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Inhibition of mutant EGFR in lung cancer cells triggers SOX2-FOXO6-dependent survival pathways.

Rothenberg SM, Concannon K, Cullen S, Boulay G, Turke AB, Faber AC, Lockerman EL, Rivera MN, Engelman JA, Maheswaran S, Haber DA - Elife (2015)

Bottom Line: Treatment of EGFR-mutant lung cancer with erlotinib results in dramatic tumor regression but it is invariably followed by drug resistance.In characterizing early transcriptional changes following drug treatment of mutant EGFR-addicted cells, we identified the stem cell transcriptional regulator SOX2 as being rapidly and specifically induced, both in vitro and in vivo.Together, these observations point to a physiological feedback mechanism that attenuates oncogene addiction-mediated cell death associated with the withdrawal of growth factor signaling and may therefore contribute to the development of resistance.

View Article: PubMed Central - PubMed

Affiliation: Cancer Center, Massachusetts General Hospital, Harvard Medical School, Charlestown, United States.

ABSTRACT
Treatment of EGFR-mutant lung cancer with erlotinib results in dramatic tumor regression but it is invariably followed by drug resistance. In characterizing early transcriptional changes following drug treatment of mutant EGFR-addicted cells, we identified the stem cell transcriptional regulator SOX2 as being rapidly and specifically induced, both in vitro and in vivo. Suppression of SOX2 sensitizes cells to erlotinib-mediated apoptosis, ultimately decreasing the emergence of acquired resistance, whereas its ectopic expression reduces drug-induced cell death. We show that erlotinib relieves EGFR-dependent suppression of FOXO6, leading to its induction of SOX2, which in turn represses the pro-apoptotic BH3-only genes BIM and BMF. Together, these observations point to a physiological feedback mechanism that attenuates oncogene addiction-mediated cell death associated with the withdrawal of growth factor signaling and may therefore contribute to the development of resistance.

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Quantitation of the effect of SOX2 knockdown on BIM levels.Each BIM isoform (EL, L, and S) was normalized to the GAPDH loadingcontrol and untreated, siCTRL cells.DOI:http://dx.doi.org/10.7554/eLife.06132.033
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fig5s4: Quantitation of the effect of SOX2 knockdown on BIM levels.Each BIM isoform (EL, L, and S) was normalized to the GAPDH loadingcontrol and untreated, siCTRL cells.DOI:http://dx.doi.org/10.7554/eLife.06132.033

Mentions: The mechanisms underlying the cell death response of cancer cells followingwithdrawal of oncogene-addicting signals are complex but appear to result in partfrom activation of the pro-apoptotic proteins BIM and PUMA (Costa et al., 2007; Gong etal., 2007; Bean et al., 2013). Tosearch for additional targets that mediate SOX2's anti-apoptotic effect, wescreened for altered expression of multiple pro-apoptotic and anti-apoptotic proteinsin cells with overexpression of ectopic SOX2, following treatment with erlotinib. Inboth HCC827 and PC9 EGFR-mutant lung cancer cells, three of 14 BH3-domain containingproteins tested showed strongly reduced mRNA induction by erlotinib in the presenceof ectopic SOX2: BIM, BMF, and HRK (but not PUMA) (Figure 6A and Figure 6—figuresupplement 1). All three of these are known to induce apoptosis todifferent degrees, depending on the type of apoptotic stimulus. The effect of ectopicSOX2 on BIM protein levels was confirmed using two different expression strategies(Figure 5—figure supplement 1B,C).Ectopic expression of SOX2, both at high and physiological levels, attenuated theerlotinib-induced induction of SOX2. In contrast, SOX2 knockdown coincident witherlotinib treatment led to an overall increase in BIM levels, although this effectwas attenuated when averaged across a cell population with heterogeneous induction ofendogenous SOX2 (Figure 5—figure supplement4).10.7554/eLife.06132.034Figure 6.Erlotinib-induced SOX2 directly regulates expression ofBIM and BMF.


