Differential expression and biological activity of retinoic acid-induced TGFbeta isoforms in embryonic palate mesenchymal cells.
The effect of retinoic acid (RA) on TGF-beta mRNA expression and protein production in murine embryonic palate mesenchymal (MEPM) cells was examined by Northern blotting and TGF-beta bioassay in association with TGF-beta isoform-specific neutralizing antibodies. Heat or acid activation was used to distinguish between latent and active TGF-beta protein released into the culture medium. RA had little or no effect on TGF-beta1 mRNA expression and protein production. In contrast, RA increased TGF-beta2 and beta3 protein released into the culture medium, the protein being mostly in an inactive or latent form. The amount of active TGF-beta released was increased relative to the total increase in TGF-beta released, suggesting that RA treatment stimulated activation of latent TGF-beta. RA also increased TGF-beta2 mRNA expression; we have previously shown that RA upregulates TGF-beta3 mRNA in these cells. RA and TGF-beta individually inhibited 3H-thymidine incorporation into MEPM cell DNA, while, when administered simultaneously, they inhibited proliferative activity to a greater extent. Heat- or acid-activated conditioned medium (CM) from MEPM cells treated with RA was able to inhibit 3H-thymidine incorporation into MEPM cell DNA to an extent greater than seen with RA treatment alone. Coincubation of heat-activated CM from RA-treated MEPM cells with pan-specific or TGF-beta2 or beta3-specific neutralizing antibodies partially relieved the inhibitory effect on 3H-thymidine incorporation, suggesting that this proliferative response was due to RA-induced TGF-beta. Simultaneous treatment with RA and TGF-beta also stimulated gycosaminoglycan (GAG) synthesis to an extent greater than that seen with TGF-beta treatment alone, this despite the ability of RA to inhibit GAG synthesis. These data demonstrate a role for RA and RA-induced TGF-beta in the regulation of palate cell proliferation and GAG synthesis and suggest a role for TGF-beta in retinoid-induced cleft palate.
Nugent
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Department of Pathology, Anatomy and Cell Biology, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania, USA. pfnuge01@homer.louisville.edu
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Greene
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D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D005786:Gene Expression Regulation / Q000187:drug effects; D006025:Glycosaminoglycans / Q000096:biosynthesis / Q000378:metabolism; D007536:Isomerism; D008168:Lung / Q000166:cytology; D008648:Mesoderm / Q000737:chemistry / Q000166:cytology / Q000378:metabolism; D051379:Mice; D008813:Mice, Inbred ICR; D008907:Mink; D010159:Palate / Q000737:chemistry / Q000166:cytology* / Q000196:embryology*; D012333:RNA, Messenger / Q000032:analysis; D016212:Transforming Growth Factor beta / Q000737:chemistry / Q000235:genetics* / Q000494:pharmacology; D014212:Tretinoin / Q000494:pharmacology*
D000970:Antineoplastic Agents; D006025:Glycosaminoglycans; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; D014212:Tretinoin