Involvement of KLF4 in Sulforaphane- and Iberin-Mediated Induction of p21waf1/cip1

Sulforaphane (SF; 4-methylsulfinylbutyl isothiocyanate), a dietary compound derived from broccoli, may exhibit chemopreventive properties by inducing cell cycle arrest via induction of cyclin-dependent kinase inhibitor 1A (p21waf1/cip1), but the exact molecular mechanism has not been determined. Here we evaluate the role of the transcription factor Kruppel-like factor 4 (KLF4) in mediating the induction of p21waf1/cip1 and cellular differentiation by SF and iberin (IB; 3-methylsulphinyl propyl isothiocyanate), also derived from broccoli. Exposure of Caco-2 and Caco-2/TC7 cells to SF and IB increased expression of both KLF4 and p21waf1/cip1, whereas exposure of HT29 cells resulted only in induction of p21waf1/cip1. In Caco-2 cells, small interfering RNA knock down of KLF4 expression attenuated induction of p21waf1/cip1 in response to either SF or IB treatment. Contrary to expectation, prolonged exposure to SF reduced sucrase isomaltase activity, a marker of small intestinal differentiation in Caco-2 cells. Additional support for the SF-mediated induction of p21waf1/cip1 by KLF4 was obtained from analyses of gastric tissue of ApcMin/+ mice following acute intervention with SF but not from the analyses of other tissue of the intestinal tract. These results suggest that induction of p21waf1/cip1 by SF or IB may be partly mediated by KLF4 in some colon cancer cells and tissues.