COMMUNICATION:
Role of Phospholipase Cbeta 3 Phosphorylation in the Desensitization of Cellular Responses to Platelet-activating Factor*

(Received for publication, December 20, 1996, and in revised form, February 13, 1997)

Hydar Ali Dagger §, Ian Fisher Dagger , Bodduluri Haribabu Dagger , Ricardo M. Richardson Dagger and Ralph Snyderman Dagger

From the Departments of Dagger  Medicine and  Immunology, Duke University Medical Center, Durham, North Carolina 27710

ABSTRACT
INTRODUCTION
EXPERIMENTAL PROCEDURES
RESULTS AND DISCUSSION
FOOTNOTES
ACKNOWLEDGEMENTS
REFERENCES


ABSTRACT

Platelet-activating factor (PAF) stimulates a diverse array of cellular responses through receptors coupled to G proteins that activate phospholipase C (PLC). Truncation of the cytoplasmic tail of the receptor to remove phosphorylation sites (mutant PAF receptor, mPAFR) results in enhancement of PAF-stimulated responses. Here we demonstrate that PAF or phorbol 12-myristate 13-acetate (PMA) pretreatment inhibited wild type PAFR-induced PLC-mediated responses by ~90%, whereas these responses to the phosphorylation-deficient mPAFR were inhibited by ~50%, despite normal G protein coupling, suggesting a distal inhibitory locus. PAF and PMA, as well as a membrane permeable cyclic AMP analog, stimulated phosphorylation of PLCbeta 3. A protein kinase C (PKC) inhibitor blocked phosphorylation of PLCbeta 3 stimulated by PAF and PMA but not by cAMP. Activation of protein kinase A (PKA) by cAMP did not result in inhibition of Ca2+ mobilization stimulated by PAF. In contrast, cAMP did inhibit the response to formylpeptide chemoattractant receptor. These data suggest that homologous desensitization of PAF-mediated responses is regulated via phosphorylation at two levels in the signaling pathway, one at the receptor and the other at PLCbeta 3 mediated by PKC but not by PKA. Phosphorylation of PLCbeta 3 by PKA could explain the inhibition of formylpeptide chemoattractant receptor signaling by cAMP. As PAF and formylpeptide chemoattractant receptors activate PLC via different G proteins, phosphorylation of PLCbeta 3 by PKC and PKA could provide distinct regulatory control for classes of G protein-coupled receptors.


INTRODUCTION

Platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine, PAF)1 plays important roles in inflammation and has physiological effects on cardiovascular, reproductive, and central nervous systems (1). PAF mediates its effects via the activation of a seven transmembrane domain G protein-coupled receptor (2, 3). One of the consequences of PAF receptor activation is the phospholipase C (PLC)-mediated hydrolysis of phosphatidylinositol 4,5-bisphosphate leading to the activation of protein kinase C (PKC) and mobilization of intracellular Ca2+ (4). Molecular cloning has revealed three classes of PLC: PLCbeta , PLCgamma , and PLCdelta , and each of these occur in several isoforms (5, 6). All four PLC beta  isoforms are activated to varying extent by alpha  subunit of a class of G proteins known as Gq (7-10). PLCbeta 2 and PLCbeta 3 are also activated by the beta gamma subunit of the Gi family of G proteins (11-13). Tyrosine phosphorylation of PLCgamma is required for its activation, but the mechanism by which PLCdelta is activated is unknown (5). PAFR couples to both pertussis toxin (Ptx)-sensitive and Ptx-insensitive G proteins in a variety of cells (4, 14, 15). In B cells and platelets, PAF activates PLCgamma (16, 17), but the identity of PLCs activated by PAF in phagocytic leukocytes is unknown.

In phagocytes, PAF-stimulated G protein activation and Ca2+ mobilization are desensitized by prior treatment of cells with PAF and other chemoattractants such as the formylated peptides, C5a and interleukin-8 (18). This laboratory has developed stably transfected RBL-2H3 cells to study molecular mechanisms of leukocyte chemoattractant receptor regulation (15, 19-21). Using wild type and phosphorylation-deficient PAFR expressed in this cell line, we now describe the novel finding that homologous desensitization of PAF-mediated phosphoinositide hydrolysis and Ca2+ mobilization is mediated via two processes; one at the level of receptor phosphorylation and the other at the level of PLC activation apparently by PKC-dependent phosphorylation of PLCbeta 3.


