Stimulation of gene expression in neonatal rat ventricular myocytes by Ras is mediated by Ral guanine nucleotide dissociation stimulator (Ral.GDS) and phosphatidylinositol 3-kinase in addition to Raf

Treatment of cultured neonatal ventricular myocytes with oncogenic Ras increases their size and stimulates the re-expression of genes which are normally restricted to the fetal stage of ventricular development, including atrial natriuretic factor (ANF) and skeletal muscle (SkM)-alpha-actin. To determine which signalling pathways mediate these responses, myocytes were transfected with oncogenic (V12) Ras mutants which interact selectively with different effectors and their effects on luciferase (LUX) reporter plasmids were examined. V12 human Ras (V12HRas), itself, activated ANF-LUX 9. 6-fold, whereas mutants of V12HRas, which selectively stimulate Ral guanine nucleotide dissociation stimulator (Ral.GDS) (E37G), c-Raf (D38E) and phosphatidylinositol 3-kinase (PI-3-K; Y40C) enhanced ANF-LUX expression 3.0-, 3.7- and 1.7-fold respectively. The full response of ANF-LUX to V12HRas was restored by using a combination of the individual effector domain mutants. Likewise, SkM-alpha-actin-LUX expression was activated 12.0-, 3.5-, 4.5- and 3. 0-fold by V12HRas, E37G, D38E and Y40C respectively, and a similar pattern of activation was also observed using a c-fos serum-response element-LUX reporter gene. Cell size was also increased by each of the mutants, but simultaneous expression of all three mutant constructs was needed to reconstitute the full effect of V12HRas on cell size (50% increase). Transfection with a constitutively active mutant of PI-3-K (p110K227E) stimulated ANF-LUX, SkM-alpha-actin-LUX, c-fos-serum-response element-LUX and Rous sarcoma virus-LUX by 3.1-, 3.2-, 2.1- and 2.9-fold respectively, but the co-transfected cytomegalovirus-beta-galactosidase reporter gene was activated to a similar extent (1.9-fold). These results suggest that Raf, Ral.GDS and PI-3-K can all transduce transcriptional responses to V12HRas, but that the specific induction of genes associated with the hypertrophic response is not mediated through PI-3-K.

Oncogenic src, raf, and ras stimulate a hypertrophic pattern of gene expression and increase cell size in neonatal rat ventricular myocytes

In response to hormones and growth factors, cultured neonatal ventricular myocytes increase in profile, exhibit myofibrillogenesis, and re-express genes whose expression is normally restricted to the fetal stage of ventricular development. These include atrial natriuretic factor (ANF), beta-myosin heavy chain (beta-MHC), and skeletal muscle (SkM)-alpha-actin. By using luciferase reporter plasmids, we examined whether oncogenes that activate the extracellular signal-regulated kinase cascade (srcF527, Ha-rasV12, and v-raf) increased expression of "fetal" genes. Transfection of myocytes with srcF527 stimulated expression of ANF, SkM-alpha-actin, and beta-MHC by 62-, 6.7-, and 50-fold, respectively, but did not induce DNA synthesis. Stimulation of ANF expression by srcF527 was greater than by Ha-rasV12, which in turn was greater than by v-raf. General gene expression was also increased but to a lesser extent. The response to srcF527 was inhibited by dominant-negative Ha-rasN17. Myocyte area was increased by srcF527, Ha-rasV12, and v-raf, and although it altered myocyte morphology by causing a pseudopodial appearance, srcF527 did not detectably increase myofibrillogenesis either alone or in combination with Ha-rasV12. A kinase-dead src mutant increased myocyte size to a much lesser extent than srcF527 and also did not inhibit ANF-luciferase expression in response to phenylephrine. We conclude that members of the Src family of tyrosine kinases may be important in mediating the transcriptional changes occurring during cardiac myocyte hypertrophy and that Ras and Raf may be downstream effectors.

