The group used the technique called RNAi to create a library of bladder cancer cells with thousands of independent, silenced genes. Then they challenged these cultures with the parasite E. histolytica.
For the vast majority of cells in this genome-wide screen, E. histolytica decimated many thousands of these independent cell cultures. However, a small number of cells seemed to resist the parasite. Researchers discarded the killed cells and retested the cells that had survived; again infected these survivor cells with E. histolytica.
They did it over nine generations of cells, each time selecting the cells that survived and then re-applying the parasite. Over these generations of selection, they saw the cultures becoming more and more enriched for cells lacking specific genes.
Using next generation sequencing, scientists identified the genes that conferred resistance and found that many were involved in managing the flow of potassium into and out of human cells. Specifically, they identified genes KCNA3, KCNB2, KCNIP4, KCNJ3, and SLC24A3 involved in what is called potassium transport. A follow-up experiment showed that new intestinal cells treated with E. histolytica showed potassium efflux - the flow of potassium from inside a cell out through the cell wall - directly before cell death.
To ensure that lack of potassium transport was, in fact, causing resistance to the parasite, the group reversed the direction of their experiments. They started with new cells and used drugs to block their ability to transport potassium. Blocking potassium efflux created cells that were resistant to E. histolytica.