Eukaryotic Elongation Factor 1A Interacts with Sphingosine Kinase and Directly Enhances Its Catalytic Activity

Abstract

Sphingosine 1-phosphate (S1P) has many important roles in mammalian cells, including contributing to the control of cell survival and proliferation. S1P is generated by sphingosine kinases (SKs), of which two mammalian isoforms have been identified (SK1 and SK2). To gain a better understanding of SK regulation, we have used a yeast two-hybrid screen to identify SK1-interacting proteins and established elongation factor 1A (eEF1A) as one such protein that associates with both SK1 and SK2. We show the direct interaction of eEF1A with the SKs in vitro, whereas the physiological relevance of this association was demonstrated by co-immunoprecipitation of the endogenous proteins from cell lysates. Although the canonical role of eEF1A resides in protein synthesis, it has also been implicated in other roles, including regulating the activity of some signaling enzymes. Thus, we examined the potential role of eEF1A in regulation of the SKs and show that eEF1A is able to directly increase the activity of SK1 and SK2 ∼3-fold in vitro. Substrate kinetics demonstrated that eEF1A increased the catalytic rate of both SKs, while having no observable effect on substrate affinities of these enzymes for either ATP or sphingosine. Overexpression of eEF1A in quiescent Chinese hamster ovary cells increased cellular SK activity, whereas a small interfering RNA-mediated decrease in eEF1A levels in MCF7 cells substantially reduced cellular SK activity and S1P levels, supporting the in vivo physiological relevance of this interaction. Thus, this study has established a novel mechanism of regulation of both SK1 and SK2 that is mediated by their interaction with eEF1A. Sphingosine 1-phosphate (S1P) has many important roles in mammalian cells, including contributing to the control of cell survival and proliferation. S1P is generated by sphingosine kinases (SKs), of which two mammalian isoforms have been identified (SK1 and SK2). To gain a better understanding of SK regulation, we have used a yeast two-hybrid screen to identify SK1-interacting proteins and established elongation factor 1A (eEF1A) as one such protein that associates with both SK1 and SK2. We show the direct interaction of eEF1A with the SKs in vitro, whereas the physiological relevance of this association was demonstrated by co-immunoprecipitation of the endogenous proteins from cell lysates. Although the canonical role of eEF1A resides in protein synthesis, it has also been implicated in other roles, including regulating the activity of some signaling enzymes. Thus, we examined the potential role of eEF1A in regulation of the SKs and show that eEF1A is able to directly increase the activity of SK1 and SK2 ∼3-fold in vitro. Substrate kinetics demonstrated that eEF1A increased the catalytic rate of both SKs, while having no observable effect on substrate affinities of these enzymes for either ATP or sphingosine. Overexpression of eEF1A in quiescent Chinese hamster ovary cells increased cellular SK activity, whereas a small interfering RNA-mediated decrease in eEF1A levels in MCF7 cells substantially reduced cellular SK activity and S1P levels, supporting the in vivo physiological relevance of this interaction. Thus, this study has established a novel mechanism of regulation of both SK1 and SK2 that is mediated by their interaction with eEF1A. Sphingosine kinases (SKs) 2The abbreviations used are:SKsphingosine kinaseS1Psphingosine 1-phosphateeEF1Aeukaryotic elongation factor 1AHAhemagglutininPI4Kphosphatidylinositol 4-kinaserec-SK1purified recombinant SK1rec-SK2purified recombinant SK2S6KS6 kinasePECAM-1platelet endothelial cell adhesion molecule-1IBimmunoblottingGSTglutathione S-transferaseCHOChinese hamster ovarysiRNAsmall interfering RNAERKextracellular