Stability of the neuronal fate determinant MEIS2 is controlled by calpain2

Calpains are non-lysosomal, Ca2+-dependent cysteine proteases, which are associated with various cellular functions but have so far been mainly studied in the context of disease. Their contribution to homeostasis in the healthy organism is still not well understood and their substrates have remained enigmatic in most cases. In the present study, we describe a previously unrecognized role for the calpain protease calpain2 in the regulation of neuronal differentiation of adult neural stem- and progenitor cells through cleavage and elimintation of the neuronal fate determinant MEIS2. Mass spectrometry analysis was performed on immunoprecipitated MEIS2 protein to identify phosphory¬lated residues in MEIS2 and on immunoprecipitated MEIS2 incubated with native porcine calpain2 to map calpain2-induced cleavage sites in the protein.