Regulation of Stearoyl-CoA Desaturase 1 mRNA Stability by Polyunsaturated Fatty Acids in 3T3-L1 Adipocytes
1996; Elsevier BV; Volume: 271; Issue: 47 Linguagem: Inglês
10.1074/jbc.271.47.29854
ISSN1083-351X
AutoresAnna M. Sessler, Navjot Kaur, Jiwan P. Palta, James M. Ntambi,
Tópico(s)Peroxisome Proliferator-Activated Receptors
ResumoThe effects of arachidonic acid (20:4, n-6) and other fatty acids on the expression of stearoyl-CoA desaturase gene 1 were investigated in fully differentiated 3T3-L1 adipocytes. Treatment of 3T3-L1 adipocytes with arachidonic acid resulted in a decrease in stearoyl-CoA desaturase (Scd) enzyme activity and scd1 mRNA. Arachidonic acid did not alter the transcription of the scd1 gene, whereas the half-life of the scd1 mRNA was reduced from 25.1 to 8.5 h. Blocking the conversion of arachidonic acid to eicosanoids by pretreatment of the cells with cyclooxygenase, lipoxygenase, or cytochrome P-450 epoxygenase inhibitors did not reverse the inhibition caused by arachidonic acid, indicating that eicosanoid synthesis is not necessary for the repression of scd1 mRNA expression. Treatment of adipocytes with linoleic (18:2, n-6) and linolenic (18:3, n-3) acids also resulted in inhibition of scd1 mRNA accumulation. By contrast, oleic acid (18:1, n-9) and stearic acid (18:0) had no effect on scd1 mRNA levels. Taken together, these results suggest that polyunsaturated fatty acids repress the expression of the scd1 gene in mature adipocytes by reducing the stability of scd1 mRNA. The effects of arachidonic acid (20:4, n-6) and other fatty acids on the expression of stearoyl-CoA desaturase gene 1 were investigated in fully differentiated 3T3-L1 adipocytes. Treatment of 3T3-L1 adipocytes with arachidonic acid resulted in a decrease in stearoyl-CoA desaturase (Scd) enzyme activity and scd1 mRNA. Arachidonic acid did not alter the transcription of the scd1 gene, whereas the half-life of the scd1 mRNA was reduced from 25.1 to 8.5 h. Blocking the conversion of arachidonic acid to eicosanoids by pretreatment of the cells with cyclooxygenase, lipoxygenase, or cytochrome P-450 epoxygenase inhibitors did not reverse the inhibition caused by arachidonic acid, indicating that eicosanoid synthesis is not necessary for the repression of scd1 mRNA expression. Treatment of adipocytes with linoleic (18:2, n-6) and linolenic (18:3, n-3) acids also resulted in inhibition of scd1 mRNA accumulation. By contrast, oleic acid (18:1, n-9) and stearic acid (18:0) had no effect on scd1 mRNA levels. Taken together, these results suggest that polyunsaturated fatty acids repress the expression of the scd1 gene in mature adipocytes by reducing the stability of scd1 mRNA. INTRODUCTIONThe mouse embryo 3T3-L1 preadipocytes (1Green H. Kehinde O. Cell. 1974; 1: 113-116Abstract Full Text PDF Scopus (737) Google Scholar, 2Green H. Kehinde O. Cell. 1975; 5: 19-27Abstract Full Text PDF PubMed Scopus (1084) Google Scholar, 3Green H. Kehinde O. Cell. 1976; 7: 105-113Abstract Full Text PDF PubMed Scopus (612) Google Scholar, 4Green H. Meuth M. Cell. 1974; 3: 127-133Abstract Full Text PDF PubMed Scopus (809) Google Scholar) represent a useful model system for studying the mechanisms of cellular differentiation and development. Under appropriate stimuli, these cells differentiate in culture into cells possessing the morphological and biochemical characteristics of adipocytes (5Mackall J.C. Student A.K. Polakis S.E. Lane M.D. J. Biol. Chem. 1976; 251: 6462-6464Abstract Full Text PDF PubMed Google Scholar, 6Coleman R.A. Reed B.C. Mackall J.C. Student A.K. Lane M.D. Bell R.M. J. Biol. Chem. 1978; 253: 7256-7261Abstract Full Text PDF PubMed Google Scholar, 7Student A.K. Hsu R.Y. Lane M.D. J. Biol. Chem. 1980; 255: 4745-4750Abstract Full Text PDF PubMed Google Scholar, 8Reed B.C. Lane M.D. Proc. Natl. Acad. Sci. U. S. A. 1980; 77: 285-289Crossref PubMed Scopus (161) Google Scholar, 9Rosen O.M. Smith C.J. Hirsch A. Lai E. Rubin C.S. Recent Prog. Horm. Res. 1979; 35: 477-499PubMed Google Scholar, 10Cornelius P. MacDougald O.A. Lane M.D. Annu. Rev. Nutr. 1994; 14: 99-129Crossref PubMed Scopus (572) Google Scholar, 11Green H. Kehinde O. J. Cell. Physiol. 1979; 101: 169-171Crossref PubMed Scopus (232) Google Scholar). Accompanying acquisition of the adipocyte phenotype, the cells become responsive to both lipogenic (insulin) and lipolytic (ACTH) hormones (10Cornelius P. MacDougald O.A. Lane M.D. Annu. Rev. Nutr. 1994; 14: 99-129Crossref PubMed Scopus (572) Google Scholar, 12Kasturi R. Joshi V.C. J. Biol. Chem. 1982; 257: 12224-12230Abstract Full Text PDF PubMed Google Scholar) and acquire increased levels of enzymes of the glycolytic, lipogenic, and lipolytic pathways (5Mackall J.C. Student A.K. Polakis S.E. Lane M.D. J. Biol. Chem. 1976; 251: 6462-6464Abstract Full Text PDF PubMed Google Scholar, 7Student A.K. Hsu R.Y. Lane M.D. J. Biol. Chem. 1980; 255: 4745-4750Abstract Full Text PDF PubMed Google Scholar, 10Cornelius P. MacDougald O.A. Lane M.D. Annu. Rev. Nutr. 1994; 14: 99-129Crossref PubMed Scopus (572) Google Scholar, 12Kasturi R. Joshi V.C. J. Biol. Chem. 1982; 257: 12224-12230Abstract Full Text PDF PubMed Google Scholar) as well as other adipocyte-specific proteins such as stearoyl-CoA desaturase (13Weiner F.R. Smith P.J. Wertheimer S. Rubin C.S. J. Biol. Chem. 1991; 266: 23525-23528Abstract Full Text PDF PubMed Google Scholar, 14Ntambi J.M. Buhrow S.A. Kaestner K.H. Christy R.J. Sibley E. Kelly Jr., T.J. Lane M.D. J. Biol. Chem. 1988; 263: 17291-17300Abstract Full Text PDF PubMed Google Scholar), the insulin receptor (8Reed B.C. Lane M.D. Proc. Natl. Acad. Sci. U. S. A. 1980; 77: 285-289Crossref PubMed Scopus (161) Google Scholar, 15Reed B.C. Ronnett G.V. Clements P.R. Lane M.D. J. Biol. Chem. 1981; 256: 3917-3925Abstract Full Text PDF PubMed Google Scholar), and myelin aP2 (16Bernlohr D.A. Angus C.W. Lane M.D. Bolanowski M.A. Kelly Jr., T.J. Proc. Natl. Acad. Sci. U. S. A. 1984; 81: 5468-5472Crossref PubMed Scopus (240) Google Scholar), which are expressed at high levels in adipocytes.Over the years, several differentiation-induced genes have been isolated and characterized, and their promoters have been analyzed (14Ntambi J.M. Buhrow S.A. Kaestner K.H. Christy R.J. Sibley E. Kelly Jr., T.J. Lane M.D. J. Biol. Chem. 1988; 263: 17291-17300Abstract Full Text PDF PubMed Google Scholar, 17Kaestner K.H. Ntambi J.M. Kelly Jr., T.J. Lane D.M. J. Biol. Chem. 1989; 264: 14755-14761Abstract Full Text PDF PubMed Google Scholar, 18Christy R.J. Yang V.W. Ntambi J.M. Geiman D.E. Landschulz W.H. Friedman A.D. Nakabeppu Y. Kelly T.J. Lane M.D. Genes Dev. 1989; 3: 1323-1335Crossref PubMed Scopus (464) Google Scholar). Two of these genes, stearoyl-CoA desaturase 1 and 2 (scd1 and scd2) (14Ntambi J.M. Buhrow S.A. Kaestner