EXPERIMENTAL PROCEDURES

Materials

Bisindolylmaleimide or GF 109203X (BIM), 8-(4-chlorophenylthio)-adenosine 3'-cyclic monophosphate (Cpt-cAMP) and the tyrosine kinase inhibitor PP1 were purchased from Calbiochem. Affinity purified polyclonal antibodies against PLCbeta 1, PLCbeta 2, and PLCbeta 3 were obtained from Santa Cruz Biotechnology. ECL Western blot analysis kit was purchased from Amersham Corp. Mouse monoclonal IgE and antigen (dinitrophenylated BSA) were generously provided by Drs. Juan Rivera and Henry Metzger (National Institutes of Health). All other materials were obtained from sources previously described (15).

Cell Culture, Phosphoinositide Hydrolysis, and Ca2+ Mobilization

RBL-2H3 cells stably expressing ~3 × 104 receptors for PAFR and mPAFR were used (21). The cells were maintained in Dulbecco's modified Eagle's medium supplemented with 15% fetal bovine serum, glutamine (2 mM), penicillin (100 units/ml), and streptomycin (100 mg/ml) (19). For phosphoinositide hydrolysis, cells (5 × 104 cells/well) were subcultured overnight in 96-well tissue culture plate with 1 µCi/ml of [3H]inositol in an inositol-free medium supplemented with 10% dialyzed fetal bovine serum. Cells were washed with HEPES-buffered saline containing 10 mM LiCl and 0.1% BSA and stimulated, and the generation of total [3H]inositol phosphates was determined. For Ca2+ mobilization, cells (3 × 106) were loaded with 1 µM indo-1/AM in the presence of 1 µM pluoronic acid for 30 min at room temperature. Cells were washed and resuspended in 1.5 ml HEPES-buffered saline, and intracellular Ca2+ mobilization was determined as described previously (19).

Western Blotting and Immunoprecipitation of PLCbeta 3

For Western blotting, lysate (150 µg protein) from RBL-2H3 cells, and for comparison, lysates from bovine brain, COS cells, and HL-60 cells were resolved on a 6% SDS-PAGE gel. The proteins were transferred to nitrocellulose membrane, blocked with 3% milk, and incubated with 1.5 µg/ml of different anti-PLCbeta antibodies. The immunoreactive proteins were visualized using ECL Western blotting detection system. Phosphorylation of PLCbeta 3 was performed essentially as described for the epitope-tagged chemoattractant receptors (19). Briefly, RBL-2H3 cells (3 × 106) were subcultured overnight in 60-mm tissue culture dishes. The following day, cells were washed twice with 5 ml of phosphate-free Dulbecco's modified Eagle's medium and incubated in the same medium plus [32P]orthophosphate (150 µCi/dish) for 90 min. The labeled cells were stimulated, and PLCbeta 3 was immunoprecipitated from cell lysate with anti-PLCbeta 3 antibody. The proteins were resolved on a 6% SDS-PAGE gel and visualized by autoradiography.


RESULTS AND DISCUSSION

The mechanism of PAF receptor desensitization was studied using the rat basophilic leukemia (RBL-2H3) cells expressing wild type PAFR and a mPAFR in which the cytoplasmic tail was truncated to delete potential phosphorylation sites (21). In contrast to PAFR, mPAFR was resistant to both ligand and PKC-induced receptor phosphorylation and desensitization of G protein coupling, as measured by [35S]GTPgamma S binding to membranes (21, 22). However, when indo-1-loaded cells expressing mPAFR were stimulated with PAF (10 nM), washed, and restimulated with PAF (10 nM), the peak Ca2+ response was still homologously desensitized by ~50% (Table I). PMA also inhibited mPAFR-mediated Ca2+ mobilization by ~50%, suggesting a locus of inhibition distal to G protein activation. In cells expressing wild type PAFR, both PAF and PMA inhibited PAF-induced Ca2+ mobilization by >90%. PMA also caused substantial inhibition of mPAF-induced generation of inositol phosphates and completely blocked the response to PAF (Fig. 1). To further test the role of PKC on PAFR desensitization, cells expressing mPAFR and PAFR were treated with PMA (100 nM) overnight to deplete PKC or incubated with the PKC-inhibitor bisindolylmaleimide for 10 min to block the activity of the enzyme. PAF-stimulated generation of inositol phosphates was then determined. Under both of these conditions, PAF-induced responses were enhanced 2-3-fold in cells expressing mPAFR (Fig. 1). Overnight PMA treatment did not enhance the response to PAF in cells expressing PAFR, but bisindolylmaleimide did potentiate the response to PAF. Because PMA-induced PKC depletion involves activation of the enzyme, it was possible that the differential effect of PMA on mPAFR and PAFR cells resulted from PKC-induced phosphorylation and down-regulation of PAFR but not mPAFR. Indeed, treatment of cells with PMA (100 nM, overnight) resulted in ~50% decrease of the wild type PAFR expression but had no effect on mPAFR as measured by the PAFR antagonist [3H]WEB 2086 binding to intact cells (data not shown). These data suggest that homologous desensitization of PAF-mediated cellular responses is mediated by two processes. One involves receptor phosphorylation, presumably by PKC and a G protein-coupled receptor kinase, which uncouple the receptor from G proteins (21). In addition, a new mechanism was identified as a consequence of PKC-induced modification of a component distal to G protein activation but proximal to the generation of inositol phosphates.

