Revisiting ubiquity and tissue specificity of human calpains

The abundance of mRNAs transcribed from human genes of the calpain superfamily was studied in 72 human tissues and cell types by the Human Multiple Tissue Expression (MTE) Array technique. The analysis included the large subunits of and mcalpains, the small subunits, calpastatin and calpain 3 (p94). Besides specific data on transcriptional activity, two major conclusions emerged: (i) ubiquitous calpains are not expressed in all cell types, and (ii) a tissuespecific calpain may be expressed in many cell types apart from the one in which it is particularly abundant. Therefore, the categoric classification of ubiquitous vs. tissuespecific calpains is a simplification.