Shared and non-overlapping functions of RECQL4 and BLM helicases in chemotherapeutics-induced glioma cell responses

Human RECQL4 and BLM helicases participate in all DNA dependent processes, including replication stress, DNA damage repair. Both helicases are overexpressed in glioblastoma (GBM), a lethal primary brain tumour, characterised by resistance to radio- and chemotherapy. BLM-depleted glioma cells exhibit senescence-associated or polypoid phenotype when exposed to temozolomide (TMZ) and olaparib (OLA), a PARP inhibitor. This study aims to investigate how RECQL4 depletion influences the response of malignant gliomas to chemotherapeutics.

We investigated the effect of RECQL4 depletion in glioma cells on cell growth, apoptosis, senescence and polyploidy in the response to combined TMZ and OLA treatment. We compared transcriptomes of RECQL4- and BLM-depleted LN18 and LN229 glioma cells. Drug-induced cytotoxicity, senescence-associated phenotypes, cell cycle alterations, and polyploidy were assessed using the MTT metabolic assay, β-galactosidase activity assay, and propidium iodide staining.

RECQL4 depletion modestly affected basal glioma cell viability and proliferation, similarly to knock out of the BLM protein. Deletion of RECQL4 in glioma cells (RQ4 KO) induced profound transcriptomic alterations, dissimilar to BLM depletion. RECQL4-depleted glioma cells treated with TMZ and OLA exhibited reduced viability and increased levels of apoptosis markers. The treatment induced cell cycle arrest, however, RQ4 KO cells did not show signs of senescence phenotype or polyploidisation, when compared to BLM KO glioma cells. Interestingly, both RQ4 KO and BLM KO cells were more resistant to WP744, a doxorubicin derivative, when compared to WT LN229 glioma cells.

Our results highlight the distinct roles of RecQ helicases in a response to chemotherapeutics and support a rationale for targeting RECQL4 as a therapeutic strategy in glioblastoma.