MiRNA-34a inhibits EGFR-signaling-dependent MMP7 activation in gastric cancer

The molecular mechanism underlying cancer invasiveness and metastasis of gastric carcinoma remains elusive. Here, we reported significant decrease in microRNA (miRNA)-34a and significant increase in phosphorylated epidermal growth factor receptor (EGFR) and matrix metalloproteinase-7 (MMP7) in the resected gastric carcinoma from the patients, compared with adjacent normal tissue. Moreover, strong correlation was detected among these three factors. To examine whether a causal link exists, we used two human gastric carcinoma lines, SNU-5 and HGC27, to study the molecular basis of miRNA-34a, EGFR signaling, and MMP7 activation. We found that EGF-induced EGFR phosphorylation in SNU-5 or HGC27 cells activated MMP7 and consequently cancer invasiveness. Both an inhibitor for EGFR and an inhibitor for Akt significantly inhibited the EGF-induced activation of MMP7, suggesting a phosphatidylinositol 3-kinase (PI3K) signaling cascade dependent pathway. Moreover, miRNA-34a levels were not affected by EGF-induced EGFR phosphorylation. However, overexpression of miRNA-34a antagonized EGF-induced MMP7 activation without affecting EGFR phosphorylation in SNU-5 or HGC27 cells. Taken together, our data suggest that miRNA-34 inhibits EGFR signaling via downstream PI3K signaling cascades to regulate MMP7 expression in gastric carcinoma. Thus, miRNA-34a, EGFR, and MMP7 appear to be promising therapeutic targets for preventing the metastasis of gastric carcinoma.