Table I. Desensitization of PAF-mediated Ca2+ mobilization

RBL-2H3 cells (3 × 106) expressing mPAFR or PAFR were loaded with indo-1 and stimulated with PAF (10 nM), and peak Ca2+ mobilization was determined as described (19). For homologous desensitization, PAF-stimulated cells were washed, and 5 min later they were restimulated with PAF (10 nM) and peak Ca2+ mobilization was determined. Cells were also preincubated with PMA (100 nM), and 5 min later they were stimulated with PAF (10 nM) and peak Ca2+ mobilization was determined. The basal unstimulated intracellular Ca2+ concentration was 150 ± 10 and was subtracted from the values shown, which are the means ± S.E. of three different experiments. RBL-2H3 cells (3 × 106) expressing mPAFR or PAFR were loaded with indo-1 and stimulated with PAF (10 nM), and peak Ca2+ mobilization was determined as described (19). For homologous desensitization, PAF-stimulated cells were washed, and 5 min later they were restimulated with PAF (10 nM) and peak Ca2+ mobilization was determined. Cells were also preincubated with PMA (100 nM), and 5 min later they were stimulated with PAF (10 nM) and peak Ca2+ mobilization was determined. The basal unstimulated intracellular Ca2+ concentration was 150 ± 10 and was subtracted from the values shown, which are the means ± S.E. of three different experiments.
Cells/treatment Ca2+ mobilization Desensitization

nM %
mPAFR
  PAF right-arrow PAF 517 ± 15 right-arrow 240 ± 19 53
  PMA right-arrow PAF 0 ± 0  right-arrow 264 ± 12 51
PAFR
  PAF right-arrow PAF 617 ± 40 right-arrow 48 ± 4 92
  PMA right-arrow PAF 0 ± 0  right-arrow 43 ± 5 93


Fig. 1. Regulation of PAF-stimulated generation of [3H]inositol phosphates by PKC. RBL-2H3 cells expressing mPAFR (A) and PAFR (B) were cultured overnight with [3H]inositol in the absence (control, black-square, bullet ) and the presence of PMA (100 nM, black-diamond ). The next day, cells were washed in a HEPES-buffered saline containing 10 mM LiCl, preincubated with the same buffer (black-square, bullet , black-diamond ), PMA (100 nM, black-triangle), or BIM (10 µM, open circle ) and then stimulated with different concentrations of PAF, and the generation of total [3H]inositol phosphates were determined. Data are the means ± S.E. of one of three similar experiments performed in triplicate.
[View Larger Version of this Image (24K GIF file)]

