Cystatin C and cathepsin B in human colon carcinoma: Expression by cell lines and matrix degradation

Abstract Expression of the cysteine proteinase cathepsin B and its physiological inhibitor cystatin C was analyzed in vitro in I human fibrosarcoma and 4 human colon carcinoma cell lines. Cystatin C antigen as well as cathepsin B activity were detected in the conditioned media of the 5 cell lines. The corresponding cell extracts expressed high levels of cathepsin B activity, whereas only trace amounts of cystatin C antigen could be found. Northern‐blot analysis revealed the presence in the 5 cell lines of a 0.8‐kb cystatin C mRNA transcript and 2 cathepsin B transcripts of 2.3 and 4.3 kb. Pepsin treatment of tumor‐cell‐released cathepsin B induced an average 7.3‐fold increase in activity, indicating that the enzyme was mainly present as a latent form in conditioned medium. The pepsin‐activated cathepsin B from one colon carcinoma cell line was further characterized using the cysteine proteinase inhibitors E‐64, recombinant cystatin C, a cystatin‐C‐derived peptidyl inhibitor (Z‐LVG‐CHN 2 ), and cathepsin‐B‐specific diazomethyl ketone inhibitors (Z‐FT(OBzl)‐CHN 2 , Z‐FS(OBzl)‐CHN 2 ). This activity was totally neutralized by recombinant cystatin C, suggesting a potential for interaction between released extracellular cathepsin B and cystatin C. In vitro assays of degradation of extracellular matrix showed that cyrteine proteinase inhibitors could decrease matrix degradation induced by pepsin‐activated conditioned media. With colon cells, this inhibition was not observed, indicating a requirement for an extracellular activation of latent cathepsin B. Our data provide evidence that cystatin C and latent cathepsin B are both released extracellularly by colon carcinoma cells in vitro. They suggest that cystatin C and cathepsin B interactions may participate, in an as yet unelucidated way, in the modulation of the invasive phenotype of human colonic tumors. © 1992 Wiley‐Liss, Inc.