Background

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) regulates tissue morphogenesis, a complex balance of polarised growth, cell death and remodelling. Cdc42 is a small Rho-like GTPase and master regulator of polarization, implicated in PTEN-dependent morphogenesis. PTEN may influence apoptosis through multiple molecular mechanisms but their role in morphogenesis remains unclear. This study tests the hypothesis that PTEN regulates apoptosis through Cdc42-dependent signalling.

Method

We used HCT 116 PTEN ^+/+ and ^-/- colorectal cells and Caco2 wild type and Caco2 PTEN shRNA stable transfectants as a model system. Cells were transfected with Cdc42 wild type (WT), constitutively active (CA) and dominant negative (DN) constructs or PTEN or Cdc42 siRNA. Cells were treated with Sodium butyrate, a pharmacological activator of PTEN; Lithium chloride, a GSK3? suppressor; and JNK inhibitor. Protein expression was assayed by immunoblotting and apoptosis was assessed by flow cytometry.

Results

Transfection of wild type or PTEN deficient HCT116 and Caco2 cells with full length PTEN or PTEN siRNA respectively activated or suppressed cdc42 and PARP cleavage. Transient expression of WT and CA Cdc42 activated JNK, suppressed GSK3? and promoted PARP cleavage. Conversely, transfection of DN Cdc42 or cdc42 siRNA inhibited JNK and suppressed apoptosis. Treatment by JNK inhibitors suppressed GSK3? phosphorylation and inhibited PARP cleavage. Treatment with LiCl enhanced PTEN induced apoptosis.

Conclusion

We conclude that PTEN regulates apoptosis through a Cdc42/ JNK/GSK3? pathway in colon cancer cells. These studies link PTEN-dependent polarization pathways to apoptosis which may be important for coordinated regulation of morphogenesis.