Although most G protein-coupled receptors activate PLCbeta , angiotensin receptors in smooth muscle cells and PAF receptors in B cells and platelets cause tyrosine phosphorylation and activation of PLCgamma (16, 17, 23). The molecular mechanism by which G protein-coupled receptors activate PLCgamma has yet to be determined. PMA, which causes serine phosphorylation of PLCgamma (24), leads to reduction of both tyrosine phosphorylation of PLCgamma and generation of inositol phosphates stimulated by cross-linking of cell surface IgE receptors with antigen (25, 26). This suggests that if PAF activates PLCgamma , a similar modification of PLCgamma by PKC could be involved in its homologous desensitization. However, the tyrosine kinase inhibitor PP1 (27), which blocked antigen (IgE)-stimulated Ca2+ mobilization by >70%, presumably by inhibiting tyrosine phosphorylation of PLCgamma , had no effect on PAF-mediated responses (Table II). Elevation of intracellular cAMP has also been shown to cause serine phosphorylation of PLCgamma and inhibition of antigen-stimulated responses (24). As shown in Table II, the membrane permeable cAMP analog 8-(4-chlorophenylthio)-adenosine 3'-cylic monophosphate (cpt-cAMP) substantially inhibited IgE-mediated Ca2+ mobilization but had no effect on the PAF-mediated response. These data suggest that unlike B cells and platelets (16, 17) PAF does not activate PLCgamma in RBL-2H3 cells and that PKA does not down-regulate PAF-mediated responses.

Table II. Effects of tyrosine phosphorylation inhibition or cAMP elevation on PAF, fMLP, and IgE-mediated Ca2+ mobilization

RBL-2H3 cells coexpressing fMLP and PAF receptors (21) were incubated with IgE (0.2 µg/ml) overnight to saturate cell surface IgE receptors. The following day cells were loaded with indo-1 for 30 min in the absence (control) and the presence of the tyrosine kinase inhibitor, PP1 (10 µM), and Ca2+ mobilization in response to PAF (0.2 nM), fMLP (1.0 nM), and antigen, dinitrophenylated (DNP) BSA (1 ng/ml) was determined. Indo-1-loaded cells were also preincubated with the membrane permeable cAMP analog, cpt-cAMP (1 mM, 5 min), and its effect on peak Ca2+ mobilization was tested. Values are the means ± S.E. of four experiments. The numbers in parenthesis represent the percentage of inhibition of response as compared with control. RBL-2H3 cells coexpressing fMLP and PAF receptors (21) were incubated with IgE (0.2 µg/ml) overnight to saturate cell surface IgE receptors. The following day cells were loaded with indo-1 for 30 min in the absence (control) and the presence of the tyrosine kinase inhibitor, PP1 (10 µM), and Ca2+ mobilization in response to PAF (0.2 nM), fMLP (1.0 nM), and antigen, dinitrophenylated (DNP) BSA (1 ng/ml) was determined. Indo-1-loaded cells were also preincubated with the membrane permeable cAMP analog, cpt-cAMP (1 mM, 5 min), and its effect on peak Ca2+ mobilization was tested. Values are the means ± S.E. of four experiments. The numbers in parenthesis represent the percentage of inhibition of response as compared with control.
Stimulation Control PP1 (10 µM) cpt-cAMP (1 mM)

PAF 495  ± 23 531  ± 51 (-7) 548  ± 25 (-10)
fMLP 249  ± 3.5 250  ± 3 (0) 44  ± 12 (82)
DNP BSA/IgE 376  ± 22 90  ± 11 (76) 103  ± 3 (72)

We therefore sought to determine whether a PLCbeta isoform is activated by PAF in RBL-2H3 cells. To identify the PLCbeta isoforms expressed in RBL-2H3 cells, their lysates and lysates from bovine brain, COS and HL-60 cells were separated by SDS-PAGE, and the presence of PLCbeta 1, PLCbeta 2, and PLCbeta 3 was determined by Western blotting using PLCbeta isoform-specific antibodies. All cells tested, including RBL-2H3 cells, expressed PLCbeta 3 in different amounts (Fig. 2). Although PLCbeta 1 and PLCbeta 2 were expressed at high levels in brain and HL-60 cells, respectively, neither could be detected in RBL-2H3 cells (Fig. 2).


Fig. 2. Identification of PLCbeta isozymes expressed in RBL-2H3 cells. Lysate (150 µg protein) from RBL-2H3 cells, bovine brain, COS, and HL-60 cells were resolved on a 6% SDS-gel and analyzed by Western blotting using antibodies directed against PLCbeta 1, PLCbeta 2, and PLCbeta 3. This experiment was repeated three times with similar results.
[View Larger Version of this Image (24K GIF file)]

