TRIM37 prevents formation of centriolar protein assemblies by regulating Centrobin

Abstract

TRIM37 is an E3 ubiquitin ligase mutated in Mulibrey nanism, a disease with impaired organ growth and increased tumor formation. TRIM37 depletion from tissue culture cells results in supernumerary foci bearing the centriolar protein Centrin. Here, we characterize these centriolar protein assemblies (Cenpas) to uncover the mechanism of action of TRIM37. We find that an atypical de novo assembly pathway can generate Cenpas that act as microtubule organizing centers (MTOCs), including in Mulibrey patient cells. Correlative light electron microscopy reveals that Cenpas are centriole-related or electron-dense structures with stripes. TRIM37 regulates the stability and solubility of Centrobin, which accumulates in elongated entities resembling the striped electron dense structures upon TRIM37 depletion. Furthermore, Cenpas formation upon TRIM37 depletion requires PLK4, as well as two parallel pathways relying respectively on Centrobin and PLK1. Overall, our work uncovers how TRIM37 prevents Cenpas formation, which would otherwise threaten genome integrity, including in Mulibrey patients.

Global cellular response to chemical perturbation of PLK4 activity and abnormal centrosome number

“…We observed that CEP120, CETN2 and CNTROB, but not PLK4 could be detected in these aggregates (Figure 5 – figure supplement 1A). PLK4 has been observed in similar structures but could only be detected using a single antibody [30, 38, 39]. To verify our results, we expressed FLAG-tagged PLK4 from a tetracycline-inducible promoter in TRIM37 -/- cells.…”

“…In the absence of TRIM37, some centriolar proteins form intracellular aggregates in interphase cells [38, 41]. We observed that CEP120, CETN2 and CNTROB, but not PLK4 could be detected in these aggregates (Figure 5 – figure supplement 1A).…”

“…A number of centrosome-centric TRIM37 functions have been recently described. In the absence of TRIM37 a collection of centriole proteins such as CNTROB, PLK4, CETN1/2, CP110 accumulate to form aberrant assemblies referred to as condensates or ‘Cenpas’ (Centriolar protein assemblies) [38, 39]. These structures are dependent on the presence of CNTROB, but it is unclear why TRIM37 might suppress their formation in normal cells TRIM37 is part of the 17q23 amplicon present in approximately 18% of breast cancer tumours [40] and overexpression of TRIM37 in these lines renders them sensitive to the PLK4 inhibitor centrinone [41, 42].…”

TRIM37 prevents formation of condensate-organized ectopic spindle poles to ensure mitotic fidelity

“…Centrobin-scaffolded condensates in TRIM37Δ cells are highly ordered and have either a linear striated or a hexagonally packed punctate sheet structure. Ectopic centrobin-containing structures with a striated morphology have also been reported in a recent study using RNAi-mediated TRIM37 depletion ( Balestra et al, 2021 ). An important question raised by the highly ordered nature of these ectopic structures in TRIM37Δ cells and their formation at centrosomes is whether they reflect a normal assembly process in a specific biological context.…”

Self-assembly of pericentriolar material in interphase cells lacking centrioles

“…Many PCM components are known to oligomerize and interact with each other, and recent work suggested that phase separation of interacting PCM components can contribute to centrosome assembly (Raff, 2019;Woodruff et al, 2017). This idea is underscored by data showing that various cell-type specific assemblies of PCM components can form clusters which can nucleate and organize microtubules and serve as MTOCs in the absence of centrioles, particularly during the formation of mitotic spindle poles (Balestra et al, 2021;Chinen et al, 2021;Gartenmann et al, 2020;Meitinger et al, 2020;Watanabe et al, 2020;Yeow et al, 2020).…”