Abstract
Nanoliposomal formulation of C6-ceramide, a proapoptotic sphingolipid metabolite, presents an effective way to treat malignant tumor. Here, we provide evidence that acute treatment (30 min) of melanoma and breast cancer cells with nanoliposomal C6-ceramide (NaL-C6) may suppress cell migration without inducing cell death. By employing a novel flow migration assay, we demonstrated that NaL-C6 decreased tumor extravasation under shear conditions. Compared with ghost nanoliposome, NaL-C6 triggered phosphorylation of PI3K and PKCζ and dephosphorylation of PKCα. Concomitantly, activated PKCζ translocated into cell membrane. siRNA knockdown or pharmacological inhibition of PKCζ or PI3K rescued NaL-C6-mediated suppression of tumor migration. By inducing dephosphorylation of paxillin, PKCζ was responsible for NaL-C6-mediated stress fiber depolymerization and focal adhesion disassembly in the metastatic tumor cells. PKCζ and PI3K regulated cell shear-resistant adhesion in a way that required integrin αvβ3 affinity modulation. In conclusion, we identified a novel role of acute nanoliposomal ceramide treatment in reducing integrin affinity and inhibiting melanoma metastasis by conferring PI3K and PKCζ tumor-suppressive activities.
Highlights
C6-ceramide nanoliposome suppresses tumor metastasis by eliciting PI3K and PKCf tumor-suppressive activities and regulating integrin affinity modulation
Pharmacological inhibitors and short interference RNA knockdown, we discovered that nanoliposomal C6-ceramide (NaL-C6)-mediated PKCf and PI3K phosphorylation and PKCa dephosphorylation were responsible for reduced cell migration
Transwell migration and flow migration assays, we revealed that short-term C6 nanoliposome treatment suppressed melanoma and breast cancer migration without inducing cell apoptosis
Summary
C6-ceramide nanoliposome suppresses tumor metastasis by eliciting PI3K and PKCf tumor-suppressive activities and regulating integrin affinity modulation. We provide evidence that acute treatment (30 min) of melanoma and breast cancer cells with nanoliposomal C6-ceramide (NaL-C6) may suppress cell migration without inducing cell death. We identified a novel role of acute nanoliposomal ceramide treatment in reducing integrin affinity and inhibiting melanoma metastasis by conferring PI3K and PKCf tumor-suppressive activities. Ceramide is a sphingolipid-derived second messenger in cell membrane in response to inflammation and stress[1] It is an integral part of cellular differentiation, proliferation and apoptosis pathways. Within circulation, tumor extravasation occurs very rapidly, especially in face of hydrodynamic force[8,9] It is unknown whether nanoliposomal C6-ceramide play roles in inhibiting tumor migration and metastasis upon this short encounter with tumor cells in blood stream. The protein kinase C (PKC) family consists of at least 11 members being classified into three groups: classical, novel, and atypical PKCs, depending on their requirement for regulation by calcium and diacylglycerol (DAG)[10]
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