The nuclear exporter, Crm1, is regulated by NFY and Sp1 in cancer cells and repressed by p53 in response to DNA damage.

摘要

The nuclear exporter protein, Crm1, plays a key role in normal cell functioning, mediating the nucleo-cytoplasmic transport of cargo proteins. Elevated Crm1 expression has recently been identified in various tumours; however, the mechanisms driving its expression have not been investigated to date. In this study we identified the Crm1 promoter and factors associated with its elevated expression and with its repression under conditions of DNA damage. The -1405 to +99 Crm1 promoter region was found to be significantly more active in cancer and transformed cells compared to normal, and the -175 to +99 region identified as responsible for the differential activity. Mutation of two CCAAT boxes and a GC box within this region significantly diminished Crm1 promoter activity and ChIP analysis revealed binding of NFY and Sp1 to these sites, with increased binding in transformed and cancer cells. In addition, p53 was found to repress Crm1 promoter activity, after induction with doxorubicin, with p53 siRNA blocking the effect. Crm1 promoter constructs with mutated CCAAT boxes were significantly less responsive to p53 repression, and in vivo binding of NFY to the CCAAT boxes was diminished upon p53 binding, suggesting that p53 mediates repression of the Crm1 promoter via interfering with NFY. This was confirmed using NFY knock-down cells, in which Crm1 promoter activity was significantly less responsive to p53. In vitro EMSAs revealed that NFY and p53 bind the CCAAT boxes as a single complex under conditions of DNA damage. In summary, this study is a first to analyse Crm1 promoter regulation and reveals NFY and Sp1 as contributors to Crm1 overexpression in cancer. In addition, this study reveals that Crm1 transcription is inhibited by DNA damage and that the mechanism of inhibition involves p53 interfering with NFY function.