Hypoxia promotes metastasis in human gastric cancer by up-regulating the 67-kDa laminin receptor.

It has been reported that the 67-kDa laminin receptor (67LR) is implicated in cancer metastasis. We recently showed that 37LRP, the 67LR precursor, is a hypoxia-inducible factor 1 (HIF-1) target gene exposed to hypoxia in gastric cancer. Here, we investigated the role of 67LR in hypoxic metastasis and invasion in gastric cancer. Immunohistochemical analysis, western blotting, and RT-PCR assays revealed that 67LR was highly expressed in metastatic gastric cancers in vivo. Knockdown of the 67LR protein by RNA interference significantly decreased the adhesive, invasive, and in vivo metastatic abilities of the gastric cancer cell lines SGC7901 and MKN-45. Western blot analysis showed that 67LR increased the expression of urokinase-type plasminogen activator (uPA) and matrix metalloproteinase (MMP)-9, and decreased tissue inhibitor of matrix metalloproteinase (TIMP)-1 protein. We further showed that hypoxia induced 67LR expression in a time-dependent manner and this induction was inhibited by HIF-1 small-interfering (si) RNA. Both ERK and JNK inhibitors significantly inhibited hypoxia-induced expression of 67LR and the subsequent expression of uPA and MMP 9. SiRNA against 67LR or antibody against MMP9 and uPA significantly inhibited hypoxia-induced in vitro invasive ability. Taken together, these results reveal that 67LR promotes the invasive and metastatic ability of the gastric cancer cells through increasing uPA and MMP 9 expression, with involvement of the ERK and JNK signal pathway in hypoxia-induced 67 LR expressions and subsequent uPA and MMP9 expression.