Transcription factor Sp1 regulates mitotic chromosome assembly and segregation.

Aneuploidy is a pervasive feature of cancer cells that results from chromosome missegregation. Several transcription factors have been associated with aneuploidy; however, no studies to date have demonstrated that mammalian transcription factors directly regulate chromosome segregation during mitosis. Here, we demonstrate that the ubiquitously expressed transcription factor specificity protein 1 (Sp1), which we have previously linked to aneuploidy, has a mitosis-specific role regulating chromosome segregation. We find that Sp1 localizes to mitotic centromeres and auxin-induced rapid Sp1 degradation at mitotic onset results in chromosome segregation errors and aberrant mitotic progression. Furthermore, rapid Sp1 degradation results in anomalous mitotic chromosome assembly characterized by loss of condensin complex I localization to mitotic chromosomes and chromosome condensation defects. Consistent with these defects, Sp1 degradation results in reduced chromosome passenger complex activity and histone H3 serine 10 phosphorylation during mitosis, which is essential for condensin complex I recruitment and chromosome condensation. Together, these data provide the first evidence of a mammalian transcription factor acting specifically during mitosis to regulate chromosome segregation.