The antimitogenic effect of the cannabinoid receptor agonist WIN55212-2 on human melanoma cells is mediated by the membrane lipid raft

Abstract

Here are reported the antiproliferative effects of the cannabinoid agonist WIN upon human melanoma cells expressing mRNA and protein for both CB1 and CB2 receptors. While WIN exerted antimitogenic effects, selective CB1 or CB2 agonists were unable to reproduce such effects and selective CB1 and CB2 antagonists did not inhibit WIN-induced cell death. Cells treated with WIN, preincubated with the lipid raft disruptor methylcyclodestrin, were rescued from death. WIN induced activation of caspases and phosphorylation of ERK that were attenuated in cultures treated with methylcyclodestrin.

Membrane lipid raft complex-mediated antimitogenic effect of WIN in melanoma could represents a potential targets for a melanoma treatment.

Introduction

Melanoma is the most fatal form of skin cancer. The incidence and mortality of this disease are increasing [1]. The lifetime risk for the development of melanoma is now 1 in 41 for men and 1 in 61 for women, making this cancer a growing public health concern.

Surgery remains the prominent treatment of melanoma and it is curative in many cases [2]. Nevertheless, metastatic melanoma is a highly lethal malignancy with few good treatment options [3].

Such treatment failure is partly due to the broad chemoresistance of melanomas, related to an altered survival capacity and inactivation of apoptotic pathways. In contrast to other cancer cells, chemoresistance of melanoma cells is not acquired selectively following drug therapy, but rather intrinsic to melanoma cells [3].

Preparations of cannabis have been used in medicine for many centuries, and currently, there is an intense renaissance in the study of the therapeutic effects of cannabinoids, the active components of Cannabis sativa, focused on the design of potent and selective synthetic cannabinoid agonists and antagonists [4].

Cannabinoids exert a wide array of effects on the central nervous system, as well as on peripheral sites, such as the immune, cardiovascular, digestive, reproductive, and ocular systems [5], [6], [7]. In addition, cannabinoids exert antimitogenic effects in various tumors in animal models [8], and directly induce apoptosis or cell cycle arrest in different transformed cells in vitro [9], [10].

Cannabinoids act through two receptors: the CB1 receptor, mostly expressed in brain, and the CB2 receptor, expressed peripherally, for example in immune system cells. The mechanism by which cannabinoids exerts their proapoptotic effects is not clear yet. Recent evidence suggests that their antiproliferative effect could be mediated through pathways alternative to those associated with CBRs. For example, some cannabinoid effects are mediated by the vanilloid receptor 1 (VR1) [11], [12], as well as by non-receptorial sites [13], [14], [15]. In this line, an involvement of lipid rafts complexes, specialized domains within the cell membrane abundant in glycosphingolipids, saturated phospholipids and cholesterol, has been suggestes. These cholesterol-rich regions can include or exclude proteins, and may serve as clues for recruitment and concentration of signaling molecules and thus have been implicated in signal transduction from cell surface receptors [15], [16], [17]. Interestingly, depletion of cholesterol in lipid rafts attenuates antiblastic drug-induced apoptosis [18].

In light of these data, with the aim to identify novel molecular targets for melanoma therapy, this study was designed to characterize mechanisms through which the non-selective CB1/CB2 receptor agonist WIN55212-2 induces apoptosis in different human melanoma cell lines.