K.H. Christy R.J. Sibley E. Kelly Jr., T.J. Lane M.D. J. Biol. Chem. 1988; 263: 17291-17300Abstract Full Text PDF PubMed Google Scholar, 17Kaestner K.H. Ntambi J.M. Kelly Jr., T.J. Lane D.M. J. Biol. Chem. 1989; 264: 14755-14761Abstract Full Text PDF PubMed Google Scholar), encode two isozymes of stearoyl-CoA desaturase, a key enzyme involved in the biosynthesis of unsaturated fatty acids as well as the regulation of this process. The enzyme activity increases 20-100-fold during the differentiation of 3T3-L1 preadipocytes (12Kasturi R. Joshi V.C. J. Biol. Chem. 1982; 257: 12224-12230Abstract Full Text PDF PubMed Google Scholar). This increase is primarily due to increased transcription of the scd genes (14Ntambi J.M. Buhrow S.A. Kaestner K.H. Christy R.J. Sibley E. Kelly Jr., T.J. Lane M.D. J. Biol. Chem. 1988; 263: 17291-17300Abstract Full Text PDF PubMed Google Scholar, 19Bernlohr D.A. Bolanowski M.A. Kelly Jr., T.J. Lane M.D. J. Biol. Chem. 1985; 260: 5563-5567Abstract Full Text PDF PubMed Google Scholar). The enzyme catalyzes the Δ9-cis desaturation of fatty acyl-CoAs (20Enoch H.G. Catala A. Strittmatter P. J. Biol. Chem. 1976; 251: 5095-5103Abstract Full Text PDF PubMed Google Scholar); the predominant products are palmitoleoyl- and oleoyl-CoA. Palmitoleic and oleic acids are the major constituents of membrane phospholipids and triacylglycerol stores found in adipocytes (12Kasturi R. Joshi V.C. J. Biol. Chem. 1982; 257: 12224-12230Abstract Full Text PDF PubMed Google Scholar). The ratio of stearic acid to oleic acid is one of the factors influencing cell membrane fluidity. Alteration of this ratio is implicated in aging, obesity, and various diseases such as cancer, diabetes, and heart disease (21Jeffcoat R. Essays Biochem. 1979; 15: 1-36PubMed Google Scholar, 22Clandinin M.T. Cheema S. Field C.J. Garg M.L. Benkatraman J. Clandinin T.R. FASEB J. 1991; 5: 2761-2769Crossref PubMed Scopus (242) Google Scholar, 23Spector A.A. Yorek M.A. J. Lipid Res. 1985; 26: 1015-1035Abstract Full Text PDF PubMed Google Scholar).Several studies using rat liver primary cultures and intact animals have established that genes encoding both glycolytic and lipogenic enzymes are regulated by dietary fatty acids (24Tebbey P.W. McGowan K.M. Stephens J.M. Buttke T.M. Pekala P.H. J. Biol. Chem. 1994; 269: 639-644Abstract Full Text PDF PubMed Google Scholar, 25Clarke S.D. Armstrong M.K. Jump D.B. J. Nutr. 1990; 120: 225-231Crossref PubMed Scopus (168) Google Scholar, 26Jump D.B. Clarke S.D. Thelen A. Liimatta M. J. Lipid Res. 1994; 35: 1076-1084Abstract Full Text PDF PubMed Google Scholar, 27Clarke S.D. Jump D.B. Annu. Rev. Nutr. 1994; 14: 83-98Crossref PubMed Scopus (267) Google Scholar, 28Liimatta M. Towle H.C. Clarke S.D. Jump D.B. Mol. Endocrinol. 1994; 8: 1147-1153PubMed Google Scholar, 29Ntambi J.M. J. Biol. Chem. 1992; 267: 10925-10930Abstract Full Text PDF PubMed Google Scholar). Polyunsaturated fatty acids (PUFAs), 1The abbreviations used are: PUFApolyunsaturated fatty acidAAarachidonic acidPIPES1,4-piperazinediethanesulfonic acidSCDstearoyl-CoA desaturase. particularly the ω-6 and ω-3 series, repress the transcription of genes such as malic enzyme, acetyl-CoA carboxylase, fatty acid synthase (FAS), glucose transporter 4 (GLUT4), S14 protein, and scd1 (24Tebbey P.W. McGowan K.M. Stephens J.M. Buttke T.M. Pekala P.H. J. Biol. Chem. 1994; 269: 639-644Abstract Full Text PDF PubMed Google Scholar, 25Clarke S.D. Armstrong M.K. Jump D.B. J. Nutr. 1990; 120: 225-231Crossref PubMed Scopus (168) Google Scholar, 26Jump D.B. Clarke S.D. Thelen A. Liimatta M. J. Lipid Res. 1994; 35: 1076-1084Abstract Full Text PDF PubMed Google Scholar, 27Clarke S.D. Jump D.B. Annu. Rev. Nutr. 1994; 14: 83-98Crossref PubMed Scopus (267) Google Scholar, 30Landschulz K.T. Jump D.B. MacDougald O.A. Lane M.D. Biochem. Biophys. Res. Commun. 