Insulin Stimulation of the Fatty Acid Synthase Promoter Is Mediated by the Phosphatidylinositol 3-Kinase Pathway

Fatty acid synthase (FAS) is a critical enzyme in de novo lipogenesis. It catalyzes the seven steps in the conversion of malonyl-CoA and acetyl-CoA to palmitate. We have shown that the rate of FAS transcription is induced dramatically when fasted animals are refed with a high carbohydrate, fat-free diet or when streptozotocin-diabetic mice are given insulin. The FAS promoter was up-regulated by insulin through the proximal insulin response sequence containing an E-box motif at the −65-base pair position. Binding of upstream stimulatory factors to the −65 E-box is functionally required for insulin regulation of the FAS promoter. In the present study, we characterized signaling pathways in the insulin stimulation of FAS transcription using specific inhibitors for various signaling molecules and transfecting engineered phosphatidylinositol (PI) 3-kinase subunits and protein kinase B (PKB)/Akt. PD98059 and rapamycin, which inhibit MAP kinase and P70 S6 kinase, respectively, had little effect on the insulin-stimulated FAS promoter activity in 3T3-L1 adipocytes. On the other hand, wortmannin and LY294002, which specifically inactivate PI 3-kinase, strongly inhibited the insulin-stimulated FAS promoter activity. As shown in RNase protection assays, LY294002 also inhibited insulin stimulation of the endogenous FAS mRNA levels in 3T3-L1 adipocytes. Cotransfection of expression vectors for the constitutively active P110 subunit of PI 3-kinase resulted in an elevated FAS promoter activity in the absence of insulin and a loss of further insulin stimulation. Transfecting a dominant negative P85 subunit of PI 3-kinase decreased FAS promoter activity and blocked insulin stimulation. Furthermore, cotransfected wild-type PKB/Akt increased FAS promoter activity in the absence of insulin and a loss of insulin responsiveness of the FAS promoter. On the other hand, kinase-dead PKB/Akt acted in a dominant negative manner to decrease the FAS promoter activity and abolished its insulin responsiveness. These results demonstrate that insulin stimulation of fatty acid synthase promoter is mediated by the PI 3-kinase pathway and that PKB/Akt is involved as a downstream effector. Fatty acid synthase (FAS) is a critical enzyme in de novo lipogenesis. It catalyzes the seven steps in the conversion of malonyl-CoA and acetyl-CoA to palmitate. We have shown that the rate of FAS transcription is induced dramatically when fasted animals are refed with a high carbohydrate, fat-free diet or when streptozotocin-diabetic mice are given insulin. The FAS promoter was up-regulated by insulin through the proximal insulin response sequence containing an E-box motif at the −65-base pair position. Binding of upstream stimulatory factors to the −65 E-box is functionally required for insulin regulation of the FAS promoter. In the present study, we characterized signaling pathways in the insulin stimulation of FAS transcription using specific inhibitors for various signaling molecules and transfecting engineered phosphatidylinositol (PI) 3-kinase subunits and protein kinase B (PKB)/Akt. PD98059 and rapamycin, which inhibit MAP kinase and P70 S6 kinase, respectively, had little effect on the insulin-stimulated FAS promoter activity in 3T3-L1 adipocytes. On the other hand, wortmannin and LY294002, which specifically inactivate PI 3-kinase, strongly inhibited the insulin-stimulated FAS promoter activity. As shown in RNase protection assays, LY294002 also inhibited insulin stimulation of the endogenous FAS mRNA levels in 3T3-L1 adipocytes. Cotransfection of expression vectors for the constitutively active P110 subunit of PI 3-kinase resulted in an elevated FAS promoter activity in the absence of insulin and a loss of further insulin stimulation. Transfecting a dominant negative P85 subunit of PI 3-kinase decreased FAS promoter activity and blocked insulin stimulation. Furthermore, cotransfected wild-type PKB/Akt increased FAS promoter activity in the absence of insulin and a loss of insulin responsiveness of the FAS promoter. On the other hand, kinase-dead PKB/Akt acted in a dominant negative manner to decrease the FAS promoter activity and abolished its insulin responsiveness. These