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PubMed2001

Continuous interleukin-6 application in vivo via macroencapsulation of interleukin-6-expressing COS-7 cells induces massive gliosis.

The inflammatory cytokine interleukin-6 (IL-6) was found in senile plaques of Alzheimer's patients and might be involved in the pathology of Parkinson's disease and multiple sclerosis. Interestingly, an astocytosis is also found in these neurodegenerative disorders. To evaluate the direct effects of IL-6 in vivo on glial cells, we created a new in vivo model. IL-6 and mock-transfected (control group) COS-7 cells were encapsulated in a poly-acryl-nitril membrane for implantation into the rat striatum. Afterward, the host immune reaction to the membrane without encapsulated cells and the biological action of IL-6-producing capsules was evaluated. Animals with an implanted membrane without cells showed a moderate astrocytosis 5 days after the operation. Furthermore, microglia and T-cells could be detected and after 30 days the astrocytosis decreased to a small layer around the membrane. In comparison to the control group, which received a sham operation, our results demonstrate that the response of glial cells is caused by the mechanical damage of the surgical procedure itself rather than due to the introduced membrane material. In contrast, we found a massive proliferation and activation of astrocytes and microglia after 10 days by IL-6-secreting capsules, indicating that IL-6 is involved in the induction of gliosis. Control animals that received encapsulated mock-transfected COS-7 cells showed only a weak response. These data point to an involvement of IL-6 in the proliferation and activation of glial cells as seen in neurodegenerative disorders.

Animals↗
PubMed1996

Cloning and sequencing of rat liver carboxylesterase ES-4 (microsomal palmitoyl-CoA hydrolase).

A cDNA which encodes a carboxylesterase of 561 amino acid residues including a cleavable signal peptide is described. The enzyme expressed in COS cells migrates during PAGE (SDS-, and non-denaturing) as a single prominent band in the region of liver ES-4. It ends in the C-terminal cell-retention signal -HNEL, which, in COS cells overexpressing the enzyme, appears to be slightly less efficient than the signals -HTEL and -HVEL of ES-3 and ES-10 respectively. Glycosylation is not essential for intracellular retention, but leads to a higher activity. As do many carboxylesterases, the enzyme expressed in COS cells hydrolyses omicron-nitrophenyl acetate and alpha-naphthyl acetate. It also hydrolyses acetanilide, although less efficiently than ES-3, and, distinctively, palmitoyl-CoA. In addition to the four canonical Cys residues of the carboxylesterases, it contains a fifth, unpaired Cys336, which apparently is not essential for the catalytic properties. Indeed, treatment with iodoacetamide or substitution of Cys336 by Phe does not markedly alter the activity of the enzyme on the various substrates. The predicted structure of ES-4 is highly homologous to that of two other recently cloned esterases which also end in -HNEL [Yan, Yang, Brady and Parkinson (1994) J. Biol. Chem. 269, 29688-29696; Yan, Yang, and Parkinson (1995) Arch. Biochem. Biophys. 317, 222-234]. Together, these isoenzymes probably account for the closely spaced bands observed in the region of ES-4 in non-denaturing PAGE.

Amino Acid Sequence↗
PubMed1999

Deletions or specific substitutions of a few residues in the NH(2)-terminal region (Ala(3) to Thr(9)) of sarcoplasmic reticulum Ca(2+)-ATPase cause inactivation and rapid degradation of the enzyme expressed in COS-1 cells.

