Abstract
A recent proteomics study identified FAM129B or MINERVA as a target of the MAP kinase (Erk1/2) signaling cascade in human melanoma cells. Phosphorylation of the protein was found to promote cell invasion and the dissociation of the protein from the cell-cell junctions. Suppression of apoptosis during metastasis is a prerequisite for the survival and spread of cancer cells. During apoptosis, the adherens junctions are disassembled as the dying cell retracts, and new contacts are formed between normal neighboring cells. In this study, we show that FAM129B was cytosolic in exponentially growing HeLa cells but was translocated to the adherens junctions where it colocalized with β-catenin whenever contact between two or more cells was established. Silencing the FAM129B gene expression by specific siRNAs did not induce apoptosis or inhibit the growth of HeLa cells. However, when apoptosis was induced by exposure to TNFα/cycloheximide or other apoptotic signaling molecules, the onset of apoptosis was accelerated 3-4-fold when FAM129B was depleted. Annexin V binding, the inactivation of the DNA repair enzyme, poly(ADP-ribose) polymerase, and the activation of the caspases occurred more rapidly in the cells lacking FAM129B. The rapid induction of apoptosis in FAM129B knockdown cells was reversed by co-transfection with recombinant FAM129B, indicating that its effect on apoptosis was specific. As apoptosis proceeded, FAM129B was degraded and disappeared from the plasma membrane. Thus, one crucial facet of the mechanism by which FAM129B promotes cancer cell invasion is likely to be the suppression of apoptosis.