results demonstrate that insulin stimulation of fatty acid synthase promoter is mediated by the PI 3-kinase pathway and that PKB/Akt is involved as a downstream effector. fatty acid synthase insulin receptor substrate phosphatidylinositol protein kinase B upstream stimulatory factor mitogen-activated protein luciferase base pair(s) kilobase pair(s). Fatty acid synthase (FAS)1 plays an important role in de novo lipogenesis in mammals and birds. Using NADPH as reducing equivalents, FAS catalyzes the seven steps in the conversion of acetyl-CoA and malonyl-CoA to palmitate. FAS activity is exquisitely sensitive to nutritional, hormonal, and developmental status (1Volpe J.J. Vagelos P.R. Physiol. Rev. 1976; 56: 339-417Crossref PubMed Scopus (215) Google Scholar, 2Wakil S.J. Stoops J.K. Joshi V.C. Annu. Rev. Biochem. 1983; 52: 537-579Crossref PubMed Google Scholar, 3Sul H.S. Wang D. Annu. Rev. Nutr. 1998; 18: 331-351Crossref PubMed Scopus (238) Google Scholar, 4Hillgartner F.B. Salati L.M. Goodridge A.G. Physiol. Rev. 1995; 75: 47-76Crossref PubMed Scopus (404) Google Scholar). We previously reported that insulin increases FAS mRNA levels in streptozotocin-diabetic mice and cultured 3T3-L1 adipocytes and that the regulation is at the transcriptional level (5Paulauskis J.D. Sul H.S. J. Biol. Chem. 1988; 263: 7049-7054Abstract Full Text PDF PubMed Google Scholar, 6Paulauskis J.D. Sul H.S. Biochem. Biophys. Res. Commun. 1989; 158: 690-695Crossref PubMed Scopus (27) Google Scholar). Using chimeric constructs of serial 5′-deletions of the rat FAS promoter linked to the luciferase reporter gene and transfection into 3T3-L1 adipocytes, we mapped the insulin response sequence to the proximal promoter region from −68 to −52 (7Moustaid N. Sakamoto K. Clarke S. Beyer R.S. Sul H.S. Biochem. J. 1993; 292: 767-772Crossref PubMed Scopus (58) Google Scholar,8Moustaid N. Beyer R.S. Sul H.S. J. Biol. Chem. 1994; 269: 5629-5634Abstract Full Text PDF PubMed Google Scholar), which contains an E-box (5′-CATGTG-3′) motif at −65. Three tandem copies of the −68/−52 FAS promoter region linked to the heterologous SV40 promoter were responsive to insulin (8Moustaid N. Beyer R.S. Sul H.S. J. Biol. Chem. 1994; 269: 5629-5634Abstract Full Text PDF PubMed Google Scholar). We also reported that upstream stimulatory factors (USFs), members of basic helix-loop-helix leucine-zipper family of transcription factors, bind to the E-box at −65 in vitro (9Wang D. Sul H.S. J. Biol. Chem. 1995; 270: 28716-28722Abstract Full Text Full Text PDF PubMed Scopus (105) Google Scholar). By correlating functional assays of mutated FAS promoter with USF binding activities and cotransfection of expression vectors of wild-type and dominant negative USFs, we demonstrated that USF binding to the E-box at −65 is functionally required for insulin regulation of the FAS promoter (10Wang D. Sul H.S. J. Biol. Chem. 1997; 272: 26367-26374Abstract Full Text Full Text PDF PubMed Scopus (128) Google Scholar). Insulin regulates a wide variety of biological responses in coordination with other hormones, such as glucagon, to maintain glucose homeostasis. Insulin stimulates glucose transport by the peripheral tissues such as muscle and adipose tissue, inhibits glycogen synthesis and gluconeogenesis in the liver, and stimulates protein synthesis and lipogenesis. Some of these effects are exerted on the transcription level through a cascade of signaling events (11O'Brien R.M. Granner D.K. Physiol. Rev. 1996; 76: 1109-1161Crossref PubMed Scopus (440) Google Scholar). Binding of insulin to the insulin receptor on cell membrane triggers tyrosine kinase activity of the insulin receptor and results in its autophosphorylation within the cytoplasmic domain (12Myers Jr., M.G. White M.F. Annu. Rev. Pharmacol. Toxicol. 1996; 36: 615-658Crossref PubMed Scopus (299) Google Scholar, 13Cheatham B. Kahn C.R. Endocr. Rev. 1995; 16: 117-142Crossref PubMed Google Scholar). Tyrosine-phosphorylated insulin receptor then interacts with insulin receptor substrates (IRSs). Phosphorylation of IRS-1 and IRS-2 on the tyrosine residues then results in the recruitment and activation of divergent signaling molecules, including those in the Ras/MAP kinase and phosphatidylinositol (PI) 3-kinase pathways. PI 3-kinase is composed of the regulatory subunit (P85) and the catalytic subunit (P110). P85 acts as an interface by interacting with the IRS-1 through its SH2 domain and thus recruits the P110 subunit to the cell membrane through its iSH2 domain (12Myers Jr., M.G. White M.F. Annu. Rev. Pharmacol. Toxicol. 