Thrombin is a novel regulator of hexokinase activity in mesangial cells.
BACKGROUND
Hexokinase (HK) activity is fundamentally important to cellular glucose uptake and metabolism. Phorbol esters increase both HK activity and glucose utilization in cultured mesangial cells via a protein kinase C (PKC)- and extracellular signal-regulated kinases 1 and 2 (ERK1/2)-dependent mechanism. In adult kidneys, increased HK activity has been reported in both glomerular injury and in diabetes, but the mechanisms responsible for these changes are unknown. Thrombin, a known activator of both PKC and ERK1/2, is increased in the settings of renal injury and diabetes. Thus, thrombin may contribute to the observed changes in HK activity in vivo.


METHODS
Thrombin and thrombin receptor agonists were tested for the ability to increase HK activity and glucose metabolism in murine mesangial (SV40 MES 13) cells. ERK1/2 activation was also evaluated in parallel. Thrombin inhibition (hirudins), PKC depletion, Ser-Thr kinase inhibition (H-7), MEK1/2 inhibition (PD98059), pertussis toxin (PTX), and general inhibitors of transcription or translation were then tested for the ability to attenuate these effects.


RESULTS
Thrombin (>/=0.01 U/mL) mimicked the effect of phorbol esters, increasing HK activity> 50% within 12 to 24 hours (P < 0.05). This effect was inhibited by hirudins, mimicked by thrombin receptor agonists, and accompanied by increased Glc utilization. H-7, PD98059, and general inhibitors of transcription or translation-but not PTX-prevented thrombin-induced HK activity at 24 hours. PKC depletion and PD98059 also blocked the associated phosphorylation and activation of ERK1/2.


CONCLUSIONS
Thrombin increases mesangial cell HK activity via a PTX-insensitive mechanism involving thrombin receptor activation, PKC-dependent activation of ERK1/2, and both ongoing gene transcription and de novo protein synthesis. As such, thrombin is a novel regulator of HK activity in mesangial cells and may play a role in coupling renal injury to metabolism.
Robey
R B
RB
Department of Medicine, Section of Nephrology, University of Illinois at Chicago College of Medicine and VA Chicago Health Care System, West Side Division, Chicago, Illinois 60612-7315, USA. RBRobey@uic.edu
Raval
B J
BJ
Ma
J
J
Santos
A V
AV
D000818:Animals; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004351:Drug Resistance; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005920:Glomerular Mesangium / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D005947:Glucose / Q000378:metabolism; D006593:Hexokinase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006629:Hirudins / Q000494:pharmacology; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D037342:Pertussis Toxin; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors; D044463:Receptor, PAR-1; D018179:Receptors, Thrombin / Q000819:agonists; D013917:Thrombin / Q000494:pharmacology*; D014158:Transcription, Genetic / Q000502:physiology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D004791:Enzyme Inhibitors; D006629:Hirudins; D044463:Receptor, PAR-1; D018179:Receptors, Thrombin; D010566:Virulence Factors, Bordetella; D037342:Pertussis Toxin; D006593:Hexokinase; D017346:Protein Serine-Threonine Kinases; D020928:Mitogen-Activated Protein Kinases; D013917:Thrombin; D005947:Glucose