Stimulation of "stress-regulated" mitogen-activated protein kinases (stress-activated protein kinases/c-Jun N-terminal kinases and p38-mitogen-activated protein kinases) in perfused rat hearts by oxidative and other stresses

"Stress-regulated" mitogen-activated protein kinases (SR-MAPKs) comprise the stress-activated protein kinases (SAPKs)/c-Jun N-terminal kinases (JNKs) and the p38-MAPKs. In the perfused heart, ischemia/reperfusion activates SR-MAPKs. Although the agent(s) directly responsible is unclear, reactive oxygen species are generated during ischemia/reperfusion. We have assessed the ability of oxidative stress (as exemplified by H2O2) to activate SR-MAPKs in the perfused heart and compared it with the effect of ischemia/reperfusion. H2O2 activated both SAPKs/JNKs and p38-MAPK. Maximal activation by H2O2 in both cases was observed at 0.5 mM. Whereas activation of p38-MAPK by H2O2 was comparable to that of ischemia and ischemia/reperfusion, activation of the SAPKs/JNKs was less than that of ischemia/reperfusion. As with ischemia/reperfusion, there was minimal activation of the ERK MAPK subfamily by H2O2. MAPK-activated protein kinase 2 (MAPKAPK2), a downstream substrate of p38-MAPKs, was activated by H2O2 to a similar extent as with ischemia or ischemia/reperfusion. In all instances, activation of MAPKAPK2 in perfused hearts was inhibited by SB203580, an inhibitor of p38-MAPKs. Perfusion of hearts at high aortic pressure (20 kilopascals) also activated the SR-MAPKs and MAPKAPK2. Free radical trapping agents (dimethyl sulfoxide and N-t-butyl-alpha-phenyl nitrone) inhibited the activation of SR-MAPKs and MAPKAPK2 by ischemia/reperfusion. These data are consistent with a role for reactive oxygen species in the activation of SR-MAPKs during ischemia/reperfusion.

Mitogen-activated protein kinase phosphatase 1 inhibits the stimulation of gene expression by hypertrophic agonists in cardiac myocytes

The effect of constitutive expression of mitogen-activated protein kinase (MAPK) phosphatase 1 (MKP-1) on gene expression in response to hypertrophic agonists was examined in cultured neonatal rat ventricular myocytes. Luciferase (LUX) reporter genes linked to promoters for atrial natriuretic factor, ventricular myosin light chain 2, beta-myosin heavy chain, skeletal muscle alpha-actin (SkM alpha-actin) and serum response element-regulated c-fos (c-fos-SRE) were transfected into cardiomyocytes. Phenylephrine (PE; 10 microM), phorbol 12-myristate 13-acetate (1 microM) and endothelin 1 (10 nM) stimulated the expression of these various reporter genes by 2. 5-20-fold. MKP-1 inhibited these effects by 60-85%. In contrast, MKP-1 had no effect on the expression of a constitutively active Rous sarcoma virus-LUX reporter gene. A catalytically inactive mutant MKP-1CS (cysteine-->serine mutation) and the broad-specificity protein tyrosine phosphatase 1B (PTP-1B) had no significant effect on any reporter gene tested. MKP-1 had much less effect on the morphological features accompanying agonist-induced cardiac hypertrophy. PE (10 microM) increased myocyte area by 59% but this effect was only decreased by one-third by MKP-1 and was also partly decreased (by 25%) by expression of PTP-1B. PE also altered cell shape but this was unaffected by MKP-1. There was also no clear effect of MKP-1 on the organization of the contractile apparatus into sarcomeric structures in the presence of 10 microM PE. We conclude that the transcriptional responses accompanying cardiac myocyte hypertrophy are dependent on an MKP-1-sensitive step, presumably the activation of one or members of the MAPK family, but that cell size, shape and myofibrillar organization are much less sensitive to inhibition by MKP-1.

