Regulation of sphingosine kinases and sphingosine-1-phosphate receptors expresion in melanoma cells resistant to VEMURAFENIB

Abstract

Over the last years, the incidence of melanoma, the deadliest formof skin cancer, has risen faster than any other cancer type. Consideringthat half of the patient?s exhibit the BRAFV600E mutation,therapies with BRAF and MEK inhibitors (BRAFi/MEKi) showed animpressive success rate. Unfortunately, treatments are marginallyeffective since tumors quickly become resistant. In that regard, accumulatingevidence supports that sphingosine-1-phosphate (S1P)is linked to multiple mechanisms leading to cancer progression andresistance. Thus, the aim of this study was to evaluate how vemurafenib(BRAFi) resistance affects the expression of sphingosine kinases(SphK) and S1P receptors (S1PR) in melanoma. To this end,we generated vemurafenib-resistant melanoma cells by continuousexposure of parental sensitive cells to increasing concentrations(0,01μM ? 1μM) of the drug for 3 months. Previously, we showedthat vemurafenib-resistant Lu1205 melanoma cell (Lu1205R) exhibithigher IC50 and pERK levels than their sensitive parents (Lu1205S).Here, we extended those studies to A375 melanoma cells. Certainly,A375R cells also showed increased resistance and pERK, butnot pAKT levels. Expression of SphK and S1PR in both cells lineswas evaluated by RT-qPCR. Surprisingly, the modulation of SphK1,S1PR1 and S1PR3 expression differ in Lu1205R and A375R cells.In addition, a bioinformatic analysis was performed using the publicGene Expression Omnibus (GEO) database (https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE24862). This study showeda differential gene expression pattern in other cell lines, includingA375, supporting the concept that melanoma heterogeneity maytrigger different mechanisms of resistance to BRAFi therapy. In summary,although our results indicate that S1P signaling may have arole in vemurafenib resistance, further studies will be necessary toelucidate its importance.