Rabbit procollagenase synthesized and secreted by a high-yield mammalian expression vector requires stromelysin (matrix metalloproteinase-3) for maximal activation

A chimeric gene composed of the mouse metallothionein promoter linked to the 5' end of the 9.1-kilobase pair rabbit procollagenase (matrix metalloproteinase-1) gene was stably transfected into baby hamster kidney (BHK) cells. Like the native protein, the recombinant procollagenase synthesized and secreted by these cells was the product of a 2.1-kilobase pair transcript which was translated into a procollagenase protein of 57 kDa, with a small amount of protein that co-migrated with the glycosylated form of the native protein at 61 kDa. The BHK cells expressed levels of recombinant procollagenase equal to or exceeding those of rabbit synovial fibroblasts stimulated with phorbol myristate acetate, where procollagenase mRNA may comprise 2% of the mRNA population. Although minimal (approximately 10%) collagenolysis was seen when the zymogen was activated with trypsin or an organ-omercurial compound, the expression of full collagenolytic activity of the recombinant protein depended on the presence of stromelysin (matrix metalloproteinase-3). Purified recombinant collagenase displayed a specific activity of 8,400 units/mg of enzyme (1 unit degraded 1 microgram of collagen/minute at 37 degrees C) when fully activated, which was accomplished by the specific cleavage of the Gln80-Phe81 bond of procollagenase by stromelysin. We conclude that 1) these stably transfected BHK cells represent a high yield source of recombinant mammalian procollagenase, 2) activation of procollagenase depends on the presence of stromelysin, and 3) recombinant procollagenase from this high yield source may be useful in future studies to elucidate the detailed mechanism(s) involved in the activation of this enzyme.