UC San Diego

Elucidating molecular mechanisms underlying transcriptional regulation of genes that are critical for normal and pathological development remains a central issue in biology and medicine. Although down-regulation of tumor metastasis suppressor genes are commonly observed in high-risk tumors, the responsible mechanisms have rarely been identified. Here I report that the down-regulation of KAI1, a metastasis suppressor gene, in prostate cancer cells involved the inhibitory function of a [Beta]-catenin -Reptin complex, which required both induced [Beta]- catenin expression and recruitment of HDAC1 by Reptin. On the contrary, the transcriptional activation of KAI1 required a sufficiently high level of Tip60 coactivator, which itself was negatively regulated by [Beta]-catenin. The coordinated actions of [Beta]-catenin-Reptin repressive complex antagonize a Tip60 coactivator complex. The balance of these opposing complexes controlled the expression of KAI1 and metastatic potential in prostate cancers. To understand how Reptin confers its transcriptional repressive function, I identified Reptin- interacting cofactors including UBC9 and ASXL1 by utilizing yeast two-hybrid screening, and investigated their roles in the functional regulation of Reptin. I discovered that Reptin was subjected to sumo conjugation and sumoylation was essential for its repressive function. Furthermore, I found that, when working together with ASXL1 and LSD1, Reptin acted as a transcriptional coactivator on multiple Hox gene promoters in NTera2 cells. Thus, Reptin appears to play dual roles in transcriptional regulation in a context-dependent manner. Lastly, I investigated how sumoylation mediated LSD1 functional switch from transcriptional repression to activation. I found that sumoylation enhanced LSD1 mediated-repression on Rest target promoters in nonneuronal cells; Knockdown of PIAS1, a LSD1 sumo E3 ligase, abrogated the recruitment of LSD1 on these target genes, concomitant with subsequent de-repression of these genes and increased H3K4me2 levels. On the other hand, activation of AR signaling by its ligand induced the recruitment of SENP1, a LSD1 sumo protease, and the de- sumoylation of LSD1 on the AR- target genes, accompanied by dramatically reduced H3K9me2 levels; Thus, sumoylated forms of LSD1 correlated with its gene repression function, while de-sumoylated forms of LSD1 correlated with its gene activation function together with AR. In summary, the changes in sumoylation-desumoylation status induced a switch of LSD1 functions in transcriptional regulation