The E3 ligase TRIM22 functions as a tumor suppressor in breast cancer by targeting CCS for proteasomal degradation to inhibit STAT3 signaling.

Deregulation of E3 ubiquitin ligases drives the proliferation and metastasis of various cancers; however, the underlying mechanisms remain unknown. This study aimed to investigate the role of tripartite motif-containing 22 (TRIM22), a poorly investigated E3 ubiquitin ligase in the TRIM family, as a tumor suppressor in breast cancer. High expression of TRIM22 in breast cancer correlated with better prognosis. Functional experiments demonstrated that TRIM22 significantly inhibited the proliferation and invasion of breast cancer cells. Label-free proteomics and biochemical analyses revealed that the copper chaperone for superoxide dismutase (CCS), an oncoprotein that is upregulated in breast cancer and promotes the growth and invasion of breast cancer cells, was a target of TRIM22 for degradation via K27-linked ubiquitination. Notably, the ability of the coiled-coil domain-defective mutants of TRIM22 to induce CCS ubiquitination and degradation diminished, with lysine 76 of the CCS serving as the ubiquitination site. Moreover, the TRIM22-mediated inhibition of the proliferation and invasion of breast cancer cells was restored by ectopic CCS expression. RNA-sequencing experiments using Gene Set Enrichment Analysis demonstrated that TRIM22 is involved in the JAK-STAT signaling pathway. TRIM22 overexpression also improved reactive oxygen species levels in breast cancer cells and inhibited STAT3 phosphorylation, which was restored via CCS overexpression or N-acetyl-l-cysteine treatment. Chromatin immunoprecipitation-quantitative polymerase chain reaction results showed that TRIM22 overexpression decreased the enrichment of phosphorylated STAT3 in FN1, VIM and JARID2 promoters. Clinically, low TRIM22 expression correlated with high CCS expression and decreased survival rates in patients with breast cancer. Moreover, TRIM22 upregulation was associated with a better prognosis in patients with breast cancer who received classical therapy. TRIM22 expression was downregulated in many cancer types, including colon, kidney, lung, and prostate cancers. To the best of our knowledge, the E3 ubiquitin ligase TRIM22 was first reported as a tumor suppressor that inhibits the proliferation and invasion of breast cancer cells through CCS ubiquitination and degradation. TRIM22 is a potential prognostic biomarker in patients with breast cancer.