Expression of Human Fibroblast Growth Factor 2 mRNA Is Post-transcriptionally Controlled by a Unique Destabilizing Element Present in the 3′-Untranslated Region between Alternative Polyadenylation Sites

Fibroblast growth factor 2 (FGF-2) belongs to a family of 18 genes coding for either mitogenic differentiating factors or oncogenic proteins, the expression of which must be tightly controlled. We looked for regulatory elements in the 5823-nucleotide-long 3′-untranslated region of the FGF-2 mRNA that contains eight potential alternative polyadenylation sites. Quantitative reverse transcription-polymerase chain reaction revealed that poly(A) site utilization was cell type-dependent, with the eighth poly(A) site being used (95%) in primary human skin fibroblasts, whereas proximal sites were used in the transformed cell lines studied here. We used a cell transfection approach with synthetic reporter mRNAs to localize a destabilizing element between the first and second poly(A) sites. Although AU-rich, the FGF-2-destabilizing element had unique features: it involved a 122-nucleotide direct repeat, with both elements of the repeat being required for the destabilizing activity. These data show that short stable FGF-2 mRNAs are present in transformed cells, whereas skin fibroblasts contain mostly long unstable mRNAs, suggesting that FGF-2 mRNA stability cannot be regulated in transformed cells. The results also provide evidence of a multilevel post-transcriptional control of FGF-2 expression; such a stringent control prevents FGF-2 overexpression and permits its expression to be enhanced only in relevant physiological situations. Fibroblast growth factor 2 (FGF-2) belongs to a family of 18 genes coding for either mitogenic differentiating factors or oncogenic proteins, the expression of which must be tightly controlled. We looked for regulatory elements in the 5823-nucleotide-long 3′-untranslated region of the FGF-2 mRNA that contains eight potential alternative polyadenylation sites. Quantitative reverse transcription-polymerase chain reaction revealed that poly(A) site utilization was cell type-dependent, with the eighth poly(A) site being used (95%) in primary human skin fibroblasts, whereas proximal sites were used in the transformed cell lines studied here. We used a cell transfection approach with synthetic reporter mRNAs to localize a destabilizing element between the first and second poly(A) sites. Although AU-rich, the FGF-2-destabilizing element had unique features: it involved a 122-nucleotide direct repeat, with both elements of the repeat being required for the destabilizing activity. These data show that short stable FGF-2 mRNAs are present in transformed cells, whereas skin fibroblasts contain mostly long unstable mRNAs, suggesting that FGF-2 mRNA stability cannot be regulated in transformed cells. The results also provide evidence of a multilevel post-transcriptional control of FGF-2 expression; such a stringent control prevents FGF-2 overexpression and permits its expression to be enhanced only in relevant physiological situations. Fibroblast growth factor 2 (FGF-2), 1The abbreviations used are: FGF-2, fibroblast growth factor 2; nt, nucleotide(s); UTR, untranslated region; ARE, AU-rich element; RT-PCR, reverse transcription-polymerase chain reaction; CAT, chloramphenicol acetyltransferase; GM-CSF, granulocyte/macrophage colony-stimulating factor; PBS, phosphate-buffered saline1The abbreviations used are: FGF-2, fibroblast growth factor 2; nt, nucleotide(s); UTR, untranslated region; ARE, AU-rich element; RT-PCR, reverse transcription-polymerase chain reaction; CAT, chloramphenicol acetyltransferase; GM-CSF, granulocyte/macrophage colony-stimulating factor; PBS, phosphate-buffered saline also known as the basic fibroblast growth factor, belongs to a family of 18 genes coding for either mitogenic differentiating factors or oncogenic proteins (1Mason I.J. Cell. 1994; 78: 547-552Abstract Full Text PDF PubMed Scopus (525) Google Scholar, 2Yamaguchi T.P. Rossant J. Curr. Opin. Genet. Dev. 1995; 5: 485-491Crossref PubMed Scopus (173) Google Scholar, 3Smallwood P.M. Munoz-Sanjuan I. Tong P. Macke J.P. Hendry S.H.C. Gilbert D.J. Copeland N.G. Jenkins N.A. Nathans J. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 9850-9857Crossref PubMed Scopus (334) Google Scholar, 4Hoshikawa M. Ohbayashi N. Yonamine A. Konishi M. Ozaki K. Fukui S. Itoh N. Biochem. Biophys. Res. Commun. 1998; 244: 187-191Crossref PubMed Scopus (89) Google Scholar, 5Ohbayashi N. Hoshikawa M. Kimura S. Yamasaki M. Fukui S. Itoh N. J. Biol. Chem. 1998; 273: 18161-18164Abstract Full Text Full Text PDF PubMed Scopus (138) Google Scholar). FGF-2 is produced in various cell types and tissues and has many biological roles. It is involved in embryogenesis and morphogenesis, especially in the nervous system and bone formation (6Wagner J.A. Curr. Top. Microbiol. Immunol. 1991; 165: 95-118PubMed Google Scholar,7Coffin J.D. Florkiewicz R.Z. Neumann J. Mort-Hopkins T. Dorn II, G.W. Lightfoot P. German R. Howles P.N. Kier A. O'Toole B.A. Sasse J. Gonzalez A.N. Baird A. Doetschman T. Mol. Biol. Cell. 1995; 6: 1861-1973Crossref PubMed Scopus (259) Google Scholar). FGF-2 is a major angiogenic factor, playing a crucial role in wound healing and in cardiovascular disease (8Yanagisawa-Miwa A. Uchida Y. Nakamura F. Tomaru T. Kido H. Kamijo T. Sugimoto T. Kaji K. Utsuyama M. Kurashima C. Ito H. Science. 1992; 257: 1401-1403Crossref PubMed Scopus (482) Google Scholar). It is also involved in cancer pathophysiology, notably in tumor neovascularization coupled with intrinsic oncogenic potential (9Kandel J. Bossy-Wetzel E. Radvanyi F. Klagsbrun M. Folkman J. Hanahan D. Cell. 1991; 66: 1095-1104Abstract Full Text PDF PubMed Scopus (477) Google Scholar, 10Couderc B. Prats H. Bayard F. Amalric F. Cell Regul. 1991; 2: 709-718Crossref PubMed Scopus (91) Google Scholar, 11Quarto N. Talarico D. Florkiewicz R. Rifkin D.B. Cell Regul. 1991; 2: 699-708Crossref PubMed Scopus (95) Google Scholar). FGF-2 expression is regulated both at the transcriptional level and more especially at the translational level. Its mRNA constitutes a complex example of alternative initiation of translation with five start codons that include four CUG codons (12Florkiewicz R.Z. Sommer A. Proc. Natl. Acad. Sci. U. S. A. 1989; 86: 3978-3981Crossref PubMed Scopus (446) Google Scholar, 13Prats H. Kaghad M. Prats A.-C. Klagsbrun M. Lélias J.M. Liauzun P. Chalon P. Tauber J.P. Amalric F. Smith J.A. Caput D. Proc. Natl. Acad. Sci. U. S. A. 1989; 86: 1836-1840Crossref PubMed Scopus (399) Google Scholar, 14Arnaud E. Touriol C. Boutonnet C. Gensac M.C. Vagner S. Prats H. Prats A.-C. Mol. Cell. Biol. 1999; 19: 505-514Crossref PubMed Scopus (174) Google Scholar). The five FGF-2 isoforms resulting from the alternative initiation process have different localizations and functions within the cell (10Couderc B. Prats H. Bayard F. Amalric F. Cell Regul. 1991; 2: 709-718Crossref PubMed Scopus (91) Google Scholar, 14Arnaud E. Touriol C. Boutonnet C. Gensac M.C. Vagner S. Prats H. Prats A.-C. Mol. Cell. Biol. 1999; 19: 505-514Crossref PubMed Scopus (174) Google Scholar, 15Bugler B. Amalric F. Prats H. Mol. Cell. Biol. 1991; 11: 573-577Crossref PubMed Scopus (304) Google Scholar, 16Brigstock D.R. Sasse J. Klagsbrun M. Growth Factors. 1991; 4: 189-196Crossref PubMed Scopus (37) Google Scholar, 17Bikfalvi A. Klein S. Pintucci G. Quarto N. Mignatti P. Rifkin D.B. J. Cell Biol. 1995; 129: 233-243Crossref PubMed Scopus (190) Google Scholar). The regulation of their expression is also different: the largest 34-kDa isoform is exclusively translated in a cap-dependent manner, whereas the other isoforms are translated by a process of internal ribosome entry mediated by an internal ribosome entry site located between the first and second CUG codons (14Arnaud E. Touriol C. Boutonnet C. Gensac M.C. Vagner S. Prats H. Prats A.-C. Mol. Cell. Biol. 1999; 19: 505-514Crossref PubMed Scopus (174) Google Scholar). In addition to its GC-rich 5′-region that contains an internal ribosome entry site as well as other elements able to regulate alternative initiation of translation (18Prats A.