Capacitation-like changes occur in mouse spermatozoa cooled to low temperatures

Previously we showed that >70% of mouse spermatozoa cooled slowly from 37 degrees C to 4 degrees C and warmed have undergone capacitation-like changes as examined by a chlortetracycline staining assay. These membrane changes are reflected in the ability of cooled spermatozoa to achieve fertilization rates in vitro similar to those of uncooled controls when added to oocytes immediately upon warming. The aim of this study was to determine the nature of these membrane changes. We found they were not dependent upon the rate of cooling to 4 degrees C and similar changes were observed when spermatozoa were cooled to higher temperatures (10 degrees and 20 degrees C), but it took longer for 50% of the spermatozoa to undergo such changes (3, 18, and 27 min for spermatozoa held at 4 degrees, 10 degrees, and 20 degrees C, respectively). Mixing cooled spermatozoa with oocytes immediately upon warming produced fertilization rates similar to fresh spermatozoa capacitated in vitro for 90 min before the oocytes were added. The rate of sperm penetration as determined by the fluorescent DNA stain Hoescht 33258 was also similar. However, the penetration time for cooled spermatozoa was significantly shortened when they were preincubated for 90 min before being added to oocytes. We conclude that membrane changes resembling capacitation (1) occur during cooling to temperatures above freezing, (2) are independent of cooling rate, (3) proceed faster at lower temperatures, and (4) obviate the need for prior capacitation in vitro before mixing with oocytes.

Patterns of differentiation among wild rabbit populations Oryctolagus cuniculus L. in arid and semiarid ecosystems of north-eastern Australia

Feral rabbit populations in Australia have generally been managed using localized control procedures. While these procedures may result in local extinctions, persistence of populations will depend on the probability of recolonization. Genetic markers developed using temperature gradient gel electrophoresis (TGGE) combined with heteroduplex analysis (HA) of mitochondrial DNA (mtDNA) were used to characterize the degree of subdivision and extent of gene flow within and among rabbit populations distributed over large distances (up to 1000 km) in southern Queensland (QLD) and north-west New South Wales (NSW), Australia. TGGE analyses revealed significant heterogeneity in mtDNA control region haplotype frequencies. From heterogeneity chi 2 tests, it was evident that the differentiation observed was largely attributable to five sites which were located in the semiarid eastern region, whereas haplotype frequencies were homogeneous throughout the arid western region. These results suggest that there are independent population systems within the study area. The extent of gene flow among local populations within each system is related to the spatial configuration of acceptable habitat patches and the persistence of the populations is determined by the probability of recolonization following local extinction. These data suggest that to provide better overall control of rabbit populations, different management strategies may be necessary in arid and semiarid ecosystems. In arid south-west QLD and north-west NSW, where extensive gene flow occurs over large distances, rabbit populations should be managed at a regional level. In semiarid eastern QLD, where gene flow is restricted and populations are more isolated, localized control procedures may provide effective short-term relief. These results indicate that in nonequilibrium systems with patchy distribution of individuals, the interpretation of migration rate from estimates of gene flow obtained using existing genetic models must include an understanding of the spatial and temporal scales over which population processes operate.

Effect of cooling mouse spermatozoa to 4 degrees C on fertilization and embryonic development

Attempts to freeze mouse spermatozoa in liquid nitrogen (-196 degrees C) have met with limited success. In an attempt to identify the factor(s) that damage mouse spermatozoa during cryopreservation, the effect of slow cooling to 4 degrees C was examined. Epididymal spermatozoa were collected into a variety of media at 37 degrees C, cooled slowly to 4 degrees C over 4 h and warmed in a water bath at 37 degrees C for 5 min. Survival of spermatozoa was assessed by motility, membrane integrity and acrosome status. Labelling with chlortetracycline showed that > 80% of spermatozoa were capacitated and had intact acrosomes immediately after warming compared with < 20% of freshly collected (control) spermatozoa. The rate of fertilization in vitro was similar using spermatozoa cooled in Dulbecco's phosphate-buffered saline and then mixed with oocytes immediately after warming and with control spermatozoa incubated for 2 h before mixing with oocytes (85%). Fewer oocytes were fertilized with spermatozoa cooled in either a modified HEPES-buffered Tyrode's medium or a simple HEPES-buffered medium with a high osmolarity (D3), 63% and 58%, respectively. Two-cell embryos were transferred to the oviducts of pseudopregnant recipients. Implantation was similar in all groups (81-88%) and 54-74% of embryos formed normal late stage fetuses.

