Deciphering TRIM69 interactors and its phosphor-proteomic regulation in centrosome dynamics

Stringent control of centrosome duplication and separation is important for preventing chromosome instability. Structural and numerical alterations in centrosomes are hallmarks of neoplastic cells and contribute to tumorigenesis. We show that a Centrosome Amplification 20 (CA20) gene signature is associated with high expression of the Tripartite Motif (TRIM) family member E3 ubiquitin ligase, TRIM69. TRIM69-ablation in cancer cells leads to centrosome scattering and chromosome segregation defects. To identify potential effectors of TRIM69 in regulating centrosome dynamics, we performed mass-spectrometry analysis of immunopurified TRIM69 complexes and defined the TRIM69 protein-interaction network. We discovered Serine/threonine-protein kinase 3 (MST2) as a new direct binding partner of TRIM69 and TRIM69 redistributes MST2 to the perinuclear cytoskeleton. Additionally, we performed IP mass- spectrometry analysis to define the MST2 interactome in the presence and absence of co-expressed TRIM69A. We found that WT TRIM69A (but not the E3 ligase mutant) promoted complex formation between MST2 and PLK1 in the detergent-insoluble CSK compartment. PLK1-mediated phosphorylation of MST2 at S15, S18 and S316 is crucial for centrosome disjunction. Analysis of MST2 phospho-peptides from the LC-MS/MS experiment revealed increased phosphorylation of S15, S316 and several other residues in the detergent-insoluble fraction of TRIM69A-overexpressing cells. Our findings suggest that TRIM69 is a new proximal regulator of distinct signaling pathways that regulate centrosome dynamics and promote bipolar mitosis. Further studies are necessary to identify the putative TRIM69A substrate(s) whose ubiquitination is necessary for regulating and interacting MST2 and centrosome dynamics. To address this issue, we have performed an unbiased mass spectrometry screen for TRIM69A-induced ubiquitination events.