EXPRESSION OF ID-1 MESSENGER-RNA AND PROTEIN IN THE POSTISCHEMIC REGENERATING RAT-KIDNEY

The basic helix-loop-helix (bHLH) class of proteins are of major impor tance in controlling tissue-specific gene expression. The actions of t he bKLH proteins are inhibited by a related class of proteins,, inhibi tors of differentiation (Id). We have studied the expression of one of these latter proteins, Id-1, in the normal and post-ischemic regenera ting rat kidney by immunocytochemistry, Western blot and RNase protect ion assay (RPA) and correlated Id-1 regulation to the expression of vi mentin and proliferating cellular nuclear antigen (PCNA). In the norma l kidney strong immunostaining for Id-1 was found in the distal nephro n, especially in the distal convoluted tubule in the cortex. In partic ular, the perinuclear region was intensely stained in the cells of the distal tubule. mRNA for Id-1 was detectable by RPA on total RNA extra cted from the renal cortex of sham-operated animals, The Id-1 monomer was detected on Western blots of normal animals. Vimentin was expresse d in the mesangial cells of the glomeruli and in cells in the intersti tium while tubule cells were negative. The labeling intensity for PCNA was low in all cellular compartments in the normal kidney. In the reg enerating kidneys at various time intervals, the expression of Id-1-li ke immunoreactivity was widespread in the regenerating dedifferentiate d tubule cells while by the end of the study period, more highly diffe rentiated tubule cells appeared to lose their staining. On Western blo ts the Id-1 monomer was undetectable and instead strong staining was s een in the high molecular range, Id-1 mRNA levels in the regenerating kidneys did not differ significantly when compared to sham. PCNA label ing was intense in the regenerating kidneys at all time periods studie d, indicating the intense proliferative activity in the regenerating k idneys. Vimentin expression in the renal tubule cells was increased fr om day 3 and onward. The data are consistent with a hypothesis in whic h Id-1 regulates differentiation of renal tubule cells in the post-isc hemic regenerating rat kidney.