-C. Vagner S. Prats H. Amalric F. Mol. Cell. Biol. 1992; 12: 4796-4805Crossref PubMed Google Scholar, 19Vagner S. Gensac M.C. Maret A. Bayard F. Amalric F. Prats H. Prats A.-C. Mol. Cell. Biol. 1995; 15: 35-44Crossref PubMed Scopus (286) Google Scholar), the 6775-nt-long FGF-2 mRNA exhibits a very uncommon feature: it is 90% composed of untranslated regions due to the presence of a huge 3′-untranslated region. This AU-rich 5823-nt-long 3′-untranslated region is not only the longest 3′-UTR described to date, but also contains eight potential polyadenylation sites. The existence of more than three FGF-2 mRNA species reported in the literature (from 1 to 7 kilobases) would suggest that several of these poly(A) sites can be functional (20Bensaid M. Malecaze F. Prats H. Bayard F. Tauber J.P. Exp. Eye Res. 1989; 45: 801-813Crossref Scopus (37) Google Scholar,21Knee R.S. Pitcher S.E. Murphy P.R. Biochem. Biophys. Res. Commun. 1994; 205: 577-583Crossref PubMed Scopus (56) Google Scholar). No information was available from the literature about the putative role of the huge and multiple-sized 3′-UTR present in the FGF-2 mRNA. However, the 3′-UTRs of many mRNAs are now known to play a pivotal role in the post-transcriptional regulation of gene expression by controlling mRNA subcellular localization, stability, or translation initiation (22Wickens M. Anderson P. Jackson R.J. Curr. Opin. Genet. Dev. 1997; 7: 220-232Crossref PubMed Scopus (282) Google Scholar). Interestingly, such regulation essentially concerns the messengers coding for proteins that have potent growth or developmental effects or whose function is temporarily restricted, for instance, during a particular phase of the cell cycle. The genes expressing unstable mRNAs include proto-oncogenes, cytokines, growth factors, hormones, receptors, and cell cycle-regulated genes (for review, see Ref. 23Jarzembowski J.A. Malter J.S. Prog. Mol. Subcell. Biol. 1997; 18: 141-172Crossref PubMed Scopus (16) Google Scholar). The stability of most of these mRNAs is regulated by AU-rich elements (AREs) present in the 3′-UTR (23Jarzembowski J.A. Malter J.S. Prog. Mol. Subcell. Biol. 1997; 18: 141-172Crossref PubMed Scopus (16) Google Scholar). The unusual length and AU-rich composition of the FGF-2 mRNA 3′-UTR, together with the existence of eight potential alternative length-modifying polyadenylation sites, prompted us to determine its regulatory role in FGF-2 isoform expression. In this report, we show that poly(A) site utilization varies with cell type, and we identify a destabilizing element between the first and second polyadenylation sites of FGF-2 mRNA. These observations suggest that regulation of FGF-2 expression occurs at the level of RNA stability, conditioned by use of the poly(A) site. PCRs were performed using the complete FGF-2 cDNA as a template and the primer couple RTA1/PA1rev, RTA2/PA2rev, or RTA8/PA8rev, hybridizing upstream from the first, second, or eighth poly(A) site, respectively (TableI). The resulting fragments were subcloned into the EcoRI site of the vector Bluescript pKS. The corresponding plasmids, pKS-PA1, pKS-PA2, and pKS-PA8, were digested by XcmI + MscI, AflIII, orDraI and religated to obtain an internal deletion, giving the plasmids pKS-PA1Δ, pKS-PA2Δ, and pKS-PA8Δ, respectively.Table ISequence of oligonucleotides used for PCROligonucleotideSequenceRTA15′-TCGACTGGCTTCTAAATGTGTTAC-3′PA1rev5′-ACACATTTATTTTCTTTTACTCTC-3′RTA25′-CTCTGATGTGCAATACATTTG-3′PA2rev5′-CCCATAATTTATTTTCAAGCATA-3′RTA85′-TATAAGTGGTTTTGTTTGGTTAA-3′PA8rev5′-CAATTTTATTCATACTACTCATG-3′CAT-RT55′-ATGGCAATGAAAGACGGTGAG-3′GMrev5′-AATTATTACGGTAAAACATCTTG-3′ Open table in a new tab The constructs pCAT-A0, p5′CAT-A0, p5′CAT-A1, and p5′CAT-A8 have been described previously (14Arnaud E. Touriol C. Boutonnet C. Gensac M.C. Vagner S. Prats H. Prats A.-C. Mol. Cell. Biol. 1999; 19: 505-514Crossref PubMed Scopus (174) Google Scholar). pCAT-A0 and p5′CAT-A8 were called pKSCAT-pA and p5′CAT-A7, respectively (see Fig. 2 A). TheBspEI-SmaI fragment of p5′CAT-A1 was introduced into pCAT-A0 digested by BspEI + SmaI to construct pCAT-A1; pCAT-A2 was obtained by insertion of theBamHI-Klenow-BspEI fragment from plasmid pSCT-DOG, containing the complete FGF-2 3′-UTR sequence downstream from CAT, into pCAT-A0 (BamHI site at position 3441 of FGF-2 cDNA) (14Arnaud E. Touriol C. Boutonnet C. Gensac M.C. Vagner S. Prats H. Prats A.