signal-regulated kinasePBSphosphate-buffered salineMOPS4-morpholinepropanesulfonic acidHPLChigh pressure liquid chromatography. catalyze the phosphorylation of sphingosine to generate the bio-active phospholipid sphingosine 1-phosphate (S1P). S1P affects many biological processes including calcium mobilization, mitogenesis, apoptosis, atherosclerosis, asthma, hypertension, inflammatory responses, and cytoskeleton rearrangement (1Hait N.C. Oskeritzian C.A. Paugh S.W. Milstein S. Spiegel S. Biochim. Biophys. Acta. 2006; 1758: 2016-2026Crossref PubMed Scopus (417) Google Scholar). In humans two sphingosine kinases, SK1 and SK2, have been identified (2Pitson S.M. D'Andrea R.J. Vandeleur L. Moretti P.A. Xia P. Gamble J.R. Vadas M.A. Wattenberg B.W. Biochem. J. 2000; 350: 429-441Crossref PubMed Scopus (166) Google Scholar, 3Liu H. Sugiura M. Nava V.E. Edsall L.C. Kono K. Poulton S. Milstien S. Kohama T. Spiegel S. J. Biol. Chem. 2000; 275: 19513-19520Abstract Full Text Full Text PDF PubMed Scopus (571) Google Scholar). These enzymes appear to be the major control elements regulating cellular S1P levels (4Baumruker T. Bornancin F. Billich A. Immunol. Lett. 2005; 96: 175-185Crossref PubMed Scopus (83) Google Scholar) and thus play a crucial role in modulating the effects attributed to S1P. sphingosine kinase sphingosine 1-phosphate eukaryotic elongation factor 1A hemagglutinin phosphatidylinositol 4-kinase purified recombinant SK1 purified recombinant SK2 S6 kinase platelet endothelial cell adhesion molecule-1 immunoblotting glutathione S-transferase Chinese hamster ovary small interfering RNA extracellular signal-regulated kinase phosphate-buffered saline 4-morpholinepropanesulfonic acid high pressure liquid chromatography. There is now convincing evidence that SK1 and S1P play roles in tumorigenesis. We have shown that overexpression of SK1 in NIH-3T3 fibroblasts results in neoplastic transformation of these cells (5Xia P. Gamble J.R. Wang L. Pitson S.M. Moretti P.A. Wattenberg B.W. D'Andrea R.J. Vadas M.A. Curr. Biol. 2000; 10: 1527-1530Abstract Full Text Full Text PDF PubMed Scopus (360) Google Scholar). Other studies have demonstrated the involvement of SK1 in estrogen-dependent regulation of breast tumor cell growth and survival (6Nava V.E. Hobson J.P. Murthy S. Milstien S. Spiegel S. Exp. Cell Res. 2002; 281: 115-127Crossref PubMed Scopus (200) Google Scholar, 7Sukocheva O.A. Wang L. Albanese N. Pitson S.M. Vadas M.A. Xia P. Mol. Endocrinol. 2003; 17: 2002-2012Crossref PubMed Scopus (137) Google Scholar). Furthermore, French et al. (8French K.J. Schrecengost R.S. Lee B.D. Zhuang Y. Smith S.N. Eberly J.L. Yun J.K. Smith C.D. Cancer Res. 2003; 63: 5962-5969PubMed Google Scholar) have shown that SK1 mRNA levels are elevated in a variety of human solid tumors and, importantly, that tumor growth can be reduced in vivo by SK inhibitors. Similarly, we have shown that the use of SK inhibitors or a dominant negative SK can block neoplastic cell transformation induced by oncogenic H-Ras (5Xia P. Gamble J.R. Wang L. Pitson S.M. Moretti P.A. Wattenberg B.W. D'Andrea R.J. Vadas M.A. Curr. Biol. 2000; 10: 1527-1530Abstract Full Text Full Text PDF PubMed Scopus (360) Google Scholar). We have established that activation of SK1 can be mediated by phosphorylation at Ser225 by ERK1/2 (9Pitson S.M. Moretti P.A. Zebol J.R. Lynn H.E. Xia P. Vadas M.A. Wattenberg B.W. EMBO J. 2003; 22: 5491-5500Crossref PubMed Scopus (466) Google Scholar). This phosphorylation not only results in a 13-fold increase in the catalytic activity of SK1 but is also required for agonist-induced translocation of this enzyme from the cytoplasm to the plasma membrane (9Pitson S.M. Moretti P.A. Zebol J.R. Lynn H.E. Xia P. Vadas M.A. Wattenberg B.W. EMBO J. 2003; 22: 5491-5500Crossref PubMed Scopus (466) Google Scholar). Our recent studies have