1994; 200: 763-768Crossref PubMed Scopus (116) Google Scholar, 31Clarke S.D. Jump D.B. Prog. Lipid Res. 1993; 32: 139-149Crossref PubMed Scopus (134) Google Scholar, 32Salati L.M. Clarke S.D. Arch. Biochem. Biophys. 1986; 246: 82-89Crossref PubMed Scopus (49) Google Scholar). Saturated and monounsaturated fatty acids have no effect on the transcription of these genes.Liver and adipose tissue are the two major tissues involved in lipid biosynthesis. Although the regulation of lipogenic gene expression by PUFAs in liver is currently being studied, the effects of these molecules on gene expression in mature, fully differentiated adipocytes have not been extensively investigated. In view of the potential role of polyunsaturated fatty acids in regulating total fatty acid synthesis and the role stearoyl-CoA desaturase plays in this process, we examined the effect of polyunsaturated fatty acids on the expression of the scd1 gene in mature adipocytes. Our results suggest that PUFAs regulate the expression of the adipocyte scd1 gene by regulating stability of mRNA transcripts.DISCUSSIONIn the present study, we have demonstrated that exposure of 3T3-L1 adipocytes to 300 μM arachidonic acid results in a decrease in Scd enzyme activity as well as scd1 mRNA levels (Fig. 1, Fig. 2). As much as a 60% decrease in enzyme activity was observed, whereas mRNA levels were repressed by 80% of the original level. Treatment of 3T3-L1 adipocytes with AA also caused a 3-fold decrease in the half-life of scd1 mRNA (Fig. 5) and no apparent decrease in scd1 gene transcription. The pretranslational regulation of scd1 gene expression by PUFAs seems, then, to result primarily from the decrease of mRNA stability. Furthermore, the repression was independent of AA metabolism to eicosanoids because cyclooxygenase, lipoxygenase, and epoxygenase inhibitors did not abolish the effect (Fig. 6). Other polyunsaturated fatty acids, such as linoleic, linolenic, and eicosapentaeinoic acids, also decreased the scd1 mRNA levels when added exogenously to mature adipocytes. By contrast, oleic acid (Fig. 7) and stearic acid did not decrease scd1 mRNA levels; therefore, this response is unique to polyunsaturated fatty acids.Stearoyl-CoA desaturase gene expression has previously been shown to be repressed by polyunsaturated fatty acids in liver tissue principally at the level of gene transcription (29Ntambi J.M. J. Biol. Chem. 1992; 267: 10925-10930Abstract Full Text PDF PubMed Google Scholar, 30Landschulz K.T. Jump D.B. MacDougald O.A. Lane M.D. Biochem. Biophys. Res. Commun. 