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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.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.

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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FOXO6 uniquely regulates SOX2 expression.(A) Same lysates as Figure7E, showing immunoblot for FOXO proteins. (B)Similar data as in Figure 7B, butshown after immunoblot of protein lysates with the indicated antibodies.Immunoblot for FOXO4 was consistently unable to detect a band of thecorrect size (65 kD). (C) Effect of individual siRNAduplexes targeting FOXO6 on the levels of other FOXO isoforms. Data arepresented as in Figure 7D.Individual siFOXO6 siRNA duplexes −01 and −02 do not alterthe levels of FOXOs 1, 3a or 4.DOI:http://dx.doi.org/10.7554/eLife.06132.040
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fig7s2: FOXO6 uniquely regulates SOX2 expression.(A) Same lysates as Figure7E, showing immunoblot for FOXO proteins. (B)Similar data as in Figure 7B, butshown after immunoblot of protein lysates with the indicated antibodies.Immunoblot for FOXO4 was consistently unable to detect a band of thecorrect size (65 kD). (C) Effect of individual siRNAduplexes targeting FOXO6 on the levels of other FOXO isoforms. Data arepresented as in Figure 7D.Individual siFOXO6 siRNA duplexes −01 and −02 do not alterthe levels of FOXOs 1, 3a or 4.DOI:http://dx.doi.org/10.7554/eLife.06132.040

Mentions: To search for mediators of SOX2 induction, we explored the Molecular Signatures andTRANSFAC databases for transcription factor target sequences within the promoters ofthe 12 highest erlotinib-induced genes (Wingenderet al., 2000; Subramanian et al.,2005). Several binding motifs for FOXO proteins were highly significantlyenriched (q-value = 0.003 or less): for SOX2, multiple sites were presentwithin 2 kb of the transcriptional start site (Figure7A and Figure 7—figure supplement1). Expression of all of the FOXO family members was detectable at baselinein HCC827 cells and erlotinib treatment (8 hr) was associated with a1.6–4.4-fold induction (Figure 7B), aswell as with loss of the AKT-mediated inhibitory N-terminal threonine phosphorylationof the FOXO proteins (Figure 7—figuresupplement 2A).10.7554/eLife.06132.036Figure 7.SOX2 expression in EGFR-mutant cells is regulated by FOXO6.


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)

FOXO6 uniquely regulates SOX2 expression.(A) Same lysates as Figure7E, showing immunoblot for FOXO proteins. (B)Similar data as in Figure 7B, butshown after immunoblot of protein lysates with the indicated antibodies.Immunoblot for FOXO4 was consistently unable to detect a band of thecorrect size (65 kD). (C) Effect of individual siRNAduplexes targeting FOXO6 on the levels of other FOXO isoforms. Data arepresented as in Figure 7D.Individual siFOXO6 siRNA duplexes −01 and −02 do not alterthe levels of FOXOs 1, 3a or 4.DOI:http://dx.doi.org/10.7554/eLife.06132.040
© Copyright Policy
Related In: Results  -  Collection

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

fig7s2: FOXO6 uniquely regulates SOX2 expression.(A) Same lysates as Figure7E, showing immunoblot for FOXO proteins. (B)Similar data as in Figure 7B, butshown after immunoblot of protein lysates with the indicated antibodies.Immunoblot for FOXO4 was consistently unable to detect a band of thecorrect size (65 kD). (C) Effect of individual siRNAduplexes targeting FOXO6 on the levels of other FOXO isoforms. Data arepresented as in Figure 7D.Individual siFOXO6 siRNA duplexes −01 and −02 do not alterthe levels of FOXOs 1, 3a or 4.DOI:http://dx.doi.org/10.7554/eLife.06132.040
Mentions: To search for mediators of SOX2 induction, we explored the Molecular Signatures andTRANSFAC databases for transcription factor target sequences within the promoters ofthe 12 highest erlotinib-induced genes (Wingenderet al., 2000; Subramanian et al.,2005). Several binding motifs for FOXO proteins were highly significantlyenriched (q-value = 0.003 or less): for SOX2, multiple sites were presentwithin 2 kb of the transcriptional start site (Figure7A and Figure 7—figure supplement1). Expression of all of the FOXO family members was detectable at baselinein HCC827 cells and erlotinib treatment (8 hr) was associated with a1.6–4.4-fold induction (Figure 7B), aswell as with loss of the AKT-mediated inhibitory N-terminal threonine phosphorylationof the FOXO proteins (Figure 7—figuresupplement 2A).10.7554/eLife.06132.036Figure 7.SOX2 expression in EGFR-mutant cells is regulated by FOXO6.

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.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.

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