Studies with purified G proteins and PLC revealed that PLCbeta 1 and PLCbeta 3 are equally responsive to activation by Galpha q (28). It was therefore possible that in RBL-2H3 cells, which do not express PLCbeta 1, PAF activates PLCbeta 3 and that PKC-induced modification of this enzyme accounts for the distal component of PAFR homologous desensitization. To test this hypothesis, cells were labeled with [32P]orthophosphate and stimulated with PAF, and cell lysate was immunoprecipitated with PLCbeta 3-specific antibody. As shown in Fig. 3 (A and B), PAF caused phosphorylation of PLCbeta 3 in a dose- and time-dependent manner. PLCbeta 3 phosphorylation was detectable at physiologic PAF concentration of 0.3 nM and was maximum by 10 nM. PAF-induced PLCbeta 3 phosphorylation was rapid, reached a maximum by 15 s, and remained elevated for 10 min. To determine whether there was a correlation between PKC-mediated PLCbeta 3 phosphorylation and inhibition of PAF-stimulated responses, cells were treated with or without the PKC inhibitor bisindolylmaleimide, stimulated with PAF (10 nM) and PMA (100 nM), and PLCbeta 3 phosphorylation was determined. As shown in Fig. 3C, PAF- and PMA-induced PLCbeta 3 phosphorylation was almost completely inhibited by bisindolylmaleimide. Cpt-cAMP also phosphorylated PLCbeta 3 presumably through activation of PKA, and this phosphorylation was not inhibited by bisindolylmaleimide. PLCbeta 3 phosphorylation was also tested in two other cell lines that endogenously express PAF receptors. These were the human monocyte-like U937 cells and the murine macrophage-like J774.1 cells. In both cases, PAF, PMA, and cpt-cAMP stimulated phosphorylation of PLCbeta 3 (Fig. 3D).


Fig. 3. Phosphorylation of PLCbeta 3. 32P-labeled RBL-2H3 cells expressing PAFR were stimulated with different concentrations of PAF for 5 min (A) or with a fixed concentration of PAF (10 nM) for different times (B). C, effects of bisindolylmaleimide on PLCbeta 3 phosphorylation. 32P-Labeled cells expressing PAFR were preincubated with BIM (10 µM; 10 min) and stimulated with PAF (10 nM), PMA (100 nM), or cpt-cAMP (1 mM) for 5 min. D, U937 cells and J774.1 cells were labeled with 32P as described for RBL-2H3 cells, stimulated with PAF (10 nM), PMA (100 nM), and cpt-cAMP (1 mM) for 5 min. Cells were lysed, immunoprecipitated with anti-PLCbeta 3 antibody, and analyzed by SDS-PAGE and autoradiography. Results shown are from one of four similar experiments.
[View Larger Version of this Image (36K GIF file)]

The effect of cAMP elevation on PLC activation was determined using the RBL-2H3 cells coexpressing PAF and formylpeptide receptors. In such cells, cpt-cAMP did not inhibit Ca2+ mobilization to PAF, although it did inhibit the response of the formylpeptide receptor (Table II). Furthermore, in cells expressing mPAFR, cpt-cAMP (1 mM, 5 min) had no effect on PAF-stimulated generation of [3H]inositol phosphates, whereas PMA (100 nM, 5 min) blocked this response by ~50%. Preincubation of cells with cpt-cAMP had no effect on PMA-mediated inhibition of PAF-stimulated response (data not shown). These data support the hypothesis that PLCbeta 3 is likely activated by PAFR and that PLCbeta 3 phosphorylation by PKC, but not by PKA, is responsible for one component of PAFR homologous desensitization.

PLCbeta 1 is phosphorylated by PKC (29), and PLCbeta 2 is phosphorylated by PKA (30). The present study revealed that both PKC and PKA phosphorylate of PLCbeta 3 in vivo (Fig. 3C). More importantly, phosphorylation of PLCbeta 3 by the different protein kinases appears to be associated with distinct functional consequences. Although phosphorylation of PLCbeta 3 by PKC resulted in the inhibition of responses stimulated by PAF, its phosphorylation by PKA was not associated with such inhibition. On the other hand, PKA activation by cpt-cAMP inhibited formylpeptide receptor-mediated responses. In RBL-2H3 cells PAF receptors activate PLC predominantly via a Ptx-insensitive G protein, whereas formylpeptide-mediated response is completely blocked by Ptx (15, 19). Therefore, differential inhibition of responses to PAF and formylpeptide by PKC and PKA is likely due to the different G protein subunits these receptors utilize to activate PLC. It was demonstrated in vitro that Galpha q and Gbeta gamma released from Ptx-sensitive G protein interact with distinct regions of PLCbeta 3 to activate the enzyme (28). This led Smrcka and Sternweis to propose that different receptors that utilize Gq or Gi could activate PLCbeta 3 by producing Galpha q or Gbeta gamma (28). The data presented herein support this hypothesis and provide a molecular basis for the differential regulation of Galpha q- and Gbeta gamma -mediated activation of PLCbeta 3. It is likely that PKC and PKA phosphorylate PLCbeta 3 on distinct sites that block its activation by Galpha q and Gbeta gamma , respectively.

