Cyclic nucleotide phosphodiesterases (PDEs): diverse regulators of cyclic nucleotide signals and inviting molecular targets for novel therapeutic agents.
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Animals↗
Biomedical subjects
E Degerman
Publications and source records attributed to E Degerman.
Protein kinase B is expressed in pancreatic beta cells and activated upon stimulation with insulin-like growth factor I.
Protein kinase B (PKB) is involved in signaling to a multitude of important cellular events and is activated by insulin and growth factors, including insulin-like growth factor I (IGF-I). We show here expression of PKB in pancreatic islets and in the beta cell lines HIT-T15, INS-1, and RINm5F. Expression of PKB mRNA and the presence of PKB isoforms (alpha, beta, and gamma) were assessed by Northern blot analysis and RT-PCR, respectively. Antibodies recognizing different parts of PKB isoforms were employed to demonstrate PKB protein expression by immunoblot analysis. By use of immunohistochemistry in rat and mouse pancreatic tissue sections, PKB was localized to predominantly beta cells. Regulation of PKB was examined in INS-1 and RINm5F cells; upon stimulation with IGF-I (5-10 min), PKB was phosphorylated and activated (approximately 3-fold) by a wortmannin-sensitive mechanism, indicating involvement of phosphatidylinositol-3 kinase. The possible participation of PKB in signal transduction pathways modulating cAMP-dependent insulin secretion and in proliferation of beta cells is discussed.
Animals↗
Insulin-induced translocation of protein kinase B to the plasma membrane in rat adipocytes.
Protein kinase B (PKB) has previously been shown to be activated in response to insulin and growth factor stimulation. The activation mechanism has been suggested to involve translocation of PKB to membranes, where it is phosphorylated and activated. Insulin-induced translocation of PKB has not been demonstrated in a physiological target cell. Therefore we have used the primary rat adipocyte to investigate insulin-induced translocation of PKB. In the presence of 1 nM insulin translocation of PKB was detected within 30 seconds and was blocked by wortmannin, a selective phosphatidylinositol 3-kinase inhibitor. This translocation was potentiated by the tyrosine phosphatase inhibitor vanadate. Subcellular localization studies revealed that PKB translocated to the plasma membrane.
Adipocytes↗
Identification of novel phosphorylation sites in hormone-sensitive lipase that are phosphorylated in response to isoproterenol and govern activation properties in vitro.
Hormone-sensitive lipase (HSL) is the rate-limiting enzyme in lipolysis. Stimulation of rat adipocytes with isoproterenol results in phosphorylation of HSL and a 50-fold increase in the rate of lipolysis. In this study, we used site-directed mutagenesis and two-dimensional phosphopeptide mapping to show that phosphorylation sites other than the previously identified Ser-563 are phosphorylated in HSL in response to isoproterenol stimulation of 32P-labeled rat adipocytes. Phosphorylation of HSL in adipocytes in response to isoproterenol and in vitro phosphorylation of HSL containing Ser --> Ala mutations in residues 563 and 565 (S563A, S565A) with protein kinase A (PKA), followed by tryptic phosphopeptide mapping resulted in two tryptic phosphopeptides. These tryptic phosphopeptides co-migrated with the phosphopeptides released by the same treatment of F654HPRRSSQGVLHMPLYSSPIVK675 phosphorylated with PKA. Analysis of the phosphorylation site mutants, S659A, S660A, and S659A,S660A disclosed that mutagenesis of both Ser-659 and Ser-660 was necessary to abolish the activation of HSL toward a triolein substrate after phosphorylation with PKA. Mutation of Ser-563 to alanine did not cause significant change of activation compared with wild-type HSL. Hence, our results demonstrate that in addition to the previously identified Ser-563, two other PKA phosphorylation sites, Ser-659 and Ser-660, are present in HSL and, furthermore, that Ser-659 and Ser-660 are the major activity controlling sites in vitro.
Adipocytes↗
Phosphorylation and activation of hormone-sensitive adipocyte phosphodiesterase type 3B.