1994; 200: 763-768Crossref PubMed Scopus (116) Google Scholar). Until now, the effect of polyunsaturated fatty acids on scd1 gene expression in adipose tissue had not been studied. The rate of transcription from the scd1 gene was not dramatically affected in this adipocyte system. Although transcriptional regulation can not be completely ruled out by these experiments, changes in transcription that are below detectable levels suggest that transcriptional regulation does not play a significant role in PUFA suppression of adipocyte scd1 gene expression. Our results also suggest that posttranslational regulation is not a major factor in AA-mediated scd1 repression. The observed reduction in enzyme activity (60%) could be completely accounted for by decreases in scd1 mRNA levels (80%). Thus, there seems to be no additional down-regulation occurring posttranslationally. As opposed to hepatocytes, changes in mRNA stability are the major determinant of scd1 mRNA abundance in adipocytes.Destabilization of mRNA encoding the predominantly expressed form of stearoyl-CoA desaturase in adipocytes may be regulated through mRNA sequences in the 3′ untranslated region. Both the mouse and rat scd1 cDNAs contain an unusually long 3′ untranslated region (14Ntambi J.M. Buhrow S.A. Kaestner K.H. Christy R.J. Sibley E. Kelly Jr., T.J. Lane M.D. J. Biol. Chem. 1988; 263: 17291-17300Abstract Full Text PDF PubMed Google Scholar, 41Theide M.A. Ozols J. Strittmatter P. J. Biol. Chem. 1986; 261: 13230-13235Abstract Full Text PDF PubMed Google Scholar). The role of such a long 3′-noncoding stretch is currently unknown, though it contains several structural motifs (AUUUA) characteristic of mRNA destabilization sequences (42Long S.D. Pekala P.H. Biochem. Biophys. Res. Commun. 1996; 220: 949-953Crossref PubMed Scopus (26) Google Scholar, 43Marzulff W.F. Genes Exp. 1992; 2: 93-97PubMed Google Scholar). Four of these sequences are clustered close to the 3′ end of the coding region (Fig. 8). Because these AU-rich elements play active roles in the selective degradation of several mRNAs in response to various factors, these sequences could be possible targets of PUFA effects on scd1 mRNA (44Alberta J.A. Rundell K. Stiles C.D. J. Biol. Chem. 1994; 269: 4532-4538Abstract Full Text PDF PubMed Google Scholar, 45Shyu A. Belasco J.G. Greenberg M.E. Genes Dev. 1991; 5: 221-231Crossref PubMed Scopus (400) Google Scholar, 46Wolford J.K. Signs S.A. Biochem. Biophys. Res. Commun. 1995; 211: 819-825Crossref PubMed Scopus (4) Google Scholar, 47Shaw G. Kamen R. Cell. 1986; 46: 659-667Abstract Full Text PDF PubMed Scopus (3107) Google Scholar). For example, Pekala and Long (42Long S.D. Pekala P.H. Biochem. Biophys. Res. Commun. 1996; 220: 949-953Crossref PubMed Scopus (26) Google Scholar) have suggested that such a motif in the GLUT4 gene expressed in 3T3-L1 adipocytes may confer destabilization of mRNA in response to tumor necrosis factor α treatment. With such generalized effects of AU-rich elements, it is possible to speculate that this motif plays a role in the adipocyte regulation of desaturase gene expression by regulating mRNA stability in response to PUFAs. Additional mapping studies would be necessary to identify whether the AU-rich elements in the scd1 3′ untranslated region are involved in this destabilization.The nature of the PUFA metabolite that mediates the observed mRNA destabilization is currently unknown. As demonstrated in the present study, inhibiting eicosanoid synthesis (Fig. 6) did not prevent the PUFA suppression of scd1 gene expression. Consistent with other studies on PUFA-regulated genes (25Clarke S.D. Armstrong M.K. Jump D.B. J. Nutr. 1990; 120: 225-231Crossref PubMed Scopus (168) Google Scholar, 27Clarke S.D. Jump D.B. Annu. Rev. Nutr. 