Limited genetic differentiation among wild Oryctolagus cuniculus L. (rabbit) populations in arid eastern Australia

A systems approach is necessary for effective control of feral rabbit (Oryctolagus cuniculus L.) populations in the arid environments of Australia. Localized control procedures may result in local extinctions, but the persistence of the overall population will depend on the probability of recolonization, and hence, the degree of isolation of each local population unit. Genetic markers obtained using allozyme electrophoresis, temperature gradient gel electrophoresis (TGGE) and heteroduplex analysis (HA) were used to characterize the degree of structuring and extent of gene flow among rabbit populations in arid Queensland, Australia. Allozyme allele frequency data showed that there was no significant differentiation among sites (average FST = 0.005) and no isolation-by-distance or environmental discontinuity effects. TGGE/HA results also revealed no significant differentiation in mitochondrial DNA Control Region haplotype frequencies among sites and low interpopulation nucleotide divergence estimates (NST = 0.013). Therefore, rabbit populations exhibited a high degree of gene flow over large geographical areas (1600 km2) and were essentially a single panmictic unit. Unpredictable environmental conditions together with the spatial configuration of habitats which possess different probabilities of extinction may have resulted in repeated local extinctions followed by recolonization and homogenizing gene flow. These data suggest that current rabbit control strategies based on individual warren management may not achieve effective control in arid Queensland.

Stimulation of the stress-activated mitogen-activated protein kinase subfamilies in perfused heart. p38/RK mitogen-activated protein kinases and c-Jun N-terminal kinases are activated by ischemia/reperfusion

It has recently been recognized that cellular stresses activate certain members of the mitogen-activated protein kinase (MAPK) superfamily. One role of these "stress-activated" MAPKs is to increase the transactivating activity of the transcription factors c-Jun, Elk1, and ATF2. These findings may be particularly relevant to hearts that have been exposed to pathological stresses. Using the isolated perfused rat heart, we show that global ischemia does not activate the 42- and 44-kD extracellular signal-regulated (protein) kinase (ERK) subfamily of MAPKs but rather stimulates a 38-kD activator of MAPK-activated protein kinase-2 (MAPKAPK2). This activation is maintained during reperfusion. The molecular characteristics of this protein kinase suggest that it is a member of the p38/reactivating kinase (RK) group of stress-activated MAPKs. In contrast, stress-activated MAPKs of the c-Jun N-terminal kinase (JNK/SAPKs) subfamily are not activated by ischemia alone but are activated by reperfusion following ischemia. Furthermore, transfection of ventricular myocytes with activated protein kinases (MEKK1 and SEK1) that may be involved in the upstream activation of JNK/ SAPKs induces increases in myocyte size and transcriptional changes typical of the hypertrophic response. We speculate that activation of multiple parallel MAPK pathways may be important in the responses of hearts to cellular stresses.

Stimulation of phosphatidylinositol hydrolysis, protein kinase C translocation, and mitogen-activated protein kinase activity by bradykinin in rat ventricular myocytes: dissociation from the hypertrophic response

