Loss of cohesin complex components STAG2 or STAG3 confers resistance to BRAF inhibition in melanoma

Abstract

The protein kinase B-Raf proto-oncogene, serine/threonine kinase (BRAF) is an oncogenic driver and therapeutic target in melanoma. Inhibitors of BRAF (BRAFi) have shown high response rates and extended survival in patients with melanoma who bear tumors that express mutations encoding BRAF proteins mutant at Val600, but a vast majority of these patients develop drug resistance1,2. Here we show that loss of stromal antigen 2 (STAG2) or STAG3, which encode subunits of the cohesin complex, in melanoma cells results in resistance to BRAFi. We identified loss-of-function mutations in STAG2, as well as decreased expression of STAG2 or STAG3 proteins in several tumor samples from patients with acquired resistance to BRAFi and in BRAFi-resistant melanoma cell lines. Knockdown of STAG2 or STAG3 expression decreased sensitivity of BRAFVal600Glu-mutant melanoma cells and xenograft tumors to BRAFi. Loss of STAG2 inhibited CCCTC-binding-factor-mediated expression of dual specificity phosphatase 6 (DUSP6), leading to reactivation of mitogen-activated protein kinase (MAPK) signaling (via the MAPKs ERK1 and ERK2; hereafter referred to as ERK). Our studies unveil a previously unknown genetic mechanism of BRAFi resistance and provide new insights into the tumor suppressor function of STAG2 and STAG3.

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Figure 1: Decreased expression of STAG2 and STAG3 in BRAFi-resistant melanoma primary patient tumors and cell lines.
Figure 2: Knockdown of STAG2 or STAG3 expression decreases BRAFi sensitivity in BRAF-mutant melanoma cells.
Figure 3: Knockdown of STAG2 or STAG3 impairs the effects of vemurafenib on inhibiting melanoma xenograft tumor growth in vivo.
Figure 4: STAG2 regulates ERK activity by controlling expression of DUSP6.

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Acknowledgements

We thank K. Swanson, Y. Zhang and G. Zhao for critical comments on the manuscript. We also thank L. Chin (MD Anderson Cancer Center), M. Herlyn (Wistar Institute), C. Pritchard (University of Leicester) and J. Zippin (Weill Cornell Medical College) for providing cell lines. This work is supported by the Dr. Miriam and Sheldon G. Adelson Medical Research Foundation (D.E.F.), the V Foundation (B.Z.), the Harry J. Lloyd Charitable Trust (B.Z.), the Melanoma Research Alliance (B.Z.) and the US National Institutes of Health (NIH) grants P01 CA163222 (D.E.F.), R01 AR043369 (D.E.F.), R21 CA175907 (D.E.F.) and R01 CA166717 (B.Z.).

Author information

C.-H.S., S.H.K., S.T., P.Y., L.C., M.L. and B.Z. designed experiments; C.-H.S., S.H.K., P.Y., L.C., S.T., M.L. and J.H.L. performed experiments; D.T.F., R.J.S. and K.T.F. provided patient samples; D.M. and D.E.F. generated and provided cell lines; D.T.F. and A.P. performed immunohistochemical and pathological analysis; L.G. performed computational analysis; all of the authors interpreted data and discussed results; and B.Z. wrote the paper with input from all of the authors.

Correspondence to Bin Zheng.

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The authors declare no competing financial interests.

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Shen, C., Kim, S., Trousil, S. et al. Loss of cohesin complex components STAG2 or STAG3 confers resistance to BRAF inhibition in melanoma. Nat Med 22, 1056–1061 (2016). https://doi.org/10.1038/nm.4155

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