Heparin inhibits Ca2+/calmodulin-dependent kinase II activation and c-fos induction in mesangial cells

On the mechanism(s) of membrane permeability transition in liver mitochondria of lamprey, Lampetra fluviatilis L.: insights from cadmium

Previously we have shown that opening of the mitochondrial permeability transition pore in its low conductance state is the case in hepatocytes of the Baltic lamprey (Lampetra fluviatilis L.) during reversible metabolic depression taking place in the period of its prespawning migration when the exogenous feeding is switched off. The depression is observed in the last year of the lamprey life cycle and is conditioned by reversible mitochondrial dysfunction (mitochondrial uncoupling in winter and coupling in spring). To further elucidate the mechanism(s) of induction of the mitochondrial permeability transition pore in the lamprey liver, we used Cd(2+) and Ca(2+) plus Pi as the pore inducers. We found that Ca(2+) plus Pi induced the high-amplitude swelling of the isolated "winter" mitochondria both in isotonic sucrose and ammonium nitrate medium while both low and high Cd(2+) did not produce the mitochondrial swelling in these media. Low Cd(2+) enhanced the inhibition of basal respiration rate of the "winter" mitochondria energized by NAD-dependent substrates whereas the same concentrations of the heavy metal evoked its partial stimulation on FAD-dependent substrates. The above changes produced by Cd(2+) or Ca(2+) plus Pi in the "winter" mitochondria were only weakly (if so) sensitive to cyclosporine A (a potent pharmacological desensitizer of the nonselective pore) added alone and they were not sensitive to dithiothreitol (a dithiol reducing agent). Under monitoring of the transmembrane potential of the "spring" lamprey liver mitochondria, we revealed that Cd(2+) produced its decrease on both types of the respiratory substrates used that was strongly hampered by cyclosporine A, and the membrane potential was partially restored by dithiothreitol. The effects of different membrane permeability modulators on the lamprey liver mitochondria function and the seasonal changes in their action are discussed.

Unusual glycosaminoglycans from a deep sea hydrothermal bacterium improve fibrillar collagen structuring and fibroblast activities in engineered connective tissues

Biopolymers produced by marine organisms can offer useful tools for regenerative medicine. Particularly, HE800 exopolysaccharide (HE800 EPS) secreted by a deep-sea hydrothermal bacterium displays an interesting glycosaminoglycan-like feature resembling hyaluronan. Previous studies demonstrated its effectiveness to enhance in vivo bone regeneration and to support osteoblastic cell metabolism in culture. Thus, in order to assess the usefulness of this high-molecular weight polymer in tissue engineering and tissue repair, in vitro reconstructed connective tissues containing HE800 EPS were performed. We showed that this polysaccharide promotes both collagen structuring and extracellular matrix settle by dermal fibroblasts. Furthermore, from the native HE800 EPS, a low-molecular weight sulfated derivative (HE800 DROS) displaying chemical analogy with heparan-sulfate, was designed. Thus, it was demonstrated that HE800 DROS mimics some properties of heparan-sulfate, such as promotion of fibroblast proliferation and inhibition of matrix metalloproteinase (MMP) secretion. Therefore, we suggest that the HE800EPS family can be considered as an innovative biotechnological source of glycosaminoglycan-like compounds useful to design biomaterials and drugs for tissue engineering and repair.

Low-concentration heparin suppresses ionomycin-activated CAMK-II/EGF receptor- and ERK-mediated signaling in mesangial cells

Heparin and endogenous heparinoids inhibit the proliferation of smooth muscle cells, including renal mesangial cells; multiple effects on signaling pathways are well established, including effects on PKC, Erk, and CaMK-II. Many studies have used heparin at concentrations of 100 microg/ml or higher, whereas endogenous concentrations of heparinoids are much lower. Here we report the effects of low-concentration (1 microg/ml) heparin on activation of several kinases and subsequent induction of the c-fos gene in mesangial cells in response to the calcium ionophore, ionomycin, in the absence of serum factors. Ionomycin rapidly increases the phosphorylation of CaMK-II (by 30 s), and subsequently of the EGF receptor (EGFR), c-Src, and Erk 1/2. Low-dose heparin suppresses the ionomycin-dependent phosphorylation of EGFR, c-Src, and Erk 1/2, but not of CaMK-II, whereas inhibition of activated CaMK-II reduces phosphorylation of EGFR, c-Src, and Erk. Our data support a mechanism whereby heparin acts at the cell surface to suppress downstream targets of CaMK-II, including EGFR, leading in turn to a decrease in Erk- (but not c-Src-) dependent induction of c-fos.

