Post-transcriptional regulation of gene expression in compensatory renal hypertrophy

An increase in cell protein content is a characteristic of renal cells undergoing compensatory hypertrophy. The contribution of transcriptional and post-transcriptional regulation of mRNAs to the increase in constitutively expressed proteins in hypertrophy was examined in mouse kidneys after unilateral nephrectomy (UNI-NX). No significant increases in steady state levels or transcription of mRNAs for eight growth-related genes (Na+K+ATPase, ADP/ATP translocase, beta-actin, ornithine decarboxylase, poly A(+)-binding protein and two genes expressed in androgen-induced hypertrophy) were observed from 30 min to 10 days after UNI-NX. In contrast, transcription of the 18S ribosomal gene increased by 24% within 24 h after surgery. By Western blotting the proportion of two specific proteins relative to total cell protein was constant over 10 days. Since total protein/kidney increased by 28% over this period the concentration of these specific proteins/kidney must also have increased. Although it is possible that one or more 'hypertrophy specific' genes are transcriptionally regulated to initiate the growth process, the present data suggest that protein accumulation in compensatory hypertrophy is regulated, predominantly, by post-transcriptional mechanisms.