Phosphodiesterases (PDEs) include a large group of structurally related enzymes that belong to at least seven related gene families (PDEs 1-7) that differ in their primary structure, affinity for cAMP and cGMP, response to specific effectors, sensitivity to specific inhibitors, and regulatory mechanism. One characteristic of PDE3s involves their phosphorylation and activation in response to insulin as well as to agents that increase cAMP in adipocytes, hepatocytes, and platelets and in response to insulin-like growth factor 1 in pancreatic beta cells. In adipocytes, activation of the membrane-associated PDE3B is the major mechanism whereby insulin antagonizes catecholamine-induced lipolysis. PDE3B activation results in increased degradation of cAMP and, thereby, a lowering of the activity of cAMP-dependent protein kinase (PKA). The reduced activity of PKA leads to a net dephosphorylation and decreased activity of hormone-sensitive lipase and reduced hydrolysis of triglycerides. Activation of the rat adipocyte PDE3B by insulin is associated with phosphorylation of serine-302. The mechanism whereby insulin stimulation leads to phosphorylation/activation of PDE3B is only partly understood. In rat adipocytes, lipolytic hormones and other agents that increase cAMP, including isoproterenol, also induce rapid phosphorylation, presumably catalyzed by PKA, of serine-302 of PDE3B. The phosphorylation is associated with activation of the enzyme, most likely representing "feedback" regulation of cAMP, presumably allowing close coupling of the regulation of steady-state concentrations of both cAMP and PKA and, thereby, control of lipolysis. In the review we describe methods and strategies used in the authors' laboratories to study phosphorylation and activation of PDE3B in adipocytes and in vitro.
3',5'-Cyclic-AMP Phosphodiesterases↗
Expression and characterization of deletion recombinants of two cGMP-inhibited cyclic nucleotide phosphodiesterases (PDE-3).
cDNAs encoding two PDE-3 or cyclic GMP-inhibited (cGI) cyclic nucleotide phosphodiesterase (PDE) isoforms, RPDE-3B (RcGIP1) and HPDE-3A (HcGIP2), were cloned from rat (R) adipose tissue and human (H) heart cDNA libraries. Deletion and N- and C-terminal truncation mutants were expressed in Escherichia coli in order to define their catalytic core. Active mutants of both RPDE-3B and HPDE-3A included the domain conserved among all PDEs plus additional upstream and downstream sequences. An RPDE-3B mutant consisting of the conserved domain alone and one from which the RPDE-3B 44-amino acid insertion was deleted exhibited little or no activity. All active recombinants exhibited a high affinity (< 1 microM) for cyclic AMP (cAMP) and cyclic GMP (cGMP), were inhibited by cAMP, cGMP, and cilostamide, but not by rolipram, and were photolabeled with [32P]-cGMP. The IC50 values for cGMP inhibition of cAMP hydrolysis were lower for HPDE-3A than for RPDE-3B recombinants. The deduced amino acid sequences of HPDE-3A and RPDE-3B catalytic domains are very similar except for the 44-amino acid insertion not found in other PDEs. It is possible that this insertion may not only distinguish PDE-3 catalytic domains from other PDEs and identify catalytic domains of PDE-3 subfamilies or conserved members of the PDE-3 gene family, but may also be involved in the regulation of sensitivity of PDE-3s to cGMP.
3',5'-Cyclic-AMP Phosphodiesterases↗
Various phosphodiesterase subtypes mediate the in vivo antilipolytic effect of insulin on adipose tissue and skeletal muscle in man.
The antilipolytic effect of insulin on human abdominal subcutaneous adipose tissue and skeletal muscle during local inhibition of cAMP-phosphodiesterases (PDEs) was investigated in vivo, by combining microdialysis with a euglycaemic, hyperinsulinaemic clamp. During hyperinsulinaemia, the glycerol concentration decreased by 40% in fat and by 33% in muscle. Addition of the selective PDE3-inhibitor amrinone abolished the insulin-induced decrease in adipose glycerol concentration, but did not influence the glycerol concentration in skeletal muscle. Nor did the PDE4-selective inhibitor rolipram or the PDE5-selective inhibitor dipyridamole influence the insulin-induced decrease in muscle tissue glycerol. However, the non-selective PDE-inhibitor theophylline counteracted the antilipolytic action of insulin at both sites. The specific activity of PDEs was also determined in both tissues. PDE3-activity was 36.8+/-6.4 pmol x min(-1) x mg(-1) in adipose tissue and 3.9+/-0.5 pmol x min(-1) x mg(-1) in muscle. PDE4-activity in skeletal muscle was high, i.e., 60.7+/-10.2 pmol x min(-1) x mg(-1) but 8.5 pmol x min(-1) x mg(-1) or less in adipose tissue. In conclusion, insulin inhibits lipolysis in adipose tissue and skeletal muscle by activation of different PDEs, suggesting a unique metabolic role of muscle lipolysis.