shown that this activation of SK1 and its subsequent translocation are one mechanism by which this enzyme is able to induce neoplastic transformation of cells (10Pitson S.M. Xia P. Leclercq T.M. Moretti P.A. Zebol J.R. Lynn H.E. Wattenberg B.W. Vadas M.A. J. Exp. Med. 2005; 201: 49-54Crossref PubMed Scopus (228) Google Scholar). However, the molecular mechanisms regulating the phosphorylation of SK1 or its translocation to the plasma membrane are not currently known. In an attempt to understand the regulatory mechanisms controlling SK1 activity and function, we have performed a yeast two-hybrid screen to identify SK1-interacting proteins. In this study we report that eukaryotic elongation factor 1A (eEF1A) interacts with both SK1 and SK2. Furthermore, we demonstrate that this interaction directly enhances the catalytic activity of these lipid kinases, both in and in Thus, this a novel of regulation of both SK1 and SK2 that is mediated by their interaction with eEF1A. Cell and cells in and cells the calcium PubMed Scopus Google by and by for at in and inhibitors of cell with as Chinese hamster ovary cells in and was by the cells for at with the quiescent cells to the cells and as MCF7 cells in as cells with and or control to the for and as two-hybrid was performed the to the human SK1 (2Pitson S.M. D'Andrea R.J. Vandeleur L. Moretti P.A. Xia P. Gamble J.R. Vadas M.A. Wattenberg B.W. Biochem. J. 2000; 350: 429-441Crossref PubMed Scopus (166) Google Scholar) was with the This was the yeast with a human in of of and for of the human the J. Biochem. PubMed Scopus Google Scholar). was from a human and hemagglutinin at the with and was for mammalian and for with and for of the the S. Wang Biochim. Biophys. Res. PubMed Scopus Google Scholar). was from and at the with and was both and with the and of the human and of and in as proteins. with at in was and with at to an of of the proteins was induced with and the with at for a cells by at for at in of and by of for on with was to a of and the and at for at was with for at with this the by at for at and in to the was with as These either used directly in or the proteins by with for with protein as (2Pitson S.M. D'Andrea R.J. Vandeleur L. Moretti P.A. Xia P. Gamble J.R. Vadas M.A. Wattenberg B.W. Biochem. J. 2000; 350: 429-441Crossref PubMed Scopus (166) Google Scholar). Sphingosine kinase activity was and as as J.L. Moretti P.A. Vadas M.A. Pitson S.M. Biochem. PubMed Scopus Google Scholar). of SK activity is as the of enzyme required to of Substrate kinetics kinetics with the In of SK1 and phosphorylation of was performed while the protein to the by these of with of and ATP in and for at with and In phosphorylation of SK1 S.M. Moretti P.A. Zebol J.R. J. D'Andrea R.J. Vadas M.A. Wattenberg B.W. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar) in was performed as and to acid by at for in of by for at To the acid but and at for In phosphorylation of to was performed in a by these of with of S6 kinase in for at with In phosphorylation of in was performed of purified and of S6 kinase in at for with the recombinant proteins used for in SK1 activity and from cells the SK1 in with eEF1A isoforms at for at to or (9Pitson S.M. Moretti P.A. Zebol J.R. Lynn H.E. Xia P. Vadas M.A. Wattenberg B.W. EMBO J. 2003; 22: 5491-5500Crossref PubMed Scopus (466) Google Scholar) to the and at for with by with protein for at with and to and the proteins to SK1 was with either the or or (9Pitson S.M. Moretti P.A. Zebol J.R. Lynn H.E. Xia P. Vadas M.A. Wattenberg B.W. EMBO J. 2003; 22: 5491-5500Crossref PubMed Scopus (466) Google Scholar). was with either or with or an was as a control from cells with of either or for at with in and and to and proteins by with either or of with purified recombinant SK1 or SK2 was performed in a with to with of S.M. Moretti P.A. Zebol J.R. J. D'Andrea R.J. Vadas M.A. Wattenberg B.W. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar) or J.L. Moretti P.A. Vadas M.A. Pitson S.M. Biochem. PubMed Scopus Google Scholar) for at with as and to and proteins by with levels by as L. M. PubMed Scopus Google Scholar). S1P was from of a S1P to the and S1P to the was used as an was and the S1P in of of S1P was by the of of a of in of was at for to to an with a rate of S1P was from the with a to with at and of and the sphingosine levels as Y. Pitson S. T. J. A. J. J. Biol. Chem. 2005; Full Text Full Text PDF PubMed Scopus Google Scholar). a SK1-interacting an attempt to understand the mechanisms regulating the activity and of we performed a yeast two-hybrid screen to identify proteins that with that was in this screen the of To the interaction and and mammalian the generated by from human interaction of with SK1 was by or to and from cells These results demonstrated a interaction of with and not with also performed or to and from cells SK1 the results demonstrated the interaction of with In purified recombinant SK1 also with that the interaction of SK1 and is direct and not mediated by To the interaction and co-immunoprecipitation studies performed on from cells and with the results of the the of SK1 in the was we able to demonstrate the physiological interaction SK1 and the co-immunoprecipitation of the endogenous proteins in cell to SK1 in the canonical role for is in elongation protein Biochem. Full Text Full Text PDF Scopus Google Scholar) other cellular have been attributed to including roles in apoptosis, and oncogenic transformation S. Biochem. 2002; PubMed Scopus Google Scholar, S. N. Lee J. J. Mol. Med. 2003; PubMed Scopus Google Scholar, M. H. M. A. H. H. PubMed Scopus Google Scholar). has been shown to directly and phosphatidylinositol 4-kinase H. Lee S. A. S. J.K. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google we that it also have an effect on the activation of Thus, we examined the effect of purified recombinant or on the catalytic activity of in vitro. Although no effect on SK1 activity these the catalytic activity of SK1 Furthermore, this effect was to be with SK1 activity as the of a with a of to SK1 This effect was not as a of having to was it to the of in the enzyme the enzyme is these as demonstrated by kinetics not We examined the effect of on SK1 substrate results show that the of SK1 for both sphingosine and ATP by the of In the for SK1 was increased by the of these results that not increase the of SK1 for its but has a direct effect on the catalytic rate of with and SK2 interacts with SK1 and has a direct effect on its activity, we examined its effect on the other human SK SK2. interaction and SK2 was or to and purified SK2 was able to with demonstrated that and SK2 we examined the effect of the interaction on the catalytic activity of SK2. and purified in vitro, and the SK activity was with was shown to increase SK2 activity by a SK1-interacting eEF1A isoforms in and Biochem. Full Text Full Text PDF Scopus Google Scholar). Although the these two proteins is high S. N. Lee J. J. Mol. Med. 2003; PubMed Scopus Google some have been in their human Biochem. Full Text Full Text PDF Scopus Google Scholar, S. N. Lee J. J. Mol. Med. 2003; PubMed Scopus Google with and only in and cells S. N. Lee J. J. Mol. Med. 2003; PubMed Scopus Google Scholar). Our yeast two-hybrid screen and the identified as a SK1-interacting the of the two we examined also with performed from cells and as with also associates with SK1 In with in studies also that was also able to increase the activity of of SK1 and by interaction and proteins is to be by either of J. Biol. Chem. Full Text PDF PubMed Google Scholar) or of its proteins S. Biochem. 2002; PubMed Scopus Google Scholar, H. Lee S. A. S. J.K. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). we examined the phosphorylation of SK1 or their interaction. We the effect of SK1 phosphorylation by to and from cells either to be (9Pitson S.M. Moretti P.A. Zebol J.R. Lynn H.E. Xia P. Vadas M.A. Wattenberg B.W. EMBO J. 2003; 22: 5491-5500Crossref PubMed Scopus (466) Google or its (9Pitson S.M. Moretti P.A. Zebol J.R. Lynn H.E. Xia P. Vadas M.A. Wattenberg B.W. EMBO J. 2003; 22: 5491-5500Crossref PubMed Scopus (466) Google Scholar). results of the that both of SK1 with to a To this we also to recombinant is to SK1 at Ser225 in vitro, which to be the only physiological phosphorylation in this protein (9Pitson S.M. Moretti P.A. Zebol J.R. Lynn H.E. Xia P. Vadas M.A. Wattenberg B.W. EMBO J. 2003; 22: 5491-5500Crossref PubMed Scopus (466) Google Scholar). This was used for with from cells and with in a these results show some other the phosphorylation of SK1 not its to with Furthermore, of the effect of on the catalytic activity on in SK1 that the activity of and SK1 Thus, with in phosphorylation of SK1 increased its catalytic activity (9Pitson S.M. Moretti P.A. Zebol J.R. Lynn H.E. Xia P. Vadas M.A. Wattenberg B.W. EMBO J. 2003; 22: 5491-5500Crossref PubMed Scopus (466) Google but this we examined the effect of phosphorylation on its to with is to be in by S6 kinase S. N. Lee J. J. Mol. Med. 2003; PubMed Scopus Google protein kinase K. H.E. F. M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google and kinase S. Biochem. 2002; PubMed Scopus Google Scholar). at including by protein kinase S. N. Lee J. J. Mol. Med. 2003; PubMed Scopus Google Scholar) and kinase S. Biochem. 2002; PubMed Scopus Google to was with and used in with and results that both and is able to with SK1 and SK2 to a Similarly, in was able to to the as the results show that the with some other the phosphorylation of or SK1 has no effect on the interaction of these two proteins and the subsequent increase in SK Overexpression in SK the in effects of eEF1A on the SKs, no increase in cellular SK activity was was in either or cells not These results not eEF1A has been to be one of the proteins in cells A. A. L. F. J. Biochem. 2003; PubMed Scopus Google Scholar). Thus, the high endogenous levels of eEF1A in these cells is to have an effect on cellular SK activity in the of In quiescent cells, which the of cells in an eEF1A is substantially reduced Exp. PubMed Scopus Google Scholar). Thus, we examined the effect of eEF1A overexpression on cellular SK activity in quiescent with Exp. PubMed Scopus Google the growth of cells to in a decrease in the levels of endogenous eEF1A protein with that in cells overexpression of in these quiescent cells, to levels in an increase in cellular SK activity a potential physiological role for eEF1A in the regulation of SK activity in of SK and S1P a physiological role for eEF1A in the regulation of cellular SK activity, we a of for of is of the of a of potential T. A. S. Y. J. Biol. Chem. Full Text PDF PubMed Google Scholar). such for and recent have demonstrated that this is the major eEF1A in MCF7 cells S. Lee J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). Thus, MCF7 cells with either or control and examined for the of eEF1A and protein in the cell by with a results of eEF1A levels in these cells to of that in control cells SK performed on these demonstrated a decrease in SK activity a physiological role for eEF1A in the regulation of endogenous SK results also demonstrated with a not of cellular S1P in to eEF1A also a decrease in the levels of this phospholipid supporting the physiological role of eEF1A in regulating cellular SK this decrease in endogenous SK activity and S1P levels was not to a decrease in cellular SK protein or sphingosine levels not of SK and the subsequent in cellular S1P levels are in modulating many cell signaling and have been implicated in the of the neoplastic cell (10Pitson S.M. Xia P. Leclercq T.M. Moretti P.A. Zebol J.R. Lynn H.E. Wattenberg B.W. Vadas M.A. J. Exp. Med. 2005; 201: 49-54Crossref PubMed Scopus (228) Google Scholar, M. Milstien S. Spiegel S. Biochim. Biophys. Acta. 2002; PubMed Scopus Google Scholar, S. Milstien S. Cell Biol. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar, Y. Lett. PubMed Scopus Google Scholar). We have that one mechanism regulating the cellular activity of SK1 its agonist-induced phosphorylation at Ser225 by ERK1/2 (9Pitson S.M. Moretti P.A. Zebol J.R. Lynn H.E. Xia P. Vadas M.A. Wattenberg B.W. EMBO J. 2003; 22: 5491-5500Crossref PubMed Scopus (466) Google Scholar). In the study we report an novel mechanism of regulating SK activity the interaction with which results in a direct of the catalytic activity of both SK1 and SK2. In humans two isoforms of eEF1A have been and S. Biochem. 2002; PubMed Scopus Google Scholar, S. N. Lee J. J. Mol. Med. 2003; PubMed Scopus Google Scholar). canonical role for eEF1A is as of the elongation that elongation mRNA P. J. Biochem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar). However, eEF1A also has a of other in the including regulating the activity of signaling enzymes S. Biochem. 2002; PubMed Scopus Google involvement in and regulating and of and S. Biochem. 2002; PubMed Scopus Google and an role in S. Biochem. 2002; PubMed Scopus Google Scholar, S. N. Lee J. J. Mol. Med. 2003; PubMed Scopus Google Scholar, M. H. M. A. H. H. PubMed Scopus Google Scholar). In with these of we now demonstrate that both and can directly the catalytic activity of SK1 and SK2 their interaction with these proteins. Although the molecular mechanism eEF1A this SK activity is not currently substrate that this effect results from a direct increase in the catalytic of an in its for either ATP or sphingosine. SK1 phosphorylation also results in increased catalytic in the for either substrate (9Pitson S.M. Moretti P.A. Zebol J.R. Lynn H.E. Xia P. Vadas M.A. Wattenberg B.W. EMBO J. 2003; 22: 5491-5500Crossref PubMed Scopus (466) Google Scholar). This the that molecular mechanisms SK activity mediated by both the interaction with eEF1A and Our subsequent that this not be the the catalytic activity of SK1 can be by the of Thus, this that at two mechanisms for the regulation of SK1 one that and one interaction with eEF1A. and its have been to directly the catalytic activity of and J. Biol. Chem. Full Text PDF PubMed Google Scholar, J. J. Biol. Chem. Full Text PDF PubMed Google Scholar, F. Lee Lee Lee Mol. to a mechanism to that by eEF1A on SK and J. Biol. Chem. Full Text PDF PubMed Google Scholar) this protein the of for in of their studies that induced activity in the of J. J. Biol. Chem. Full Text PDF PubMed Google this to an effect of on the of J. Biol. Chem. Full Text PDF PubMed Google Scholar). recent studies demonstrated the of eEF1A to mammalian activity in MCF7 cells S. Lee J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). eEF1A is a protein in the we examined the mechanisms regulating its effects on SK interaction of eEF1A with some including F. Lee Lee Lee Mol. Scholar) and protein L. M. S. M. R.J. Cell Biol. PubMed Scopus Google are by cell to growth the mechanism this is currently that eEF1A is in to growth factor and other growth has to that this its agonist-induced protein S. Biochem. 2002; PubMed Scopus Google Scholar). phosphorylation of eEF1A important in its to T. Y. T. A. K. K. Biochim. Biophys. Res. 2000; PubMed Scopus Google as as its interaction and activation of J. Biol. Chem. Full Text PDF PubMed Google Scholar). In growth phosphorylation of has been to its interaction with eEF1A F. Lee Lee Lee Mol. Scholar). Thus, phosphorylation a controlling the effects of eEF1A on its cellular of the involvement of phosphorylation of either or SK1 in their to demonstrate this as a regulatory mechanism for the effect of eEF1A on cellular SK Although is no evidence for of eEF1A regulating its effects on SK activity, one is that the of eEF1A protein cellular SK is that cells a increase in eEF1A levels with that in Exp. PubMed Scopus Google Scholar, J. Res. Scholar). in an attempt to a physiological role for we in and cells to its effect on cellular SK effect was of the high of eEF1A in these cells A. A. L. F. J. Biochem. 