-C. Mol. Cell. Biol. 1999; 19: 505-514Crossref PubMed Scopus (174) Google Scholar). Plasmid pCAT-A3 was obtained by subcloning thePstI-Klenow-AvrII fragment from pSCT-DOG (AvrII and PstI sites at positions 3115 and 4028 of FGF-2 cDNA, respectively) into plasmid pCAT-A2. Plasmid pCAT-A4 was obtained by subcloning the NsiI-Klenow-AvrII fragment from pSCT-DOG (AvrII and NsiI sites at positions 3115 and 5403 of FGF-2 cDNA, respectively) into plasmid pCAT-A2. Plasmid pCAT-A8 was constructed by introducing the pSCT-DOGXbaI-Klenow-BspEI fragment containing the long 3′-UTR sequence into plasmid pCAT-A0 (14Arnaud E. Touriol C. Boutonnet C. Gensac M.C. Vagner S. Prats H. Prats A.-C. Mol. Cell. Biol. 1999; 19: 505-514Crossref PubMed Scopus (174) Google Scholar). of the were obtained by subcloning fragments obtained from plasmids of the into Plasmid was obtained by subcloning the fragment of pSCT-DOG the into the SmaI site of pCAT-A0 (see Fig. A). The and constructs were obtained by fragments by using and from plasmids and respectively by G. These fragments were digested by BspEI into sites of and were obtained by subcloning the fragments of between the sites of pCAT-A0 (see and were obtained by subcloning the fragments of into pCAT-A0 digested by SmaI and sites at positions and from the of FGF-2 cDNA, fragments from the plasmids were subcloned into plasmid to obtain the corresponding and were obtained by of plasmid by and by (see Fig. was obtained by of pCAT-A8 by by and were obtained either by plasmid or by using (for was performed with or RNA using by the was used for mRNAs, and the or the for RNA were by at and and their was The for of the element were obtained by using and by or and respectively) (see Fig. of human skin obtained from the of was for at in at a of at a of at a of at a of at a of and at a of The skin was into which were to in a for and were and was for fibroblasts from the skin and into new The fibroblasts be used for and (see Ref. S. Touriol C. B. S. Gensac M.C. Amalric F. Bayard F. Prats H. Prats A.-C. J. Cell Biol. 1996; PubMed Scopus Google were by the of containing 2 of RNA RNA was with of containing of addition of of the was to and for at human skin fibroblasts were using a were in and at for The was with and were in at a of of cell was with 2 of RNA and to a of was and the were in and at for in were with 1 of to mRNA for 2 the was the were with and was The were either or of were performed as described previously (14Arnaud E. Touriol C. Boutonnet C. Gensac M.C. Vagner S. Prats H. Prats A.-C. Mol. Cell. Biol. 1999; 19: 505-514Crossref PubMed Scopus (174) Google Scholar). was using the The cell were in or 1 of in or was by of of and the phase with 1 of at the were with The RNA was by the at and for by and The were using the system to the The reverse reaction was using 1 of RNA and of in a of of internal from the pKS-PA1Δ, pKS-PA2Δ, and plasmids (see were to the as described previously S. Touriol C. B. S. Gensac M.C. Amalric F. Bayard F. Prats H. Prats A.-C. J. Cell Biol. 1996; PubMed Scopus Google to the different regions of the FGF-2 mRNA was performed with the primer couple RTA1/PA1rev, RTA2/PA2rev, or RTA8/PA8rev, hybridizing upstream from the first, second, or eighth poly(A) site, The resulting fragments as and of the FGF-2 cDNA, The were using of in a of with of cDNA or The reaction was performed a the for and of for for 1 for 1 and for results of the were by The of the was by a by with as described previously S. Touriol C. B. S. Gensac M.C. Amalric F. Bayard F. Prats H. Prats A.-C. J. Cell Biol. 1996; PubMed Scopus Google Scholar). site utilization was in different cell types by were from three transformed or human cell lines and as well as from primary human skin was performed as described in S. Touriol C. B. S. Gensac M.C. Amalric F. Bayard F. Prats H. Prats A.