Adipose Tissue↗
Insulin-induced phosphorylation and activation of phosphodiesterase 3B in rat adipocytes: possible role for protein kinase B but not mitogen-activated protein kinase or p70 S6 kinase.
Insulin stimulation of adipocytes results in serine phosphorylation/activation of phosphodiesterase 3B (PDE 3B) and activation of a kinase that phosphorylates PDE 3B in vitro, key events in the antilipolytic action of this hormone. We have investigated the role for p70 S6 kinase, mitogen-activated protein kinases (MAP kinases), and protein kinase B (PKB) in the insulin signaling pathway leading to phosphorylation/activation of PDE 3B in adipocytes. Insulin stimulation of adipocytes resulted in increased activity of p70 S6 kinase, which was completely blocked by pretreatment with rapamycin. However, rapamycin had no effect on the insulin-induced phosphorylation/activation of PDE 3B or the activation of the kinase that phosphorylates PDE 3B. Stimulation of adipocytes with insulin or phorbol myristate acetate induced activation of MAP kinases. Pretreatment of adipocytes with the MAP kinase kinase inhibitor PD 98059 was without effect on the insulin-induced activation of PDE 3B. Furthermore, phorbol myristate acetate stimulation did not result in phosphorylation/activation of PDE 3B or activation of the kinase that phosphorylates PDE 3B. Using Mono Q and Superdex chromatography, the kinase that phosphorylates PDE 3B was found to co-elute with PKB, but not with p70 S6 kinase or MAP kinases. Furthermore, both PKB and the kinase that phosphorylates PDE 3B were found to translocate to membranes in response to peroxovanadate stimulation of adipocytes in a wortmannin-sensitive way. Whereas these results suggest that p70 S6 kinase and MAP kinases are not involved in the insulin-induced phosphorylation/activation of PDE 3B in rat adipocytes, they are consistent with PKB being the kinase that phosphorylates PDE 3B.
3',5'-Cyclic-AMP Phosphodiesterases↗
Regulation of protein kinase B in rat adipocytes by insulin, vanadate, and peroxovanadate. Membrane translocation in response to peroxovanadate.
Protein kinase B (PKB) (also referred to as RAC/Akt kinase) has been shown to be controlled by various growth factors, including insulin, using cell lines and transfected cells. However, information is so far scarce regarding its regulation in primary insulin-responsive cells. We have therefore used isolated rat adipocytes to examine the mechanisms, including membrane translocation, whereby insulin and the insulin-mimicking agents vanadate and peroxovanadate control PKB. Stimulation of adipocytes with insulin, vanadate, or peroxovanadate caused decreased PKB mobility on sodium dodecyl sulfate-polyacrylamide gels, indicative of increased phosphorylation, which correlated with an increase in kinase activity detected with the peptide KKRNRTLTK. This peptide was found to detect activated PKB selectively in crude cytosol and partially purified cytosol fractions from insulin-stimulated adipocytes. The decrease in electrophoretic mobility and activation of PKB induced by insulin was reversed both in vitro by treatment of the enzyme with alkaline phosphatase and in the intact adipocyte upon removal of insulin or addition of the phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor wortmannin. Significant translocation of PKB to membranes could not be demonstrated after insulin stimulation, but peroxovanadate, which appeared to activate PI 3-kinase to a higher extent than insulin, induced substantial translocation. The translocation was prevented by wortmannin, suggesting that PI 3-kinase and/or the 3-phosphorylated phosphoinositides generated by PI 3-kinase are indeed involved in the membrane targeting of PKB.
