A role for PKC epsilon and MAP kinase in bradykinin-induced arachidonic acid release in rabbit CCD cells

Renal Autocrine and Paracrine Signaling: A Story of Self-protection

Autocrine and paracrine signaling in the kidney adds an extra level of diversity and complexity to renal physiology. The extensive scientific production on the topic precludes easy understanding of the fundamental purpose of the vast number of molecules and systems that influence the renal function. This systematic review provides the broader pen strokes for a collected image of renal paracrine signaling. First, we recapitulate the essence of each paracrine system one by one. Thereafter the single components are merged into an overarching physiological concept. The presented survey shows that despite the diversity in the web of paracrine factors, the collected effect on renal function may not be complicated after all. In essence, paracrine activation provides an intelligent system that perceives minor perturbations and reacts with a coordinated and integrated tissue response that relieves the work load from the renal epithelia and favors diuresis and natriuresis. We suggest that the overall function of paracrine signaling is reno-protection and argue that renal paracrine signaling and self-regulation are two sides of the same coin. Thus local paracrine signaling is an intrinsic function of the kidney, and the overall renal effect of changes in blood pressure, volume load, and systemic hormones will always be tinted by its paracrine status.

Human tissue kallikrein in the treatment of acute ischemic stroke

Acute ischemic stroke (AIS) remains a major cause of death and disability throughout the world. The most severe form of stroke results from large vessel occlusion of the major branches of the Circle of Willis. The treatment strategies currently available in western countries for large vessel occlusion involve rapid restoration of blood flow through removal of the offending blood clot using mechanical or pharmacological means (e.g. tissue plasma activator; tPA). This review assesses prospects for a novel pharmacological approach to enhance the availability of the natural enzyme tissue kallikrein (KLK1), an important regulator of local blood flow. KLK1 is responsible for the generation of kinins (bradykinin and kallidin), which promote local vasodilation and long-term vascularization. Moreover, KLK1 has been used clinically as a direct treatment for multiple diseases associated with impaired local blood flow including AIS. A form of human KLK1 isolated from human urine is approved in the People's Republic of China for subacute treatment of AIS. Here we review the rationale for using KLK1 as an additional pharmacological treatment for AIS by providing the biochemical mechanism as well as the human clinical data that support this approach.

Implication of the Kallikrein-Kinin system in neurological disorders: Quest for potential biomarkers and mechanisms

Neurological disorders represent major health concerns in terms of comorbidity and mortality worldwide. Despite a tremendous increase in our understanding of the pathophysiological processes involved in disease progression and prevention, the accumulated knowledge so far resulted in relatively moderate translational benefits in terms of therapeutic interventions and enhanced clinical outcomes. Aiming at specific neural molecular pathways, different strategies have been geared to target the development and progression of such disorders. The kallikrein-kinin system (KKS) is among the most delineated candidate systems due to its ubiquitous roles mediating several of the pathophysiological features of these neurological disorders as well as being implicated in regulating various brain functions. Several experimental KKS models revealed that the inhibition or stimulation of the two receptors of the KKS system (B1R and B2R) can exhibit neuroprotective and/or adverse pathological outcomes. This updated review provides background details of the KKS components and their functions in different neurological disorders including temporal lobe epilepsy, traumatic brain injury, stroke, spinal cord injury, Alzheimer's disease, multiple sclerosis and glioma. Finally, this work will highlight the putative roles of the KKS components as potential neurotherapeutic targets and provide future perspectives on the possibility of translating these findings into potential clinical biomarkers in neurological disease.

The bradykinin B(2) receptor induces multiple cellular responses leading to the proliferation of human renal carcinoma cell lines

Background

The vasoactive peptide bradykinin (BK) acts as a potent growth factor for normal kidney cells, but there have been few studies on the role of BK in renal cell carcinomas.

Purpose

In this study, we tested the hypothesis that BK also acts as a mitogen in kidney carcinomas, and explored the effects of BK in human renal carcinoma A498 cells.

Methods

The presence of mRNAs for BK B₁ and BK B₂ receptors in A498 cells was demonstrated by reverse transcription–polymerase chain reaction. To study BK signaling pathways, we employed fluorescent measurements of intracellular Ca²⁺, measured changes in extracellular pH as a reflection of Na⁺/H⁺ exchange (NHE) with a Cytosensor microphysiometer, and assessed extracellular signal-regulated kinase (ERK) activation by Western blotting.

