The influence of cell culture variables on human collagenase inhibitor expression

This study investigated the modulation of human collagenase inhibitor expression by a variety of cell culture variables. Inhibitor production was found to be largely invariant with respect to the concentration of serum incorporated into culture medium. Similarly, environmental pH failed to affect inhibitor expression over the pH range of 6.8-8.2. When inhibitor production was examined as a function of cell culture density, synthesis of this protein per cell was greatest during logarithmic growth and early confluence, but even in late post-confluent cultures levels approaching 50% of maximal were routinely observed. When basal levels of collagenase and inhibitor were compared in 8 different normal human skin fibroblast cell lines, inhibitor production varied by only 2-fold, whereas collagenase levels displayed a range exceeding 20-fold. Thus, despite manipulations in the presence or absence of serum and even across different cell lines, inhibitor production seemed to be marked most conspicuously by its constancy. The kinetics of inhibitor secretion into culture medium were also examined. Whether cultured in the presence or absence of serum, inhibitor levels reached maximal values in the medium after 24-48 hours of incubation and remained constant thereafter. Interestingly, assessment of intracellular versus extracellular quantities of inhibitor demonstrated that there was no significant intracellular storage of this protein. Thus, the data suggest that human collagenase inhibitor is a secretory protein which is rapidly exported into the extracellular space without significant accumulation intracellularly.