induces not only Mmp9 but also Mmp3 and Mmp13 mRNA expressions but not obvious Mmp2 and Mmp14 mRNA expressions. Sub-confluent cell cultures were pretreated overnight with serum-free medium at pH 7.4 and stimulated by serum-free media at pH 6.8 or 7.4. After 24 h, total RNA was extracted, reverse-transcribed, and amplified by qPCR with specific primer sets. Data are shown as relative expression compared with LLCm1 cells cultured at pH 7.4. Representative results were shown from three or more independent experiments. **P < 0.01; ***P < 0.001; NS, not significant.