In vitro studies further demonstrate that miR-21 negatively regulates miR-145 and vice versa. k-Ras appears to play critical role in regulation of this process, as evidenced by the fact that the absence of k-Ras in CR colon cancer cells increases miR-145 expression, suppresses miR-21, and interrupts the negative cooperation between miR-21 and miR-145. This evidence concerns the gene KRAS and malignant colon neoplasm.