Suppression of hnRNP K expression downregulates the expression and activity of MMP12 in NPC. (A) NPC-TW02 and -HK1 cells were transfected with hnRNP K-targeting (K) or control (C) siRNA. Twenty-four hours after transfection, cells were further cultured in serum-free medium for another 48 h. MMP12 mRNA levels were determined by quantitative RT-PCR, and MMP12 and hnRNP K protein levels in the culture supernatant (Sup) and in the cell extract (CE), respectively, were examined by Western blotting. PGK1 and Actin protein levels were used as the loading control for the secreted and the cytoplasmic proteins, respectively. (B) The enzymatic activity of MMP12 was analyzed by zymography. The supernatants from the NPC cells treated with either hnRNP K-targeting (K) or control (C) siRNA were collected after 48 h, and were subjected to zymographic analysis. The protein levels of hnRNP K and actin in the cell extracts were analyzed by Western blotting.