Amino acid residues in the NH(2)-terminal region (Glu(2) - Ala(14)) of adult fast twitch skeletal muscle sarcoplasmic reticulum Ca(2+)-ATPase (SERCA1a) were deleted or substituted, and the mutants were expressed in COS-1 cells. Deletion of any single residue in the Ala(3)-Ser(6) region or deletion of two or more consecutive residues in the Ala(3)-Thr(9) region caused strongly reduced expression. Substitution mutants A4K, A4D, and H5K also showed very low expression levels. Deletion of any single residue in the Ala(3)-Ser(6) region caused only a small decrease in the specific Ca(2+) transport rate/mg of SERCA1a protein. In contrast, other mutants showing low expression levels had greatly reduced specific Ca(2+) transport rates. In vitro expression experiments indicated that translation, transcription, and integration into the microsomal membranes were not impaired in the mutants that showed very low expression levels in COS-1 cells. Pulse-chase experiments using [(35)S]methionine/cysteine labeling of transfected COS-1 cells demonstrated that degradation of the mutants showing low expression levels was substantially faster than that of the wild type. Lactacystin, a specific inhibitor of proteasome, inhibited the degradation accelerated by single-residue deletion of Ala(3). These results suggest that the NH(2)-terminal region (Ala(3) -Thr(9)) of SERCA1a is sensitive to the endoplasmic reticulum-mediated quality control and is thus critical for either correct folding of the SERCA1a protein or stabilization of the correctly folded SERCA1a protein or both.

Animals↗
PubMed1995

Reassessment of the subcellular localization of p63.

p63 is a type II integral membrane protein that has previously been suggested to be a resident protein of a membrane network interposed between the ER and the Golgi apparatus. In the present study, we have produced a polyclonal antibody against the purified human p63 protein to reassess the subcellular distribution of p63 by confocal immunofluorescence, immunoelectron microscopy, and cell fractionation. Double immunofluorescence of COS cells showed significant colocalization of p63 and a KDEL-containing lumenal ER marker protein, except for differences in the staining of the outer nuclear membrane. Immunoelectron microscopy of native HepG2 cells and of COS cells transfected with p63 revealed that both endogenous and overexpressed p63 are predominantly localized in the rough ER. While p63 was colocalized with protein disulfide isomerase, an ER marker protein, very little overlap of p63 was found with ERGIC-53, an established marker for the ER-Golgi intermediate compartment. When rough and smooth membranes were prepared from rat liver, p63 was found to copurify with ribophorin II, a rough ER protein. Both p63 and ribophorin II were predominantly recovered in rough microsomes and were largely separated from the intermediate compartment marker protein p58. From these results it is concluded that p63 is localized in the rough ER.

Amino Acid Sequence↗
PubMed1989

Transient expression of B19 parvovirus gene products in COS-7 cells transfected with B19-SV40 hybrid vectors.

Hybrid B19 parvovirus-SV40 origin vectors were transfected into COS-7 cells and replication of these plasmids studied. Plasmids that have a frameshift mutation within the nonstructural gene region replicated to high level (copy number approximately 10,000/transfected cell) although somewhat lower than pSVOd, the SV40 origin vector without B19 sequence (copy number approximately 100,000/transfected cell). However, hybrid B19 parvovirus-SV40 origin vectors that do not contain these frameshift mutations replicated to a much lower level (copy number approximately 1000/transfected cell). Although the hybrid vectors studied replicated at different efficiencies in COS-7 cells, they are transcribed at approximately the same level, resulting in RNA species that are indistinguishable from those seen in B19 virus-infected erythroid bone marrow cells. Western blot analysis demonstrated that the mRNAs are translated into polypeptides of the same size and, in the case of viral structural proteins, in same relative abundance as seen in a B19-infected clinical sample.

Blotting, Northern↗
PubMedDate not supplied

Expression of the murine prostaglandin (PGH) synthase-1 and PGH synthase-2 isozymes in cos-1 cells.

Plasmid vectors were constructed which allowed expression of the mouse prostaglandin endoperoxide (PGH) synthase-1 and PGH synthase-2 isozymes in cos-1 cells. Efficient expression of the PGHS-2 isozyme required the truncation of the entire 3'-untranslated region of the PGHS-2 cDNA, possibly due to the presence of multiple AUUUA sequences which may destabilize the PGHS-2 mRNA. The length of the 3'-untranslated regions of the murine and ovine PGHS-1 isozymes, which do not contain AUUUA sequences, did not affect the efficiency of expression of these proteins. The murine PGHS-2 isozyme catalyzes the same cyclooxygenase and hydroperoxidase activities as the ovine and murine PGHS-1 isozymes. The maximal activities of the mouse enzymes expressed in cos-1 cells was about equal, but both were only about a third that seen with the sheep enzyme. Whether this reflects differences in the turnover rate of the mouse and sheep enzymes, or differences in the efficiency of expression in cos-1 cells is not known.