In ventricular myocytes cultured from neonatal rat hearts, bradykinin (BK), kallidin or BK(1-8) [(Des-Arg9)BK] stimulated PtdinsP2 hydrolysis by 3-4-fold. EC50 values were 6 nM (BK), 2 nM (kallidin), and 14 microM [BK(1-8)]. BK or kallidin stimulated the rapid (less than 30 s) translocation of more than 80% of the novel protein kinase C (PKC) isoforms nPKC-delta and nPKC-epsilon from the soluble to the particulate fraction. EC50 values for nPKC-delta translocation by BK or kallidin were 10 and 2 nM respectively. EC50 values for nPKC-epsilon translocation by BK or kallidin were 2 and 0.6 nM respectively. EC50 values for the translocation of nPKC-delta and nPKC-epsilon by BK(1-8) were more than 5 microM. The classical PKC, cPKC-alpha, and the atypical PKC, nPKC-zeta, did not translocate. BK caused activation and phosphorylation of p42-mitogen-activated protein kinase (MAPK) (maximal at 3-5 min, 30-35% of p42-MAPK phosphorylated). p44-MAPK was similarly activated. EC50 values for p42/p44-MAPK activation by BK were less than 1 nM whereas values for BK(1-8) were more than 10 microM. The order of potency [BK approximately equal to kallidin >> BK (1-8)] for the stimulation of PtdInsP2 hydrolysis, nPKC-delta and nPKC-epsilon translocation, and p42/p44-MAPK activities suggests involvement of the B2 BK receptor subtype. In addition, stimulation of all three processes by BK was inhibited by the B2BK receptor-selective antagonist HOE140 but not by the B1-selective antagonist Leu8BK(1-8). Exposure of cells to phorbol 12-myristate 13-acetate for 24 h inhibited subsequent activation of p42/p44-MAPK by BK suggesting participation of nPKC (and possibly cPKC) isoforms in the activation process. Thus, like hypertrophic agents such as endothelin-1 (ET-1) and phenylephrine (PE), BK activates PtdInsP2 hydrolysis, translocates nPKC-delta, and nPKC-epsilon, and activates p42/p44-MAPK. However, in comparison with ET-1 and PE, BK was only weakly hypertrophic as assessed by cell morphology and patterns of gene expression. This difference could not be attributed to dissimilarities between the duration of activation of p42/p44-MAPK by BK or ET-1. Thus activation of these signalling pathways alone may be insufficient to induce a powerful hypertrophic response.

Depletion of mitogen-activated protein kinase using an antisense oligodeoxynucleotide approach downregulates the phenylephrine-induced hypertrophic response in rat cardiac myocytes

An antisense oligodeoxynucleotide (ODN) approach was used to investigate whether mitogen-activated protein kinase (MAPK) is necessary for the hypertrophic response in cardiac myocytes. A phosphorothioate-protected 17-mer directed against the initiation of translation sites of the p42 and p44 MAPK isoform mRNAs was introduced into cultured cardiac myocytes by liposomal transfection. At an antisense ODN concentration of 0.2 mumol/L, p42 MAPK protein was reduced by 82% (immunoblot) after 48 hours, and p42 and p44 MAPK activities were reduced by 44% and 60%, respectively. The same concentration of anti-MAPK ODN inhibited development of the morphological features of hypertrophy (sarcomerogenesis, increased cell size) in myocytes exposed to phenylephrine. Phenylephrine-induced activation of the atrial natriuretic factor (ANF) promoter (measured by the activity of a transfected ANF promoter/luciferase reporter gene) and induction of ANF mRNA (measured by RNase protection assay) were also attenuated. We conclude that MAPK is important for the development of the hypertrophic phenotype in this model of hypertrophy.

Adrenergic receptor stimulation of the mitogen-activated protein kinase cascade and cardiac hypertrophy

Phenylephrine and noradrenaline (alpha-adrenergic agonism) or isoprenaline (beta-adrenergic agonism) stimulated protein synthesis rates, increased the activity of the atrial natriuretic factor gene promoter and activated mitogen-activated protein kinase (MAPK). The EC50 for MAPK activation by noradrenaline was 2-4 microM and that for isoprenaline was 0.2-0.3 microM. Maximal activation of MAPK by isoprenaline was inhibited by the beta-adrenergic antagonist, propranolol, whereas the activation by noradrenaline was inhibited by the alpha1-adrenergic antagonist, prazosin. FPLC on a Mono-Q column separated two peaks of MAPK (p42MAPK and p44MAPK) and two peaks of MAPK-activating activity (MEK) activated by isoprenaline or noradrenaline. Prolonged phorbol ester exposure partially down-regulated the activation of MAPK by noradrenaline but not by isoprenaline. This implies a role for protein kinase C in MAPK activation by noradrenaline but not isoprenaline. A role for cyclic AMP in activation of the MAPK pathway was eliminated when other agonists that elevate cyclic AMP in the cardiac myocyte did not activate MAPK. In contrast, MAPK was activated by exposure to ionomycin, Bay K8644 or thapsigargin that elevate intracellular Ca2+. Furthermore, depletion of extracellular Ca2+ concentrations with bis-(o-aminophenoxy)ethane-NNN'N'-tetra-acetic acid (BAPTA) or blocking of the L-type Ca2+ channel with nifepidine or verapamil inhibited the response to isoprenaline without inhibiting the responses to noradrenaline. We conclude that alpha- and beta-adrenergic agonists can activate the MEK/MAPK pathway in the heart by different signalling pathways. Elevation of intracellular Ca2+ rather than cyclic AMP appears important in the activation of MAPK by isoprenaline in the cardiac myocyte.