1994; 14: 83-98Crossref PubMed Scopus (267) Google Scholar, 31Clarke S.D. Jump D.B. Prog. Lipid Res. 1993; 32: 139-149Crossref PubMed Scopus (134) Google Scholar, 48Schwartz R.S. Abraham S. Biochim. Biophys. Acta. 1982; 711: 316-326Crossref PubMed Scopus (34) Google Scholar), our investigations of AA-oxidative metabolism suggest that the products of eicosanoid synthesis are not involved in the AA-mediated decrease of scd1 mRNA stability in 3T3-L1 adipocytes. Furthermore, the desaturase gene is regulated by a range of polyunsaturated acids and not by mono- or unsaturated fatty acids (Fig. 7), suggesting that repression is PUFA-specific.The data presented here suggest that PUFAs regulate scd1 gene expression through different mechanisms in different tissue types, the reasons for which are not yet understood. However, scd1 provides a good model to study the effects of PUFAs on mRNA stability. The ongoing search, in our lab and others, for possible protein mediators that destabilize scd1 mRNA may provide further definition to the molecular basis of PUFA regulation of lipogenic gene expression. INTRODUCTIONThe mouse embryo 3T3-L1 preadipocytes (1Green H. Kehinde O. Cell. 1974; 1: 113-116Abstract Full Text PDF Scopus (737) Google Scholar, 2Green H. Kehinde O. Cell. 1975; 5: 19-27Abstract Full Text PDF PubMed Scopus (1084) Google Scholar, 3Green H. Kehinde O. Cell. 1976; 7: 105-113Abstract Full Text PDF PubMed Scopus (612) Google Scholar, 4Green H. Meuth M. Cell. 1974; 3: 127-133Abstract Full Text PDF PubMed Scopus (809) Google Scholar) represent a useful model system for studying the mechanisms of cellular differentiation and development. Under appropriate stimuli, these cells differentiate in culture into cells possessing the morphological and biochemical characteristics of adipocytes (5Mackall J.C. Student A.K. Polakis S.E. Lane M.D. J. Biol. Chem. 1976; 251: 6462-6464Abstract Full Text PDF PubMed Google Scholar, 6Coleman R.A. Reed B.C. Mackall J.C. Student A.K. Lane M.D. Bell R.M. J. Biol. Chem. 1978; 253: 7256-7261Abstract Full Text PDF PubMed Google Scholar, 7Student A.K. Hsu R.Y. Lane M.D. J. Biol. Chem. 1980; 255: 4745-4750Abstract Full Text PDF PubMed Google Scholar, 8Reed B.C. Lane M.D. Proc. Natl. Acad. Sci. U. S. A. 1980; 77: 285-289Crossref PubMed Scopus (161) Google Scholar, 9Rosen O.M. Smith C.J. Hirsch A. Lai E. Rubin C.S. Recent Prog. Horm. Res. 1979; 35: 477-499PubMed Google Scholar, 10Cornelius P. MacDougald O.A. Lane M.D. Annu. Rev. Nutr. 1994; 14: 99-129Crossref PubMed Scopus (572) Google Scholar, 11Green H. Kehinde O. J. Cell. Physiol. 1979; 101: 169-171Crossref PubMed Scopus (232) Google Scholar). Accompanying acquisition of the adipocyte phenotype, the cells become responsive to both lipogenic (insulin) and lipolytic (ACTH) hormones (10Cornelius P. MacDougald O.A. Lane M.D. Annu. Rev. Nutr. 1994; 14: 99-129Crossref PubMed Scopus (572) Google Scholar, 12Kasturi R. Joshi V.C. J. Biol. Chem. 1982; 257: 12224-12230Abstract Full Text PDF PubMed Google Scholar) and acquire increased levels of enzymes of the glycolytic, lipogenic, and lipolytic pathways (5Mackall J.C. Student A.K. Polakis S.E. Lane M.D. J. Biol. Chem. 1976; 251: 6462-6464Abstract Full Text PDF PubMed Google Scholar, 7Student A.K. Hsu R.Y. Lane M.D. J. Biol. Chem. 1980; 255: 4745-4750Abstract Full Text PDF PubMed Google Scholar, 10Cornelius P. MacDougald O.A. Lane