Animals↗
PubMed2002

Agonist-like activity of antibodies directed against the second extracellular loop of the human cardiac serotonin 5-HT4(e) receptor in transfected COS-7 cells.

We have previously reported that antipeptide antibodies directed against the second extracellular loop of the cardiac h5-HT4 receptor could block the activation of the L-type Ca channel in human atrial cardiomyocytes. In this paper we investigate the immunological and physiological activity of these antibodies, in a cell system expressing a larger amount of receptors than the atrial cells. The recombinant receptor was expressed at the surface of COS-7 cells under an active form (serotonin, EC50 = 1.81 x 10(-7) M), at a high level (375 +/- 25 fmol receptor/mg total protein) and was able to bind a specific ligand (GR113808) with a high affinity (Kd = 0.28 +/- 0.05 nM). In this system, the same anti-peptide antibodies used for the cardiac cells induced an "agonist-like" effect on the recombinant h5-HT4 receptor. These results are in line with those shown for others G-protein coupled receptors, as adrenoreceptors. In addition, this work showed that the effect of the antibodies is not only dependent on the epitopic region recognised but also on the molecular density and/or the cellular environment of the target receptors. Finally, our results support the hypothesis that the h5-HT4 receptor could be a new target for autoantibodies in patients with atrial arrhythmia.

Adenylyl Cyclases↗
PubMed2000

Further characterisation of the interaction of haloperidol metabolites with neurotransmitter transporters in rat neuronal cultures and in transfected COS-7 cells.

It has been proposed that the extrapyramidal symptoms such as tardive dyskinesia developed by patients on long-term haloperidol treatment may be the result of uptake of haloperidol metabolites into neurons via the monoamine neurotransmitter transporters followed by neurotoxic events, as occurs for MPP+, the pyridinium metabolite of MPTP. We recently showed that haloperidol and its metabolites are inhibitors of the human noradrenaline transporter (NAT), dopamine transporter (DAT) and serotonin transporter (SERT), and determined their Ki values for inhibition of the three transporters expressed in transfected COS-7 cells. In this study, we extended the investigation of these compounds to their inhibitory effects on DAT, SERT and the high affinity choline uptake (HACU) in neuronal cultures from embryonic rat brain, and investigated whether the compounds are substrates or non-transported inhibitors of the NAT, DAT and SERT in transfected COS-7 cells and DAT and SERT in the neuronal cultures. Haloperidol and its metabolites inhibited DAT, SERT and HACU in the neuronal cultures, indicating that they are not specific inhibitors of the monoamine neurotransmitter transporters. The ratio of the Ki values of the least and most potent inhibitors were found to be 2.8 for DAT, 24 for SERT and 7.6 for HACU. The compounds were more potent inhibitors of DAT and SERT in neuronal cultures than we found previously in transfected COS-7 cells. The question of whether the compounds are substrates or non-transported inhibitors of the monoamine transporters was investigated by determining whether they caused an increase in efflux of [3H]amine in transfected COS-7 cells or neuronal cultures preloaded with [3H]amine. Haloperidol metabolites were weak substrates for SERT, but not for NAT or DAT, in transporter-transfected COS-7 cells. In neuronal cultures, the metabolites appeared to be non-transported inhibitors or very weak substrates of DAT and SERT. Despite inhibition of the monoamine transporters by haloperidol and its metabolites, there is little evidence to support the proposal that these compounds are likely to cause neurotoxic effects via neuronal uptake using the monoamine transporters. The mechanisms of the side effects of haloperidol therapy, such as tardive dyskinesia, are still unclear, but are unlikely to depend on interactions of the drug or its metabolites with NAT, DAT or SERT.

