Dynamics of four rat liver plasma membrane proteins and polymeric IgA receptor. Rates of synthesis and selective loss into the bile.
We have determined the half-lives and amounts per hepatocyte of the polymeric IgA receptor (pIgA-R) and four rat hepatocyte plasma membrane proteins and subsequently have predicted their rates of synthesis and possible routes of degradation. Using in vivo pulse-chase metabolic labeling with L-[35S]cysteine, we found that the pIgA-R had an apparent half-life of 1.1 h. Additional metabolic labeling experiments showed that CE9, HA4, and HA321 had apparent half-lives of 4-5 days, and dipeptidyl peptidase IV had an apparent half-life of 9 days. To quantify the amount of each protein per hepatocyte, homogenates and a standard curve of purified protein were compared by immunoblotting. We found that these proteins were present at 1-8 x 10(6) molecules/hepatocyte. The calculated rate of synthesis for pIgA-R was 1.6 x 10(6) molecules/hepatocyte/h, whereas the others were synthesized at much lower rates (0.9-5 x 10(4) molecules/hepatocyte/h). Using immunoblot analysis, we found that pIgA-R was released into bile at a rate of 30%/h (700%/day), whereas dipeptidyl peptidase IV and HA4 were released at a rate of 2-3%/day. While the majority of the loss of pIgA-R from hepatocytes occurred by release into the bile, less than 30% of the degradation of dipeptidyl peptidase IV and HA4 could be accounted for by this pathway, suggesting that the remaining molecules must be retrieved from the apical surface before degradation.
Scott
L J
LJ
Department of Cell Biology and Anatomy, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Hubbard
A L
AL
D000818:Animals; D000911:Antibodies, Monoclonal; D001646:Bile / Q000276:immunology*; D002462:Cell Membrane / Q000276:immunology; D003545:Cysteine / Q000378:metabolism; D006207:Half-Life; D015151:Immunoblotting; D007070:Immunoglobulin A / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000276:immunology*; D008297:Male; D008565:Membrane Proteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism; D008715:Methionine / Q000378:metabolism; D011865:Radioisotope Dilution Technique; D051381:Rats; D011919:Rats, Inbred Strains; D011961:Receptors, Fc; D011971:Receptors, Immunologic / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D013462:Sulfur Radioisotopes
D000911:Antibodies, Monoclonal; C045281:IgA receptor; D007070:Immunoglobulin A; D008565:Membrane Proteins; D011961:Receptors, Fc; D011971:Receptors, Immunologic; D013462:Sulfur Radioisotopes; D008715:Methionine; D003545:Cysteine