1996; 36: 615-658Crossref PubMed Scopus (299) Google Scholar). P110 then catalyzes the reaction to release phosphatidylinositol (3,4,5)-triphosphate as the second messenger using phosphatidylinositol (4,5)-bisphosphate as the substrate. Recently, the 3-phosphoinositide-dependent protein kinase (14Alessi D.R. Deak M. Casamayor A. Caudwell F.B. Morrice N. Norman D.G. Gaffney P. Reese C.B. MacDougall C.N. Harbison D. Ashworth A. Bownes M. Curr. 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M. 1997; PubMed Scopus Google Scholar, A. Williams L.T. J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Scopus Google and activation of glycogen synthase D.A. Alessi D.R. Cohen P. M. 1995; PubMed Scopus Google Scholar). Recently, PI 3-kinase shown to insulin of the transcription of the which the enzyme in gluconeogenesis R.A. C. L. Kahn R.M. Granner D.K. J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Scopus Google Scholar, C. R.M. Granner D.K. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar, C. M. L. Kahn Granner D.K. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). insulin regulation of the signaling pathways is FAS is a critical enzyme involved in we to the signaling pathways involved in the regulation of FAS transcription by insulin. In we to demonstrate that the PI 3-kinase signaling pathway insulin regulation of FAS of MAP kinase and S6 kinase activity by PD98059 and rapamycin, respectively, had little effect on the insulin stimulation of FAS promoter wortmannin and LY294002, which inhibit PI 3-kinase, blocked the insulin stimulation of FAS promoter activity. of the endogenous FAS mRNA by insulin was also blocked by 3T3-L1 adipocytes with Cotransfection of expression vectors a constitutively active P110 subunit of PI 3-kinase resulted in elevated FAS promoter activity in the absence of insulin and a loss of insulin response of the FAS promoter. On the other hand, a dominant negative P85 subunit of PI 3-kinase inhibited FAS promoter activity and abolished insulin stimulation of the FAS promoter. cotransfection of PKB/Akt FAS promoter activity in the absence of insulin to that to the insulin-stimulated in a kinase-dead PKB/Akt inhibited FAS promoter activity in the and the absence of insulin. These that insulin regulation of FAS transcription is mediated by the PI 3-kinase signaling pathway and that PKB/Akt is involved as a downstream effector. The reporter gene constructs of and which the and of wild-type rat FAS promoter with luciferase respectively, were previously (8Moustaid N. Beyer R.S. Sul H.S. J. Biol. Chem. 1994; 269: 5629-5634Abstract Full Text PDF PubMed Google Scholar). vectors which were as previously (10Wang D. Sul H.S. J. Biol. Chem. 1997; 272: 26367-26374Abstract Full Text Full Text PDF PubMed Scopus (128) Google Scholar). vectors for the wild-type and kinase-dead PKB/Akt as as for the catalytic subunit of PI 3-kinase A. Reinhard C. Kavanaugh W.M. Apell G. Escobedo M.A. Williams L.T. Biol. 1996; 16: PubMed Scopus Google Scholar, A. Williams L.T. Science. 1995; PubMed Scopus Google Scholar), including the constitutively active and kinase-dead were by L. Williams and A. at the vectors for the P85 regulatory subunit of PI 3-kinase were by the wild-type P85 as as the for dominant negative from and vectors H. K. M. Biol. 1995; PubMed Scopus Google Scholar, K. K. H. A. K. H. L. Hawkins P.T. M. S. A. 1994; PubMed Scopus Google Scholar), by M. at and S. at the of into expression The MAP kinase was from PI 3-kinase LY294002, was from and acid were from 3T3-L1 were cultured in containing and induced to into adipocytes by and as previously (8Moustaid N. Beyer R.S. Sul H.S. J. Biol. Chem. 1994; 269: 5629-5634Abstract Full Text PDF PubMed Google Scholar). 