Slow motility in hair cells of the frog amphibian papilla: myosin light chain-mediated shape change

Using video, fluorescence and confocal microscopy, quantitative analysis and modeling, we investigated intracellular processes mediating the calcium/calmodulin (Ca(2+)/CaM)-dependent slow motility in hair cells dissociated from the rostral region of amphibian papilla, one of the two auditory organs in frogs. The time course of shape changes in these hair cells during the period of pretreatment with several specific inhibitors, as well as their response to the calcium ionophore, ionomycin, were recorded and compared. These cells respond to ionomycin with a tri-phasic shape change: an initial phase of iso-volumetric length decrease; a period of concurrent shortening and swelling; and the final phase of increase in both length and volume. We found that both the myosin light chain kinase inhibitor, ML-7, and antagonists of the multifunctional Ca(2+)/CaM-dependent kinases, KN-62 and KN-93, inhibit the iso-volumetric shortening phase of the response to ionomycin. The type 1 protein phosphatase inhibitors, calyculin A and okadaic acid induce minor shortening on their own, but do not significantly alter phase 1 response. However, they appear to counter effects of the inhibitors of Ca(2+)/CaM-dependent kinases. We hypothesize that an active actomyosin-based process mediates the iso-volumetric shortening in the frog rostral amphibian papillar hair cells.

Heparin suppresses lipid raft-mediated signaling and ligand-independent EGF receptor activation

Heparin is well known to suppress vascular smooth muscle cell (VSMC) proliferation, and attempts to exploit this therapeutically have led to recognition of multiple pathways for heparin's anti-mitogenic actions. At low concentrations (ca. 1 microg.ml(-1)), these suppressive effects may reflect physiological activities of endogenous heparan sulfates, and appear to be rapid responses to extracellular or cell surface-associated heparin. Because heparin has been shown to influence expression of caveolin proteins, and caveolae/lipid rafts are critical structures modulating cell signaling, we examined the effect of heparin on signaling involving cholesterol-rich membrane microdomains. The VSMC line PAC-1 activates the MAP kinase Erk in response to the cholesterol-sequestering agents methyl-beta-cyclodextrin and nystatin. This follows a temporal sequence that involves Ras-GTP activation of MEK, and is independent of PKC, Src, and PI3 kinase. However, ligand-independent phosphorylation of the EGF receptor (EGFR) by removal of cholesterol precedes Ras activation, and the EGFR kinase inhibitor AG1478 blocks Erk phosphorylation, supporting occurrence of the signaling sequence EGFR-Ras-MEK-Erk. Phosphorylation of EGFR occurs predominantly in caveolin-rich microdomains as identified by Western blotting of fractions from density gradient centrifugation of membranes prepared under detergent-free conditions. In these situations, heparin inhibits phosphorylation of EGFR on the Src-dependent site Tyr(845), but not the autophosphorylation of Tyr(1173), and decreases Ras activation and Erk phosphorylation. We conclude that heparin can suppress Erk signaling in VSMC with effects on site-specific phosphorylation of EGFR localized in caveolin-enriched lipid rafts.

Cadmium activates CaMK-II and initiates CaMK-II-dependent apoptosis in mesangial cells

Cadmium is a toxic metal that initiates both mitogenic responses and cell death. We show that Cd(2+) increases phosphorylation and activity of Ca(2+)/calmodulin-dependent protein kinase II (CaMK-II) in mesangial cells, in a concentration-dependent manner. Activation is biphasic with peaks at 1-5 min and 4-6 h. Cadmium also activates Erk, but this appears to be independent of CaMK-II. At 10-20 microM, Cd(2+) initiates apoptosis in 25-55% of mesangial cells by 6h. Inhibition of CaMK-II, but not of Erk, suppresses Cd(2+)-induced apoptosis. We conclude that activation of CaMK-II by Cd(2+) contributes to apoptotic cell death, independent of Erk activation.