Gelatinase A possesses a beta-secretase-like activity in cleaving the amyloid protein precursor of Alzheimer's disease

The ability of the 72 kDa gelatinase A to cleave the amyloid protein precursor (APP) was investigated. HeLa cells were transfected with an APP695 plasmid. The cells were incubated with gelatinase A, which cleaved the 110 kDa cell-surface APP, releasing a 100 kDa form of the protein. A peptide homologous to the beta-secretase site was cleaved by gelatinase A adjacent to a glutamate residue at position -3 (beta A4 numbering system). A peptide homologous to the alpha-secretase site was not cleaved. The results demonstrate that 72 kDa gelatinase A is not an alpha-secretase, but that it may have a beta-secretase activity.

The mitogen-activated protein kinase kinase MEK1 stimulates a pattern of gene expression typical of the hypertrophic phenotype in rat ventricular cardiomyocytes

Adult mammalian ventricular cardiomyocytes are terminally differentiated cells that enlarge adaptively by hypertrophy. In this situation, genes normally expressed in the fetal ventricular cardiomyocyte (e.g. atrial natriuretic factor (ANF), beta-myosin heavy chain (beta-MHC), and skeletal muscle (SkM) alpha-actin) are re-expressed, and there is transient expression of immediate early genes (e.g. c-fos). Using appropriate reporter plasmids, we studied the effects of transfection of the constitutively active or dominant negative mitogen-activated protein kinase kinase MEK1 on ANF, beta-MHC, and SkM alpha-actin promoter activities in cultured ventricular cardiomyocytes. ANF expression was stimulated (maximally 75-fold) by the hypertrophic agonist phenylephrine in a dose-dependent manner (EC50, 10 microM), and this stimulation was inhibited by dominant negative MEK1. Cotransfection of dominant negative MEK1 with a dominant negative mitogen-activated protein kinase (extracellular signal-regulated protein kinase (ERK2)) increased this inhibition. Transfection with constitutively active MEK1 constructs doubled ANF promoter activity. The additional cotransfection of wild-type ERK2 stimulated ANF promoter activity by about 5-fold. Expression of beta-MHC and SkM alpha-actin was also stimulated. Promoter activity regulated by activator protein-1 or c-fos serum response element consensus sequences was also increased. We conclude that the MEK1/ERK2 cascade may play a role in regulating gene expression during hypertrophy.

Expression of the amyloid precursor protein of Alzheimer's disease on the surface of transfected HeLa cells

The principal component of the amyloid which accumulates in Alzheimer's Disease brain is a 4-kDa beta A4 fragment of the amyloid precursor protein (APP). Although APP has the structural features of an integral transmembrane receptor, there has been limited evidence for expression of APP at the plasma membrane. The function of APP and related molecules is unknown. Using rabbit antisera to purified human brain APP, surface labeling of APP is demonstrable in HeLa cells transfected with the APP695 isoform. Indirect immunofluorescence indicates the presence of APP at the surface of unfixed or aldehyde-fixed cells; preembedding immunoelectron microscopy using 5- or 1-nm gold particles and silver enhancement confirms plasma membrane labeling as well as labeling within intracellular membrane vesicles. Immunolabeling of unfixed cells at 4 degrees C followed by incubation at 37 degrees C shows APP within endocytic vesicles. Transfected HeLa cells with prominent surface APP were larger with more extensive microvilli than nonimmunoreactive HeLa cells. This is consistent with the postulated role of APP as a mediator of cell surface adhesion and membrane-matrix stabilization.

