Participation of p97^Eps8 in Src-mediated Transformation

Histone acetylase and histone deacetylase are two crucial enzymes that determine the structure of chromatin, regulating gene expression. In this study, we observed that trichostatin A (TSA), a specific histone deacetylase inhibitor, could effectively inhibit the growth of v-Src-transformed (IV5) cells and abrogate their ability to form colonies in soft agar. Further analysis demonstrated that, although TSA reduced the expression of Eps8 in a dose- and time-dependent manner, both the protein expression and kinase activity of v-Src remained constant, and the abundance and phosphotyrosine levels of Src substrates, including cortactin, focal adhesion kinase, p130 ^Cas, paxillin, and Shc, were not altered. Notably, removal of TSA from the medium restored not only the expression of Eps8, but also cellular growth. Northern and reverse transcription-PCR analyses revealed the significant reduction of eps8 transcripts in TSA-treated IV5 cells relative to control cells. When active Src-expressing chicken embryonic cells were forced to overexpress p97^Eps8, they became resistant to TSA-mediated anti-proliferation. Furthermore, using small interference RNA of eps8, we demonstrated the requirement for Eps8 in IV5 cell proliferation. Thus, our results highlight a critical role for p97^Eps8 in TSA-exerted growth inhibition of v-Src-transformed cells.