Adipocytes↗
Partial purification and identification of hormone-sensitive lipase from chicken adipose tissue.
HSL from chicken adipose tissue exhibits remarkable activation upon phosphorylation with cAMP-dependent protein kinase (cAMP-PK) compared to HSL from rat and human adipose tissue. In order to characterize the chicken HSL enzyme, it was purified 3500 fold from a chicken adipose tissue homogenate using pH 5.2 precipitation and anion-exchange chromatography. The purified chicken HSL was identified as an 86 kDa protein using Western blot analysis. The HSL diacylglycerol lipase activity was inhibited by 98% upon incubation with anti-rat HSL antiserum, and the specific activity of chicken HSL was estimated to be approximately the same as for the rat enzyme. Furthermore, the 86 kDa polypeptide was phosphorylated by cAMP-PK to about the same stoichiometry as for the recombinant rat enzyme. Hence, our results demonstrate that HSL from chicken adipose tissue is comparable in size and specific activity to HSL from mammalian species, and not a smaller 42 kDa polypeptide with 1000-fold lower specific activity as previously reported (Berglund, L., Khoo, J. C., Jensen, D., and Steinberg, D., 1980 J. Biol. Chem. 255, 5420-5428).
Adipose Tissue↗
Protein kinase A-dependent activation of PDE4 (cAMP-specific cyclic nucleotide phosphodiesterase) in cultured bovine vascular smooth muscle cells.
Incubation of cultured bovine vascular smooth muscle cells (VSMC) with forskolin increased cAMP as measured by an increase in cAMP-dependent protein kinase (PKA) activation (PKA ratio). Forskolin also produced a concentration- and time-dependent increase in activity (3-5-fold within 15 min) of a PDE4 (cAMP-specific cyclic nucleotide phosphodiesterase). The increase in PDE4 activity was not affected by cycloheximide and thus not likely due to increased synthesis of the enzyme. Activation, which was preserved during partial purification of the enzyme by chromatography on Sephacryl S-200 and MonoQ, was most likely due to a covalent modification. Incubation of cell homogenates with the catalytic subunit of PKA (PKA(c)) induced a approximately 5-fold activation of PDE4 with a time course similar to that in intact cells after forskolin addition. The forskolin-mediated activation was reversed during incubation of homogenates at room temperature for two hours. Addition of PKA(c) resulted in rapid reactivation of PDE4. These data are consistent with the hypothesis that rapid, reversible activation of PDE4 in cultured VSMC is mediated by PKA.
3',5'-Cyclic-AMP Phosphodiesterases↗
Structure, localization, and regulation of cGMP-inhibited phosphodiesterase (PDE3).
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3',5'-Cyclic-AMP Phosphodiesterases↗
Regulation of hormone-sensitive lipase activity in adipose tissue.
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3',5'-Cyclic-AMP Phosphodiesterases↗
Domain-structure analysis of recombinant rat hormone-sensitive lipase.
Hormone-sensitive lipase (HSL) plays a key role in lipid metabolism and overall energy homoeostasis, by controlling the release of fatty acids from stored triglycerides in adipose tissue. Lipases and esterases form a protein superfamily with a common structural fold, called the alpha/beta-hydrolase fold, and a catalytic triad of serine, aspartic or glutamic acid and histidine. Previous alignments between HSL and lipase 2 of Moraxella TA144 have been extended to cover a much larger part of the HSL sequence. From these extended alignments, possible sites for the catalytic triad and alpha/beta-hydrolase fold are suggested. Furthermore, it is proposed that HSL contains a structural domain with catalytic capacity and a regulatory module attached, as well as a structural N-terminal domain unique to this enzyme. In order to test the proposed domain structure, rat HSL was overexpressed and purified to homogeneity using a baculovirus/insect-cell expression system. The purification, resulting in > 99% purity, involved detergent solubilization followed by anion-exchange chromatography and hydrophobic-interaction chromatography. The purified recombinant enzyme was identical to rat adipose-tissue HSL with regard to specific activity, substrate specificity and ability to serve as a substrate for cAMP-dependent protein kinase. The recombinant HSL was subjected to denaturation by guanidine hydrochloride and limited proteolysis. These treatments resulted in more extensive loss of activity against phospholipid-stabilized lipid substrates than against water-soluble substrates, suggesting that the hydrolytic activity can be separated from recognition of lipid substrates. These data support the concept that HSL has at least two major domains.
