Insulin receptor-related receptor messenger ribonucleic acid: quantitative distribution and localization to subpopulations of epithelial cells in stomach and kidney.

A novel member of the insulin receptor family, the insulin receptor-related receptor (IRR), was initially identified by cloning genomic DNA homologous to the insulin receptor. We have now used Northern blot and polymerase chain reaction analyses of a variety of human tissues to demonstrate that the kidney is a major site of IRR gene expression. IRR transcripts (approximately 6 and approximately 2 kilobases) were detected only in human kidney by Northern blot analyses. Quantitative competitive polymerase chain reaction analysis revealed that IRR messenger RNA levels were distributed more widely. IRR transcripts in human kidney were approximately 3- to 10-fold greater than those in thymus, brain, heart, and stomach and approximately 150-fold higher than those in placenta, skeletal muscle, and liver. In situ hybridization histochemical analysis revealed that IRR transcripts were present in a subpopulation of cells within distal tubules of human kidney, beyond the most proximal segment of the distal convoluted tubule. In rat stomach, IRR messenger RNA was localized to a subset of neuroendocrine cells in gastric glands of the fundic mucosa. This selective distribution of IRR transcripts in human and rat tissues suggests that IRR may mediate the responses of a neuroendocrine factor involved in regulating select aspects of cell function in a highly tissue-specific manner.