin mimics LPA in inducing the first two responses but fails to activate Gi and to stimulate DNA synthesis. Our data suggest that the mitogenic action of LPA occurs through Gi or a related pertussis toxin substrate and that the phosphoinositide hydrolysis-protein kinase C pathway is neither required nor sufficient, by itself, for mitogenesis. The results further suggest that LPA or LPA-like phospholipids may have a novel role in G protein-mediated signal transduction.

Adenylate Cyclase Toxin↗