c-MYC Delays Prometaphase by Direct Transactivation of MAD2 and BubR1: Identification of Mechanisms Underlying c-MYC-Induced DNA Damage and Chromosomal Instability

Abstract

Here we show that the human BubR1 and MAD2 genes, which encode inhibitors of the anaphase promoting complex (APC/C), are directly activated by the oncogenic transcription factor c-MYC via E-box sequences in their first introns. In colorectal cancer biopsies elevated expression of c-MYC correlated with increased MAD2 levels. Activation of a conditional c-MYC allele delayed progression through mitosis in pro-metaphase in a MAD2- and BubR1-dependent manner. A fraction of the daughter cells derived from extended mitotic events underwent synchronous apoptosis, which was in part mediated by BubR1. Furthermore, c-MYC activation resulted in CIN (chromosomal instability) in the diploid MIN (microsatellite instability) cell line DLD-1 and further enhanced CIN in the aneuploid CIN-line MCF7. Unexpectedly, c-MYC-induced CIN was independent of c-MYC-induced BubR1/MAD2 expression and mitotic delay. Therefore, c-MYC-induced CIN may be caused be alternative pathways. We observed that activation of c-MYC induced DNA double-strand breaks, as evidenced by formation of gamma-H2AX foci, which colocalized with foci of active DNA replication. Furthermore, c-MYC activation resulted in mitotic chromosomes exhibiting DNA damage. Therefore, oncogenic deregulation of c-MYC prevents repair of replication-stress induced DNA lesions in the G(2)-phase. We suggest that the c-MYC-mediated persistence of DNA lesions throughout mitosis leads to chromosomal missegregation and underlies c-MYC-induced CIN. The effects of deregulated c-MYC on progression through mitosis described here may have important implications for the origin of chromosomal instability in many tumor types and the sensitivity towards cancer therapeutic agents targeting DNA or the mitotic spindle.

Transformation, genomic instability and senescence mediated by platelet/megakaryocyte glycoprotein Ibα

“…Independent of this, DSBs may produce dysmorphic nuclei, micronuclei and chromosomal bridging ( Figure 5; Supplementary Figure 2). Chromosomal bridging in fission yeast is a consequence of compromised kinetochore function (Ekwall et al, 1999) whereas in mammalian cells, it may arise from telomere defects, abnormalities in DNA replication and/or recombination, translocations associated with bi-centromeric chromosomes or overexpression of mitotic checkpoint genes (Harley and Villeponteau, 1995;Menssen et al, 2007;Sotillo et al, 2007). Chromosomal bridging has also been implicated in the creation of micronuclei similar to those reported here ( Figure 5; Saunders et al, 2000) and leads to other structural and numerical abnormalities (Saunders, 2003).…”

Induction of Cullin 7 by DNA damage attenuates p53 function

“…Cell lysis and immunoblotting were done as described in ref. 36. For immunodetection, membranes were incubated with antibodies specific for Cul7 (mouse hybridoma clone SA12 (37), p53 (DO-1; Santa Cruz Biotechnology, Santa Cruz, CA), p21 (Ab-11; NeoMarkers, Fremont, CA), HA (clone HA.11; Covance, Princeton, NJ), Flag (M2, F-3165; Sigma), P-Chk2 (Thr-68, sc-16297-R; Santa Cruz Biotechnology), ␣-tubulin (clone DM1A; Sigma), or ␤-actin (A-2066; Sigma).…”

The Ever Expanding Role for c-Myc in Promoting Genomic Instability

“…A recent report 44 has highlighted a potentially important relationship between c-Myc, CIN, and the mitotic spindle assembly checkpoint (SAC). The latter is a signaling pathway that oversees the proper alignment of sister chromatids on the metaphase plate and their attachment to the bipolar mitotic spindle.…”

“…45,46 It now turns out that two integral components of this checkpoint, namely Mad2 and BubR1, are direct c-Myc targets. 44 Both Mad2 and BubR1 are . This leads to two basic types of DNA damage: point mutations resulting from oxidized bases, and both single-stranded and double-stranded DNA breaks.…”