Production of sinusoidal endothelium-stimulating factors enables B16 melanoma cells to metastasize in liver by interleukin-1-dependent mechanism

Interleukin-1beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) h ave been involved in melanoma-endothelial cell adhesion and metastasis by v ery late antigen-4 (VLA-4)/vascular cell adhesion molecule-1 (VCAM-1)-media ted interaction. However, most metastasizing melanoma cells are unable to p roduce these pro-inflammatory cytokines, and, therefore, how endothelial ce ll expression of VCAM-1 is upregulated during capillary transit of metastas izing melanoma cells is unclear. We tested the hypothesis that melanoma cel l-derived factors would stimulate endothelial cell secretion of IL-1 beta a nd TNF-alpha, thus upregulating its VCAM-1-dependent adhesiveness. Primary cultured mouse hepatic sinusoidal endothelium (HSE) cells were trea ted or not with B16 melanoma (B16M) cell-conditioned medium (CM), and their adhesiveness and secretion of IL-1 beta and TNF-alpha determined along tim e. Recombinant human IL-1 receptor antagonist (IL-1Ra) and mouse TNF-alpha soluble receptor (TNF- alpha sR) were used to study the possible role of HS E-derived IL-1 beta and TNF-alpha in the control of HSE adhesiveness. Anti- mouse VCAM-1 antibodies were used to determine the contribution of VCAM-1 t o the mechanism of adhesion to HSE and metastasis of intrasplenically-injec ted B16M cells. B16M-CM significantly (p < 0.01) increased in vitro HSE cell production of TNF-alpha and IL-1 beta, and their adhesiveness for other B16M cells. There was a statistically significant (p < 0.01) increase of B16M cell adhesion to HSE isolated on the 10th hour from B16M cell intrasplenically-injected m ice, compared to HSE from saline-injected mice. Anti-mouse VCAM-1 antibodie s abolished B16M-dependent HSE adhesion augmentation, and 70-80% inhibited hepatic metastasis, indicating that other VCAM-1-independent cytokine-induc ed adhesion mechanisms very little contributed to metastasis formation in t his system. Addition of either TNF-alpha sR or IL-1Ra together with B16M-CM to HSE significantly (p < 0.01) reduced HSE adhesiveness (p < 0.01) by 75% as compared to untreated HSE. Moreover, complete abrogation of B16M-CM-dep endent adhesion was found when HSE cells received TNF-a sR plus IL-1Ra toge ther with B16M-CM. Thus, production of TNF-alpha- and IL-1 beta-stimulating factors, which sub sequently increased VCAM-1-dependent adhesion in HSE, may constitute a rele vant phenotypic property of non-IL-1 producing melanoma cells able to metas tasize in liver by IL-1-dependent mechanism.