KLF4 functions both as a tumour suppressor and an oncogene. The ability of KLF4 to affect the levels of expression of the cell-cycle regulator p21 (CDKN1A) seems to be involved, in that this protein might function as a switch that determines the outcome of KLF4 signalling.
See also
References
Rowland BD, Peeper DS. KLF4, p21 and context-dependent opposing forces in cancer. Nat Rev Cancer. 2006 Jan;6(1):11-23. PMID: 16372018