Posttranscriptional regulation of the asialoglycoprotein receptor by cGMP

The human asialoglycoprotein receptor expressed by the HepG2 cell line is composed of the two homologous polypeptides H1 and H2. Transblot analysis of HepG2 cell lysates indicated that the progressive loss in the steady-state level of asialoglycoprotein receptor (ASGR) when cells were maintained in medium supplemented with dialyzed fetal bovine serum was reversed by the addition of cell-permeant 8-bromo-cGMP. Estimates of the steady-state levels of H1- and H2-related mRNA by Northern blot analysis indicated that the reduction of ASGR was not the result of a concomitant reduction in gene transcript number. No difference in the translatability of the mRNAs derived from cells grown in medium supplemented with fetal bovine serum or its dialyzed counterpart was detected. Resolution of the mRNAs by sucrose gradient centrifugation suggests that cGMP-mediated posttranscriptional regulation of ASGR expression was due to a shift of both H1 and H2 mRNAs from the ribonucleoprotein fraction into a translationally active membrane-associated polysomal pool.