Exploring the Role of Mob1 in the p53 Response to Mitotic Arrest

Genomic integrity relies upon a system of checkpoints that ensure accurate duplication of genomic information that are capable of halting cell cycle progression in response to cellular stresses. Central to this response is the transcription factor p53, which mediates the transcription of the cyclin-dependent kinase inhibitor p21 as well as other factors to affect cell cycle arrest and eventually promote apoptosis. Another pathway is the Salvador-Wartz-Hippo (SWH), which plays significant roles in regulating cell proliferation, organ size, and apoptosis. LATS2, a core component of SWH plays roles as a repressor of Mdm2, a known p53 inhibitor, which connect the p53 response to mitotic arrest. Our lab demonstrated that p53 is stabilized and enriched in the nucleus in response to prolonged mitosis, and using yeast two-hybrid screens identified LATS2 as a MOB1 binding protein. Since many questions remain regarding the crosstalk between the p53 and SWH pathways, our efforts attempt to elucidate the relationship between the two. To explore the role of Mob1 in the p53 response, mitotic arrest was induced in RPE1 cells by inhibition of Eg5 with S-Trityl-L-Cysteine resulting in prolonged mitosis, then were allowed to synchronously exit mitosis using Flavopiridol or Reversine. We observed stabilization of p53 in cells treated with Flavopiridol, but not with Reversine. Although we did not observe an enrichment of pMob1 in the nucleus in any of the treatments, we observed pMob1 localized to cytokinetic factors such as midbodies and spindle poles in cells treated with Reversine, and mislocalized after treatments with Flavopiridol.