Expression of protein kinase C isoforms during cardiac ventricular development

The expression of protein kinase C (PKC) isoforms (PKC-alpha, PKC-beta 1, PKC-delta, PKC-epsilon, and PKC-zeta) was studied by immunoblotting in whole ventricles of rat hearts during postnatal development (1-26 days) and in the adult. PKC-alpha, PKC-beta 1, PKC-delta, PKC-epsilon, and PKC-zeta were detected in ventricles of 1-day-old rats, although PKC-alpha and PKC-beta 1 were only barely detectable. All isoforms were rapidly downregulated during development, with abundances relative to total protein declining in the adult to < 25% of 1-day-old values. PKC-beta 1 was not detectable in adult ventricles. The specific activity of PKC was also downregulated. The rat ventricular myocyte becomes amitotic soon after birth but continues to grow, increasing its protein content 40- to 50-fold between the neonate and the 300-g adult. An important question is thus whether the amount of PKC per myocyte is downregulated. With the use of isolated cells, immunoblotting showed that the contents per myocyte of PKC-alpha and PKC-epsilon increased approximately 10-fold between the neonatal and adult stages. In rat ventricles, the rank of association with the particulate fraction was PKC-delta > PKC-epsilon > PKC-zeta. Association of these isoforms with the particulate fraction was less in the adult than in the neonate. In primary cultures of ventricular myocytes prepared from neonatal rat hearts, 1 microM 12-O-tetradecanoylphorbol-13-acetate (TPA) elicited translocation of PKC-alpha, PKC-delta, and PKC-epsilon from the soluble to the particulate fraction in < 1 min, after which time no further translocation was observed. Prolonged exposure (16 h) of myocytes to 1 microM TPA caused essentially complete downregulation of these isoforms, although downregulation of PKC-epsilon was slower than for PKC-delta. In contrast, PKC-zeta was neither translocated nor downregulated by 1 microM TPA. Immunoblotting of human ventricular samples also revealed downregulation of PKC relative to total protein during fetal/postnatal development.

Intracellular production of beta A4 amyloid of Alzheimer's disease: modulation by phosphoramidon and lack of coupling to the secretion of the amyloid precursor protein

The amyloid precursor protein (APP) undergoes abnormal metabolism in Alzheimer's disease, resulting in the accumulation of beta A4 amyloid in the brain. Normal APP metabolism includes the release of a truncated form (sAPP) which has been cleaved at the alpha-secretase site within the beta A4 amyloidogenic domain. However, intact forms of beta A4 protein may also be generated by the beta- and gamma-secretases. Soluble forms of beta A4 have been detected in various cell lines and in cerebrospinal fluid. Previous studies of protein kinase C activation have suggested a reciprocal relationship between sAPP secretion and beta A4 production and release. We find that phorbol ester activation of protein kinase C in untransfected SH-SY5Y neuroblastoma cells increases the release of sAPP without affecting beta A4 secretion. We provide further evidence for intracellular beta A4 production. Treatment of SY5Y cells with the protease inhibitor phosphoramidon results in a 2-fold increase in beta A4 secretion and an increase in the amount of beta A4 recovered from cell lysates, yet it does not affect sAPP secretion. The protease inhibitors thiorphan and N-[(RS)-2-carboxy-3-phenylpropanoyl]-L-leucine had no effect on beta A4 or sAPP secretion. The lysosomotropic agents chloroquine and NH4Cl decreased beta A4 secretion, providing additional evidence for the involvement of intracellular acidic compartments in the production of beta A4. Our results therefore demonstrate a double dissociation between the secretion of sAPP and beta A4 in the SH-SY5Y cell line. The effect of phosphoramidon supports previous studies which show that metalloproteases are involved in the biogenesis of beta A4.

