Cutaneous melanoma is one of the most aggressive and lethal forms of skin cancer. Some specific driver mutations have been described in multiple oncogenes including BRAF and NRAS that are mutated in 60–70% and 15–20% of melanoma, respectively. The aim of this study was to evaluate the role of Small Heat Shock Protein B8 (HSPB8) on cell growth and migration of both BLM (BRAF^wt/NRAS^Q61R) and A375 (BRAF^V600E/NRAS^wt) human melanoma cell lines. HSPB8 is a member of the HSPB family of chaperones involved in protein quality control (PQC) system and contributes to chaperone assisted selective autophagy (CASA) as well as in the regulation of mitotic spindle. In cancer, HSPB8 has anti- or pro-tumoral action depending on tumor type. In melanoma cell lines characterized by low HSPB8 levels, we demonstrated that the restoration of HSPB8 expression causes cell growth arrest, reversion of EMT (Epithelial-Mesenchymal Transition)-like phenotype switching and antimigratory effect, independently from the cell mutational status. We demonstrated that HSPB8 regulates the levels of the active prenylated form of NRAS in NRAS-mutant and NRAS-wild-type melanoma cell lines. Consequently, the inhibition of NRAS impairs the activation of Akt/mTOR pathway inducing autophagy activation. Autophagy can play a dual role in regulating cell death and survival. We have therefore demonstrated that HSPB8-induced autophagy is a crucial event that counteracts cell growth in melanoma. Collectively, our results suggest that HSPB8 has an antitumoral action in melanoma cells characterized by BRAF and NRAS mutations.

皮肤黑色素瘤是最具侵袭性和致命性的皮肤癌之一。在包括BRAF和NRAS在内的多种致癌基因中描述了一些特定的驱动突变，它们分别在 60-70% 和 15-20% 的黑色素瘤中发生突变。本研究的目的是评估小热休克蛋白 B8 (HSPB8) 对 BLM (BRAF ^wt /NRAS ^Q61R ) 和 A375 (BRAF ^V600E /NRAS ^{wt ) 细胞生长和迁移的作用}) 人黑色素瘤细胞系。HSPB8 是参与蛋白质质量控​​制 (PQC) 系统的伴侣蛋白 HSPB 家族的成员，有助于伴侣蛋白辅助选择性自噬 (CASA) 以及有丝分裂纺锤体的调节。在癌症中，HSPB8 根据肿瘤类型具有抗肿瘤或促肿瘤作用。在以低 HSPB8 水平为特征的黑色素瘤细胞系中，我们证明 HSPB8 表达的恢复会导致细胞生长停滞、EMT（上皮-间质转化）样表型转换和抗迁移作用的逆转，与细胞突变状态无关。我们证明了 HSPB8 调节NRAS突变体和NRAS中NRAS活性异戊二烯化形式的水平- 野生型黑色素瘤细胞系。因此，抑制 NRAS 会损害 Akt/mTOR 通路的激活，从而诱导自噬激活。自噬可以在调节细胞死亡和存活方面发挥双重作用。因此，我们已经证明 HSPB8 诱导的自噬是抵消黑色素瘤细胞生长的关键事件。总的来说，我们的结果表明 HSPB8 在以BRAF和NRAS突变为特征的黑色素瘤细胞中具有抗肿瘤作用。