Involvement of Ca2+/calmodulin-dependent protein kinase II in heparin-stimulated release of hepatic lipase activity from rat hepatocytes

The release of hepatic lipase (HTGL), which is responsible for the hydrolysis of lipoprotein triacylglyceride, produced by heparin from the isolated rat hepatocytes in primary culture has been examined. Tyrosine kinase (TK) inhibitors (ST-638 and biochanin A) inhibited the heparin-stimulated release of HTGL activity. The activity of partially purified TK preparation from the hepatocytes was found to be increased following incubation with heparin in a manner which was both time- and dose-dependent. An intracellular Ca(2+)-chelator (Quin2/AM), a calmodulin inhibitor (W-7) and a Ca(2+)/calmodulin-dependent protein kinase II (CaMK-II) inhibitor (KN-93) suppressed the release of HTGL activity by heparin. In addition, CaMK-II activity in the hepatocytes incubated with heparin was recognized to elevate in a time- and dose-dependent manner. The increase in CaMK-II activity by heparin was markedly reduced in the presence of the inhibitors of TK. These results suggest that the release of HTGL activity from the hepatocytes by heparin is, in part, caused through a pathway involving an activation of CaMK-II associated with an increase in membrane TK activity.

Ca(2+)/calmodulin-dependent protein kinase II inhibition by heparin in mesangial cells

Heparin exerts an antiproliferative effect in smooth muscle cells, and the Ca(2+)/calmodulin-dependent protein kinase (CaMK) signaling pathway is heparin sensitive. Here, we report that transfection with a truncated 326-amino acid fragment of CaMK-IIalpha increases basal activity of CaMK-II in mesangial cells. Ionomycin increased CaMK-II activity in both transfected and untransfected cells, with a concomitant increase in activated Ca(2+)/calmodulin. Heparin (1 microg/ml), but not chondroitin or dermatan sulfate, significantly attenuated both serum- or ionomycin-induced CaMK-II activity, and attendant c-fos mRNA expression, but did not affect upstream Ca(2+)/calmodulin. Autophosphorylation of Thr286 generates an autonomously active CaMK-II. Both serum and ionomycin increased phosphorylation at this site and increased CaMK-II activity in antiphosphothreonine immunoprecipitates. Heparin (1 microg/ml) did not inhibit phosphorylation of Thr286 (although much higher concentrations did). Replacement of Thr286 with Asp produces a constitutively active mutant that was insensitive to ionomycin but was inhibited by heparin maximally at 1 microg/ml. These results suggest that heparin at physiological concentrations acts at or downstream of CaMK-II to suppress its activity independent of an effect on autophosphorylation.

Suppression of mitogen-activated protein kinase phosphatase-1 (MKP-1) by heparin in vascular smooth muscle cells

Heparin inhibits vascular smooth muscle cell (VSMC) proliferation, but mechanisms remain elusive. Because heparin inhibits signaling through multiple kinase cascades, we investigated the possibility that phosphatases could be involved. Mitogen-activated protein kinase phosphatase-1 (MKP-1) was the predominant MKP detected in VSMC lines. MKP-1 protein was increased by serum stimulation of quiescent cells, and this increase was diminished by heparin (1 microg/mL). Increased MKP-1 expression was dependent on the mitogen-activated protein kinase, Erk. Decreased Erk activity in the presence of heparin preceded, and may account for, decreased MKP-1. The antimitogenic effects of heparin are therefore unlikely to act through a shift in the kinase/phosphatase balance, but rather through direct kinase suppression. However, because MKP-1 is known to cause an increase in activity of kinases upstream of Erk, that may signal through additional pathways, the decrease in MKP-1 activity may paradoxically enhance heparin's antiproliferative effects. VSMC selected to grow in the presence of heparin express decreased levels of MKP-1 that are unresponsive to heparin, and Erk activity becomes unresponsive to heparin in one cell line. We conclude that phosphatase activation is not a direct mechanism of suppression of multiple kinase cascades by heparin.

