p38 MAPK Down-regulates Fibulin 3 Expression through Methylation of Gene Regulatory Sequences

Abstract

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. We have characterized in detail how p38 MAPK regulates fibulin 3 expression and its role. We describe here for the first time that p38, p38 , and p38 down-regulate fibulin 3 expression. p38 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, but once re-introduced represses Fibulin 3 expression. p38 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/ inhibition. Hence, p38 promigratory/invasive effect might be, at least in part, mediated by fibulin 3 downregulation in MEFs. In contrast, in HCT116 cells, Fibulin 3 promotes migration and invasion through a mechanism dependent on p38 and/or p38 activation. Furthermore, Fibulin 3 promotes in vitro and in vivo tumor growth of HCT116 cells through a mechanism dependent on p38, which surprisingly acts as a potent inducer of tumor growth. At the sametime, p38 limits fibulin 3 expression, which might represent a negative feed-back loop.