Detection of mRNAs for urokinase-type plasminogen activator, its receptor, and type 1 inhibitor in giant cell tumors of bone with in situ hybridization.

Although giant cell tumor of bone (GCT) is generally considered to be an uncommon benign neoplasm, it can pursue an aggressive course with local recurrence and metastasis. Attempts to predict the biological behavior of GCT with histopathological parameters, however, have not been successful. The urokinase-type plasminogen activation system has been implicated in tumor invasion and metastasis and abnormalities of the components of this system have been found in several malignancies. In this study we postulated that the urokinase-type plasminogen activation system associated with bone destruction and local invasion is present in GCT. We therefore evaluated the mRNA levels for urokinase-type plasminogen activator (u-PA), urokinase-type plasminogen activator receptor (u-PAR), and plasminogen activator inhibitor type 1 (PAI-1) by using Northern blot analysis and in situ hybridization in four cases of GCT and spindle-shaped mononuclear cells at the 35th passage from a GCT. Our results showed that giant cell tumors of bone contained variable levels of u-PA, u-PAR, and PAI-1 mRNA, respectively, 2.3, 1.4, and 3.2 kb in size. In situ hybridization showed that u-PA, u-PAR, and PAI-1 mRNA were expressed in both the mononuclear cells and the osteoclast-like giant cells; the signal for u-PA mRNA in the spindle-shaped mononuclear cells was more intense than that in the osteoclast-like multinuclear giant cells. Some spherical mononuclear cells (macrophage-like cells) expressed high levels of PAI-1 mRNA in comparison with the spindle-shaped mononuclear cells. In addition, the 35th passaged spindle-shaped mononuclear cells were used to study the gene expression of u-PA during cell proliferation. The results showed that the level of u-PA mRNA increases after adding 10% fetal calf serum to quiescent cells. The induction was maximal at 16 hours and remained high during 48 hours of treatment. In conclusion, even though osteoclast-like cells are ultimately responsible for the bone resorption of GCT, the mononuclear neoplastic cells of GCT may also be involved in degradation of the extracellular matrix during invasive growth by facilitating the urokinase plasminogen activation system. In addition, our observation of upregulation of u-PA mRNA in spindle-shaped mononuclear cells after serum stimulation indicated that u-PA production may be linked to tumor growth.