Side Population Cells from Human Melanoma Tumors Reveal Diverse Mechanisms for Chemoresistance

Abstract

Side population (SP) is identified as cells capable of excluding the fluorescent Hoechst dye and anticancer drugs, and represents hematopoietic stem cells and chemoresistant cells from several solid tumors. In this study, we confirmed the presence of SP cells in tumors from melanoma patients. Melanoma SP cells overexpressed ATP-binding-cassette (ABC) transporters, ABCB1 and ABCB5. We generated a direct in vivo xenograft model, and demonstrated that SP cells were resistant to paclitaxel, a substrate of ABCB1, both in vitro and in vivo. However, melanoma SP cells were also resistant to temozolomide, which is not a substrate for ABC transporters, through IL-8 upregulation. In addition, gene profiling studies identified three signaling pathways (NF- κB, α6-β4-integrin and IL-1) as differentially upregulated in melanoma SP cells, and there was a significant increase of PCDHB11 and decrease of FUK and TBX2 in these cells. Therefore, we provide evidence that SP is an enriched source of chemoresistant cells in human melanomas, and suggest that the selected genes and signaling pathways of SP cells may be a potential target for effective melanoma therapies. To our knowledge, this is previously unreported study to isolate SP cells from melanoma patients and to investigate the gene expression profiling of these cells.

Quantitative histopathology identifies patients with thin melanomas who are at risk for metastases

“…Our results are compatible with those observations, and may allow a new avenue to investigate epigenetic changes in patients with thin melanomas [20,22]. The concept that subpopulations of cells dominate a tumor's biology is well described in the literature for multiple cancers, including melanomas [23][24][25].…”

ABCB5 is a limbal stem cell gene required for corneal development and repair

“…ABCB5, first identified as a marker of skin progenitor cells 6 and melanoma stem cells 7,9 , functions as a regulator of cellular differentiation 6 . On the basis of this function and its expression on stem cells in additional organ systems 10 , we hypothesized that ABCB5 might also identify slow-cycling, label-retaining LSCs in the eye.…”

Contemporary and potential future molecular diagnosis of melanoma

“…This does not exclude the existence of melanoma cells retaining CSCs features, which has been widely observed and documented [58][59], but rather increases the level of complexity of this tumor by introducing "CSCs heterogeneity". In this respect, in melanoma, numerous cell surface markers such as CD133, CD271, ABCB5 [59][60][61] and intra-cellular enzymes such as aldehyde dehydrogenase (ALDH) isozymes [58,62] have been successfully used to isolate cells with CSCs features.…”

“…The Side Population (SP) is a subset of drug resistant cells expressing specific ABC transporters, which allow them to exclude the Hoechst-33342 dye. In melanoma, SP is enriched in chemoresistant cells [58]. Consistently, ABCB5-overexpressing melanoma cells participate to chemoresistance and display stem cell features [59,65].…”

“…In this respect, in melanoma, numerous cell surface markers such as CD133, CD271, ABCB5 [59][60][61] and intra-cellular enzymes such as aldehyde dehydrogenase (ALDH) isozymes [58,62] have been successfully used to isolate cells with CSCs features.…”