Ca(2+)/calmodulin-dependent and cAMP-dependent kinases in induction of c-fos in human mesangial cells

Mesangial cell proliferation is an early event in several progressive renal diseases. When mesangial cells in culture are rendered quiescent by serum starvation and subsequently stimulated to proliferate, induction of c-fos is an early indicator of entry into the cell cycle. Several heparin-sensitive signals transduce these events. We have examined the potential roles of CaMK and PKA. Selective stimulation of CaMK with Ca(2+) ionophores and of PKA with forskolin or dibutyryl cAMP both result in induction of c-fos mRNA. CaMK but not PKA signaling is suppressed by low concentrations of heparin. Cross talk between the pathways has been demonstrated in some cells, with evidence of CaMK phosphorylating cAMP response element binding protein (CREB) at an inhibitory site and PKA suppressing CaMK-dependent signaling. However, in the present study, both pathways phosphorylated CREB on Ser(133) and induced c-fos in an additive manner. Serum, ionomycin, and forskolin all caused a rapid decline in cyclin D1 levels, but only serum effected a subsequent increase, indicative of cell cycle progression. We conclude that, in human mesangial cells, CaMK and PKA can both contribute to cell cycle entry, and, although induction of c-fos by CaMK requires active PKA, neither pathway antagonizes or synergizes c-fos induction by the other.

Heparin inhibits phosphorylation and autonomous activity of Ca(2+)/calmodulin-dependent protein kinase II in vascular smooth muscle cells

Vascular smooth muscle cell (VSMC) hyperproliferation is a characteristic feature of both atherosclerosis and restenosis seen after vascular surgery. A number of studies have shown that heparin inhibits VSMC proliferation in vivo and in culture. To test our hypothesis that heparin mediates its antiproliferative effect by altering Ca(2+) regulated pathways involved in mitogenic signaling in VSMC, we analyzed the effect of heparin on multifunctional Ca(2+)/calmodulin dependent protein kinase II (CaM kinase II) which is abundantly expressed in VSMC. Using activity assays, radioactive labeling, and immunoprecipitation it was found that heparin inhibits the overall phosphorylation of the delta-subunit of CaM kinase II which is consistent with inhibition of autophosphorylation-dependent, Ca(2+)/calmodulin-independent CaM kinase II activity. This effect was less evident in heparin-resistant cells, consistent with a role for CaM kinase II in mediating the antiproliferative effect of heparin. Finally, the effects of pharmacological inhibitors of phosphatases like okadaic acid, calyculin, and tautomycin suggest that heparin inhibits CaM kinase II phosphorylation by activating protein phosphatases 1 and 2A. These findings support the hypothesis that alterations in calcium-mediated mitogenic signaling pathways may be involved in the antiproliferative mechanism of action of heparin.

TGF-beta-induced Ca(2+) influx involves the type III IP(3) receptor and regulates actin cytoskeleton

Ca(2+) influx has been postulated to modulate the signaling pathway of transforming growth factor-beta (TGF-beta); however, the underlying mechanism and functional significance of TGF-beta-induced stimulation of Ca(2+) influx are unclear. We show here that TGF-beta stimulates Ca(2+) influx in mesangial cells without Ca(2+) release. The influx of Ca(2+) is prevented by pharmacological inhibitors of inositol 1,4,5-trisphosphate receptors (IP(3)R) as well as specific antibodies to type III IP(3)R (IP(3)RIII) but not to type I IP(3)R (IP(3)RI). TGF-beta enhances plasma membrane localization of IP(3)RIII, whereas the sarcoplasmic-endoplasmic reticulum Ca(2+)-ATPase (SERCA) preferentially translocates to the nucleus. Untreated mesangial cells exhibit actin filamentous protrusions on the cell surface, and treatment with TGF-beta dramatically reduces this pattern. The alterations in the actin cytoskeleton by TGF-beta are dependent on TGF-beta-induced Ca(2+) influx. These studies identify a novel pathway by which TGF-beta regulates Ca(2+) influx and induces cytoskeletal alterations.

