Ubiquitylome analysis identifies dysregulation of effector substrates in SPOP-mutant prostate cancer

Abstract

Cancer genome characterization has revealed driver mutations in genes that govern ubiquitylation; however, the mechanisms by which these alterations promote tumorigenesis remain incompletely characterized. Here, we analyzed changes in the ubiquitin landscape induced by prostate cancer-associated mutations of SPOP, an E3 ubiquitin ligase substrate binding protein. SPOP mutants impaired ubiquitylation of a subset of proteins in a dominant-negative fashion. Of these, DEK and TRIM24 emerged as effector substrates consistently up-regulated by SPOP mutants. We highlight DEK as a SPOP substrate that exhibited decreases in ubiquitylation and proteasomal degradation resulting from heteromeric complexes of wild-type and mutant SPOP protein. DEK stabilization promoted prostate epithelial cell invasion, implicating DEK as an oncogenic effector. More generally, these results provide a framework to decipher tumorigenic mechanisms linked to dysregulated ubiquitylation.

Higher‐order oligomerization promotes localization of SPOP to liquid nuclear speckles

“…Crystal structures of subsets of CRL complexes and SPOP can be used to build a model of CRL3 SPOP without additional assumptions (Movie EV2). The model suggests that cullin/Rbx1 binding to each SPOP monomer is not impeded by SPOP oligomerization, which is in agreement with experimental data (Theurillat et al , 2014). The helical propensity of the SPOP oligomer places the cullin molecules in a spiral arrangement, with each arm bent toward the helical axis (van Geersdaele et al , 2013).…”

“…Truncated SPOP constructs encoding the BTB and BACK domains self‐associate into higher‐order oligomers (Errington et al , 2012) that possess increased ubiquitination efficiency, supporting the functional importance of oligomerization (Zhuang et al , 2009; Errington et al , 2012). Mutations within the MATH domain perturb interactions with substrates (Geng et al , 2013, 2014; Theurillat et al , 2014; Zeng et al , 2014; Zhang et al , 2015). Mutations within both self‐association domains are also found in cancers [Appendix Fig S1 and www.cbioportal.org (Cerami et al , 2012; Gao et al , 2013)], further supporting a functional role for higher‐order oligomerization, but their pathological mechanism is unclear.…”

Comprehensive assessment of cancer missense mutation clustering in protein structures

“…S6B). Theurillat et al recently analyzed the protein levels of a novel SPOP substrate, DEK, in prostate tumor cell lines, where different SPOP variants were overexpressed (36). Consistent with our findings, they observed that DEK levels were significantly elevated in the case of missense variants in the substrate-binding pocket (cluster S) but not in the case of SPOP-E50K (which falls in our cluster E).…”

MicroRNA-424 impairs ubiquitination to activate STAT3 and promote prostate tumor progression

“…Intriguingly, functional annotation analysis revealed among the 323 putative targets a striking prevalence of genes involved in protein ubiquitination and specifically encoding components of the E3 ubiquitin ligase complexes (n = 29) ( Figure 5B and Supplemental Table 2). Proteins of the E3 ubiquitin ligase complex are emerging as important oncogenic or tumor suppressor factors deregulated as a consequence of genetic events in various cancers, including prostate cancer (16,18,19). Notably, among the top miR-424 targets we found the E3 ubiquitin ligase COP1 (also known as RFWD2), which is a known tumor suppressor deleted in 3%-8% of prostate cancers and other types of tumors (16,19).…”

“…Deregulated expression of miRNAs is very frequent in human cancers, including prostate cancer (13)(14)(15). Mutations and deletions of genes encoding components of the ubiquitin ligase complexes resulting in altered protein ubiquitination and turnover are also emerging as important mechanisms driving prostate tumorigenesis (16)(17)(18)(19).…”