Amino Acid Sequence↗
Characterization of two recombinant PDE3 (cGMP-inhibited cyclic nucleotide phosphodiesterase) isoforms, RcGIP1 and HcGIP2, expressed in NIH 3006 murine fibroblasts and Sf9 insect cells.
cDNAs encoding PDE3 [cGMP-inhibited cyclic nucleotide phosphodiesterase (cGI PDE)] isoforms, cGIP1 and cGIP2, have been cloned from rat (R) and human (H) cDNA libraries. The deduced amino acid sequences of RcGIP1 and HcGIP2 are very similar in their conserved catalytic domains but differ in their N-terminal regulatory domains [Meacci, E., et al. (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 3721-3725; Taira, M., et al. (1993) J. Biol. Chem. 268, 18573-18579]. cDNAs encoding both rat adipocyte RcGIP1 and human myocardial HcGIP2 (full-length forms and truncated forms lacking much of the putative N-terminal domain) were expressed in NIH 3006 fibroblasts and in Sf9 insect cells. The recombinant proteins exhibited the expected subunit molecular mass, immunologic reactivities, and characteristics of native membrane-associated forms of the enzymes, e.g., high affinity for cAMP (Km), sensitivity to the selective cGI PDE inhibitors OPC 3689 and OPC 3911 and to cGMP. The full-length recombinants were predominantly particulate, whereas the truncated HcGIP2 forms were cytosolic suggesting that N-terminal domains contain structural determinants important for membrane association. Both fibroblast RcGIP1 and authentic adipocyte cGI PDE were phosphorylated in vitro by cAMP-dependent protein kinase; tryptic [32P]peptides released from rat adipocyte 32P-cGI PDE and 32P-RcGIP1 exhibited identical electrophoretic profiles suggesting that the same peptides are phosphorylated in both.
3',5'-Cyclic-AMP Phosphodiesterases↗
Identification of the site in the cGMP-inhibited phosphodiesterase phosphorylated in adipocytes in response to insulin and isoproterenol.
Stimulation of rat adipocytes with insulin and isoproterenol results in serine phosphorylation and activation of the adipocyte cGMP-inhibited phosphodiesterase (cGI PDE), events believed to be important in the antilipolytic action of insulin (Degerman, E., Smith, C.J., Tornqvist, H., Vasta, V., Manganiello, V.C., and Belfrage, P. (1990) Proc. Natl. Acad. Sci. U.S.A. 87,533-537). Here we demonstrate, by two-dimensional phosphopeptide mapping, that the major phosphopeptide generated by trypsin, or trypsin followed by Asp-N protease digestion of [32P]cGI PDE phosphorylated in adipocytes in response to isoproterenol and/or insulin, in each case co-migrates with the phosphopeptide released by the same treatment of M297FRRPS(P)LPCISREQ310. This peptide was synthesized based on the deduced sequence of the cloned rat adipocyte cGI PDE and phosphorylated by cAMP-dependent protein kinase (protein kinase A). Radiosequencing of authentic and synthetic tryptic 32P-peptides showed that a single site in cGI PDE (Ser302) was phosphorylated in adipocytes incubated with isoproterenol and/or insulin. The more than additive phosphorylation and activation of cGI PDE in response to the two hormones found in this report and previously (Smith, C.J., Vasta, V., Degerman, E., Belfrage, P., and Manganiello, V.C. (1991) J. Biol. Chem. 266, 13385-13390) is proposed to reflect cross-talk between their respective signal transduction pathways at the level of the cGI PDE serine protein kinase or upstream regulatory component(s).
3',5'-Cyclic-AMP Phosphodiesterases↗
Type III cyclic nucleotide phosphodiesterases and insulin action.
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3',5'-Cyclic-AMP Phosphodiesterases↗
cGMP-inhibited phosphodiesterases (PDE3 gene family).
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3',5'-Cyclic-AMP Phosphodiesterases↗