Insulin-like growth factors (IGFs) stimulate and dexamethasone inhibits IGF binding protein (BP)-5 expression in a mouse pituitary cell line.
The mouse pituitary cell line AtT-20 was found to secrete two low MW IGFBPs into conditioned medium (CM). The major IGFBP migrated at approximately 29 kDa and a minor IGFBP of 24 kDa was also present on western ligand blots (WLB). Both IGFBPs were purified from CM by IGF-affinity chromatography followed by reverse phase-FPLC. N-terminal analysis revealed that the first 10 amino acids of the 29 kDa and the 24 kDa IGFBPs were homologous to corresponding sequences of both human and rat IGFBP-5 and IGFBP-4, respectively. The 24 kDa IGFBP also crossreacted with a new antiserum specific for rodent IGFBP-4. The concentrations of both IGFBPs were increased by the addition of IGF-I, IGF-II, or insulin to the cell cultures, with IGFBP-5 demonstrating the greatest hormonal stimulation. The effects of IGF-I on IGFBP-5 expression were both time and dose dependent, with IGF-I being more potent than IGF-II, and IGF-II more potent than insulin. The relative potencies of these hormones in stimulating IGFBP-5 production were consistent with the peptides acting through the type-I IGF receptor. Similarly, the IGF-II analog [Leu 27]-IGF-II, which has very low affinity for the type-I receptor, only slightly stimulated an increase in IGFBP-5. Addition of dexamethasone to the cultures decreased both basal and IGF-stimulated IGFBP-5 production. Northern blotting demonstrated that IGF-I increased the expression of the mRNA for IGFBP-5, whereas dexamethasone decreased it. Together, these data suggest that the IGFs can increase IGFBP-5 production at both the protein and mRNA level.
Fielder
P J
PJ
Department of Pediatrics, Stanford University Medical School, CA 94305.
Tauber
J P
JP
Wilson
K F
KF
Pham
H M
HM
Rosenfeld
R G
RG
D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D002352:Carrier Proteins / Q000037:antagonists & inhibitors* / Q000096:biosynthesis* / Q000276:immunology / Q000302:isolation & purification; D002460:Cell Line; D003907:Dexamethasone / Q000494:pharmacology*; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D018974:Insulin-Like Growth Factor Binding Protein 4; D018975:Insulin-Like Growth Factor Binding Protein 5; D051379:Mice; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010902:Pituitary Gland / Q000737:chemistry / Q000378:metabolism*; D011233:Precipitin Tests; D011817:Rabbits; D051381:Rats; D013002:Somatomedins / Q000037:antagonists & inhibitors* / Q000096:biosynthesis* / Q000494:pharmacology*
D002352:Carrier Proteins; D018974:Insulin-Like Growth Factor Binding Protein 4; D018975:Insulin-Like Growth Factor Binding Protein 5; D013002:Somatomedins; D003907:Dexamethasone