TRIM25 promotes Capicua degradation independently of ERK in the absence of ATXN1L

Abstract

Background Aberrations in Capicua (CIC) have recently been implicated as a negative prognostic factor in a multitude of cancer types through the derepression of targets downstream of the mitogen-activated protein kinase (MAPK) signaling cascade, such as oncogenic E26 transformation-specific (ETS) transcription factors. The Ataxin-family protein ATXN1L has previously been reported to interact with CIC in both developmental and disease contexts to facilitate the repression of CIC target genes and promote the post-translational stability of CIC. However, little is known about the mechanisms at the base of ATXN1L-mediated CIC post-translational stability. Results Functional in vitro studies utilizing ATXN1LKO human cell lines revealed that loss of ATXN1L leads to the accumulation of polyubiquitinated CIC protein, promoting its degradation through the proteasome. Although transcriptomic signatures of ATXN1LKO cell lines indicated upregulation of the mitogen-activated protein kinase pathway, ERK activity was found to contribute to CIC function but not stability. Degradation of CIC protein following loss of ATXN1L was instead observed to be mediated by the E3 ubiquitin ligase TRIM25 which was further validated using glioma-derived cell lines and the TCGA breast carcinoma and liver hepatocellular carcinoma cohorts. Conclusions The post-translational regulation of CIC through ATXN1L and TRIM25 independent of ERK activity suggests that the regulation of CIC stability and function is more intricate than previously appreciated and involves several independent pathways. As CIC status has become a prognostic factor in several cancer types, further knowledge into the mechanisms which govern CIC stability and function may prove useful for future therapeutic approaches.

ERK phosphorylation disrupts the intramolecular interaction of capicua to promote cytoplasmic translocation of capicua and tumor growth

“…Consistent with this observation, the inhibition of MAPK kinase (MEK), an upstream kinase of ERK, increases CIC levels in human cells treated with EGF ( Okimoto et al, 2017 ; Wang et al, 2017 ; Bunda et al, 2019 ). However, other studies have shown that EGF treatment does not induce CIC degradation in mammalian cells ( Ren et al, 2020 ; Wong et al, 2020 ), suggesting that the RTK activation-induced CIC degradation may depend on experimental conditions. Inactivation of MEK and p90RSK, a downstream kinase of ERK, suppresses the cytoplasmic translocation of CIC in HEK293T cells upon EGF or fibroblast growth factor treatment ( Ren et al, 2020 ).…”

Efp/TRIM25 and Its Related Protein, TRIM47, in Hormone-Dependent Cancers

“…It is of note that interaction of Efp and DDX5 requires SLC26A4-AS, suggesting the feature of Efp as an RNA-binding protein. In a study mainly using glioma cells, Efp was reported to be responsible for poly-ubiquitination and degradation of Capicua, a protein functioning as a transcriptional repressor of receptor tyrosine kinase signaling [ 42 ]. In this context, Efp has a tumor promotive effect.…”

TRIM25: A central factor in breast cancer

“…Previous studies have shown that the Capicua (CIC) protein has an important role as a prognostic factor in different types of cancer, and this role is related to changes in the expression of targets downstream of the MAPK signaling cascade[ 47 ]. However, a MAPK-independent mechanism has been proposed where the interaction of CIC with ATXN1L prevents CIC degradation by TRIM25[ 48 ]. Whereas TRIM25 repression increases CIC levels and its tumor suppressor function, TRIM25 induction decreases it, indicating that CIC degradation is mediated by TRIM25 via the UPS.…”

“…Whereas TRIM25 repression increases CIC levels and its tumor suppressor function, TRIM25 induction decreases it, indicating that CIC degradation is mediated by TRIM25 via the UPS. TRIM25 is enriched in both ATXN1L knockout and knockdown cell systems[ 48 ]. Another CIC interacting protein is 14-3-3 sigma, which has been shown to act as a tumor suppressor by negatively regulating the cell cycle and causing G2/M arrest.…”