REGULATION OF PLASMINOGEN ACTIVATION, MATRIX METALLOPROTEINASES AND UROKINASE-TYPE PLASMINOGEN ACTIVATOR-MEDIATED EXTRACELLULAR-MATRIX DEGRADATION IN HUMAN OSTEOSARCOMA CELL-LINE MG63 BY INTERLEUKIN-1-ALPHA

Plasmin-mediated extracellular proteolysis has been implicated in the degradation of bone in normal and pathological conditions. Normal and malignant osteoblasts can produce both tissue-type plasminogen activat or (t-PA) and urokinase-type plasminogen activator (n-PA), We have use d the osteosarcoma cell line MG63 to address the question of whether t he enhanced bone turnover in osteosarcomas is mediated by t-PA or by u -PA and to study the effect of the cytokine interleukin-1 alpha (IL-1 alpha), known to influence bone degradation, on the plasminogen activa tor production and extracellular matrix degradation in malignant osteo blastic cells, Furthermore, the effect of IL-1 alpha on the synthesis of matrix metalloproteinases (MMPs) and their inhibitors (TIMPs) was a nalyzed, u-PA production by MG63 was high (approximately 180 ng/10(6) cells/24 h), Also t-PA and PAI-1 production was observed. u-PA product ion was rapidly increased in MG63 by IL-1 alpha (10 ng/ml), whereas an effect on t-PA production was only found after a prolonged incubation and hardly any effect of IL-1 alpha on PAI-1 production was observed, mRNA analysis revealed similar effects. u-PA receptor (u-PAR) mRNA wa s detectable in MG63 cells and could be increased by IL-1 alpha after 24 h. In MG63, u-PA-mediated extracellular matrix degradation was dete ctable, and IL-1 alpha increased the u-PA-mediated matrix degradation (approximately 2-fold), Under control conditions in MG63, only MMP-2, TIMP-1, and TIMP-2 mRNA could be observed, After the addition of IL-1 alpha, a very rapid increase in MMP-1 and MMP-3 mRNA could be observed as well as a moderate increase in TIMP-1 mRNA The presence of MMP-2 w as demonstrated by gelatin zymography. These results show that IL-1 al pha can stimulate u-PA production and can regulate extracellular prote olytic activity mainly via u-PA induction in the MG63 osteosarcoma cel l line. Furthermore, IL-1 alpha has a strong stimulating effect on the production of MMP-1 and MMP-3, These findings suggest that u-PA and p ossibly MMP-1 and MMP-3 play an important role in the process of bone turnover in osteosarcomas.