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Abstract
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 (p21 waf1/cip1 ), but the exact molecular mechanism has not been determined. Here we evaluate the role of the transcription factor Krüppel-like factor 4 (KLF4) in mediating the induction of p21 waf1/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 p21 waf1/cip1 , whereas exposure of HT29 cells resulted only in induction of p21 waf1/cip1 . In Caco-2 cells, small interfering RNA knock down of KLF4 expression attenuated induction of p21 waf1/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 p21 waf1/cip1 by KLF4 was obtained from analyses of gastric tissue of Apc Min/+ mice following acute intervention with SF but not from the analyses of other tissue of the intestinal tract. These results suggest that induction of p21 waf1/cip1 by SF or IB may be partly mediated by KLF4 in some colon cancer cells and tissues.
ACKNOWLEDGMENTS
We would like to thank Barbara Cross and Robert Rudling from Cancer Research UK for help with maintaining the mice. This study was supported by a grant from the UK Biotechnology and Biological Sciences Research Council.