Inhibition of mutant EGFR in lung cancer cells triggers SOX2-FOXO6-dependent survival pathways.

Rothenberg SM, Concannon K, Cullen S, Boulay G, Turke AB, Faber AC, Lockerman EL, Rivera MN, Engelman JA, Maheswaran S, Haber DA - Elife (2015)

Quantitation of the effect of SOX2 knockdown on BIM levels.Each BIM isoform (EL, L, and S) was normalized to the GAPDH loadingcontrol and untreated, siCTRL cells.DOI:http://dx.doi.org/10.7554/eLife.06132.033
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4384750&req=5

fig5s4: Quantitation of the effect of SOX2 knockdown on BIM levels.Each BIM isoform (EL, L, and S) was normalized to the GAPDH loadingcontrol and untreated, siCTRL cells.DOI:http://dx.doi.org/10.7554/eLife.06132.033
Mentions: The mechanisms underlying the cell death response of cancer cells followingwithdrawal of oncogene-addicting signals are complex but appear to result in partfrom activation of the pro-apoptotic proteins BIM and PUMA (Costa et al., 2007; Gong etal., 2007; Bean et al., 2013). Tosearch for additional targets that mediate SOX2's anti-apoptotic effect, wescreened for altered expression of multiple pro-apoptotic and anti-apoptotic proteinsin cells with overexpression of ectopic SOX2, following treatment with erlotinib. Inboth HCC827 and PC9 EGFR-mutant lung cancer cells, three of 14 BH3-domain containingproteins tested showed strongly reduced mRNA induction by erlotinib in the presenceof ectopic SOX2: BIM, BMF, and HRK (but not PUMA) (Figure 6A and Figure 6—figuresupplement 1). All three of these are known to induce apoptosis todifferent degrees, depending on the type of apoptotic stimulus. The effect of ectopicSOX2 on BIM protein levels was confirmed using two different expression strategies(Figure 5—figure supplement 1B,C).Ectopic expression of SOX2, both at high and physiological levels, attenuated theerlotinib-induced induction of SOX2. In contrast, SOX2 knockdown coincident witherlotinib treatment led to an overall increase in BIM levels, although this effectwas attenuated when averaged across a cell population with heterogeneous induction ofendogenous SOX2 (Figure 5—figure supplement4).10.7554/eLife.06132.034Figure 6.Erlotinib-induced SOX2 directly regulates expression ofBIM and BMF.

Bottom Line: Treatment of EGFR-mutant lung cancer with erlotinib results in dramatic tumor regression but it is invariably followed by drug resistance.In characterizing early transcriptional changes following drug treatment of mutant EGFR-addicted cells, we identified the stem cell transcriptional regulator SOX2 as being rapidly and specifically induced, both in vitro and in vivo.Together, these observations point to a physiological feedback mechanism that attenuates oncogene addiction-mediated cell death associated with the withdrawal of growth factor signaling and may therefore contribute to the development of resistance.

View Article: PubMed Central - PubMed

Affiliation: Cancer Center, Massachusetts General Hospital, Harvard Medical School, Charlestown, United States.

ABSTRACT
Treatment of EGFR-mutant lung cancer with erlotinib results in dramatic tumor regression but it is invariably followed by drug resistance. In characterizing early transcriptional changes following drug treatment of mutant EGFR-addicted cells, we identified the stem cell transcriptional regulator SOX2 as being rapidly and specifically induced, both in vitro and in vivo. Suppression of SOX2 sensitizes cells to erlotinib-mediated apoptosis, ultimately decreasing the emergence of acquired resistance, whereas its ectopic expression reduces drug-induced cell death. We show that erlotinib relieves EGFR-dependent suppression of FOXO6, leading to its induction of SOX2, which in turn represses the pro-apoptotic BH3-only genes BIM and BMF. Together, these observations point to a physiological feedback mechanism that attenuates oncogene addiction-mediated cell death associated with the withdrawal of growth factor signaling and may therefore contribute to the development of resistance.

Show MeSH
Related in: MedlinePlus