Since miRs mediate post-transcriptional gene silencing by translational inhibition, the inverse relationship between the levels of selected miRs and the levels of uPAR/CXCR4 expression, observed in KG1 and THP-1 and U937 cells, suggested that miR-146a, miR-335 and miR-622 could regulate uPAR and CXCR4 expression in leukaemia cells. The gene discussed is PLAUR; the disease is leukemia.