Animals↗
PubMed2004

Regulated compartmentalization of the putative DEAD-box helicase MDDX28 within the mitochondria in COS-1 cells.

We recently cloned a putative DEAD-box helicase MDDX28 and found that it was localized to the nuclei and mitochondria of COS-1 cells. The mitochondrial localization of MDDX28 is largely diffuse. We have, however, used immunofluorescence and immunogold cytochemistry to show that the MDDX28 protein is localized in a distinct mitochondrial subcompartment in 5-10% of COS-1 cells. This proportion increases to approximately 35% after treatment with ethidium bromide, suggesting upregulation following transcription inhibition. To our knowledge, this is the first example of protein relocation in the mitochondria caused by transcription inhibition. The mitochondrial subcompartmentation of MDDX28 was negatively affected by mutations in a RNA-binding domain and three basic domains previously shown to be important in transcription-dependent intranuclear localization. Furthermore, immunogold cytochemistry and fractionation of rat liver indicated that the protein is a part of an RNA-protein (RNP) complex interacting peripherally with the mitochondrial inner membrane. Our results reveal new principles for regulation of protein localization in the mitochondria and suggest parallels between the function of the MDDX28 protein in the nucleus and mitochondria.

Animals↗
PubMed1990

Lateral diffusion of nerve growth factor receptor: modulation by ligand-binding and cell-associated factors.

We compared the properties in human melanoma cell line A875 and rat pheochromocytoma cell line PC12 of nerve growth factor receptor (NGFr). We also analyzed NGFr and a truncated NGFR lacking the cytoplasmic domain, which were transiently expressed in COS cells. The full-length NGFR expressed in COS cells bound nerve growth factor (NGF) with positive cooperativity, but A875 NGFr and truncated NGFr in COS cells did not display positive cooperativity. The anti-human NGFr monoclonal antibody NGFR5 was characterized and found not to compete with NGF for binding to NGFr. Fabs were prepared from NGFR5 and 192, an anti-rat NGFR monoclonal antibody that was previously shown not to compete with NGF for binding. Fluorescein-labeled Fabs were used to measure the distribution and lateral diffusion of the NGFr. NGFr expressed on COS and A875 cells are diffusely distributed, but NGFr on the surface of PC12 cells appeared, for some cells, to be patched. In A875 cells, 51% of the NGFr was free to diffuse with diffusion coefficient (D) approximately 7 X 10(-10) cm2/s. In COS cells, 43% diffused with D approximately 5 X 10(-10) cm2/s. There was no significant difference in diffusibility between the full-length NGFr and the truncated NGFr. We compared NGFr diffusion on PC12 cells in suspension or adherent to collagen-coated coverslips. For suspension cells, we obtained 32% recovery with D approximately 2.5 X 10(-9) cm2/s. On adherent cells, we obtained 17% recovery with 6 X 10(-9) cm2/s. Binding of NGF enhanced lateral diffusion of NGFr in A875 cells and in PC12 cells in suspension but did not alter lateral diffusion of NGFr in COS cells or in adherent PC12 cells. NGF had no effect on the diffusing fraction or the distribution of NGFR for any cell line.

Animals↗
PubMed2006

[Construction and identification of eukaryotic expression plasmid pcDNA3. 1-BACE and its transient expression in COS-7 cells].

OBJECTIVE: To generate eukaryotic expression vector of pcDNA3. 1-beta-site amyloid precursor protein cleaving enzyme (BACE) and obtain its transient expression in COS-7 cells. METHODS: A 1.5 kb cDNA fragment was amplified from the total RNA of the human neuroblastoma cells by the RT-PCR method and was cloned into the plasmid pcDNA3.1. The vector was identified by the double digestion with restriction enzymes BamHI and XhoI and was sequenced by the Sanger-dideoxy-mediated chain termination. The expression of the BACE gene was detected by immunocytochemistry. RESULTS: The results showed that the cDNA fragment included 1.5 kb total coding region. The recombinant eukaryotic cell expression vector of pcDNA3. 1-BACE was constructed successfully, and the sequence of insert was identical to the published sequence. The COS-7 cells transfected with the pcDNA3. 1-BACE plasmid expressed a high level of the BACE protein in the cytoplasm. CONCLUSION: The recombinant plasmid pcDNA3. 1-BACE can provide a very useful tool for the research on the cause of Alzheimer's disease and lay an important foundation for preventing Alzheimer's disease.