Similar to RBL-2H3 cells, many human cell lines and tissues express PLCbeta 3 but not PLCbeta 1 or PLCbeta 2 (9, 11, 28, 31). Given the duality of PLCbeta 3 activation by both Galpha q and Gbeta gamma and its ubiquitous tissue distribution, phosphorylation of PLCbeta 3 by PKC and PKA may be general mechanisms by which functions of different G protein/PLC-coupled receptors are regulated.


FOOTNOTES

*   This work was supported by National Institutes of Health Grants HL-54166 (to H. A.), AI-38910 (to R. M. R.), and DE-03738 (to R. S.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
§   To whom correspondence should be addressed: Dept. of Medicine, Duke University Medical Center, 201C MSRB Box 3680, Durham, NC 27710. Tel.: 919-681-6756; Fax: 919-684-4434; E-mail: ali00001 @mc.duke.edu.
1   The abbreviations used are: PAF, platelet-activating factor; PAFR, PAF receptor; mPAFR, mutant PAFR; PLC, phospholipase C; PMA, phorbol 12-myristate 13-acetate; RBL, rat basophilic leukemia; Cpt-cAMP, 8-(4-chlorophenylthio)-adenosine 3'-cyclic monophosphate; PKA, protein kinase A, PKC; protein kinase C; BIM, bisindolylmaleimide; Ptx, pertussis toxin; BSA, bovine serum albumin; PAGE, polyacrylamide gel electrophoresis; GTPgamma S, guanosine 5'-3-O-(thio)triphosphate.

ACKNOWLEDGEMENTS

We thank Drs. Juan Rivera and Henry Metzger (National Institutes of Health) for providing IgE and dinitrophenylated bovine serum albumin.


