Chromosomal passenger protein INCENP exists in constitutive and mitotic isoforms regulated by phosphorylation and proteolysis.

Abstract

The chromosomal passenger protein INCENP has a targeting and regulatory function as it is required for proper localization and activation of Aurora B during mitosis. As such INCENP undergoes sequential interactions with chromosomes, particular centromeres, the central spindle, the contractile ring and the midbody. INCENP has a predicted molecular mass of 105 kDa whereas the form associated with and phosphorylated by Aurora B migrates as 130 – 140 kDa protein suggesting that the latter represents a processed form. Indeed, immunoblot analyses with different antibodies revealed at least four distinct forms of Mr between 110 and 140 kDa. Of these, the 110 to 130 kDa forms were present throughout the cell cycle, whereas the 140 K form was restricted to mitosis. With the onset of mitosis, the 130 kDa form, but not the faster migrating species, became complexed with and phosphorylated by aurora B resulting in conversion to the 140 kDa form. This latter form was strictly dependent on aurora B activity as inhibition of aurora B by Hesperadin or exit from mitosis resulted in rapid degradation of both aurora B and INCENP140 while treatment of cells with phosphatase or proteasome inhibitors preserved the 140 kDa form. Thus, the activity and stability of the chromosomal passenger complex appears to be regulated by phosphorylation through aurora B and presumably other modifications. Additionally, our data suggest that there is a pool of uncomplexed, but stable INCENP present throughout the cell cycle which can be converted to the active form during mitosis. This work was supported by DFG, grant SHE246/16-1