Chaperonin-containing TCP1 subunit 6A inhibition via TRIM21-mediated K48-linked ubiquitination suppresses triple-negative breast cancer progression through the AKT signalling pathway.

Background: Triple-negative breast cancer (TNBC) is distinguished by a significant likelihood of distant recurrence and an unfavourable prognosis. However, the underlying molecules and mechanisms have not been fully elucidated.

Methods: We investigated the expression profile and clinical relevance of chaperonin-containing TCP1 subunit 6A (CCT6A) in TNBC. We performed cell function assays on TNBC cells with CCT6A knockdown or overexpression. To further explore the mechanism of action of CCT6A, RNA sequencing and co-immunoprecipitation-mass spectrometry analyses were utilized. Rescue and ubiquitination assays evaluated the impact of TRIM21-mediated CCT6A ubiquitination and degradation on TNBC progression in vitro and in vivo. Finally, we studied the potential of Ipatasertib, a pharmacological AKT inhibitor, and/or anti-PD1 therapy in inhibiting TNBC progression.

Results: Elevated CCT6A expression in TNBC patients was associated with an adverse prognosis and lymph node metastasis. Mechanistically, CCT6A facilitated cell migration, invasion, epithelial-mesenchymal transition and proliferation by activating the phosphatidylinositol 3-kinase (PI3K)/AKT pathway. The TRIM21 RING domain is an E3 ligase, facilitating the K48-linked ubiquitination-mediated degradation of CCT6A, thereby impeding TNBC progression. Moreover, in the tumour tissues of the CCT6A-overexpressing mice, the quantity of CD8+ T cells and the concentration of secreted interferon-gamma were decreased, whereas in the group double-overexpression of CCT6A and TRIM21, they were elevated; the opposite was observed in the knockdown and double-knockdown groups. Ipatasertib demonstrated enhanced efficacy in inhibiting cell proliferation, invasion and migration in TNBC cells ectopically expressing CCT6A. When Ipatasertib and anti-PD1 therapies were combined, both the tumour volume and mass exhibited a notable reduction, while the expression of CD45+CD8+ T cells increased, and that of CD45+CD4+CTLA4+ and CD45+CD4+PD1+ T cells decreased.

Conclusions: Our findings indicate that TRIM21 inhibits TNBC progression by facilitating the K48-linked ubiquitination-mediated degradation of CCT6A via the PI3K/AKT signalling pathway. This highlights the potential of Ipatasertib and/or anti-PD1 as therapeutic strategies, particularly for TNBC patients overexpressing CCT6A.

Key points: Chaperonin TCP1 subunit 6A (CCT6A) plays an oncogenic role in triple-negative breast cancer (TNBC) through the AKT signaling pathway. TRIM21 facilitated K48-linked ubiquitination-mediated degradation of CCT6A, thereby impeding TNBC progression. Our study collectively underscores the potential of Ipatasertib in conjunction with anti-PD1 therapy as a promising strategy to counteract CCT6A/AKT hyperactivity-driven TNBC progression.