REFERENCES

  1. Izumi, T., and Shimizu, T. (1995) Biochim. Biophys. Acta 1259, 317-333 [Medline] [Order article via Infotrieve]
  2. Honda, Z., Nakamura, M., Miki, I., Minami, M., Watanabe, T., Seyama, Y., Okado, H., Toh, H., Ito, K., Miyamoto, T., and Shimizu, T. (1991) Nature 349, 342-346 [CrossRef][Medline] [Order article via Infotrieve]
  3. Kunz, D., Gerard, N. P., and Gerard, C. (1992) J. Biol. Chem. 267, 9101-9106 [Abstract/Free Full Text]
  4. Verghese, M. W., Charles, L., Jakoi, L., Dillon, S. B., and Snyderman, R. (1987) J. Immunol. 138, 4374-4380 [Abstract/Free Full Text]
  5. Rhee, S. G. (1991) Trends Biochem. Sci. 16, 297-301 [CrossRef][Medline] [Order article via Infotrieve]
  6. Lee, C. W., Park, D. J., Lee, K. H., Kim, C. G., and Rhee, S. G. (1993) J. Biol. Chem. 268, 21318-21327 [Abstract/Free Full Text]
  7. Wu, D., Katz, A., Lee, C. H., and Simon, M. I. (1992) J. Biol. Chem. 267, 25798-25802 [Abstract/Free Full Text]
  8. Park, D., Jhon, D. Y., Lee, C. W., Ryu, S. H., and Rhee, S. G. (1993) J. Biol. Chem. 268, 3710-3714 [Abstract/Free Full Text]
  9. Jhon, D. Y., Lee, H. H., Park, D., Lee, C. W., Lee, K. H., Yoo, O. J., and Rhee, S. G. (1993) J. Biol. Chem. 268, 6654-6661 [Abstract/Free Full Text]
  10. Lee, C. W., Lee, K. H., Lee, S. B., Park, D., and Rhee, S. G. (1994) J. Biol. Chem. 269, 25335-25338 [Abstract/Free Full Text]
  11. Camps, M., Carozzi, A., Schnabel, P., Scheer, A., Parker, P. J., and Gierschik, P. (1992) Nature 360, 684-686 [CrossRef][Medline] [Order article via Infotrieve]
  12. Katz, A., Wu, D., and Simon, M. I. (1992) Nature 360, 686-689 [CrossRef][Medline] [Order article via Infotrieve]
  13. Murthy, K. S., and Makhlouf, G. M. (1995) Mol. Pharmacol. 47, 1172-1179 [Abstract]
  14. Honda, Z., Takano, T., Gotoh, Y., Nishida, E., Ito, K., and Shimizu, T. (1994) J. Biol. Chem. 269, 2307-2315 [Abstract/Free Full Text]
  15. Ali, H., Richardson, R. M., Tomhave, E. D., DuBose, R. A., Haribabu, B., and Snyderman, R. (1994) J. Biol. Chem. 269, 24557-24563 [Abstract/Free Full Text]
  16. Kuruvilla, A., Pielop, C., and Shearer, W. T. (1994) J. Immunol. 153, 5433-5442 [Abstract/Free Full Text]
  17. Dhar, A., and Shukla, S. D. (1994) J. Biol. Chem. 269, 9123-9127 [Abstract/Free Full Text]
  18. Tomhave, E. D., Richardson, R. M., Didsbury, J. R., Menard, L., Snyderman, R., and Ali, H. (1994) J. Immunol. 153, 3267-3275 [Abstract/Free Full Text]
  19. Ali, H., Richardson, R. M., Tomhave, E. D., Didsbury, J. R., and Snyderman, R. (1993) J. Biol. Chem. 268, 24247-24254 [Abstract/Free Full Text]
  20. Richardson, R. M., DuBose, R. A., Ali, H., Tomhave, E. D., Haribabu, B., and Snyderman, R. (1995) Biochemistry 34, 14193-14201 [Medline] [Order article via Infotrieve]
  21. Richardson, R. M., Haribabu, B., Ali, H., and Snyderman, R. (1996) J. Biol. Chem. 271, 28717-28724 [Abstract/Free Full Text]
  22. Takano, T., Honda, Z., Sakanaka, C., Izumi, T., Kameyama, K., Haga, K., Haga, T., Kurokawa, K., and Shimizu, T. (1994) J. Biol. Chem. 269, 22453-22458 [Abstract/Free Full Text]
  23. Marrero, M. B., Schieffer, B., Paxton, W. G., Schieffer, E., and Bernstein, K. E. (1995) J. Biol. Chem. 270, 15734-15738 [Abstract/Free Full Text]
  24. Park, D. J., Min, H. K., and Rhee, S. G. (1992) J. Biol. Chem. 267, 1496-1501 [Abstract/Free Full Text]
  25. Kim, U. H., Kim, J. W., and Rhee, S. G. (1989) J. Biol. Chem. 264, 20167-20170 [Abstract/Free Full Text]
  26. Ozawa, K., Yamada, K., Kazanietz, M. G., Blumberg, P. M., and Beaven, M. A. (1993) J. Biol. Chem. 268, 2280-2283 [Abstract/Free Full Text]
  27. Hanke, J. H., Gardner, J. P., Dow, R. L., Changelian, P. S., Brissette, W. H., Weringer, E. J., Pollok, K., and Connelly, P. A. (1996) J. Biol. Chem. 71, 695-701 [Free Full Text]
  28. Smrcka, A. V., and Sternweis, P. C. (1993) J. Biol. Chem. 268, 9667-9674 [Abstract/Free Full Text]
  29. Ryu, S. H., Kim, U. H., Wahl, M. I., Brown, A. B., Carpenter, G., Huang, K. P., and Rhee, S. G. (1990) J. Biol. Chem. 265, 17941-17945 [Abstract/Free Full Text]
  30. Liu, M. Y., and Simon, M. I. (1996) Nature 382, 83-87 [CrossRef][Medline] [Order article via Infotrieve]
  31. Lagercrantz, J., Carson, E., Phelan, C., Grimmond, S., Rosen, A., Dare, E., Nordenskjold, M., Hayward, N. K., Larsson, C., and Weber, G. (1995) Genomics 6, 467-472 [CrossRef]

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