TSC loss distorts DNA replication programme and sensitises cells to genotoxic stress

Abstract

Tuberous Sclerosis (TSC) is characterized by exorbitant mTORC1 signalling and manifests as non-malignant, apoptosis-prone neoplasia. Previous reports have shown that TSC-/- cells are highly susceptible to mild, innocuous doses of genotoxic stress, which drive TSC-/- cells into apoptotic death. It has been argued that this hypersensitivity to stress derives from a metabolic/energetic shortfall in TSC-/- cells, but how metabolic dysregulation affects the DNA damage response and cell cycle alterations in TSC-/- cells exposed to genotoxic stress is not understood. We report here the occurrence of futile checkpoint responses and an unusual type of replicative stress (RS) in TSC1-/- fibroblasts exposed to low-dose genotoxins. This RS is characterized by elevated nucleotide incorporation rates despite only modest origin over-firing. Strikingly, an increased propensity for asymmetric fork progression and profuse chromosomal aberrations upon mild DNA damage confirmed that TSC loss indeed proved detrimental to stress adaptation. We conclude that low stress tolerance of TSC-/- cells manifests at the level of DNA replication control, imposing strong negative selection on genomic instability that could in turn detain TSC-mutant tumours benign.

The GATOR complex regulates an essential response to meiotic double-stranded breaks in Drosophila

“…In humans, mutations in components of TSC sensitize cells to multiple forms of genotoxic stress (Paterson et al, 1982; Deschavanne and Fertil, 1996; Lee et al, 2007; Pai et al, 2016). Thus, we predicted that the GATOR1 mutants, which have a two to three-fold increase in TORC1 activity, might have a globally diminished ability to respond to DNA damage.…”

“…Hyperactivation of TORC1 has been linked to defects in the DNA damage response in single celled and multicellular organisms (Begley et al, 2004; Feng et al, 2007; Klermund et al, 2014; Pai et al, 2016; Ma et al, 2018; Xie et al, 2018). The observation that meiotic DSBs likely promote the GATOR1 dependent downregulation of TORC1 activity during Drosophila oogenesis, suggested that limiting TORC1 activity may be important to the regulation of meiotic DSB repair.…”

mTORC1 Is Not Principally Involved in the Induction of Human Endotoxin Tolerance

“…Interestingly, while we observed an inhibitory effect of chronic everolimus therapy on the secretory activity of TSC monocytes, e.g., for IL-1ß or TNFα ( Figure 2B ), acute mTORC1 inhibition did not cause the same effect. This evidenced that not every consequence of aberrantly high mTORC1 activity in TSC cells could be reversed by the acute inhibition of mTORC1, an observation that is not unprecedented ( 33 ). In this context, it is interesting to consider mTOR-independent effects of TSC loss in human monocytes.…”

The GATOR complex regulates an essential response to meiotic double-stranded breaks inDrosophila

“…In humans, mutations in components of TSC sensitize cells to multiple forms of genotoxic stress (Deschavanne & Fertil, 1996;C. H. Lee et al, 2007;Pai et al, 2016;Paterson, Sell, Smith, & Bech-Hansen, 1982). Thus, we predicted that the GATOR1 mutants, which have a two to three-fold increase in TORC1 activity, might have a globally diminished ability to respond to DNA damage.…”

“…Hyperactivation of TORC1 has been linked to defects in the DNA damage response in single celled and multicellular organisms (Begley, Rosenbach, Ideker, & Samson, 2004;Feng et al, 2007;Klermund, Bender, & Luke, 2014;Ma, Vassetzky, & Dokudovskaya, 2018;Pai et al, 2016;Xie et al, 2018). The observation that meiotic DSBs promote the GATOR1 dependent downregulation of TORC1 activity during Drosophila oogenesis, suggested the low TORC1 activity may be important to the regulation of meiotic DSB.…”