Increased protein kinase A regulatory subunit content and cGMP binding in erythrocyte membranes in liver cirrhosis.
OBJECTIVE
Patients with liver disease show increased plasma cGMP and decreased intracellular cGMP in lymphocytes. The initial aim of this work was to assess whether decreased intracellular cGMP and increased plasma cGMP may be due to increased ATP-dependent release of cGMP from cells. The results obtained led to a new aim: to identify and quantify a protein responsible for the increased cGMP binding found in erythrocyte membranes from patients with liver disease.


METHODS
ATP-dependent cGMP transport was determined in inside-out vesicles from erythrocyte membranes. cGMP-binding proteins were isolated from the membranes and identified by MALDI-TOF peptide mass fingerprint. Protein kinase A was quantified by immunoblotting.


RESULTS
ATP-independent cGMP binding is increased in erythrocyte membranes from patients. There is a significant increase in the membrane content of a cGMP-binding protein with Mr 48,000, which was identified as the regulatory subunit of protein kinase A.


CONCLUSIONS
The content of the regulatory subunit of protein kinase A is significantly increased (twice) in erythrocyte membranes from patients with liver cirrhosis. This protein binds cGMP strongly and may be responsible for the decrease in intracellular cGMP in liver disease.
Montoliu
Carmina
C
Servicio de Hepatología, Hospital Clínico Universitario, Departamento de Medicina, Universidad de Valencia, Valencia, Spain.
Kosenko
Elena
E
Calvete
Juan J
JJ
Nies
Anne T
AT
Del Olmo
Juan A
JA
Serra
Miguel A
MA
Rodrigo
José M
JM
Felipo
Vicente
V
D000328:Adult; D000368:Aged; D001693:Biological Transport, Active; D016022:Case-Control Studies; D017868:Cyclic AMP-Dependent Protein Kinases / Q000097:blood* / Q000737:chemistry; D006152:Cyclic GMP / Q000097:blood*; D004910:Erythrocyte Membrane / Q000378:metabolism*; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008103:Liver Cirrhosis / Q000097:blood* / Q000201:enzymology; D008297:Male; D008875:Middle Aged; D008970:Molecular Weight; D021122:Protein Subunits; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D021122:Protein Subunits; D017868:Cyclic AMP-Dependent Protein Kinases; D006152:Cyclic GMP