-C. J. Cell Biol. 1996; PubMed Scopus Google with internal and primer to the region upstream from the first second and eighth poly(A) sites, respectively see We were able from the results to the FGF-2 mRNAs into three of at between and and at in and and short mRNAs at whereas skin fibroblasts long mRNAs at a more with and of mRNA The presence of mRNA was also by in cells, the of a in due to 3′-UTR species between and not These data a regulation of the use of the poly(A) sites the of the longest 5823-nt-long 3′-UTR in skin fibroblasts and of the and 3′-UTRs in the three transformed cell The in the 3′-UTR length due to cell alternative polyadenylation prompted us to for regulatory elements in the 5823-nt-long 3′-UTR of FGF-2 mRNA. from the alternative polyadenylation process and to the expression of mRNA species at a cell transfection was performed and mRNAs D.R. Dev. 1991; 5: PubMed Scopus Google Scholar). This has been previously for mRNA in a of the Malter J.S. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). were with mRNAs five of the different FGF-2 mRNA 3′-UTRs and nt, or not to the region of FGF-2 mRNA 2 A). mRNA expression was first by 2 mRNA with the 3′-UTR was in to the whereas expression from and mRNAs was very The were obtained in the presence of the FGF-2 mRNA 2 This the existence of an element in the FGF-2 mRNA 3′-UTR between the first and second poly(A) sites. The of the different mRNAs were to determine this element was an element or a translational 2 This revealed a mRNA to the mRNA whereas a of the was for and mRNAs and This that the element located between the first and second poly(A) sites was a destabilizing The destabilizing was in the presence of the FGF-2 mRNA the mRNAs were more stable than their mRNAs were also in skin fibroblasts and and The destabilizing element the mRNA by in these cell as in cells, that the of the FGF-2 element was not cell to of the FGF-2 the of a destabilizing due to the of the 3′-UTR was by the of the 5823-nt-long 3′-UTR in a reverse mRNA The results that the the control was four more stable than the both in and in skin fibroblasts, the of effects by the unusual length of the 3′-UTR be The of the FGF-2 element was also with that of the well and skin fibroblasts were with mRNAs the 3′-UTR of the with or its and of the mRNA that the was able to the mRNA by a factor of in with the of and Malter Malter J.S. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). The FGF-2 which the mRNA by a factor of be an destabilizing The destabilizing element was more by a approach RNA transfection of human skin fibroblasts that of the upstream from the second poly(A) site the destabilizing However, this of the was not to mRNA In a fragment corresponding to the upstream from the second poly(A) site was to the destabilizing of this fragment from the complete FGF-2 3′-UTR also RNA of the sequence revealed the existence of direct with of which of and However, of these only a whereas described in and mRNAs contain (23Jarzembowski J.A. Malter J.S. Prog. Mol. Subcell. Biol. 1997; 18: 141-172Crossref PubMed Scopus (16) Google Scholar). were performed within the and RNA transfection was in skin fibroblasts as described The of a fragment corresponding to the of the upstream repeat not RNA and whereas the of a which a complete repeat, the destabilizing and alternative was to mRNA with an of different of the The results in Fig. show that an RNA the complete element was able to RNA whereas an RNA the sequence had and and or of the downstream repeat were also able to the destabilizing and These data show that the element the AU-rich direct both for the of the upstream repeat, are required and are for the destabilizing of the long FGF-2 mRNA We show in this that the length of the FGF-2 mRNA 3′-UTR is conditioned by a process of alternative to the cell The proximal poly(A) sites to be used in three transformed cell whereas the eighth poly(A) site is mostly used in primary skin fibroblasts, giving to the huge 5823-nt-long This regulation of alternative polyadenylation has for the regulation of FGF-2 as a destabilizing corresponding to AU-rich has been between the first and second poly(A) sites. No of FGF-2 mRNA had been to now