Cancer stem cells render a complex cascade of events that facilitates highly invasive melanoma malignancy. Interplay between immunocytes and cancer stem cells within tumor microenvironment with the participation of sphingolipid signaling mediators skews the immune evasion strategies toward metastatic neoplasm. In this context, we aimed to explore the functional aspect of glucosylceramide synthase (GCS), a key enzyme of sphingolipid biosynthesis in the maintenance of melanoma stem cell-like cancer cells (CSCs). Our findings demonstrated that tumor hypoxia was responsible for elevated GCS expression in melanoma, which was correlated with substantially increased melanoma CSCs. Moreover, hypoxia-induced TGF-β from TAMs and Tregs promoted GCS induction in B16F10 murine melanoma CSCs via PKCα signaling and facilitated the expansion of melanoma CSCs. Interestingly, GCS ablation hindered the immunosuppressiveness of TAMs and Tregs. Therefore, our study for the first time demonstrated a novel paracrine pathway of melanoma CSC maintenance and tumorigenicity, exploiting the bidirectional signaling with immunocytes. Furthermore, our study showed that the combinatorial immunotherapy involving immunomodulators like Mw and DTA-1 repressed CSC pool affecting GCS functions in advanced-stage B16F10 murine melanoma tumor. Moreover, GCS inhibition sensitized conventional chemotherapeutic drug-resistant melanoma CSCs to the genotoxic drugs paving the way toward selective melanoma treatment. Better therapeutic efficacy with inhibition of GCS and CSC depletion suggests a crucial role of GCS in melanoma treatment, therefore, implying its application concerning clinical challenges of chemotherapy resistance leading to prolonged survival.

中文翻译：

---

葡萄糖神经酰胺合酶在 B16F10 鼠黑色素瘤干细胞样癌细胞调控中的关键作用

癌症干细胞呈现复杂的级联事件，促进高侵袭性黑色素瘤恶性肿瘤。在鞘脂信号介质的参与下，肿瘤微环境中免疫细胞和癌症干细胞之间的相互作用使免疫逃避策略偏向于转移性肿瘤。在此背景下，我们旨在探索葡萄糖神经酰胺合酶 (GCS) 的功能方面，该酶是维持黑色素瘤干细胞样癌细胞 (CSC) 中鞘脂生物合成的关键酶。我们的研究结果表明，肿瘤缺氧是导致黑色素瘤中 GCS 表达升高的原因，这与黑色素瘤 CSC 的显着增加有关。此外，来自 TAM 和 Treg 的缺氧诱导的 TGF-β 通过 PKCα 信号传导促进 B16F10 鼠黑色素瘤 CSC 中的 GCS 诱导，并促进黑色素瘤 CSC 的扩增。有趣的是，GCS 消融阻碍了 TAM 和 Treg 的免疫抑制。因此，我们的研究首次证明了黑色素瘤 CSC 维持和致瘤性的新旁分泌途径，利用免疫细胞的双向信号传导。此外，我们的研究表明，涉及免疫调节剂的组合免疫疗法，如Mw和 DTA-1 抑制 CSC 池，影响晚期 B16F10 鼠黑色素瘤肿瘤中的 GCS 功能。此外，GCS 抑制使传统的化疗耐药黑色素瘤 CSC 对基因毒性药物敏感，为选择性黑色素瘤治疗铺平了道路。通过抑制 GCS 和 CSC 消耗获得更好的治疗效果表明 GCS 在黑色素瘤治疗中的关键作用，因此，暗示其应用涉及导致延长生存期的化疗耐药性的临床挑战。