The chemokine RANTES is secreted by human melanoma cells and is associatedwith enhanced tumour formation in nude mice

Modulation of tumour cell growth by tumour-infiltrating leucocytes is of hi gh importance for the biological behaviour of malignant neoplasms. In melan oma, tumour-associated macrophages (TAM) and tumour-infiltrating lymphocyte s (TIL) are of particular interest as inhibitors or enhancers of cell growt h. Recruitment of leucocytes from the peripheral blood into the tumour site is mediated predominantly by chemotaxins, particularly by the group of che mokines. The aim of this study was to identify peptides released by human melanoma c ells with monocyte chemotactic properties. To assure the presence of biolog ically active mediators, biochemical purification and biological characteri zation of peptides was based on a detection system dependent on bioactive, monocyte chemotactic activity in vitro. Cell culture supernatants of melano ma cells were fractioned by heparin-sepharose followed by preparative rever sed-phase HPLC steps to enrich monocyte chemotactic activity in one single band on a sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-P AGE) gel. These purified fractions were shown to react with RANTES-specific antibodies in an enzyme-linked immunosorbent assay (ELISA) as well as in W estern blot analysis. Amino acid sequencing of the N-terminal protein fragm ent confirmed 100% homology to the RANTES protein. Further analysis showed that four out of eight melanoma cell lines constitutively expressed and sec reted the beta-chemokine RANTES as detected by ELISA. The amount of RANTES protein secreted (up to 50 ng ml(-1)) was about 5-50 times higher than inte rleukin 8 (IL-8), determined in the same supernatant samples. Tumour necros is factor a (TNF-alpha), not, however, IL-2, interferon-gamma (IFN-gamma), or alpha-melanocyte-stimulating hormone (alpha-MSH) was able to up-regulate RANTES and interleukin 8 secretion. Furthermore, higher levels of RANTES s ecretion in vitro were associated with increased tumour formation upon s.c. injection of six human melanoma cell lines in nude mice. Our data provide evidence that a subset of melanoma cells express mRNA and secrete RANTES pr otein which may be partly responsible for the recruitment of monocytes, T-c ells and dendritic cells into the tumours. However, transplantation experim ents in nude mice suggest that effects of RANTES may also benefit tumour pr ogression. Further studies are needed to dissect the underlying mechanisms.