Inhibition of Histone Deacetylase Impacts Cancer Stem Cells and Induces Epithelial-Mesenchyme Transition of Head and Neck Cancer

Fernanda S Giudice,Cristiane H Squarize,Jacques E Nör,Decio S Pinto,Rogerio M Castilho,Irene Söderhäll

doi:10.1371/journal.pone.0058672

Abstract

The genome is organized and packed into the nucleus through interactions with core histone proteins. Emerging evidence suggests that tumors are highly responsive to epigenetic alterations that induce chromatin-based events and dynamically influence tumor behavior. We examined chromatin organization in head and neck squamous cell carcinoma (HNSCC) using acetylation levels of histone 3 as a marker of chromatin compaction. Compared to control oral keratinocytes, we found that HNSCC cells are hypoacetylated and that microenvironmental cues (e.g., microvasculature endothelial cells) induce tumor acetylation. Furthermore, we found that chemical inhibition of histone deacetylases (HDAC) reduces the number of cancer stem cells (CSC) and inhibits clonogenic sphere formation. Paradoxically, inhibition of HDAC also induced epithelial-mesenchymal transition (EMT) in HNSCC cells, accumulation of BMI-1, an oncogene associated with tumor aggressiveness, and expression of the vimentin mesenchymal marker. Importantly, we observed co-expression of vimentin and acetylated histone 3 at the invasion front of human HNSCC tumor tissues. Collectively, these findings suggest that environmental cues, such as endothelial cell-secreted factors, modulate tumor plasticity by limiting the population of CSC and inducing EMT. Therefore, inhibition of HDAC may constitute a novel strategy to disrupt the population of CSC in head and neck tumors to create a homogeneous population of cancer cells with biologically defined signatures and predictable behavior.

Highlights

Among malignant head and neck tumors, head and neck squamous cell carcinoma (HNSCC) is the most common epithelial neoplasia and is one of the six most common malignancies worldwide [1]
We found that inhibition of histone deacetylases (HDAC) disrupts the accumulation of cancer stem cells (CSC) and paradoxically induces tumor cells to undergo epithelial-mesenchymal transition (EMT)
After determining the optimal concentration of Trichostatin A (TSA) (300 nM) capable of inducing head and neck cancer cell acetylation (Fig. S2) [76,77,78,79,80,81,82], we found that inhibition of HDACs directly impaired the proliferation of HNSCC cells (Fig. 2B, HN6 *p,0.05, HN13 ***p,0.001)

Summary

Introduction

Among malignant head and neck tumors, head and neck squamous cell carcinoma (HNSCC) is the most common epithelial neoplasia and is one of the six most common malignancies worldwide [1]. Chromatin condensation is associated with chemoresistance in tumors [11,12,13,14] This phenotype is partially attributed to specialized cells that reactivate stem cell-like transcription programs [15]. We observed hypoacetylated chromatin in a panel of HNSCC-derived cell lines and identified a distinct population of CSC in these cells. These observations prompted us to ask whether chromatin acetylation dictates the biological behavior of tumors and whether pharmacological interference with HDAC alters CSC behavior. We found that inhibition of HDAC disrupts the accumulation of CSC and paradoxically induces tumor cells to undergo epithelial-mesenchymal transition (EMT)

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Results

Conclusion