2003; PubMed Scopus Google Scholar, Exp. PubMed Scopus Google Scholar). However, in quiescent cells, endogenous eEF1A levels are substantially overexpression of eEF1A in a increase in cellular SK Furthermore, the levels of endogenous eEF1A in MCF7 cells in a in both endogenous SK activity and cellular S1P these eEF1A be a of SK in Thus, eEF1A that with cell not only for increased protein but also cellular SK activity to and survival of other SK1-interacting proteins have been including platelet endothelial cell adhesion molecule-1 Y. Y. A. Y. Biochim. Biophys. Acta. PubMed Scopus Google T. T. S. S. N. S. Biochem. J. PubMed Scopus Google tumor factor factor P. Wang L. Moretti P.A. Albanese N. F. Pitson S.M. D'Andrea R.J. Gamble J.R. Vadas M.A. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google a protein kinase protein M. Milstien S. Spiegel S. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google M. Nava V.E. Milstien S. Spiegel S. Lett. PubMed Scopus Google S. T. N. T. S. S. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google kinase N. A. Billich A. Bornancin F. M. J. T. Mol. Biol. PubMed Scopus Google kinase A. N. K. Y. Y. H. T. J. Biol. Chem. 2006; 281: Full Text Full Text PDF PubMed Scopus Google and factor J. A. J.K. Res. 2006; PubMed Scopus Google Scholar). of these proteins have been to SK1 has been shown to with SK1 and directly increase its activity in T. T. S. S. N. S. Biochem. J. PubMed Scopus Google Scholar). Similarly, the kinases, and have also been to with and SK1 N. A. Billich A. Bornancin F. M. J. T. Mol. Biol. PubMed Scopus Google Scholar, A. N. K. Y. Y. H. T. J. Biol. Chem. 2006; 281: Full Text Full Text PDF PubMed Scopus Google while also of SK1 to the to cell such as and N. A. Billich A. Bornancin F. M. J. T. Mol. Biol. PubMed Scopus Google Scholar, A. N. K. Y. Y. H. T. J. Biol. Chem. 2006; 281: Full Text Full Text PDF PubMed Scopus Google Scholar). and not SK1 this to that these kinases SK1 activity a in the protein directly by the interaction N. A. Billich A. Bornancin F. M. J. T. Mol. Biol. PubMed Scopus Google Scholar). activity of SK1 also be by eEF1A a the of the two eEF1A isoforms not show to or it is to of these proteins on SK1 by the whereas proteins have now been shown to SK1 activity, overexpression of some other SK1-interacting such as Y. Y. A. Y. Biochim. Biophys. Acta. PubMed Scopus Google M. Milstien S. Spiegel S. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google and M. Nava V.E. Milstien S. Spiegel S. Lett. PubMed Scopus Google Scholar) in a decrease in cellular SK this effect is only it these are overexpression of has been shown to in a decrease in cellular SK1 activity and also the effects of SK1 J. A. J.K. Res. 2006; PubMed Scopus Google Scholar). other SK1-interacting including S. T. N. T. S. S. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Y. Y. A. Y. Biochim. Biophys. Acta. PubMed Scopus Google and M. Nava V.E. Milstien S. Spiegel S. Lett. PubMed Scopus Google Scholar) also appear to SK1 their involvement in the of this enzyme to cellular Thus, it that activation of SK1 can be mediated by phosphorylation (9Pitson S.M. Moretti P.A. Zebol J.R. Lynn H.E. Xia P. Vadas M.A. Wattenberg B.W. EMBO J. 2003; 22: 5491-5500Crossref PubMed Scopus (466) Google other mechanisms for the of the activity of this enzyme by This the novel mechanism in this study the direct interaction and activation of SK1 by eEF1A.