Purification and analysis of growth regulating proteins secreted by a human melanoma cell line

Supernatants of a human malignant cell line established from a CNS metastasis, contained several proteins with putative growth regulating functions. BioGel P-10 gel filtration chromatography, reverse phase HPLC purification, and amino-terminal sequencing of purified peptides resulted in characterization of beta 2-microglobulin (beta 2M, 10 kD), ubiquitin (6 kD), and tissue inhibitor of metalloproteinases 2 (TIMP-2, 21 kD). In addition, CNBr cleavage and purification of resulting peptides revealed diazepam binding inhibitor (DBI, 8 kD) and melanoma inhibiting activity (MIA, 11 kD). The secretion of beta 2M as part of the HLA-class I complex may be related to impaired autologous anti-tumour immune function; ubiquitin may play a role in activation or deactivation of extracellular proteins or cell-cell interactions. As HTZ-19 cells respond in a dose-dependent manner to midozolam, DBI may interfere with growth regulation mediated by diazepam receptor sites. In a collagenolytic assay, TIMP-2 interfered with metalloproteinase functions, which are required for degradation of collagen type IV and organotopic metastasis. MIA is clearly associated with a proliferation inhibiting effect on HTZ-19 cells. In conclusion, although this tumour shows a degree of progression, several proteins with putative functions at different cellular levels were identified, related to proliferation as well as to the type of metastasis.