Results

Exposure to 100 nM of BK resulted in the rapid elevation of intracellular Ca²⁺, caused a ≥30% increase in NHE activity, and a ≥300% increase in ERK phosphorylation. All BK signals were blocked by HOE140, a BK B₂ receptor antagonist, but not by a B₁ receptor antagonist. Inhibitor studies suggest that BK-induced ERK activation requires phospholipase C and protein kinase C activities, and is Ca²⁺/calmodulin-dependent. The amiloride analog 5-(N-methyl-N-isobutyl)-amiloride (MIA) blocked short-term NHE activation and inhibited ERK phosphorylation, suggesting that NHE is critical for ERK activation by BK. BK induced an approximately 40% increase in the proliferation of A498 cells as assessed by bromodeoxyuridine uptake. This effect was blocked by the ERK inhibitor PD98059, and was dependent on NHE activity.

Conclusion

We conclude that BK exerts mitogenic effects in A498 cells via the BK B₂ receptor activation of growth-associated NHE and ERK.

Identification of functional bradykinin B(2) receptors endogenously expressed in HEK293 cells

The human embryonic kidney (HEK) 293 cell line is widely used in cell biology research. Although HEK293 cells have been meticulously studied, our knowledge about endogenous G protein-coupled receptors (GPCR) in these cells is incomplete. While studying the effects of bradykinin (BK), a potent growth factor for renal cells, we unexpectedly discovered that BK activates extracellular signal-regulated protein kinase 1 and 2 (ERK) in HEK293 cells. Thus, we hypothesized that HEK293 cells possess endogenous BK receptors. RT-PCR demonstrated the presence of mRNAs for BK B(1) and BK B(2) receptors in HEK293 cells. Western blotting with BK B(1) and BK B(2) receptor antibodies confirmed this result at the protein level. To establish that BK receptors are functional, we employed fluorescent measurements of intracellular Ca(2+), measured changes in extracellular acidification rate (ECAR) as a reflection of the Na(+)/H(+) exchange (NHE) with a Cytosensortrade microphysiometer, and assessed ERK activation by Western blotting with a phospho-specific ERK antibody. Exposure of HEK293 cells to BK produced a concentration-dependent rise in intracellular Ca(2+) (EC(50)=36.5+/-8.0 x 10(-9)M), a rapid increase in tyrosine phosphorylation of ERK (EC(50)=9.8+/-0.4 x 10(-9)M), and elevation in ECAR by approximately 20%. All of these signals were blocked by HOE-140 (B(2) receptor antagonist) but not by des-Arg(10)-HOE-140 (B(1) receptor antagonist). We conclude that HEK293 cells express endogenous functional BK B(2) receptors, which couple to the mobilization of intracellular Ca(2+), increases in ECAR and increases in ERK phosphorylation.

Docosahexaenoic acid and arachidonic acid release in rat brain astrocytes is mediated by two separate isoforms of phospholipase A2 and is differently regulated by cyclic AMP and Ca2+

1. Docosahexaenoic acid (DHA) and arachidonic acid (AA), polyunsaturated fatty acids (PUFAs), are important for central nervous system function during development and in various pathological states. Astrocytes are involved in the biosynthesis of PUFAs in neuronal tissue. Here, we investigated the mechanism of DHA and AA release in cultured rat brain astrocytes. 2. Primary astrocytes were cultured under standard conditions and prelabeled with [(14)C]DHA or with [(3)H]AA. Adenosine 5'-triphosphate (ATP) (20 micro M applied for 15 min), the P2Y receptor agonist, stimulates release of both DHA (289% of control) and AA (266% of control) from astrocytes. DHA release stimulated by ATP is mediated by Ca(2+)-independent phospholipase A(2) (iPLA(2)), since it is blocked by the selective iPLA(2) inhibitor 4-bromoenol lactone (BEL, 5 micro M) and is not affected either by removal of Ca(2+) from extracellular medium or by suppression of intracellular Ca(2+) release through PLC inhibitor (U73122, 5 micro M). 3. AA release, on the other hand, which is stimulated by ATP, is attributed to Ca(2+)-dependent cytosolic PLA(2) (cPLA(2)). AA release is abolished by U73122 and, by removal of extracellular Ca(2+), is insensitive to BEL and can be selectively suppressed by methyl arachidonyl fluorophosphonate (3 micro M), a general inhibitor of intracellular PLA(2) s. 4. Western blot analysis confirms the presence in rat brain astrocytes of 85 kDa cPLA(2) and 40 kDa protein reactive to iPLA(2) antibodies. 5. The influence of cAMP on regulation of PUFA release was investigated. Release of DHA is strongly amplified by the adenylyl cyclase activator forskolin (10 micro M), and by the protein kinase A (PKA) activator dibutyryl-cAMP (1 mM). In contrast, release of AA is not affected by forskolin or dibutyryl-cAMP, but is almost completely blocked by 2,3-dideoxyadenosine (20 micro M) and inhibited by 34% by H89 (10 micro M), inhibitors of adenylyl cyclase and PKA, respectively. 6. Other neuromediators, such as bradykinin, glutamate and thrombin, stimulate release of DHA and AA, which is comparable to the release stimulated by ATP. 7. Different sensitivities of iPLA(2) and cPLA(2) to Ca(2+) and cAMP reveal new pathways for the regulation of fatty acid release and reflect the significance of astrocytes in control of DHA and AA metabolism under normal and pathological conditions in brain.

