Emerging evidence from The Cancer Genome Atlas has revealed that nuclear factor κB2 (nfκb2) gene encoding p100 is genetically deleted or mutated in human cancers, implicating NFκB2 as a potential tumor suppressor. However, the molecular mechanism underlying the antitumorigenic action of p100 remains poorly understood. Here we report that p100 inhibits cancer cell anchorageindependent growth, a hallmark of cellular malignancy, by stabilizing the tumor-suppressor phosphatase and tensin homolog (PTEN) mRNA via a mechanism that is independent of p100's inhibitory role in NFκB activation. We further demonstrate that the regulatory effect of p100 on PTEN expression is mediated by its downregulation of miR-494 as a result of the inactivation of extracellular signal-regulated kinase 2 (ERK2), in turn leading to inhibition of c-Jun/activator protein-1-dependent transcriptional activity. Furthermore, we identify that p100 specifically interacts with non-phosphorylated ERK2 and prevents ERK2 phosphorylation and nuclear translocation. Moreover, the death domain at C-terminal of p100 is identified as being crucial and sufficient for its interaction with ERK2. Taken together, our findings provide novel mechanistic insights into the understanding of the tumor-suppressive role for NFκB2 p100.