Amyloid Precursor Protein Secretases↗
PubMed1989

Transient expression of the angiotensin II receptor: a rapid and functional analysis of a calcium-mobilizing seven-transmembrane domain receptor in COS-7 cells.

The mas oncogene/angiotensin II receptor was subcloned into a mammalian expression vector pCDM8 and used to transiently transfect monkey kidney derived COS-7 cells. As a result, the mas transfected COS-7 cells expressed a functional angiotensin II receptor capable of transducing an increase in intracellular Ca2+ following stimulation with angiotensin II. The angiotensin II stimulated changes in Ca2+ could be measured 24 hours after transfection in both a fluorimeter and a fluorescence activated cell sorter. These results describe a rapid method for the functional analysis of the 7-transmembrane domain receptor genes.

Angiotensin II↗
PubMed2003

[Construction of single-chain Fv Gene of Anti-HBsAg and its expression in COS-7 cells].

AIM: To subclone the V(L) gene and V(H) genes of anti-HBsAg and construct the single-chain Fv gene and to analyse the expression of the constructed gene in COS-7 cells. METHODS: A set of oligonucleotide primers were designed and used to amplify the V(H) and V(L) genes from Fab antibodies screened from phage antibody library. The products were cloned into pUC19 vector and their sequences were analysed. The V(H) and V(L) gene fragments were linked up by a peptide linker and a leader sequence added at 5' terminus of each gene (L-V(H)-Linker-V(L)) and designated as L-ScFv. The L-ScFv genes were inserted into the eukaryotic fusion protein expression vector pEGFP-N3 and transfected into COS-7 cells to express respectively. RESULTS: The coding sequences of V(H),V(L), linker and leader in all constructs were all correct. The expression of ScFv fusion protein was detectable by fluorescence microscope after transient expression in COS-7. The secretive expression of L-ScFv was confirmed by SDS-PAGE and Western blot analysis. And the binding specificity of the ScFvs with HBsAg were proved by indirect ELISA. CONCLUSIONS: Anti-HBsAg ScFv genes have been successfully constructed and expressed in COS-7 cells.

Animals↗
PubMed2001

Creation and activity of COS-1 cells stably expressing the F2 fusion of the human cholesterol side-chain cleavage enzyme system.

A fusion construct for the human cholesterol side-chain cleavage enzyme system termed F2 (H(2)N-P450scc-adrenodoxin reductase-adrenodoxin-COOH), was stably expressed in nonsteroidogenic COS-1 cells. Multiple clones were obtained and analyzed, identifying the clone COS-F2-130 as the most active in converting 22R-hydroxycholesterol (22R-OH-C) to pregnenolone. The F2 fusion construct was properly transcribed and translated in COS-F2-130 cells, indicating that these cells did not proteolytically cleave the F2 protein. Steroid analyses show that the COS-F2-130 cells do not convert appreciable quantities of pregnenolone to other steroids. Isolated COS-F2-130 mitochondria showed enhanced steroidogenesis when incubated with biosynthetic N-62 StAR protein in vitro. The cells were easily transfectable with StAR expression vectors, showing that COS-F2-130 cells exhibited both StAR-independent and StAR-dependent activity. Transient expression of either full-length or N-62 StAR stimulated steroidogenesis to approximately 45% of the maximal steroidogenic capacity, as indicated by incubation with 22R-OH-C. Single, double, and triple transfections of individual vectors expressing P450scc, adrenodoxin reductase, and adrenodoxin demonstrated that the P450 moiety of the F2 fusion protein could only receive electrons from the covalently linked adrenodoxin moiety, but that free adrenodoxin reductase could foster activity of the fusion enzyme. COS-F2-130 cells provide a useful system for studying steroidogenesis, as these are the only cells described to date that convert cholesterol to pregnenolone but lack downstream enzymes that catalyze other steroidogenic reactions.

