Insulin-like growth factors decrease oxygen-regulated erythropoietin production by human hepatoma cells (Hep G2).
We examined the effects of insulin-like growth factors (IGFs) and insulin on erythropoietin (EPO) production by human hepatoma cells (Hep G2). Compared with normoxia (20% O2), EPO production by Hep G2 cells during a 72-h incubation was stimulated fivefold by exposure to low oxygen tension (1% O2) and nearly threefold by exposure to cobalt chloride (100 microM). IGF-I caused a concentration-dependent attenuation of EPO formation under normoxic conditions and inhibited (maximally 50%) EPO production stimulated by either low oxygen tension or cobalt [half-maximal effect (ED50) approximately 5 nM]. The increase of EPO mRNA levels in response to hypoxia was significantly reduced by IGF-I. Similarly to IGF-I, IGF-II (ED50 approximately 8 nM) and insulin (ED50 approximately 80 nM) also inhibited EPO formation in Hep G2 cells. IGF-I (100 pM-100 nM) stimulated the incorporation of radiolabeled alanine as a measure for total protein synthesis, 3H-labeled thymidine incorporation into DNA, and glycogen synthesis at 20 and 1% O2 in a concentration-dependent fashion. IGF-I exhibited a high affinity for the IGF-I receptor (apparent Kd approximately 3 nM). Unlabeled insulin was greater than 100-fold less potent than IGF-I in competing for 125I-IGF-I binding (apparent Kd approximately 360 nM). Conversely, insulin bound to the insulin receptor with high affinity (apparent Kd approximately 0.3 nM), whereas IGF-I was less than 1% as potent in competing for 125I-insulin binding. In summary, IGFs and insulin exert a negative control function on oxygen-regulated EPO production in Hep G2 cells. The inhibitory effect of IGFs and insulin on EPO formation appears to be mediated via the IGF-I receptor.
Scholz
H
H
Physiologisches Institut, Universität Zürich, Switzerland.
Baier
W
W
Ratcliffe
P
P
Eckardt
K
K
Zapf
J
J
Kurtz
A
A
Bauer
C
C
D000818:Animals; D003470:Culture Media; D004305:Dose-Response Relationship, Drug; D004921:Erythropoietin / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D007335:Insulin-Like Growth Factor II / Q000494:pharmacology; D008113:Liver Neoplasms / Q000378:metabolism* / Q000473:pathology; D008114:Liver Neoplasms, Experimental / Q000378:metabolism* / Q000473:pathology; D010100:Oxygen / Q000494:pharmacology*; D011972:Receptor, Insulin / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism; D017451:Receptors, Somatomedin; D013002:Somatomedins / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D003470:Culture Media; D007328:Insulin; D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D013002:Somatomedins; D004921:Erythropoietin; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D011972:Receptor, Insulin; D010100:Oxygen