3T3-L1 with were by with the into 3T3-L1 and (10Wang D. Sul H.S. J. Biol. Chem. 1997; 272: 26367-26374Abstract Full Text Full Text PDF PubMed Scopus (128) Google Scholar). transfection of 3T3-L1 adipocytes was in for using the H. K. in as previously (8Moustaid N. Beyer R.S. Sul H.S. J. Biol. Chem. 1994; 269: 5629-5634Abstract Full Text PDF PubMed Google Scholar). using the inhibitors for various signaling molecules, the of the of of or was as the negative of inhibitors at in the were to 3T3-L1 adipocytes for a second of inhibitors was of insulin activities were of transfection in transfection and insulin in the a of the FAS sequence J.D. Sul H.S. Biochem. Biophys. Res. Commun. 1989; 158: 690-695Crossref PubMed Scopus (27) Google was with and using the high The reaction was with and and into the to in was by in vitro transcription of using and insulin from was from the 3T3-L1 adipocytes cultured in the and the absence of various of the PI 3-kinase LY294002 using the of were to the RNase protection using the from the The in was on a in The was and to at 3T3-L1 adipocytes were with of the wild-type PKB/Akt expression and of or the were in for and then with insulin for The in cell was with and the kinase activity was as previously A. Kavanaugh W.M. D. Williams L.T. Biol. 1997; PubMed Scopus Google using as a substrate K. A. D.K. D.R. 1995; Full Text PDF PubMed Scopus Google Scholar). The reaction was to and to for we demonstrated that the insulin regulation of FAS transcription is mediated by the proximal promoter at −68/−52 and that USF binding to the E-box motif within is required for the insulin regulation (8Moustaid N. Beyer R.S. Sul H.S. J. Biol. Chem. 1994; 269: 5629-5634Abstract Full Text PDF PubMed Google Scholar, D. Sul H.S. J. Biol. Chem. 1997; 272: 26367-26374Abstract Full Text Full Text PDF PubMed Scopus (128) Google Scholar). As we reported the reporter gene contains the FAS promoter region to that insulin response (8Moustaid N. Beyer R.S. Sul H.S. J. Biol. Chem. 1994; 269: 5629-5634Abstract Full Text PDF PubMed Google Scholar). In USF further insulin-stimulated promoter activity when is in transfection assays (10Wang D. Sul H.S. J. Biol. Chem. 1997; 272: 26367-26374Abstract Full Text Full Text PDF PubMed Scopus (128) Google Scholar). the signaling pathways involved in the insulin regulation of FAS we inhibitors for various insulin signaling pathways to effects on the insulin stimulation of FAS The inhibitors were for effects in 3T3-L1 adipocytes with the insulin is a of phosphorylation we acid M. H. H. S. M. M. M. K. K. S. A. 1988; PubMed Scopus Google Scholar, J. D.G. Cohen P. FEBS Lett. 1989; PubMed Scopus Google Scholar). As shown in insulin the FAS promoter activity in the and as we reported previously (10Wang D. Sul H.S. J. Biol. Chem. 1997; 272: 26367-26374Abstract Full Text Full Text PDF PubMed Scopus (128) Google Scholar). 3T3-L1 adipocytes with of acid the in the and absence of to a level of of the insulin FAS promoter activity in the that phosphorylation of is involved in the stimulation of FAS promoter activity by insulin. we wortmannin and to the of PI 3-kinase and P70 S6 kinase, which are of the insulin-stimulated in the insulin stimulation. rapamycin, an that inhibits P70 S6 kinase J. Science. PubMed Scopus Google Scholar), and a effect on FAS promoter activity in the absence and the of insulin On the other hand, of a specific PI 3-kinase A. Biochem. J. 1993; PubMed Scopus Google Scholar, J. PubMed Scopus Google Scholar), decreased FAS promoter activity in the absence and the of insulin. Insulin FAS promoter activity in the of wortmannin was that of the in the absence of wortmannin In insulin responsiveness was decreased by the wortmannin These results that PI 3-kinase activity by wortmannin with the insulin stimulation of FAS promoter activity. the which the of PI 3-kinase in the insulin regulation of FAS we further the effects of various inhibitors on the insulin regulation of the FAS gene in a promoter of in 3T3-L1 adipocytes. using mice demonstrated that the contains the that insulin response in M. Sul H.S. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar). We the specific PI 3-kinase LY294002 J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google Scholar), which is from to the of PI 3-kinase as as the MAP kinase PD98059 K. P. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar). As shown in the and in and for the inhibitors resulted in a in the promoter activity by insulin acid increased the promoter activity in the of insulin. In the of PD98059 or insulin responsiveness of the FAS promoter was to those in the 3T3-L1 adipocytes with LY294002 resulted in a decrease in the insulin activity to of the activity in the absence of insulin These results are with those in that PI 3-kinase, MAP kinase or P70 S6 kinase, is involved in the insulin stimulation of FAS The results demonstrate that the PI 3-kinase pathway is involved in insulin stimulation of the FAS promoter in transfection of the 3T3-L1 adipocytes. further the of PI 3-kinase in the regulation of FAS gene we RNase protection assays to the effect of LY294002 on the insulin regulation of endogenous FAS mRNA 3T3-L1 adipocytes were with of LY294002 for and then with insulin for As shown in 3T3-L1 with LY294002 at of or the of FAS mRNA levels by insulin. with the effect of LY294002 in insulin-stimulated FAS promoter activity in we that a of LY294002 inhibited the endogenous FAS mRNA levels the FAS promoter to the for transfection assays that for of the endogenous mRNA these results that the PI 3-kinase pathway is required for the insulin stimulation of the FAS PI 3-kinase activation of PI 3-kinase FAS promoter activity. In the increased FAS promoter activity PI 3-kinase is a downstream of insulin binding to its we cotransfected expression vectors for the constitutively active and the kinase-dead catalytic subunit with the reporter into 3T3-L1 adipocytes. contains the iSH2 region of P85 at its that the by the binding A. Reinhard C. Kavanaugh W.M. Apell G. Escobedo M.A. Williams L.T. Biol. 1996; 16: PubMed Scopus Google Scholar, A. Williams L.T. Science. 1995; PubMed Scopus Google Scholar). These P110 expression vectors have by other to demonstrate of PI 3-kinase in such as glucose transport A. Reinhard C. Kavanaugh W.M. Apell G. Escobedo M.A. Williams L.T. Biol. 1996; 16: PubMed Scopus Google Scholar, A. Williams L.T. Science. 1995; PubMed Scopus Google Scholar). As shown in cotransfection of at to resulted in elevated FAS promoter activities to which are to the insulin activity when was Furthermore, FAS promoter activity further insulin On the other hand, cotransfection of the kinase-dead at the effect on the insulin stimulation of FAS promoter activity. These results the PI 3-kinase activity is required for insulin stimulation of the FAS promoter. the is mutated in the other such as the P85 interacting domain are the to with the endogenous P110 subunit for on the membrane and the decrease of the promoter activity in In the of insulin P85 regulatory subunit of PI 3-kinase recruits the P110 catalytic subunit to the negative which the binding of was shown to inhibit insulin by the recruitment of P110 H. K. M. Biol. 1995; PubMed Scopus Google Scholar, K. K. H. A. K. H. L. Hawkins P.T. M. S. A. 1994; PubMed Scopus Google Scholar). further that PI 3-kinase the insulin stimulation of the FAS we cotransfected dominant negative and wild-type P85 subunit with the reporter into 3T3-L1 adipocytes. Cotransfection of and effect on FAS promoter activity its responsiveness as shown in Cotransfection of the dominant negative P85 resulted in decrease in FAS promoter activity Furthermore, insulin responsiveness of the FAS promoter was in the dominant negative P85 These strongly that PI 3-kinase activity is required for the insulin stimulation of FAS PKB/Akt was suggested to a major downstream of the PI 3-kinase in the insulin signaling pathway 1995; PubMed Scopus Google Scholar, K. A. D.K. D.R. 1995; Full Text PDF PubMed Scopus Google Scholar). serine-threonine kinase was suggested to involved in the insulin stimulation of glucose glycogen protein and expression K. K. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, H. L. M.A. 1997; PubMed Google Scholar, S. A. S. A. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). is also involved in the insulin stimulation of the FAS we cotransfected expression vectors for the wild-type and kinase-dead PKB/Akt with the into 3T3-L1 adipocytes. The expression with the PKB/Akt sequence was as a As shown in cotransfection of the and a insulin stimulation of FAS promoter activity. Cotransfection of the wild-type PKB/Akt resulted in stimulation of FAS promoter activity in the and absence of insulin. Insulin further promoter activity when wild-type PKB/Akt was cotransfected and The effects with wild-type PKB/Akt are to those when the constitutively active P110 subunit of PI 3-kinase was cotransfected of the kinase-dead PKB/Akt inhibited FAS promoter activity by Furthermore, of abolished the insulin stimulation of the FAS promoter activity cotransfected with the expression the wild-type PKB/Akt, abolished the insulin stimulation of the wild-type PKB/Akt activity and On the other hand, that the effect of on wild-type PKB/Akt is specific had effect on the insulin stimulation of the MAP as by the in vitro MAP kinase activity kinase-dead containing a acid within the domain K. K. H. A. K. H. L. Hawkins P.T. M. S. A. 1994; PubMed Scopus Google was reported to to insulin-stimulated H. L. M.A. 1997; PubMed Google Scholar). kinase-dead PKB/Akt that the to was also reported to a dominant negative PKB/Akt to the insulin stimulation of phosphorylation of the M.A. N. N. 1998; PubMed Scopus Google Scholar). these that is a downstream of PI 3-kinase in the insulin regulation of FAS insulin is is an in lipogenesis in and adipose These in coordination with the in glucose by peripheral tissues such as muscle and adipose tissue, with of gluconeogenesis and and in lipogenesis is when insulin is and of insulin the rate to its FAS is a and insulin increases its activity through or through in transcription (5Paulauskis J.D. Sul H.S. J. Biol. Chem. 1988; 263: 7049-7054Abstract Full Text PDF PubMed Google Scholar, 6Paulauskis J.D. Sul H.S. Biochem. Biophys. Res. Commun. 1989; 158: 690-695Crossref PubMed Scopus (27) Google Scholar). and high level of the FAS gene by insulin FAS an for the transcriptional activation of by insulin. we had the FAS insulin response sequence to the proximal promoter region at −68/−52 and had shown that USF binding to the E-box motif within region is functionally required for insulin stimulation of FAS the signaling that to the in lipogenesis or the activation of by insulin is In we that the PI 3-kinase signaling the P70 S6 kinase the MAP kinase the insulin effect on FAS of PI 3-kinase and abolished the insulin stimulation of endogenous FAS mRNA as as the FAS in 3T3-L1 adipocytes of the constitutively active P110 catalytic subunit of PI 3-kinase resulted in the loss of insulin responsiveness of the FAS promoter at an elevated activity level of the dominant negative P85 regulatory subunit also resulted in loss of insulin responsiveness of the FAS at a activity level effects on the insulin responsiveness of FAS promoter were also when wild-type and kinase-dead PKB/Akt were PKB/Akt is a downstream of the insulin stimulation of the FAS transcription is the to that the of the PI 3-kinase and PKB/Akt signaling pathway in the transcriptional regulation of that PI 3-kinase is involved in the stimulation of glucose glycogen and of also in the stimulation of lipogenesis. It also that the effect of PI 3-kinase is a major of the insulin signaling pathways that the insulin effect at levels of gene including of transcription stimulation of FAS and of phosphorylation of glycogen and of the MAP kinase activity by PD98059 had effect on insulin stimulation of the FAS that the MAP kinase which plays an important role in the of is to involved in insulin stimulation of lipogenesis. the results in is suggested that PKB/Akt is the downstream of the insulin stimulation of FAS further of signaling pathway We previously reported that binding of the helix-loop-helix transcription factor USF to the insulin response sequence of the FAS gene is required for insulin regulation (10Wang D. Sul H.S. J. Biol. Chem. 1997; 272: 26367-26374Abstract Full Text Full Text PDF PubMed Scopus (128) Google Scholar), thus on the regulation of USF by a It is that USF is by phosphorylation or a protein is by In including H. J. 1998; PubMed Scopus Google Scholar), P. C. M. H. A. H. 1997; PubMed Scopus Google Scholar), C. Biochem. Biophys. Res. Commun. 1997; PubMed Scopus Google Scholar), and M.A. Science. PubMed Scopus Google Scholar), which are to were reported to to with USF and are the for regulation by phosphorylation of of these USF interacting plays a role in stimulation of transcription by USF further of these USF interacting is required for insulin regulation of FAS promoter to We M. J. and M. for the P85 expression L. Williams and A. for the P110 and PKB/Akt expression We also L. Williams for on using the PKB/Akt expression vectors in