Transforming growth factor-beta stimulates the expression of alpha 2-macroglobulin by cultured bovine adrenocortical cells.
Adrenocortical cell major secreted protein was purified from the conditioned medium of primary cultures of bovine adrenocortical (BAC) cells. Immunochemical analysis and N-terminal sequencing of the purified protein identified it to alpha 2-macroglobulin (alpha 2-M). It appeared that 15 out of the 17 N-terminal amino acids were conserved between adrenocortical cell major secreted protein and human alpha 2-M. Study of alpha 2-M production by BAC cells revealed that its secretion was stimulated severalfold by transforming growth factor-beta 1 (TGF-beta 1). The stimulation occurred in a time-dependent (reaching a plateau at 24 h) and dose-dependent (ED50 = 0.1 ng/ml TGF-beta 1) manner. It was blocked when BAC cells were exposed to 5,6-dichlorobenzimidazole riboside, a potent inhibitor of RNA polymerase II, suggesting that TGF-beta 1 acts as an activator of alpha 2-M gene expression at the transcriptional level. Northern blot analysis confirmed that the alpha 2-M mRNA level was increased (4-fold) in BAC cells following TGF-beta 1 treatment. TGF-beta 2, TGF-beta 1,2, basic fibroblast growth factor, and angiotensin II also appeared able to stimulate alpha 2-M secretion in BAC cells, whereas adrenocorticotropin was strongly inhibitory. Given the previous reports that TGF-beta 1 is a potent inhibitor of adrenocortical steroidogenesis (Feige J.J., Cochet, C., Rainey, W.E., Madani, C., and Chambaz, E. M. (1987) J. Biol. Chem. 262, 13491-13495) and that alpha 2-M is a TGF-beta 1-binding protein, these observations suggest that alpha 2-M may play an important role in conjunction with hormones and growth factors in the homeostatic regulation of adrenocortical functions.
Laboratoire de Biochimie des Régulations Cellulaires Endocrines, Institut National de la Santé et de la Recherche Medicale, Grenoble, France.
D L
DL
Shi
C
C
Savona
J
J
Gagnon
C
C
Cochet
E M
EM
Chambaz
J J
JJ
Feige
D000302:Adrenal Cortex / Q000187:drug effects / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D005346:Fibroblast Growth Factors / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D006133:Growth Substances / Q000494:pharmacology; D006801:Humans; D008969:Molecular Sequence Data; D051381:Rats; D011994:Recombinant Proteins / Q000494:pharmacology; D012689:Sequence Homology, Nucleic Acid; D013552:Swine; D015291:Transforming Growth Factors / Q000494:pharmacology*; D000511:alpha-Macroglobulins / Q000096:biosynthesis / Q000235:genetics* / Q000302:isolation & purification
D006133:Growth Substances; D011994:Recombinant Proteins; D000511:alpha-Macroglobulins; D005346:Fibroblast Growth Factors; D015291:Transforming Growth Factors