Classical, novel and atypical isoforms of PKC stimulate ANF- and TRE/AP-1-regulated-promoter activity in ventricular cardiomyocytes

Cultured neonatal rat ventricular myocytes were co-transfected with expression plasmids encoding protein kinase C (PKC) isoforms from each of the PKC subfamilies (classical PKC-alpha, novel PKC-epsilon or atypical PKC-zeta) together with an atrial natriuretic factor (ANF) reporter plasmid. Each PKC had been rendered constitutively active by a single Ala-->Glu mutation or a small deletion in the inhibitory pseudosubstrate site. cPKC-alpha, nPKC-epsilon or aPKC-zeta expression plasmids each stimulated ANF-promoter activity and expression of a reporter gene under the control of a 12-O-tetradecanoylphorbol 13-acetate-response element (TRE). Upregulation of the ANF promoter is characteristic of the hypertrophic response in the heart ventricle and a TRE is present in the ANF promoter. Thus all subfamilies of PKC may have the potential to contribute to hypertrophic response in cardiomyocytes.

Regulation of mitogen-activated protein kinase cascade in adult rat heart preparations in vitro

The regulation of mitogen-activated protein kinase (MAPK) and MAPK kinase (MEK) was studied in freshly isolated adult rat heart preparations. In contrast to the situation in ventricular myocytes cultured from neonatal rat hearts, stimulation of MAPK activity by 1 mumol/L phorbol 12-myristate 13-acetate (PMA) was not consistently detectable in crude extracts. After fast protein liquid chromatography, MAPK isoforms p42MAPK and p44MAPK and two peaks of MEK were shown to be activated > 10-fold in perfused hearts or ventricular myocytes exposed to 1 mumol/L PMA for 5 minutes. The identities of MAPK or MEK were confirmed by immunoblotting and, for MAPK, by the "in-gel" myelin basic protein phosphorylation assay. In retrogradely perfused hearts, high coronary perfusion pressure (120 mm Hg for 5 minutes), norepinephrine (50 mumol/L for 5 minutes), or isoproterenol (50 mumol/L for 5 minutes) stimulated MAPK and MEK approximately 2- to 5-fold. In isolated myocytes, endothelin 1 (100 nmol/L for 5 minutes) also stimulated MAPK, but stimulation by norepinephrine or isoproterenol was difficult to detect. Immunoblotting showed that the relative abundances of MAPK and MEK protein in ventricles declined to < 20% of their postpartal abundances after 50 days. This may explain the difficulties encountered in assaying the activity of MAPK in crude extracts from adult hearts. We conclude that potentially hypertrophic agonists and interventions stimulate the MAPK cascade in adult rats and suggest that the MAPK cascade may be an important intracellular signaling pathway in this response.

Characterization of stimulation of phosphoinositide hydrolysis by alpha 1-adrenergic agonists in adult rat hearts

The coupling of the pharmacologically defined alpha 1A- and alpha 1B-adrenoceptors to the hydrolysis of phospho[3H]inositides (PI) was investigated in ventricular myocytes freshly isolated from adult rat hearts. The alpha 1-adrenoceptor population in the heart was characterized by competitive binding experiments using [3H]prazosin and the alpha 1A-adrenoceptor-selective antagonist 5-methyl urapidil. It was heterogeneous with approximately 25% being pharmacologically of the alpha 1A-adrenoceptor subtype and 75% being of the alpha 1B-adrenoceptor subtype. Epinephrine, norepinephrine, or phenylephrine stimulated PI hydrolysis in the presence or absence of propranolol. The greatest stimulation (7-fold) was with epinephrine. The half-maximum effective concentrations for agonists were approximately 0.5-3.5 and 0.2 microM in the absence and presence of propranolol, respectively. The inhibition by 5-methyl urapidil of the stimulation of PI hydrolysis by a fixed concentration of epinephrine fitted a two-site competition curve. The distribution between high-affinity (25%) and low-affinity (75%) sites suggested that both the alpha 1A- and alpha 1B-adrenoceptors were coupled to PI hydrolysis in proportion to their relative abundance. Equally, the stimulation of PI hydrolysis by epinephrine in the presence of a fixed concentration of 5-methyl urapidil was biphasic. In addition, chloroethylclonidine, an irreversible inhibitor of the alpha 1B-adrenoceptor, inhibited the epinephrine stimulation of PI hydrolysis by 35%. We conclude that the pharmacologically defined alpha 1A- and alpha 1B-adrenoceptor subtypes are both coupled to PI hydrolysis in the ventricular myocyte.