The hyperresponsiveness of cells expressing truncated erythropoietin receptors is contingent on insulin-like growth factor-1 in fetal calf serum.
We demonstrate herein that the well documented hyperresponsiveness to erythropoietin (Epo) of Ba/F3 cells expressing C-terminal truncated erythropoietin receptors (EpoRs) is contingent on these cells being in fetal calf serum (FCS). In the absence of FCS, their Epo-induced proliferation is far poorer than Ba/F3 cells expressing wild-type (WT) EpoRs. This hyporesponsiveness in the absence of serum is also seen in DA-3 cells expressing these truncated EpoRs. In fact, long-term proliferation studies performed in the absence of serum show that even at saturating concentrations of Epo, Ba/F3 cells expressing these truncated receptors die via apoptosis, while cells bearing WT EpoRs do not, and this programmed cell death correlates with an inability of Epo-stimulated Ba/F3 cells expressing truncated EpoRs to induce the tyrosine phosphorylation of MAPK and the activation of p70(S6K). Using neutralizing antibodies to insulin-like growth factor (IGF)-1, we show that a major non-Epo factor in FCS that contributes to the hyperresponsive phenotype of Ba/F3 cells expressing truncated EpoRs is IGF-1. Our results suggest that the Epo-hypersensitivity of truncated EpoR expressing Ba/F3 cells is due to the combined effects of these EpoRs not possessing a binding site for the negative regulator, SHP-1, and the triggering of proliferation-inducing/apoptosis-inhibiting cascades, lost through EpoR truncation, by IGF-1.
Damen
J E
JE
Terry Fox Laboratory, British Columbia Cancer Agency and Kinetek, Vancouver, British Columbia, Canada.
Krosl
J
J
Morrison
D
D
Pelech
S
S
Krystal
G
G
D000818:Animals; D001798:Blood Proteins / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D016895:Culture Media, Serum-Free; D004347:Drug Interactions; D004921:Erythropoietin / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D051379:Mice; D017467:Receptors, Erythropoietin / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects
D001798:Blood Proteins; D016895:Culture Media, Serum-Free; D017467:Receptors, Erythropoietin; D004921:Erythropoietin; D007334:Insulin-Like Growth Factor I