Cystatins and stefins in ascites fluid from ovarian carcinoma

Cysteine proteinase inhibitors (CpI) of all three families were found in ascites fluid from patients with ovarian carcinoma. CPIs were isolated by affinity chromatography on carboxymethylated papain Sepharose, followed by gel filtration, anti-stefin-Sepharose and ion exchange chromatography. The highest apparent inhibition against cathepsin B (Cat B) was found in the low molecular mass (LMM) CPI fraction. Immunochemical analysis of this fraction revealed the presence of cystatin C and both stefins A and B while the high molecular mass (HMM) CPI fraction contained kininogens. We demonstrated that CPIs were not completely associated with cysteine proteinases (CPs): about 20% of HMM CPIs and 50% of LMM CPIs were free in native ascites fluid. Affinity chromatography on anti-Cat B-Sepharose revealed that the major LMM CPI, associated with Cat B in native ascites fluid, was the full length form of cystatin C, pI 9.3, and not its truncated form, pI 7.85. The latter was isolated and found to inhibit Cat B in vitro with apparent Ki 0.18 +/- 0.2 nM. Stefin A was isolated from alkaline activated ascites fluid in its two isoforms, pI 4.6 and 4.9. In native ascites, the pI 4.9 isoform was mostly associated with Cat B. Ki for Cat B was 3.55 +/- 1.7 nM, not significantly different from the Ki values measured for stefin A, isolated from other human tissues and biological fluids.