Honokiol induces apoptosis through p53-independent pathway in human colorectal cell line RKO

AIM:To investigate the signal pathway of honokiol-inducedapoptosis on human colorectal carcinoma RKO cells and toevaluate whether p53 and p53-related genes were involvedin honokiol-treated RKO cells.METHODS:Cell cycle distribution and subdiploid peak wereanalyzed with a flow cytometer and DNA fragment withelectrophoresis on agarose gels.Transcriptional level ofBax,Bcl-2,Bid and Bcl-xl was accessed by RT-PCR.Western blotting was used to measure p53 proteinexpression and other factors related to apoptosis.Proliferation inhibition of two cell lines(RKO,SW480)withhigh expression of p53 and one cell line with p53 negativeexpression(LS180)was monitored by MTT assay.RESULTS:Honokiol induced RKO cell apoptosis in a dose-dependent manner.The mRNA expression level and proteinlevel of Bid were up-regulated while that of Bcl-xl wasdown-regulated,but no changes in Bax and Bcl-2 wereobserved.Western blotting showed p53 expression hadno remarkable changes in honokiol-induced RKO cellapoptosis.LS180 cells treated with honokiol exhibitedapparent growth inhibition like RKO cells and Sw480 cells.CONCLUSION:Honokiol can induce RKO cells apoptosisthrough activating caspase cascade by p53-indepenentpathway.