Biology subjects

Kampen, R. A.

Publications and source records attributed to Kampen, R. A..

3 recordsLinked to original sources

bioRxiv2026

S6K1 and S6K2 regulate homologous recombination DNA repair through control of BRCA1 protein stability

Recent studies have suggested that S6 kinase 1 (S6K1) contributes to DNA repair (DR). However, the specific pathways and mechanisms involved in this regulation remain unclear. Moreover, it has not been investigated whether S6K2, a functional homologue of S6K1, also contributes to DR. In this study, we investigated the function of both S6K1 and S6K2 (S6K1/2) proteins in DR and demonstrate that both are important for efficient Homologous Recombination-mediated repair (HR). Double knockout of S6K1/2 prevented the formation of BRCA1 and RAD51 foci and increases sensitivity to DNA-damaging agents such as PARP1 inhibitors, cisplatin, and X-ray irradiation. In addition, double knockout of S6K1/2 increased markers of genomic instability, while single knockout had little effect on HR markers and genome stability, which suggests that one kinase can compensate for the loss of the other. Mechanistically, we show that S6K1/2 regulate BRCA1 protein stability, limiting its degradation by the proteasome. Finally, pharmacological inhibition of S6K1/2 sensitised HR-proficient breast cancer cells to Olaparib. Our findings clarify the role of S6K1/2 proteins in HR and suggest that targeting these kinases may be a therapeutic strategy to enhance PARP inhibitor efficacy in HR-proficient tumours.

molecular biology↗

bioRxiv2026

DNA end-resection is stimulated by an interaction between BRCA1 exon 11 and TOPBP1

Approximately 60% of the tumour suppressor protein BRCA1 is encoded by a single exon. Many tumours carry mutations in this exon, often resulting in exon skipping and thus a protein of a severely reduced size. Although none of the well-described protein domains of BRCA1 are encoded by this exon 11, the isoform lacking this part shows a hypomorphic activity in homologous recombination. To better understand the function of this large exon, we performed proteomic analyses to identify interaction partners via this part of the protein. Here, we report a DNA damage-and phospho-dependent interaction of TOPBP1 to the protein region of BRCA1 encoded by exon 11. Mechanistically, this interaction is required for BRCA1s role in end-resection during homologous recombination. In contrast, the interaction is not required for TOPBP1s role in ATR activation. Our data provide novel mechanistic insight into the function of this poorly characterized part of the BRCA1 protein.

molecular biology↗

bioRxiv2024

Finding novel vulnerabilities of hypomorphic BRCA1 alleles

With the recent rise in CRISPR/Cas9-mediated genome-wide synthetic lethality screens, many new synthetic lethal targets have been identified for diseases with underlying genetic causes such as tumours with BRCA1 mutations. Such screens often use full deficiency of a protein to identify novel vulnerabilities. However, patient-derived mutations not only result in loss of the protein but often also concern missense mutations with hypomorphic phenotypes. Here we study the genetic vulnerabilities of two previously described hypomorphic BRCA1 missense mutations and compare these to a BRCA1-depleted setting to study whether this affects screening for synthetic lethal interactions. Our research showed that BRCA1I26A mutated cells have very similar vulnerabilities to BRCA1 wildtype cells, confirming its low tumorigenic effect. In contrast, the BRCA1R1699Q mutation induced a more similar phenotype to BRCA1-deficient cells. For this mutation, we also unveiled a unique vulnerability to the loss of NDE1. Specifically in BRCA1R1699Q mutated cells, and not BRCA1-proficient or -deficient cells, NDE1 loss leads to increased genomic instability. Altogether our findings highlight the importance to differentiate between patient-derived mutations when assessing novel treatment targets.

cancer biology↗