Urea signaling to ERK phosphorylation in renal medullary cells requires extracellular calcium but not calcium entry.
The renal cell line mIMCD3 exhibits markedly upregulated phosphorylation of the extracellular signal-regulated kinase (ERK) 1 and 2 in response to urea treatment (200 mM for 5 min). Previous data have suggested the involvement of a classical protein kinase C (cPKC)-dependent pathway in downstream events related to urea signaling. We now show that urea-inducible ERK activation requires extracellular calcium; unexpectedly, it occurs independently of activation of cPKC isoforms. Pharmacological inhibitors of known intracellular calcium release pathways and extracellular calcium entry pathways fail to inhibit ERK activation by urea. Fura 2 ratiometry was used to assess the effect of urea treatment on intracellular calcium mobilization. In single-cell analyses using subconfluent monolayers and in population-wide analyses using both confluent monolayers and cells in suspension, urea failed to increase intracellular calcium concentration. Taken together, these data indicate that urea-inducible ERK activation requires calcium action but not calcium entry. Although direct evidence is lacking, one possible explanation could include involvement of a calcium-dependent extracellular moiety of a cell surface-associated protein.
Yang
X Y
XY
Divisions of Nephrology, Oregon Health Sciences University, Portland, Oregon 97201, USA.
Zhao
H
H
Zhang
Z
Z
Rodland
K D
KD
Roullet
J B
JB
Cohen
D M
DM
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D018929:Cell Culture Techniques / Q000379:methods; D002460:Cell Line; D004789:Enzyme Activation; D004815:Epidermal Growth Factor / Q000494:pharmacology; D015759:Ionomycin / Q000494:pharmacology; D007679:Kidney Medulla / Q000166:cytology / Q000502:physiology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D014508:Urea / Q000494:pharmacology*
D000001:Calcimycin; D015759:Ionomycin; D004815:Epidermal Growth Factor; D019284:Thapsigargin; D014508:Urea; D011493:Protein Kinase C; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium