Proteome response in HT-29 human colorectal cancer cells to two apoptosis-inducing compounds with different mode of action.

Flavone and camptothecin were both shown to potently induce apoptosis in HT-29 human colon cancer cells. Whereas camptothecin acts on the basis of topoisomerase-I inhibition, flavone appears to burst mitochondrial production of reactive oxygen species by increasing respiratory chain activity. In our study, we searched for similarities and differences in the proteome response of HT-29 cells when treated with the two different compounds. The accessible proteome of HT-29 cells was separated subsequent to the exposure to flavone or camptothecin by 2D-polyacrylamide-gel electrophoresis using pH-gradients between 4 and 7 and 6 and 11 in the first dimension and proteins with changed expression level were identified by peptide mass fingerprints of tryptic digests of the protein spots. Whereas there was a high congruence with regard to the identities of regulated proteins and their grade of regulation, a number of spots changed specifically only in response to either flavone or camptothecin. Nuclear envelope proteins were specifically increased by camptothecin indicating the intervention of this drug with cell division processes. Increased levels of coproporphyrinogen III oxidase, involved in cytochrome synthesis, and ubiquinol-cytochrome-c reductase suggest adaptations to flavone in order to enable a higher substrate flux through the respiratory chain. In conclusion, HT-29 cells respond to camptothecin and flavone with regulations of many proteins in a similar manner suggesting those alterations to be caused by apoptosis induction. Some protein regulations, however, were specific for each compound and point to the mechanism of their action.