Figure 5.

 Effect of folylpolyglutamate synthetase (FPGS) modulation on p53 and p21. p53 is integrally involved in cell cycle control, DNA repair, and apoptosis⁵⁰ while p21 is a member of the cyclin dependent kinase inhibitor family, which inhibits G₁ and S phase progression.⁵¹ p53 promotes cell cycle arrest in late G₁ through upregulation of p21 in response to cell injury, thereby allowing time for repair, whereas in the event that DNA damage is more severe and non-reparable, p53 performs its alternative role of moving the cell into apoptosis.⁵⁰ FPGS overexpression (FPGS-S) downregulated, whereas FPGS inhibition (FPGS-AS) upregulated, p53 and p21 protein expression compared with endogenous FPGS (vector alone (VA)) in HCT116 cells (densitometry of bands: p53:β-actin ratio 1.9 (FPGS-S) v 3.1 (VA) v 4.1 (FPGS-AS); p21:β-actin ratio 1.7 (FPGS-S) v 2.5 (VA) v 3.2 (FPGS-AS)).