Decreases in calmodulin binding proteins and calmodulin dependent protein phosphorylation in the medial preoptic area at the onset of maternal behavior in the rat

The onset of maternal behavior is characterized by the action of certain hormones, neuropeptides and neurotransmitters and a concomitant increase in the expression of c-Fos in the medial preoptic area (MPOA) but the signaling events that lie between have not been characterized. Because several of these hormones, neuropeptides and neurotransmitters function by activating Ca(2+)/calmodulin (CaM) mediated signaling pathways, many of which can lead to c-Fos expression, the goal of the current work was to identify calmodulin binding proteins (CaMBPs) or specific CaM-dependent phosphoproteins that might be involved. Probing of SDS-PAGE gels of extracts from the hippocampus, parietal cortex, basolateral amygdala and MPOA with recombinant (35)S-VU1-calmodulin (CaM) revealed 30 Ca(2+)-dependent and 4-6 Ca(2+)-independent CaMBPs. Statistically significant maternal behavior-related decreases in four Ca(2+)-dependent CaMBPs ( approximately 31 kDa, 50% decrease; approximately 33 kDa, 32%; approximately 50 kDa, 35%; approximately 60 kDa, 33%) were observed specifically in the MPOA. Numerous proteins were phosphorylated in a Ca(2+) CaM-dependent manner with two (MWs approximately 61 Da, approximately 58 kDa) showing a lack of phosphophorylation only in the MPOA. The selective decrease in CaMBPs coupled with the absence of CaM-dependent phosphoproteins implies that changes in Ca(2+)/CaM-mediated signaling may mediate some of the MPOA-specific processes during the onset of maternal behavior in the rat.

Calcium-dependent threonine phosphorylation of nonmuscle myosin in stimulated RBL-2H3 mast cells

Stimulation of RBL-2H3 m1 mast cells through the IgE receptor with antigen, or through a G protein-coupled receptor with carbachol, leads to the rapid appearance of phosphothreonine in nonmuscle myosin heavy chain II-A (NMHC-IIA). We demonstrate that this results from phosphorylation of Thr-1940 by calcium/calmodulin-dependent protein kinase II (CaM kinase II), activated by increased intracellular calcium. The phosphorylation site in rodent NMHC-IIA was localized to the carboxyl terminus of NMHC-IIA distal to the coiled-coil region, and identified as Thr-1940 by site-directed mutagenesis. A fusion protein containing the NMHC-IIA carboxyl terminus was phosphorylated by CaM kinase II in vitro, while mutation of Thr-1940 to Ala eliminated phosphorylation. In contrast to rodents, in humans Thr-1940 is replaced by Ala, and human NMHC-IIA fusion protein was not phosphorylated by CaM kinase II unless Ala-1940 was mutated to Thr. Similarly, co-transfected Ala --> Thr-1940 human NMHC-IIA was phosphorylated by activated CaM kinase II in HeLa cells, while wild type was not. In RBL-2H3 m1 cells, inhibition of CaM kinase II decreased Thr-1940 phosphorylation, and inhibited release of the secretory granule marker hexosaminidase in response to carbachol but not to antigen. These data indicate a role for CaM kinase stimulation and resultant threonine phosphorylation of NMHC-IIA in RBL-2H3 m1 cell activation.

MAPK signaling and the kidney

Following an overview of the biochemistry of mitogen-activated protein kinase (MAPK) pathways, the relevance of these signaling events to specific models of renal cell function and pathophysiology, both in vitro and in vivo, will be emphasized. In in vitro model systems, events activating the principal MAPK families [extracellular signal-regulated and c-Jun NH(2)-terminal kinase and p38] have been best characterized in mesangial and tubular epithelial cell culture systems and include peptide mitogens, cytokines, lipid mediators, and physical stressors. Several in vivo models of proliferative or toxic renal injury are also associated with aberrant MAPK regulation. It is anticipated that elucidation of downstream effector signaling mechanisms and a clearer understanding of the immediate and remote upstream activating pathways, when applied to these highly clinically relevant model systems, will ultimately provide much greater insight into the basis for specificity now seemingly absent from these signaling events.

