Kabotyanski, E. B. | Search bioRxiv

bioRxiv2024

RPS19 and RPL5, the most commonly mutated genes in Diamond Blackfan anemia, impact DNA double-strand break repair

Diamond Blackfan anemia (DBA) is caused by germline heterozygous loss-of-function pathogenic variants (PVs) in ribosomal protein (RP) genes, most commonly RPS19 and RPL5. In addition to red cell aplasia, individuals with DBA are at increased risk of various cancers. Importantly, the mechanism(s) underlying cancer predisposition are poorly understood. We found that DBA patient-derived lymphoblastoid cells had persistent {gamma}-H2AX foci following ionizing radiation (IR) treatment, suggesting DNA double-strand break (DSB) repair defects. RPS19- and RPL5-knocked down (KD) CD34+ cells had delayed repair of IR-induced DSBs, further implicating these RPs in DSB repair. Assessing the impact of RPS19- and RPL5-KD on specific DSB repair pathways, we found RPS19-KD decreased the efficiency of pathways requiring extensive end-resection, whereas RPL5-KD increased end-joining pathways. Additionally, RAD51 was reduced in RPS19- and RPL5-KD and RPS19- and RPL5-mutated DBA cells, whereas RPS19-deficient cells also had a reduction in PARP1 and BRCA2 proteins. RPS19-KD cells had an increase in nuclear RPA2 and a decrease in nuclear RAD51 foci post-IR, reflective of alterations in early, critical steps of homologous recombination. Notably, RPS19 and RPL5 interacted with poly(ADP)-ribose chains noncovalently, were recruited to DSBs in a poly(ADP)-ribose polymerase activity-dependent manner, and interacted with Ku70 and histone H2A. RPL5s recruitment, but not RPS19s, also required p53, suggesting that RPS19 and RPL5 directly participate in DSB repair via different pathways. We propose that defective DSB repair arising from haploinsufficiency of these RPs may underline the cancer predisposition in DBA. KEY POINTSO_LIRPS19- and RPL5-deficiency alters DNA double-strand break repair, which may underlie cancer predisposition in Diamond Blackfan anemia. C_LIO_LIRPS19 and RPL5 bind PAR chains and are rapidly recruited to sites of DNA double-strand breaks, suggesting active roles in repair. C_LI

molecular biology↗

bioRxiv2021

Tumor suppressor PLK2 may serve as a biomarker in triple-negative breast cancer for improved response to PLK1 therapeutics

Polo-like kinase (PLK) family members play important roles in cell cycle regulation. The founding member PLK1 is oncogenic and preclinically validated as a cancer therapeutic target. Paradoxically, PLK2 (chromosome 5q11.2) is frequently deleted in human breast cancers, preferentially in basal-like and triple-negative breast cancer subtypes. Here, we found that PLK2 was tumor suppressive in breast cancer and knockdown of PLK1 rescued phenotypes induced by PLK2-loss both in vitro and in vivo. We also demonstrated that PLK2 directly interacted with PLK1 at prometaphase and that mutations in the kinase domain of PLK2, but not polo-box binding domains, changed their interaction pattern. Furthermore, treatment of syngeneic transplantation mouse tumor models and patient-derived xenografts using the PLK1 inhibitor volasertib alone, or in combination with carboplatin, indicated that PLK2-low breast tumors had a significantly better response to these drugs. Re-expression of PLK2 in an inducible PLK2-null mouse model reduced the therapeutic efficacy of volasertib. Taken together, our data suggest PLK2 loss may serve as a biomarker to predict response to PLK1 therapeutics, alone and in combination with chemotherapy. SignificanceThe tumor suppressive role of PLK2, and its relationship with the oncogene PLK1, provide a mechanistic rationalization to use PLK1 inhibitors in combination with chemotherapy to treat PLK2 low/deleted tumors. TNBC, and other cancers with low PLK2 expression, are such candidates to leverage precision medicine to identify patients who might benefit from treatment with these inhibitors.

cancer biology↗