Bradykinin B2 receptor activates extracellular signal-regulated protein kinase in mIMCD-3 cells via epidermal growth factor receptor transactivation

Bradykinin (BK) has been implicated in the regulation of renal function. Activation of extracellular signal-regulated protein kinase (ERK1/2) has been demonstrated in several models of toxic or proliferative renal injury. We studied activation of ERK1/2 by BK in a cell model of the most distal part of the nephron, inner medullary collecting duct (mIMCD-3) cells. Exposure of mIMCD-3 cells to BK (10(-10)-10(-5) M) resulted in a concentration-dependent increase in tyrosine phosphorylation of ERK1/2, with maximal effect at 10(-8) M BK. ERK1/2 activation by BK was observed as early as 1 min, peaked at 5 min, and was sustained at least for 1 h. The effect of BK was mediated by the B(2) receptor and was pertussis toxin-independent. Inhibition of phospholipase C, protein kinase C, or phosphatidylinositol 3-kinase did not alter ERK1/2 activation by BK. BK-induced ERK1/2 activation was Ca(2+)-calmodulin-independent but was sensitive to genistein, an inhibitor of tyrosine kinase(s). AG1478, a specific inhibitor of epidermal growth factor receptor (EGFR) kinase, completely blocked the effect of BK, suggesting an essential role of EGFR in ERK1/2 activation by BK. Immunoprecipitation/Western blot studies revealed that BK stimulated tyrosine phosphorylation of EGFR, its association with an adapter molecule Grb2, and complex formation between Grb2 and the adapter protein Shc. Activation studies of monomeric G protein Ras showed that BK-induced stimulation of Ras was dependent on EGFR tyrosine kinase activity. These studies demonstrate that BK stimulates Ras-dependent activation of ERK1/2 in mIMCD-3 cells via transactivation of EGFR through a novel mechanism.

alpha(2B)-Adrenergic receptors activate MAPK and modulate proliferation of primary cultured proximal tubule cells

In the rat proximal tubule, the alpha(2B)-adrenergic receptor (alpha(2B)-AR) enhances Na(+) reabsorption by increasing the activity of Na(+)/H(+) exchanger isoform NHE3. The mechanisms involved are unclear, and inhibition of cAMP production remains controversial. In this study, we reinvestigated alpha(2B)-AR signaling pathways using rat proximal tubule cells (PTC) in primary culture and LLC-PK(1) cells permanently transfected with the RNG gene (rat nonglycosylated alpha(2)-AR). Binding experiments indicated that PTC express substantial amounts of alpha(2B)-AR (130 fmol/mg protein), and only RNG transcripts were detected. In both cell types, the alpha(2B)-AR is coupled to G protein, and its stimulation by dexmedetomidine, but not by UK-14304, provoked a significant inhibition of the accumulation of cAMP induced by forskolin or parathyroid hormone. Exposure to alpha(2)-agonists increased arachidonic acid release and caused extracellular signal-regulated kinase (ERK)1/2 phosphorylation, which correlated with enhanced mitogen-activated protein kinse (MAPK) activity and nuclear translocation. MAPK phosphorylation was blunted by pertussis toxin but not by protein kinase C desensitization, and it coincided with transient phosphorylation of Shc. Finally, treatment with UK-14304 accelerated cell growth. Further studies will be necessary to clarify the precise mechanism of MAPK activation, but the present data suggest that alpha(2B)-AR may play a positive role during tubular regeneration.

