p38 MAPK Down-regulates Fibulin 3 Expression through Methylation of Gene Regulatory Sequences ROLE IN MIGRATION AND INVASION

p38 MAPKs regulate migration and invasion. However, the mechanisms involved are only partially known. We had previously identified fibulin 3, which plays a role in migration, invasion, and tumorigenesis, as a gene regulated by p38 alpha. We have characterized in detail how p38 MAPK regulates fibulin 3 expression and its role. We describe here for the first time that p38 alpha, p38 gamma, and p38 delta down-regulate fibulin 3 expression. p38 alpha has a stronger effect, and it does so through hypermethylation of CpG sites in the regulatory sequences of the gene. This would be mediated by the DNA methylase, DNMT3A, which is down-regulated in cells lacking p38 alpha, but once re-introduced represses Fibulin 3 expression. p38 alpha through HuR stabilizes dnmt3a mRNA leading to an increase in DNMT3A protein levels. Moreover, by knocking-down fibulin 3, we have found that Fibulin 3 inhibits migration and invasion in MEFs by mechanisms involving p38 alpha/beta inhibition. Hence, p38 alpha pro-migratory/invasive effect might be, at least in part, mediated by fibulin 3 down-regulation in MEFs. In contrast, in HCT116 cells, Fibulin 3 promotes migration and invasion through a mechanism dependent on p38 alpha and/or p38 beta activation. Furthermore, Fibulin 3 promotes in vitro and in vivo tumor growth of HCT116 cells through a mechanism dependent on p38 alpha, which surprisingly acts as a potent inducer of tumor growth. At the same time, p38 alpha limits fibulin 3 expression, which might represent a negative feed-back loop.