C74
p53-dependent cell cycle regulation of NDRG1 phosphorylation in colorectal cancer cells
Catherine McCaig, James T. Murray
Centre for Cancer Research and Cell Biology, Queen's university, Belfast, Northern Ireland, UK
Background
NDRG1 is a metastasis suppressor, down-regulated in a wide range of cancers including colon cancer. It is a p53-responsive gene, involved in p53 regulation of the cell cycle and apoptosis. NDRG1 is multisite phosphorylated by SGK1 and GSK3beta; two Ser/Thr protein kinases that are also involved in cell cycle regulation. However, the cell-cycle regulation of NDRG1 by these upstream kinases in cells that are defective for p53 has not been investigated.
Results
We have addressed the p53-dependent cell cycle regulation of NDRG1 using the model colorectal cancer cell line, HCT116, that is either wild-type (WT) for p53 or has had p53 genetically ablated (null). We have profiled the NDRG1 expression and phosphorylation status at different points of the cell cycle following synchronisation and release of cells from G1/S or G2/M -phase blocks induced by aphidicolin or nocodazole, respectively. NDRG1 protein levels are comparable in p53 WT and null cells and expression levels do not change as cells proceed through the cell cycle. However, in contrast to WT cells, NDRG1 is hyperphosphorylated in the nulls.
We also investigated what affect G1-arrest, induced by contact inhibition of cell growth, had on NDRG1. We found that compared to p53 WT cells the p53 null cells had up-regulated NDRG1 expression, which was also hyper-phosphorylated.
Conclusion
These data suggest that phosphorylation of NDRG1 is functionally important during the cell cycle and that p53-status affects NDRG1 phosphorylation. Aberrant regulation of NDRG1 phosphorylation could be important for its ability to function as a metastasis suppressor.
