MicroRNAs are negative regulators of mRNA, and latest studies show that "mRNAs can also inhibit microRNAs". With these reciprocal interactions, different mRNAs with identical "microRNA binding site" cim regulate each other by competitively binding to the same microRNA pool. This is the novel competing endogenous RNA (ceRN A)regulating mechanism. The ceRN A mechanism, which is a totally new regulating mechanism , greatly expands the regulatory network across genes. It has been proved by experimental evidence that, in HCT116 colon cancer cells,KRAS and PTEN , ZEB2 and PTEN can regulate each other by ceRNA mechanism.