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 differen tiation. RA, which can promote tumor cell differentiation, has also be en shown to regulate tumor-infiltrating leukocytes. In an attempt to e xplore the relationship between RA-induced neuroblastoma cell differen tiation and leukocyte chemotaxis, we investigated expression of IL-1be ta, IL-8, granulocyte-macrophage colony stimulating factor, and tumor necrosis factor-a in the undifferentiated and RA-induced differentiate d neuroblastoma cells. Using SK-N-SH neuroblastoma cells, we found tha t RA induced differentiation of SK-N-SH cells as demonstrated by down- regulation of N-myc gene expression, cell-cycle arrest in G1 phase, an d phenotypic change. Neither RA-treated nor untreated neuroblastoma ce lls expressed IL-1beta, granulocyte-macrophage colony stimulating fact or, or tumor necrosis factor-alpha mRNA. RA-treated but not untreated SK-N-SH cells expressed IL-8 mRNA in a time- and dose-dependent fashio n. As determined by ELISA, IL-8 levels were detectable in the culture supernatants from RA-treated, but not untreated, neuroblastoma cells ( 2.65 +/- 0.43 versus 0.05 +/- 0.04 ng/mL). Using neutrophil and lympho cyte chemotactic assays, we found that RA-treated but not untreated cu lture supernatants of neuroblastoma cells promoted neutrophil and lymp hocyte chemotaxis. The RA enhancement of neuroblastoma cell-mediated l eukocyte chemotaxis was significantly blocked by anti-IL-8 neutralizin g antibodies. These results suggest that RA-induced neuroblastoma cell differentiation is associated with production of functional IL-8, whi ch may be involved in the leukocyte infiltration and activation result ing in tumor regression.