Dopamine-induced translocation of protein kinase C isoforms visualized in renal epithelial cells

Short-term regulation of sodium metabolism is dependent on the modulation of the activity of sodium transporters by first and second messengers. In understanding diseases associated with sodium retention, it is necessary to identify the coupling between these messengers. We have examined whether dopamine, an important first messenger in tubular cells, activates and translocates various protein kinase C (PKC) isoforms. We used a proximal tubular-like cell line, LLCPK-1 cells, in which dopamine was found to inhibit Na(+)-K(+)-ATPase in a PKC-dependent manner. Translocation of PKC isoforms was studied with both subcellular fractionation and confocal microscopy. Both techniques revealed a dopamine-induced translocation from cytosol to plasma membrane of PKC-alpha and -epsilon, but not of PKC-delta, -gamma, and -zeta. The process of subcellular fractionation resulted in partial translocation of PKC-epsilon. This artifact was eliminated in confocal studies. Confocal imaging permitted detection of translocation within 20 s. Translocation was abolished by a phospholipase C inhibitor and by an antagonist against the dopamine 1 subtype (D(1)) but not the 2 subtype of receptor (D(2)). In conclusion, this study visualizes in renal epithelial cells a very rapid activation of the PKC-alpha and -epsilon isoforms by the D(1) receptor subtype.

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.

Developmental changes in endothelium-derived vasorelaxant factors in cerebral circulation

Endothelium-derived prostanoids are predominant vasorelaxant factors in the cerebral circulation of newborn pigs in vivo, whereas in older pigs nitric oxide (NO)-mediated responses also contribute to the regulation of cerebral vascular tone. We compared the expression and activities of NO synthase and cyclooxygenase in the cerebral microcirculation of newborn and adult pigs. In adult animals, expression and activity of endothelial NO synthase in cerebral microvessels and in cultured cerebral endothelial cells is two- to threefold higher than in newborn pigs; acetylcholine and bradykinin cause a greater increase in NO production in adult pigs. Expression and activity of cyclooxygenase in cerebral microvascular endothelial cells is similar in newborn and adult pigs; acetylcholine and bradykinin stimulated dilator prostanoid production to the same degree in both age groups. Endothelial prostanoid synthesis in cerebral microvessels and cultured endothelial cells was inhibited 30-70% by NS-398, reflecting a large contribution of COX-2 in both newborn and adult animals. These data indicate that in the cerebral circulation of pigs, NO synthase is age-dependently upregulated, whereas endothelial cyclooxygenase is not altered during postnatal development.

In vivo B1 kinin-receptor upregulation. Evidence for involvement of protein kinases and nuclear factor kappaB pathways

1. Intradermal (i.d.) injection of cytokines, IL-1beta and TNFalpha (5 ng, 60 and 30 min prior) produces a rapid onset up-regulation of des-Arg9-BK-mediated rat paw oedema. Here we analyse the mechanisms involved in des-Arg9-BK-induced oedema in animals pre-treated with IL-1beta or TNFalpha. 2. Co-injection of anti-IL-1beta, anti-TNFalpha and anti-IL-8 (50 ng) significantly inhibited des-Arg9-BK-induced oedema in animals pre-treated with IL-1beta (65, 37 and 42%) or TNFalpha (39, 64, 25%). IL-1 receptor antagonist (IRA, 100 microg) or IL-10 (10 ng) inhibited the oedema caused by des-Arg9-BK, in rats that had received either IL-1beta (67 and 63%) or TNFalpha (46 and 35%). 3. Co-injection of the PKC inhibitors, staurosporine (10 nmol) or RO 318220 (30 nmol) inhibited des-Arg9-BK-induced paw oedema (44 and 42% for IL-1beta and, 53 and 30% for TNFalpha, respectively). Genistein (tyrosine kinase inhibitor, 2.5 mg kg-1, s.c.) or PD 098059 (MAP-kinase inhibitor, 30 nmol) produced marked inhibition of des-Arg9-BK-induced oedema (58 and 39% for IL-1beta and 31 and 35% for TNFalpha respectively). 4. The NF-kappaB inhibitors TLCK (2 mg kg-1, i.p.) and PDCT (100 mg kg-1, i.p.) significantly inhibited the oedema of des-Arg9-BK in IL-1beta (27 and 83%) or TNFalpha (28 and 80%) pre-treated animals. 5. It is concluded that up-regulation of B1 receptors modulated by IL-1beta or TNFalpha involves the release of other cytokines, activation of PKC and tyrosine kinase pathways, co-ordinated with the activation of MAP-kinase and nuclear factor kappaB, reinforcing the view that B1 receptors may exert a pivotal role in modulating chronic inflammatory processes.