Adrenodoxin↗
PubMed1991

Two point mutations in the transmembrane domain of P68gag-ros inactive its transforming activity and cause a delay in membrane association.

The transforming protein of the avian sarcoma virus UR2 is a 68-kDa transmembrane tyrosine protein kinase. We examined the relationship between membrane localization and transforming activity of P68 by changing Val-168-Val-169 in its hydrophobic domain into Asp-168-Glu-169. The resulting transmembrane (TM) mutant (P68TM) lost transforming activity toward chicken embryo fibroblasts (CEF). We found that the mutant protein was expressed and rapidly degraded into a smaller form which was still membrane associated and kinase active. The instability of the TM mutant protein is a phenomenon only manifested in CEF, because the same mutant protein was expressed with efficiency and stability similar to those of the wild-type protein in a transient expression system in COS cells. However, there are several differences between the wild-type and the TM mutant proteins in COS cells. The wild-type protein is more heavily phosphorylated and associated with membrane fractions in a cotranslational manner. It is enzymatically active when recovered from membrane fractions. The TM mutant protein is less phosphorylated, more labile toward protease degradation, and delayed in membrane association, with a lag period of 30 min or longer, and has little kinase activity when recovered from membrane fractions. Most of the kinase-active TM mutant protein was found in the cytosol fractions. Despite the delay, most of the TM protein in COS cells was found to be membrane associated, and its orientation on the cell surface was similar to that of the wild-type protein. It is probable that loss of the CEF-transforming activity of the TM mutant protein is due to its susceptibility to protease degradation resulting from improper membrane association of the newly synthesized product. The differences in the kinetics of membrane association and the distribution of kinase activity in COS cells might not be directly applicable in explaining the inability of the TM mutant to transform CEF but are intriguing as regards protein biosynthesis and translocation. The difference between CEF and COS cells implies that different factors or pathways are involved in the biosynthesis and processing of the TM mutant protein in these two cellular environments. Changes of P68TM in the kinetics of membrane association indicate that the transmembrane domain of ros, besides functioning as a membrane anchor, also plays a role in directing initial membrane association.

Animals↗
PubMed1997

Human lactase-phlorizin hydrolase expressed in COS-1 cells is proteolytically processed by the lysosomal pathway.

Lactase-phlorizin hydrolase (LPH) (EC 3.2.1.23/62), a major glycoprotein of the microvillus membrane of human small intestinal epithelial cells (enterocytes), is vital for the digestion of lactose during early infancy. The enzyme is synthesized in enterocytes as a single-chain precursor and subsequently proteolytically processed to the mature microvillus membrane-bound form. Because it has been reported that COS-1 cells were not able to proteolytically process LPH to the mature protein, these cells have been used as a model system to study potential roles of different proteases. COS-1 cells transfected with a full-length cDNA for human LPH synthesized enzymatically active enzyme. Immunoprecipitation of the expressed glycoproteins and their subsequent analysis by SDS-PAGE showed synthesis of two polypeptide species having apparent molecular masses of 210 and 220 kDa, respectively, corresponding to the high-mannose (pro-LPHh) form and the complex glycosylated (pro-LPHc) form of the LPH precursor. Surprisingly, an additional polypeptide species corresponding in size to the mature LPH found in human intestinal cells was also detected after longer chase periods. The source of this species was clearly pro-LPH, as its formation was inhibited by Brefeldin A. The cleaved form of LPH was not found on the cell surface; furthermore, its formation was prevented by an inhibitor of lysosomal function. We conclude from these data that in transfected COS-1 cells pro-LPH is transported to the cell surface, from which it is internalised and enters the lysosomal pathway, where proteolytic cleavage leads to a molecule not unlike mature LPH.

