HDAC8 Regulates a Stress Response Pathway in Melanoma to Mediate Escape from BRAF Inhibitor Therapy

Abstract

Increased HDAC8 activity deacetylates c-JUN, leading to increased EGFR signaling and BRAF inhibitor resistance Low HDAC8 activity RTK c-Jun High HDAC8 activity BRAFi c-Jun Ras RAF ERK Cell death Survival and invasion BRAFi Ras RAF ERK RTK (EGFR) ac ac ac TRE ac ac TRE p TR HDAC8 Melanoma cells have the ability to switch to a dedifferentiated, invasive phenotype in response to multiple stimuli. Here, we show that exposure of melanomas to multiple stresses including BRAF-MEK inhibitor therapy, hypoxia, and UV irradiation leads to an increase in histone deacetylase 8 (HDAC8) activity and the adoption of a drugresistant phenotype. Mass spectrometry-based phosphoproteomics implicated HDAC8 in the regulation of MAPK and AP-1 signaling. Introduction of HDAC8 into drug-na€ ve melanoma cells conveyed resistance both in vitro and in vivo. HDAC8mediated BRAF inhibitor resistance was mediated via receptor tyrosine kinase activation, leading to MAPK signaling. Although HDACs function at the histone level, they also regulate nonhistone substrates, and introduction of HDAC8 decreased the acetylation of c-Jun, increasing its transcriptional activity and enriching for an AP-1 gene signature. Mutation of the putative c-Jun acetylation site at lysine 273 increased transcriptional activation of c-Jun in melanoma cells and conveyed resistance to BRAF inhibition. In vivo xenograft studies confirmed the key role of HDAC8 in therapeutic adaptation, with both nonselective and HDAC8-specific inhibitors enhancing the durability of BRAF inhibitor therapy. Our studies demonstrate that HDAC8-specific inhibitors limit the adaptation of melanoma cells to multiple stresses including BRAF-MEK inhibition. Significance: This study provides evidence that HDAC8 drives transcriptional plasticity in melanoma cells in response to a range of stresses through direct deacetylation of c-Jun.

A population of stress-like cancer cells in melanoma promotes tumorigenesis and confers drug resistance

“…One important clinical implication of this study is that the existence of the stress program can have consequences for the intrinsic responsiveness to therapy. In melanoma, for example, HDCA8 has been shown to mediate drug resistance under multiple stress conditions such as BRAF-MEK treatment, hypoxia, UV and radiation through regulation of MAPK, decrease in jun acetylation and enrichment of AP-1 signaling (Emmons et al, 2019) . HSF1 has been demonstrated to be essential for chemotherapeutic agent-induced cytoprotective autophagy by directly binding to ATG7 in breast cancer (Desai et al, 2013) and active in colon and lung tumors as well (Mendillo et al, 2012) .…”

Phenotype-based probabilistic analysis of heterogeneous responses to cancer drugs and their combination efficacy

“…The list of compounds based on their nominal targets included two HDAC inhibitors (Fimepinostat and Givinostat), two BET bromodomain inhibitors (Birabresib and I-BET762), two KDM1A inhibitors (SP2509 and ORY-1001), a pan Jmj-KDM inhibitor (JIB-04), a KDM5 inhibitor (CPI-455), two Tankyrase inhibitors (AZ6102 and NVP-TNKS656), and two CDK4/6 inhibitors (Palbociclib and Abemaciclib). These compounds were selected from two broad classes of anti-cancer drugs, referred to as epigenetic-modifying compounds and cell cycle inhibitors, which have been proposed to be used in combination with standard of care BRAF and MEK inhibitors to overcome drug-adapted subpopulations of cells in BRAF-mutant melanomas [10,21,[41][42][43][44][45][46][47][48][49].…”

Cancer stem cells, plasticity, and drug resistance

“…The high heterogeneity of the tumor cells and their plasticity lead to the possibility that the same drug might induce the switch to slow-cycling resistant phenotype associated to high melanocyte inducing transcription factor levels and to a mesenchymal-like phenotype [42][43][44][45][46] . Early adaptation involving transcriptome reprogramming seems to be particularly relevant even at long time scale, allowing the tumor to survive until a genetic mutation and permanent resistance mechanism is acquired [43,47] . Interestingly, melanoma cells can display profound transcriptional variability at the level of single cell that can involve the transcription of a number of resistance markers at high level in a very small percentage of cells [48] .…”