M.D. Annu. Rev. Nutr. 1994; 14: 99-129Crossref PubMed Scopus (572) Google Scholar, 12Kasturi R. Joshi V.C. J. Biol. Chem. 1982; 257: 12224-12230Abstract Full Text PDF PubMed Google Scholar) as well as other adipocyte-specific proteins such as stearoyl-CoA desaturase (13Weiner F.R. Smith P.J. Wertheimer S. Rubin C.S. J. Biol. Chem. 1991; 266: 23525-23528Abstract Full Text PDF PubMed Google Scholar, 14Ntambi J.M. Buhrow S.A. Kaestner K.H. Christy R.J. Sibley E. Kelly Jr., T.J. Lane M.D. J. Biol. Chem. 1988; 263: 17291-17300Abstract Full Text PDF PubMed Google Scholar), the insulin receptor (8Reed B.C. Lane M.D. Proc. Natl. Acad. Sci. U. S. A. 1980; 77: 285-289Crossref PubMed Scopus (161) Google Scholar, 15Reed B.C. Ronnett G.V. Clements P.R. Lane M.D. J. Biol. Chem. 1981; 256: 3917-3925Abstract Full Text PDF PubMed Google Scholar), and myelin aP2 (16Bernlohr D.A. Angus C.W. Lane M.D. Bolanowski M.A. Kelly Jr., T.J. Proc. Natl. Acad. Sci. U. S. A. 1984; 81: 5468-5472Crossref PubMed Scopus (240) Google Scholar), which are expressed at high levels in adipocytes.Over the years, several differentiation-induced genes have been isolated and characterized, and their promoters have been analyzed (14Ntambi J.M. Buhrow S.A. Kaestner K.H. Christy R.J. Sibley E. Kelly Jr., T.J. Lane M.D. J. Biol. Chem. 1988; 263: 17291-17300Abstract Full Text PDF PubMed Google Scholar, 17Kaestner K.H. Ntambi J.M. Kelly Jr., T.J. Lane D.M. J. Biol. Chem. 1989; 264: 14755-14761Abstract Full Text PDF PubMed Google Scholar, 18Christy R.J. Yang V.W. Ntambi J.M. Geiman D.E. Landschulz W.H. Friedman A.D. Nakabeppu Y. Kelly T.J. Lane M.D. Genes Dev. 1989; 3: 1323-1335Crossref PubMed Scopus (464) Google Scholar). Two of these genes, stearoyl-CoA desaturase 1 and 2 (scd1 and scd2) (14Ntambi J.M. Buhrow S.A. Kaestner K.H. Christy R.J. Sibley E. Kelly Jr., T.J. Lane M.D. J. Biol. Chem. 1988; 263: 17291-17300Abstract Full Text PDF PubMed Google Scholar, 17Kaestner K.H. Ntambi J.M. Kelly Jr., T.J. Lane D.M. J. Biol. Chem. 1989; 264: 14755-14761Abstract Full Text PDF PubMed Google Scholar), encode two isozymes of stearoyl-CoA desaturase, a key enzyme involved in the biosynthesis of unsaturated fatty acids as well as the regulation of this process. The enzyme activity increases 20-100-fold during the differentiation of 3T3-L1 preadipocytes (12Kasturi R. Joshi V.C. J. Biol. Chem. 1982; 257: 12224-12230Abstract Full Text PDF PubMed Google Scholar). This increase is primarily due to increased transcription of the scd genes (14Ntambi J.M. Buhrow S.A. Kaestner K.H. Christy R.J. Sibley E. Kelly Jr., T.J. Lane M.D. J. Biol. Chem. 1988; 263: 17291-17300Abstract Full Text PDF PubMed Google Scholar, 19Bernlohr D.A. Bolanowski M.A. Kelly Jr., T.J. Lane M.D. J. Biol. Chem. 1985; 260: 5563-5567Abstract Full Text PDF PubMed Google Scholar). The enzyme catalyzes the Δ9-cis desaturation of fatty acyl-CoAs (20Enoch H.G. Catala A. Strittmatter P. J. Biol. Chem. 1976; 251: 5095-5103Abstract Full Text PDF PubMed Google Scholar); the predominant products are palmitoleoyl- and oleoyl-CoA. Palmitoleic and oleic acids are the major constituents of membrane phospholipids and triacylglycerol stores found in adipocytes (12Kasturi R. Joshi V.C. J. Biol. Chem. 1982; 257: 12224-12230Abstract Full Text PDF PubMed Google Scholar). The ratio of stearic acid to oleic acid is one of the factors influencing cell membrane fluidity. Alteration of this ratio is implicated in aging, obesity, and various diseases such as cancer, diabetes, and heart disease (21Jeffcoat R. Essays Biochem. 1979; 15: 1-36PubMed Google Scholar, 22Clandinin M.T. Cheema S. Field C.J. Garg M.L. Benkatraman J. Clandinin T.R. FASEB J. 1991; 5: 2761-2769Crossref PubMed Scopus (242) Google Scholar, 23Spector A.A. Yorek M.A. J. Lipid Res. 1985; 26: 1015-1035Abstract Full Text PDF PubMed Google Scholar).Several studies using rat liver primary cultures and intact animals have established that genes encoding both glycolytic and lipogenic enzymes are regulated by dietary fatty acids (24Tebbey P.W. McGowan K.M. Stephens J.M. Buttke T.M. Pekala P.H. J. Biol. Chem. 1994; 269: 639-644Abstract Full Text PDF PubMed Google Scholar, 25Clarke S.D. Armstrong M.K. Jump D.B. J. Nutr. 1990; 120: 225-231Crossref PubMed Scopus (168) Google Scholar, 26Jump D.B. Clarke S.D. Thelen A. Liimatta M. J. Lipid Res. 1994; 35: 1076-1084Abstract Full Text PDF PubMed Google Scholar, 27Clarke S.D. Jump D.B. Annu. Rev. Nutr. 1994; 14: 83-98Crossref PubMed Scopus (267) Google Scholar, 28Liimatta M. Towle H.C. Clarke S.D. Jump D.B. Mol. Endocrinol. 1994; 8: 1147-1153PubMed Google Scholar, 29Ntambi J.M. J. Biol. Chem. 1992; 267: 10925-10930Abstract Full Text PDF PubMed Google Scholar). Polyunsaturated fatty acids (PUFAs), 1The abbreviations used are: PUFApolyunsaturated fatty acidAAarachidonic acidPIPES1,4-piperazinediethanesulfonic acidSCDstearoyl-CoA desaturase. particularly the ω-6 and ω-3 series, repress the transcription of genes such as malic enzyme, acetyl-CoA carboxylase, fatty acid synthase (FAS), glucose transporter 4 (GLUT4), S14 protein, and scd1 (24Tebbey P.W. McGowan K.M. Stephens J.M. Buttke T.M. Pekala P.H. J. Biol. Chem. 1994; 269: 639-644Abstract Full Text PDF PubMed Google Scholar, 25Clarke S.D. Armstrong M.K. Jump D.B. J. Nutr. 1990; 120: 225-231Crossref PubMed Scopus (168) Google Scholar, 26Jump D.B. Clarke S.D. Thelen A. Liimatta M. J. Lipid Res. 1994; 35: 1076-1084Abstract Full Text PDF PubMed Google Scholar, 27Clarke S.D. Jump D.B. Annu. Rev. Nutr. 1994; 14: 83-98Crossref PubMed Scopus (267) Google Scholar, 30Landschulz K.T. Jump D.B. MacDougald O.A. Lane M.D. Biochem. Biophys. Res. Commun. 1994; 200: 763-768Crossref PubMed Scopus (116) Google Scholar, 31Clarke S.D. Jump D.B. Prog. Lipid Res. 1993; 32: 139-149Crossref PubMed Scopus (134) Google Scholar, 32Salati L.M. Clarke S.D. Arch. Biochem. Biophys. 1986; 246: 82-89Crossref PubMed Scopus (49) Google Scholar). Saturated and monounsaturated fatty acids have no effect on the transcription of these genes.Liver and adipose tissue are the two major tissues involved in lipid biosynthesis. Although the regulation of lipogenic gene expression by PUFAs in liver is currently being studied, the effects of these molecules on gene expression in mature, fully differentiated adipocytes have not been extensively investigated. In view of the potential role of polyunsaturated fatty acids in regulating total fatty acid synthesis and the role stearoyl-CoA desaturase plays in this process, we examined the effect of polyunsaturated fatty acids on the expression of the scd1 gene in mature adipocytes. Our results suggest that PUFAs regulate the expression of the adipocyte scd1 gene by regulating stability of mRNA transcripts.
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