Phosphorylation of MCPH1 isoforms during mitosis followed by isoform-specific degradation by APC/C-CDH1

Abstract

Microcephalin-1 (MCPH1) exists as 2 isoforms that regulate cyclin-dependent kinase-1 activation and chromosome condensation duringmitosis, withMCPH1mutations causing primarymicrocephaly.MCPH1 is also a tumor suppressor protein, with roles in DNA damage repair/checkpoints. Despite these important roles, there is little information on the cellular regulation ofMCPH1.Weshow that bothMCPH1isoforms are phosphorylatedin a cyclin-dependent kinase-1-dependent manner in mitosis and identify several novel phosphorylation sites. Upon mitotic exit, MCPH1 isoforms were degraded by the anaphase-promoting complex/cyclosome-CDH1 E3 ligase complex. Anaphase-promoting complex/cyclosome-CDH1 target proteins generally have D-Box or KEN-Box degron sequences.We found thatMCPH1 isoforms are degraded independently,with the long isoformdegradation beingD-Box dependent,whereas the short isoformwas KEN-Box dependent.Our research identifies several novel mechanisms regulating MCPH1 and also highlights important issues with several commercialMCPH1 antibodies, with potential relevance to previously published data.