Ammonium Chloride↗
PubMed1999

Bradykinin B(2) receptor-mediated mitogen-activated protein kinase activation in COS-7 cells requires dual signaling via both protein kinase C pathway and epidermal growth factor receptor transactivation.

The signaling routes linking G-protein-coupled receptors to mitogen-activated protein kinase (MAPK) may involve tyrosine kinases, phosphoinositide 3-kinase gamma (PI3Kgamma), and protein kinase C (PKC). To characterize the mitogenic pathway of bradykinin (BK), COS-7 cells were transiently cotransfected with the human bradykinin B(2) receptor and hemagglutinin-tagged MAPK. We demonstrate that BK-induced activation of MAPK is mediated via the alpha subunits of a G(q/11) protein. Both activation of Raf-1 and activation of MAPK in response to BK were blocked by inhibitors of PKC as well as of the epidermal growth factor (EGF) receptor. Furthermore, in PKC-depleted COS-7 cells, the effect of BK on MAPK was clearly reduced. Inhibition of PI3-Kgamma or Src kinase failed to diminish MAPK activation by BK. BK-induced translocation and overexpression of PKC isoforms as well as coexpression of inactive or constitutively active mutants of different PKC isozymes provided evidence for a role of the diacylglycerol-sensitive PKCs alpha and epsilon in BK signaling toward MAPK. In addition to PKC activation, BK also induced tyrosine phosphorylation of EGF receptor (transactivation) in COS-7 cells. Inhibition of PKC did not alter BK-induced transactivation, and blockade of EGF receptor did not affect BK-stimulated phosphatidylinositol turnover or BK-induced PKC translocation, suggesting that PKC acts neither upstream nor downstream of the EGF receptor. Comparison of the kinetics of PKC activation and EGF receptor transactivation in response to BK also suggests simultaneous rather than consecutive signaling. We conclude that in COS-7 cells, BK activates MAPK via a permanent dual signaling pathway involving the independent activation of the PKC isoforms alpha and epsilon and transactivation of the EGF receptor. The two branches of this pathway may converge at the level of the Ras-Raf complex.

Androstadienes↗
PubMed2002

Functional properties of EGFP-tagged skeletal muscle calcium-release channel (ryanodine receptor) expressed in COS-7 cells: sensitivity to caffeine and 4-chloro-m-cresol.

We constructed and expressed in COS-7 cells, three E-green fluorescent protein (EGFP) tagged recombinant skeletal muscle ryanodine receptors (RYR). EGFP was tagged to (i) the NH2-terminus (nEGFP-RYR(FL)) and to (ii) the COOH-terminus (cRYR(FL)-EGFP) of the full length RYR; we also tagged the EGFP to (iii) the NH2-terminus of a truncated version of the RYR (nEGFP-RYR(Bhat)) lacking the bulk of the protein. The fluorescent pattern EGFP with all three constructs colocalize with that of an endoplasmic reticulum (ER) membrane tracker fluorescent dye, indicating that the RYR constructs are targeted to ER membranes. Our results show that: (i) COOH-terminal tagging abolishes the sensitivity of the RYR to caffeine, whereas the presence of EGFP at the NH2-terminus does not affect caffeine sensitivity and (ii) 4-Cl-m-cresol sensitivity is lost both with the truncated nEGFP-RYR(Bhat) and the nEGFP-RYR(FL), while COOH-terminal tagging does not affect sensitivity to 4-chloro-m-cresol. The dose-response curves of caffeine-induced calcium release of nEGFP-RYR(FL) differ from those of the truncated nEGFP-RYR(Bhat). Maximal calcium release was approached at 10 mM caffeine with the nEGFP-RYR(FL), while cells expressing the nEGFP-RYR(Bhat) construct displayed a bell shaped curve and the maximal concentration for caffeine-induced calcium release was 5 mM. Equilibrium [3H]-ryanodine binding confirmed the calcium photometry data. Our results demonstrate that EGFP tagging modifies the pharmacological properties of RYR, and suggest that 4-chloro-m-cresol and caffeine act through different mechanisms and probably interact with different sites on the RYR calcium release channel.

Animals↗