Sphingosine Kinase and Sphingosine-1-Phosphate Regulate Migration, Endocytosis and Apoptosis of Dendritic Cells

Abstract

Dendritic cells (DC) are inducers of primary immune responses and represent an attractive vector for cancer immunotherapy. Sphingosine kinase (SphK) and its product sphingosine-1-phosphate (S1P) play an important role in the regulation of immune cells and cancer, affecting processes such as differentiation, growth or migration. We studied the role of SphK and S1P on migration of DC. RT-PCR showed mRNA expression of SphK in DC, declining from immature (iDC) to mature DC (mDC) to antigen-loaded mDC. Expression of S1P receptors was S1P₁ > S1P₂ = S1P₃, unrelated to maturation or antigen uptake. In transwell assays, iDC migrated towards SDF-1, MIP-1α, MCP and S1P, whereby S1P combined with a chemokine had a synergistic effect. mDC migrated towards 6Ckine and MIP-3β, but not towards S1P. The SphK-inhibitor dihydro-sphingosine (DHS) reduced migration of iDC but not of mDC. In addition S1P₃-inhibitor suramin inhibited DC migration in response to S1P. DHS had a reverse effect on endocytosis, enhancing the uptake of FITC dextran. We also observed an anti-apoptotic effect of S1P on mDC for the first time. This indicates that SphK/S1P may play a role in accumulation of peripheral iDC at the location of antigen and subsequent antigen-uptake. These findings may help to optimise DC-based cancer immunotherapy by modulation of SphK/S1P.

Keywords:

• Dendritic cells
• Sphingosine kinase
• Migration
• Endocytosis
• Immunotherapy