ER Stress Signaling Promotes the Survival of Cancer “Persister Cells” Tolerant to EGFR Tyrosine Kinase Inhibitors

Abstract

An increasingly recognized component of resistance to tyrosine kinase inhibitors (TKI) involves persistence of a drug-tolerant subpopulation of cancer cells that survive despite effective eradication of the majority of the cell population. Multiple groups have demonstrated that these drug-tolerant persister cells undergo transcriptional adaptation via an epigenetic state change that promotes cell survival. Because this mode of TKI drug tolerance appears to involve transcriptional addiction to specific genes and pathways, we hypothesized that systematic functional screening of EGFR TKI/transcriptional inhibitor combination therapy would yield important mechanistic insights and alternative drug escape pathways. We therefore performed a genome-wide CRISPR/Cas9 enhancer/suppressor screen in EGFR-dependent lung cancer PC9 cells treated with erlotinib + THZ1 (CDK7/12 inhibitor) combination therapy, a combination previously shown to suppress drug-tolerant cells in this setting. As expected, suppression of multiple genes associated with transcriptional complexes (EP300, CREBBP, and MED1) enhanced erlotinib/THZ1 synergy. Unexpectedly, we uncovered nearly every component of the recently described ufmylation pathway in the synergy suppressor group. Loss of ufmylation did not affect canonical downstream EGFR signaling. Instead, absence of this pathway triggered a protective unfolded protein response associated with STING upregulation, promoting protumorigenic inflammatory signaling but also unique dependence on Bcl-xL. These data reveal that dysregulation of ufmylation and ER stress comprise a previously unrecognized TKI drug tolerance pathway that engages survival signaling, with potentially important therapeutic implications. These findings reveal a novel function of the recently described ufmylation pathway, an ER stress survival signaling in drug-tolerant persister cells, which has important biological and therapeutic implications. .

Lung cancer cells survive epidermal growth factor receptor tyrosine kinase inhibitor exposure through upregulation of cholesterol synthesis

“…53 It has been shown that ER stress induces activation of SREBP2 and a subsequent cholesterol accumulation in cancer cell lines. 56 Taken together, these studies highlight the possibility that EGFR TKI induced ER stress is causing activation of SREBP2 and subsequent activation of cholesterol synthesis ( Figure 6). 55,56 Another study found that erlotinib-induced ER stress signaling can promote the survival of EGFR TKI-persister cells after exposure to erlotinib through transcriptional adaptation via an epigenetic state change.…”

“…In our model we found upregulation of SREBP2, which is a transcription factor that controls the transcription of cholesterol synthesis genes. 55,56 Another study found that erlotinib-induced ER stress signaling can promote the survival of EGFR TKI-persister cells after exposure to erlotinib through transcriptional adaptation via an epigenetic state change. 54 EGFR TKI-treatment has been linked to the induction of ER stress response and this is one of the reasons that patients experience diarrhea as a common side effect of EGFR TKIs.…”

“…54 EGFR TKI-treatment has been linked to the induction of ER stress response and this is one of the reasons that patients experience diarrhea as a common side effect of EGFR TKIs. 55,56 Another study found that erlotinib-induced ER stress signaling can promote the survival of EGFR TKI-persister cells after exposure to erlotinib through transcriptional adaptation via an epigenetic state change. 56 Taken together, these studies highlight the possibility that EGFR TKI induced ER stress is causing activation of SREBP2 and subsequent activation of cholesterol synthesis ( Figure 6).…”

“…55,56 Another study found that erlotinib-induced ER stress signaling can promote the survival of EGFR TKI-persister cells after exposure to erlotinib through transcriptional adaptation via an epigenetic state change. 56 Taken together, these studies highlight the possibility that EGFR TKI induced ER stress is causing activation of SREBP2 and subsequent activation of cholesterol synthesis ( Figure 6). EGFR TKI exposure leadin to ER stress dependant induction of SREBP2 would require further testing in our model.…”

Tumor Milieu Controlled by RB Tumor Suppressor

“…Activation of STING subsequently induces upregulation of its downstream cytokines, including type I interferon and CXCL10, which promotes T-cell-mediated therapeutic antitumor immunity via enhancing neoantigen presentation and T-cell recruitment into the TME [100]. Not only DNA damage accumulation but also excessive ER stress activate the STING pathway [101]. Considering these mechanisms, it is not surprising that the increased genomic instability and metabolic stress that accumulates in RB-inactive cancer cells potentiate the efficacy of immunotherapy in certain contexts.…”