IGF-I is a mitogen involved in differentiation-related gene expression in fetal rat brown adipocytes.
Fetal rat brown adipocytes at time zero of culture constitute a population of cells of broad spectrum, as estimated by cell size, endogenous fluorescence and lipid content, and show an intrinsic mitogenic competence. They express constitutively early growth-related genes such as c-myc, c-fos, and beta-actin, tissue specific-genes such as the uncoupling protein (UCP) and the lipogenic marker malic enzyme (ME). Fetal brown adipocytes bear a high expression of insulin-like growth factor receptor (IGF-IR), and show a high affinity IGF-I specific-binding to its receptor, and a high number of binding sites per cell. After cell quiescence, insulin-like growth factor I (IGF-I) was as potent as 10% FCS in inducing DNA synthesis, cell number increase, and the entry of cells into the cell-cycle. In addition, IGF-I or 10% FCS for 48 h increased the percentage of [3H]thymidine-labeled nuclei as compared to quiescent cells. Single cell autoradiographic microphotographs show typical multilocular fat droplets brown adipocytes, resulting positive to [3H]thymidine-labeled nuclei in response to IGF-I. IGF-I increased mRNA expression of the early-response genes c-fos (30 min), c-myc (2 and 24 h), and H-ras (4 and 24 h). 10% FCS also increased c-fos and c-myc, but failed to increase H-ras as an early event. IGF-I or 10% FCS, however, similarly increased the mRNA late expression of c-myc, H-ras, c-raf, beta-actin, and glucose 6-phosphate dehydrogenase (G6PD) at 72 h, as compared to quiescent cells. IGF-I or FCS maintained at 24 h or increased at 48 and 72 h UCP mRNA expression. The results demonstrate that IGF-I is a mitogen for fetal rat brown adipocytes, capable of inducing the expression of early and late growth-regulated genes, and of increasing the lipogenic marker ME and the tissue-specific gene UCP, suggesting the involvement of IGF-I in the differentiation as well as in the proliferation processes.
Lorenzo
M
M
Departamento de Bioquímica y Biología Molecular, Facultad de Farmacia, Universidad Complutense, Madrid, Spain.
Valverde
A M
AM
Teruel
T
T
Benito
M
M
D002001:Adipose Tissue, Brown / Q000166:cytology*; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics; D002453:Cell Cycle; D002454:Cell Differentiation; D002455:Cell Division; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis; D005786:Gene Expression Regulation / Q000187:drug effects; D016762:Genes, fos; D016259:Genes, myc; D011905:Genes, ras; D005954:Glucosephosphate Dehydrogenase / Q000235:genetics; D066298:In Vitro Techniques; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007473:Ion Channels; D008565:Membrane Proteins / Q000235:genetics; D024101:Mitochondrial Proteins; D008934:Mitogens; D011518:Proto-Oncogene Proteins / Q000235:genetics; D019908:Proto-Oncogene Proteins c-raf; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar / Q000196:embryology; D017526:Receptor, IGF Type 1 / Q000378:metabolism; D000071256:Uncoupling Protein 1
D002352:Carrier Proteins; D007473:Ion Channels; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D008934:Mitogens; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D000071256:Uncoupling Protein 1; D007334:Insulin-Like Growth Factor I; D004247:DNA; D005954:Glucosephosphate Dehydrogenase; D017526:Receptor, IGF Type 1; D019908:Proto-Oncogene Proteins c-raf