AbstractThe ubiquitin‐proteasome pathway (UPP) is involved in the degradation of the extracellular matrix (ECM) and trophoblastic invasion during early pregnancy. Our previous studies demonstrated that inhibition of UPP suppresses expression of matrix metalloproteinase (MMP)‐2 and ‐9. LMP2 is an important proteasome subunit that is critical for proteasome activity. This study investigated the regulatory mechanism of LMP2 on the expression and activities of MMP‐2 and MMP‐9. Our results showed that transfection of LMP2 siRNA plasmid into the human invasive extravillous trophoblast cell line (HTR8/Svneo) could significantly suppress expression of LMP2 mRNA and protein. The mRNA expression of MMP‐2 and MMP‐9 and their activities were markedly decreased in the LMP2‐inhibited cells. Inhibition of LMP2 could also reduce IκBα mRNA level, although the expression of phosphorylated IκBα was increased. In the LMP2‐inhibited cells, expression of mRNA encoding NF‐κB subunits p50 and p65 remained normal, but the p50 protein level was significantly decreased in the cytosolic and nuclear extracts, while p65 protein was markedly reduced only in the nuclear extract. We also demonstrated that blockage of the NF‐κB pathway by the NF‐κB translocation inhibitor SN50 markedly reduced the expression of MMP‐2 and MMP‐9 in HTR8/Svneo cells, a result that is fully consistent with the results from the LMP2‐inhibited HTR8/Svneo cells. These data suggest that LMP2 contributes to IκBα degradation and p50 generation, and that inhibition of LMP2 suppresses expression and activities of MMP‐2 and MMP‐9 by blocking the transfer of active NF‐κB heterodimers into the nucleus. © 2005 Wiley‐Liss, Inc.