Effects of native and cleaved forms of alpha1-antitrypsin on ME 1477 tumor cell functional activity

Tumor cells synthesize and release a variety of substances, including proteases and protease inhibitors involved in cell growth and proliferation. alpha1-Antitrypsin (AAT) is a serine proteinase inhibitor synthesized primarily in the liver, but also in extra-hepatic tissues and cells, including tumor cells. AAT exists not only in a native, active inhibitory form, but also in several, non-inhibitory forms, such as cleaved and/or degraded. This study was designed to investigate the synthesis of AAT by melanoma cells, ME 1477, and the effects of native, cleaved and C-terminal fragment of AAT (C-36) on cell functional activity. We found that ME 1477 cells synthesize and secrete AAT with the same apparent molecular mass as described for AAT purified from plasma, but with no measurable inhibitory activity. As determined by Western blot after immunoprecipitation of [32S]-labeled AAT, exogenous native or modified forms of AAT added to the cells at a concentration of 10 microM did not change AAT synthesis. Moreover, cells exposed to native AAT show decreased [3H]-thymidine incorporation by 53% and tissue inhibitor of metalloproteinases (TIMP)-1 levels by 36%. In contrast, cells treated with C-36 peptide significantly increased metalloproteinase activity, and [3H]-thymidine incorporation by 35%. Specifically, pro-collagenase-1 levels were found to be increased by 1.4-fold and decreased by 1.5-fold in cells treated with C-36 peptide and native AAT, respectively. Cleaved form of AAT had no significant effects on parameters measured. Data obtained from this study suggest that specific forms of AAT have multiple effects on tumor cell viability and play diverse roles in tumorogenesis.