Induction of interleukin-8 expression in neuroblastoma cells by retinoic acid: Implication of leukocyte chemotaxis and activation

Neuroblastoma cells in response to retinoic acid (RA) exhibit differentiation. RA, which can promote tumor cell differentiation, has also been shown to regulate tumor-infiltrating leukocytes. In an attempt to explore the relationship between RA-induced neuroblastoma cell differentiation and leukocyte chemotaxis, we investigated expression of IL-1β, IL-8, granulocyte-macrophage colony stimulating factor, and tumor necrosis factor-a in the undifferentiated and RA-induced differentiated neuroblastoma cells. Using SK-N-SH neuroblastoma cells, we found that RA induced differentiation of SK-N-SH cells as demonstrated by down-regulation of N-myc gene expression, cell-cycle arrest in Gl phase, and phenotypic change. Neither RA-treated nor untreated neuroblastoma cells expressed IL-1/β, granulocyte-macrophage colony stimulating factor, or tumor necrosis factor-α mRNA. RA-treated but not untreated SK-N-SH cells expressed IL-8 mRNA in a time- and dose-dependent fashion. As determined by ELISA, IL-8 levels were detectable in the culture super-natants from RA-treated, but not untreated, neuroblastoma cells (2.65 ± 0.43 versus 0.05 ± 0.04 ng/mL). Using neutrophil and lymphocyte chemotactic assays, we found that RA-treated but not untreated culture supernatants of neuroblastoma cells promoted neutrophil and lymphocyte chemotaxis. The RA enhancement of neuroblastoma cell-mediated leukocyte chemotaxis was significantly blocked by anti-IL-8 neutralizing antibodies. These results suggest that RA-induced neuroblastoma cell differentiation is associated with production of functional IL-8, which may be involved in the leukocyte infiltration and activation resulting in tumor regression.