HERV-K activation is strictly required to sustain CD133+ melanoma cells with stemness features

Ayele Argaw-Denboba,Ilaria Sciamanna,Paola Sinibaldi-Vallebona,Chiara Cipriani,Emanuela Balestrieri,Alessandra Gambacurta,Annalucia Serafino,Claudia Matteucci,Ilaria Bucci,Roberta Sorrentino

doi:10.1186/s13046-016-0485-x

Abstract

BackgroundMelanoma is a heterogeneous tumor in which phenotype-switching and CD133 marker have been associated with metastasis promotion and chemotherapy resistance. CD133 positive (CD133+) subpopulation has also been suggested as putative cancer stem cell (CSC) of melanoma tumor. Human endogenous retrovirus type K (HERV-K) has been described to be aberrantly activated during melanoma progression and implicated in the etiopathogenesis of disease. Earlier, we reported that stress-induced HERV-K activation promotes cell malignant transformation and reduces the immunogenicity of melanoma cells. Herein, we investigated the correlation between HERV-K and the CD133+ melanoma cells during microenvironmental modifications.MethodsTVM-A12 cell line, isolated in our laboratory from a primary human melanoma lesion, and other commercial melanoma cell lines (G-361, WM-115, WM-266-4 and A375) were grown and maintained in the standard and stem cell media. RNA interference, Real-time PCR, flow cytometry analysis, self-renewal and migration/invasion assays were performed to characterize cell behavior and HERV-K expression.ResultsMelanoma cells, exposed to stem cell media, undergo phenotype-switching and expansion of CD133+ melanoma cells, concomitantly promoted by HERV-K activation. Notably, the sorted CD133+ subpopulation showed stemness features, characterized by higher self-renewal ability, embryonic genes expression, migration and invasion capacities compared to the parental cell line. RNA interference-mediated downregulation experiments showed that HERV-K has a decisive role to expand and maintain the CD133+ melanoma subpopulation during microenvironmental modifications. Similarly, non nucleoside reverse transcriptase inhibitors (NNRTIs) efavirenz and nevirapine were effective to restrain the activation of HERV-K in melanoma cells, to antagonize CD133+ subpopulation expansion and to induce selective high level apoptosis in CD133+ cells.ConclusionsHERV-K activation promotes melanoma cells phenotype-switching and is strictly required to expand and maintain the CD133+ melanoma cells with stemness features in response to microenvironmental modifications.

Highlights

Melanoma is a heterogeneous tumor in which phenotype-switching and CD133 marker have been associated with metastasis promotion and chemotherapy resistance
TVM-A12 human melanoma cells led to phenotype switching and expansion of the CD133+ melanoma subpopulation when cultured in stem cell medium In order to investigate the phenotype modifications of melanoma cells undergoing change of the microenvironment, the TVM-A12 melanoma cell line was cultured in a serum free stem cell medium (X-VIVO-15) and morphological features, cellular markers and antigens expression were characterized
In the present study, we used only short cultured sorted cells analysed by FACS for CD133 expression immediately before the experiments, for the confirmation of the relative percentage of expression. These results demonstrated that TVMA12 human melanoma cells have a change-prone phenotype responding to microenvironment modification, characterized by the expansion of a CD133+ melanoma subpopulation, enhanced expression of Human endogenous retrovirus type K (HERV-K) and of markers related to immune evasion and metastasis formation

Summary

Introduction

Melanoma is a heterogeneous tumor in which phenotype-switching and CD133 marker have been associated with metastasis promotion and chemotherapy resistance. The specificity of these markers are still under debate, the stem cell marker CD133 has been widely used to characterize and isolate the putative melanoma CSC in both in vitro and in vivo studies [4, 5]. It was revealed that CD133+ melanoma cells have an enhanced capability to initiate primary tumors and metastasis in NOD/SCID mice, while showing higher self-renewing and migration capacity and differentiation potential into mesenchymal lineages in in vitro studies [4, 6, 7]. Recent studies revealed that CD133+ melanoma cells are highly resistant to chemotherapy, indicating that they are responsible for tumor recurrence [2, 10]. Recent evidence indicated knocking down CD133 in NRASQ61R/BRAFWT mutant melanoma renders cells more sensitive to clinically employed-MEK/BRAF inhibitors [12]

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