Erythropoietin receptor-operated Ca2+ channels: activation by phospholipase C-gamma 1.
Erythropoietin (EPO) increases Ca2+ influx in vascular smooth muscle cells and acts both as a direct vasoconstrictor and vascular growth factor (that is, angiogenesis). However, the mechanism by which EPO promotes extracellular Ca2+ entry in contractile cells has not been elucidated. In hematopoietic cells, EPO induces tyrosine kinase (TK)-dependent activation of phospholipase C (PLC)-gamma 1 and Ca2+ influx via a voltage-independent Ca2+ conductance. In contractile mesangial cells, we have recently characterized a voltage-independent, 1 pS Ca2+ channel that is dependent on both TK and PLC-gamma 1 activity. Therefore, we examined cultured rat glomerular mesangial cells after timed exposure to recombinant human EPO (20 U/ml). Erythropoietin increased the tyrosine phosphorylation of PLC-gamma 1, promoted membrane complex formation between PLC-gamma 1 and the EPO receptor itself, and raised the levels of intracellular inositol 1,4,5-trisphosphate and intracellular Ca2+. Consistent with our previous studies, 1 pS Ca2+ channel activity was extremely low under basal, unstimulated conditions in cell-attached patches, but was dramatically increased when EPO was present in the patch pipette. Tyrosine kinase inhibition with 100 micron genistein or 1 micron PP1 (Src; selective tyrosine kinase inhibitor) prevented all of these EPO-induced responses. We conclude that: (1) EPO-induced stimulation of 1 pS Ca2+ channels is mediated via a cytosolic Src TK in glomerular mesangial cells. (2) Stimulation of this Ca2(+)-activated, Ca2(+)-permeable channel is dependent on the tyrosine phosphorylation/activation of PLC-gamma 1. (3) This cascade provides a possible mechanism for the vasoconstriction and hypertension observed with clinical EPO use for the treatment of chronic anemias.
Marrero
M B
MB
Renal Division, Emory University School of Medicine, Atlanta, Georgia, USA. mmarrero@ccms-renal.physio.emory.edu
Venema
R C
RC
Ma
H
H
Ling
B N
BN
Eaton
D C
DC
D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects; D004921:Erythropoietin / Q000494:pharmacology / Q000633:toxicity; D005920:Glomerular Mesangium / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007424:Intracellular Fluid / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism*; D008954:Models, Biological; D051966:Phospholipase C gamma; D010766:Phosphorylation; D051381:Rats; D017467:Receptors, Erythropoietin / Q000378:metabolism*; D011994:Recombinant Proteins; D010738:Type C Phospholipases / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism; D019061:src-Family Kinases / Q000378:metabolism
D015220:Calcium Channels; D007527:Isoenzymes; D017467:Receptors, Erythropoietin; D011994:Recombinant Proteins; D004921:Erythropoietin; D014443:Tyrosine; D015544:Inositol 1,4,5-Trisphosphate; D019061:src-Family Kinases; D010738:Type C Phospholipases; D051966:Phospholipase C gamma; D002118:Calcium