Differences in cathepsin B mRNA levels in rat tissues suggest specialized functions.

The tissue distribution of mRNAs encoding two lysosomal proteases, cathepsin B and cathepsin D, was examined using cloned cDNAs to probe Northern and dot blots of RNAs extracted from various rat tissues. Cathepsin B mRNA showed a wide range of variation in expression in the tissues analyzed with the highest concentrations found in spleen and kidney, while the cathepsin D mRNA levels were relatively uniform in these same tissues. Significant quantities of cathepsin B mRNA were detected in total RNA from isolated islets of Langerhans but was not detectable in equivalent amounts of RNA from whole pancreas. The wide variations in tissue levels of cathepsin B mRNA suggest that tissue specific controls may regulate its expression and are compatible with the participation of this protease in specialized cellular functions other than intralysosomal protein degradation.