of the of the mRNA the presence of several mRNA species resulting from alternative polyadenylation very complex and the expression of mRNAs The and of the RNA transfection described for primary cells, were crucial in the expression of a mRNA species in the of alternative We provide the first evidence that a of the family is regulated at the level of mRNA stability by the presence of which is by alternative of FGF-2 mRNA stability has been reported only in in which the RNA that FGF-2 mRNA by a process of RNA is involved D. Cell. 1989; Full Text PDF PubMed Scopus Google Scholar). However, the present in cells, has been to FGF-2 mRNA stability P.R. R.S. Mol. 1994; PubMed Scopus Google Scholar). results suggest that FGF-2 mRNA stability is regulated by a process to that controlling other and AU-rich The AU-rich FGF-2 element described is It not contain the described for most proto-oncogenes, cytokines, and growth factor mRNAs or the long region the destabilizing of in for example (23Jarzembowski J.A. Malter J.S. Prog. Mol. Subcell. Biol. 1997; 18: 141-172Crossref PubMed Scopus (16) Google Scholar). In sequence revealed of the FGF-2 element to the and growth factor which are also unusual T. A. E. J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar, A. S. M. Mol. Biol. Cell. 1998; PubMed Scopus Google Scholar). However, of these destabilizing elements contains the direct repeat for FGF-2 is that the presence of is not to FGF-2 the 3′-UTR contains the which not mRNA H. Kaghad M. Prats A.-C. Klagsbrun M. Lélias J.M. Liauzun P. Chalon P. Tauber J.P. Amalric F. Smith J.A. Caput D. Proc. Natl. Acad. Sci. U. S. A. 1989; 86: 1836-1840Crossref PubMed Scopus (399) Google Scholar). the located in the of repeat in the element are to RNA by and the presence of for RNA This the of in the regulation of FGF-2 activity. The proteins have been to date, with different for RNA (23Jarzembowski J.A. Malter J.S. Prog. Mol. Subcell. Biol. 1997; 18: 141-172Crossref PubMed Scopus (16) Google Scholar). of are able to to the and of are able to to of these proteins, and are to to the or Interestingly, the to the P.R. B. T. Mol. Cell. Biol. 1991; 11: PubMed Scopus Google Scholar). the of the growth factor ARE, involved in mRNA is with the of three proteins with of and A. S. M. Mol. Biol. Cell. 1998; PubMed Scopus Google Scholar). This the that the FGF-2 element also be regulated by The of both elements of the repeat for RNA that the potential regulatory has sites in the element; would be the of only as a to the are in the literature of regulation of alternative polyadenylation coupled with RNA of stability polyadenylation is by the mRNA. This mRNA is with of 3′-UTR, the of which contains a stability element N. J. 1996; Google Scholar). growth factor mRNA stability is regulated by a located between alternative polyadenylation sites S. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). The FGF-2 located between the first and second poly(A) sites, a of the FGF-2 mRNA in polyadenylation at or The coupled polyadenylation and of FGF-2 mRNA in such a the cell to provide a regulation in to is by the results in Fig. which show that the mRNA at is present in the three transformed cell lines but constitutes only of the FGF-2 mRNA in primary skin These results suggest that the FGF-2 mRNA can be in skin fibroblasts, but is stable in transformed cells, it is of the destabilizing We have in a that FGF-2 expression is regulated in skin fibroblasts, but in transformed cell lines and as well as in skin fibroblasts transformed by B. Maret A. Prats A.-C. Prats H. Res. 1999; Google Scholar). The present data suggest that FGF-2 expression cannot be regulated in transformed cells, a that be a or a of the transformed these observations that FGF-2 expression transcriptional it is mostly regulated at three mRNA stability, and The existence of several post-transcriptional for a mRNA the control of FGF-2 expression very which permits its expression only relevant It also the for to very the level of FGF-2 expression in to The of these be of the for cell We R. for and D. for We also for human skin and G. for plasmids and