Regulation of FANCD2 by the mTOR Pathway Contributes to the Resistance of Cancer Cells to DNA Double-Strand Breaks

Abstract

Deregulation of the mTOR pathway is closely associated with tumorigenesis. Accordingly mTOR inhibitors such as rapamycin and mTOR-selective kinase inhibitors have been tested as cancer therapeutic agents. Inhibition of mTOR results in sensitization to DNA damaging agents, however the molecular mechanism is not well understood. We found that an mTOR-selective kinase inhibitor, AZD8055, significantly enhanced sensitivity of a pediatric rhabdomyosarcoma xenograft toradiotherapy and sensitized rhabdomyosarcoma cells to interstrand crosslinker (ICL) melphalan. Sensitization correlated with drug-induced downregulation of a key component of the Fanconi anemia (FA) pathway, FANCD2 through mTOR regulation of FANCD2 gene transcripts via mTORC1-S6K1. Importantly, we show that FANCD2 is required for the proper activation of ATM-Chk2 checkpoint in response to ICL and that mTOR signaling promotes ICL-induced ATM-Chk2 checkpoint activation by sustaining FANCD2. In FANCD2 deficient lymphoblasts, FANCD2 is essential to suppress endogenous and induced DNA damage, and FANCD2-deficient cells demonstrated impaired ATM-Chk2 and ATR-Chk1 activation, which was rescued by re-introduction of wild type FANCD2. Pharmacological inhibition of PI3K-mTOR-AKT pathway in Rh30 rhabdomyosarcoma cells attenuated ICL-induced activation of ATM, accompanied with the decrease of FANCD2. These data suggest that the mTOR pathway may promote the repair of DNA double strand breaks by sustaining FANCD2 and provide a novel mechanism of how the FA pathway modulates DNA damage response and repair.

Temsirolimus combined with cisplatin or bevacizumab is active in osteosarcoma models

“…In other studies, mTOR inhibition was also shown to sensitize cancer cells to chemotherapy, including pediatric sarcoma models. 24,25 Moreover, the mTOR inhibitor everolimus dramatically enhanced cisplatin-induced apoptosis in wildtype p53, but not mutant p53, tumor cells. 26 Both OS-1 and OS-33 models are p53-wildtype, as is the majority (62%) of clinical osteosarcoma samples.…”

Glutaminolysis and autophagy in cancer

“…113,[136][137][138] The mechanism that explains this observation is related to the ability of MTORC1 to regulate the expression of FAN1/FANCD2, a protein involved in the activation of ATM. Thus, the inhibition of MTORC1 decreases FAN1, which impairs the activation of ATM and thereby the DDR of cancer cells.…”

“…Thus, the inhibition of MTORC1 decreases FAN1, which impairs the activation of ATM and thereby the DDR of cancer cells. 113,136,139 Furthermore, AMPK is another link between ATM and MTORC1, as AMPK regulates both ATM and MTORC1. 50,51,[140][141][142] Those results highlight the potential synergy of a combined therapy targeting both MTOR and DDR as a better strategy to prevent tumor resistance to chemotherapeutic agents.…”

Molecularly targeting the PI3K-Akt-mTOR pathway can sensitize cancer cells to radiotherapy and chemotherapy

“…The monoubiquitinated FANCI-FANCD2 complex, together with endonucleases, cuts both sides of ICL to generate DNA strand breaks and promotes TLS, NER, and HR [32][33][34][35]. It was recently found that FANCD2 promotes early ATM-Chk2 activation in response to ICL-induced DNA lesions [36]. Accurate and complete genetic information is maintained by the ATM checkpoint [37].…”

“…These findings suggest that one of the mechanisms by which FANCD2 functions as a genome caretaker is by promoting timely ATM checkpoint activation. Most importantly, it was revealed that Akt-mTOR signaling maintains FANCD2 gene transcription by enhancing the activity of CDK4 and NF-B [36,38], thus providing a mechanism by which molecular inhibition of PI3K-Akt-mTOR signaling sensitizes cancer cells to DNA damage agents, especially ICL-based chemotherapies (Fig. 1).…”