Regulation of Ca(2+)-activated K(+) channels by multifunctional Ca(2+)/calmodulin-dependent protein kinase

Activation of mesangial cells by ANG II provokes release of intracellular Ca(2+) stores and subsequent Ca(2+) influx through voltage-gated channels, events that are reflected by a large transient increase in intracellular concentration [Ca(2+)](i) followed by a modest sustained elevation in [Ca(2+)](i). These ANG II-induced alterations in [Ca(2+)](i) elicit activation of large Ca(2+)-activated K(+) channels (BK(Ca)) in a negative-feedback manner. The mechanism of this BK(Ca) feedback response may involve the direct effect of intracellular Ca(2+) on the channel and/or channel activation by regulatory enzymes. The present study utilized patch-clamp and fura 2 fluorescence techniques to assess the involvement of multifunctional calcium calmodulin kinase II (CAMKII) in the BK(Ca) feedback response. In cell-attached patches, KN62 (specific inhibitor of CAMKII) either abolished or reduced to near zero the ANG II-induced BK(Ca) feedback response. This phenomenon did not reflect direct effects of KN62 on the BK(Ca) channel, because this agent alone did not significantly alter BK(Ca) channel activity in inside-out patches. KN62 also failed to alter either the transient peak or sustained plateau phases of the [Ca(2+)](i) response to ANG II. In inside-out patches (1 microM Ca(2+) in bath), calmodulin plus ATP activated BK(Ca) channels in the presence but not the absence of CAMKII. These observations are consistent with the postulate that CAMKII is involved in the BK(Ca) feedback response of mesangial cells, acting to potentiate the influence of increased [Ca(2+)](i) on the BK(Ca) channel or a closely associated regulator of the channel. An additional effect of CAMKII to activate a voltage-gated Ca(2+) channel cannot be ruled out by these experiments.

MAP kinase-independent induction of proto-oncogene c-fos mRNA by hemin in human cells

Treatment of HeLa cells or human skin fibroblast cells with hemin led to a time- and dose-dependent rapid induction of c-fos mRNA. This induction was absent in the cells treated with actinomycin D, indicating that the c-fos induction by hemin occurs at the level of transcription. Metalloporphyrins, including zinc-, cobalt-, and tin-protoporphyrin, ferric ion, and protoporphyrin also induced c-fos mRNA. Transient reporter assay with the reporter constructs of the human c-fos gene promoter up to -404 bp connected to the luciferase gene showed high activity but no induction by hemin, suggesting that cis-acting elements, including the serum response element located about -310 bp upstream of the human c-fos gene promoter, may not contribute to the heme-dependent induction. With in-gel assay of protein kinases, the activity of the mitogen-activated protein (MAP) kinases such as extracellular signal-regulated kinase 12 or p38 MAP kinase in hemin-treated HeLa cells was not stimulated. Stimulation of c-Jun N-terminal kinase by hemin was nil. Furthermore, PD58059 and SB203580, inhibitors for MAP kinases, did not affect the hemin-dependent c-fos induction. Of the inhibitors for protein kinases so far tested, KN-62, a specific inhibitor for calmodulin-dependent protein kinase II (CaMK II), inhibited the induction of c-fos mRNA by hemin. Phosphorylation of CaMK II in hemin-treated cells increased. With gel mobility assay, the DNA AP-1 binding activity transiently increased when treating HeLa cells with hemin. Therefore, induction of c-fos led to an activation of AP-1 in the presence of hemin. We suggest that calmodulin-dependent protein kinase II rather than the MAP kinase family regulates the induction of the human c-fos gene expression by hemin.

Inactivation of kinase cascades in mesangial cells grown on collagen type I

Growth on collagen type I gels is known to suppress the mitogenic responsiveness of mesangial cells. Because these cells proliferate in some renal diseases and themselves synthesize collagen type I, we examined the influence of growth on collagen upon several kinase signaling cascades involved in mesangial cell proliferation. Quiescent mesangial cells grown on collagen type I and then stimulated with serum showed a markedly diminished induction of the protooncogene c-fos, compared with their counterparts on plastic or fibronectin. This effect was accompanied by decreased activation of mitogen-activated (Erk family) and Ca2+/calmodulin-dependent protein kinases. Cells on collagen showed lower basal protein kinase C (PKC) activity and diminished levels of PKC-alpha and -zeta isoforms. Global phosphorylation of tyrosine residues was diminished on collagen, and tyrosine phosphorylation of Erk and focal adhesion kinase in response to serum was not detected, in contrast to cells on plastic. We conclude that attachment of mesangial cells to collagen type I results in a broad suppression of protein phosphorylation that is reflected in diminished induction of the c-fos gene and probably underlies the conversion of cultured mesangial cells to a nonproliferative phenotype.