MMP9 and lung adenocarcinoma: Concerning PCNA, Cui and others demonstrated that small hairpin RNA(shRNA)-mediated knockdown of a nuclear effector of the Hippo pathway, Yes-associated protein 1 (YAP1), down-regulate the expression of AxI, PCNA, and MMP-9, and inhibit the proliferation and invasion of human lung adenocarcinomas and gastric adenocarcinoma cells (Cui et al., 2012).