A melanocyte lineage program confers resistance to MAP kinase pathway inhibition

1] The Broad Institute of Harvard University and Massachusetts Institute of Technology, 7 Cambridge Center, Cambridge, Massachusetts 02142, USA [2] Department of Medical Oncology, Dana-Farber Cancer Institute, 44 Binney Street, Boston, Massachusetts 02115, USA [3] Harvard Medical School, 25 Shattuck Street, Boston, Massachusetts 02115, USA.
Nature (Impact Factor: 41.46). 11/2013; 504(7478). DOI: 10.1038/nature12688
Source: PubMed
Malignant melanomas harbouring point mutations (Val600Glu) in the serine/threonine-protein kinase BRAF (BRAF(V600E)) depend on RAF-MEK-ERK signalling for tumour cell growth. RAF and MEK inhibitors show remarkable clinical efficacy in BRAF(V600E) melanoma; however, resistance to these agents remains a formidable challenge. Global characterization of resistance mechanisms may inform the development of more effective therapeutic combinations. Here we carried out systematic gain-of-function resistance studies by expressing more than 15,500 genes individually in a BRAF(V600E) melanoma cell line treated with RAF, MEK, ERK or combined RAF-MEK inhibitors. These studies revealed a cyclic-AMP-dependent melanocytic signalling network not previously associated with drug resistance, including G-protein-coupled receptors, adenyl cyclase, protein kinase A and cAMP response element binding protein (CREB). Preliminary analysis of biopsies from BRAF(V600E) melanoma patients revealed that phosphorylated (active) CREB was suppressed by RAF-MEK inhibition but restored in relapsing tumours. Expression of transcription factors activated downstream of MAP kinase and cAMP pathways also conferred resistance, including c-FOS, NR4A1, NR4A2 and MITF. Combined treatment with MAPK-pathway and histone-deacetylase inhibitors suppressed MITF expression and cAMP-mediated resistance. Collectively, these data suggest that oncogenic dysregulation of a melanocyte lineage dependency can cause resistance to RAF-MEK-ERK inhibition, which may be overcome by combining signalling- and chromatin-directed therapeutics.

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    • "These novel predicted genes that regulate NFκB via NR4A2 suggest a key role of this nuclear receptor within the NFκB pathway. NR4A2 is a family member of AR (NR3C4), which is known to be activated downstream of the MAPK pathway in cancer [57] and directly interacts with NFκB (specifically the REL subunit), as correctly predicted for NR4A2 [58]. Along with these genes (ATF3, JUNB, and NR4A2) that we predicted to be regulated by the MAP kinase MAP3K8, a known oncogene involved in prostate cancer growth [48], we additionally suggest the dual specificity phosphatase 5 (DUSP5) as another upstream regulator of NFκB in prostate cancer: DUSP5 was not only predicted to be highly functionally related to NFκB in the positive regulation of NFκB transcription factor activity (Table 1), but also correctly predicted to be regulated by MAP3K8 (Fig 2) [59]. "
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    • "Importantly, the cells that had been exposed to the drug in the tumors of treated mice were more tolerant to BRAF inhibition than cells isolated from untreated tumors, with an over 10-fold increase in the concentration causing 50% of maximal growth inhibition (GI 50 ) (Figure 1E). Moreover, in agreement with the previously described function of MITF in resistance to MAPK inhibitors (Haq et al., 2013b; Johannessen et al., 2013; Muller et al., 2014; Smith et al., 2013 ), depletion of MITF rendered drug-tolerant A375- GFP cells sensitive again (Figure 1F). Notably, after drug removal the upregulation of MITF seen in A375-GFP cells was reversible in vivo as well as in vitro (Figure 1G). "
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