Plasminogen activation is implicated in solid tumor growth, invasion and metatastic spread. extracellular proteolytic enzymes of the urokinase-type plasminogen activator (uPA) and metalloproteinase (MMP) family play a crucial role in the matrix degradation and tissue remodeling process characteristic of malignant disorders. The receptor for urokinase plasminogen activator (uPAR) serves to localize and intensify the action of uPA and is expressed on the surface of malignant cells. However, little is known about its role in leukemia. Since uPA and uPAR expression correlates with the progression of leukemia, therapies designed to inhibit uPA and uPAR expression would be beneficial. In this study, we utilized small hairpin RNAs (shRNAs), also referred to as small interfering RNAs, to target human uPAR. These small interfering RNA constructs significantly inhibited uPAR expression at both the mRNA and protein levels in myeloid leukemia cell line, HEL. uPAR knockdown in HEL cells resulted in a dramatic reduction of MMPs expression (MMP- 2,–9, MT-MMP-1) and tumor cell invasion as indicated by a Matrigel invasion assay. Furthermore, RNA interference for uPAR abrogated uPA-uPAR signaling to downstream target molecules such as JAK2, JNK, ERK1/2 and Stat-3. These findings uncovered evidence of a complex signaling network operating downstream of uPA-uPAR that actively contributes to leukemia progression. Thus, RNA interference-directed targeting of uPAR is a convenient and novel tool for studying the biological role of the uPAR system and suggests the potential of its application for leukemia therapy.

[Proc Amer Assoc Cancer Res, Volume 47, 2006]