SV40-transformed Human Lung Fibroblasts Secrete a 92-kDa Type IV Collagenase Which Is Identical to That Secreted by Normal Human Macrophages

TLDR

The SV40‑transformed fibroblasts synthesize a 92‑kDa glycosylated proenzyme that is secreted after signal‑peptide cleavage, complexes with TIMP, and is activated by organomercurials to produce an active collagenase that digests native type IV and V collagen. The activated 92‑kDa metalloprotease is identical to the enzyme secreted by normal alveolar macrophages, U937 cells, HT1080 cells, keratinocytes, and possibly polymorphonuclear cells, and it digests native type IV and V collagen with specificity indistinguishable from the 72‑kDa type IV collagenase, comprising five domains including a unique proline‑rich region.

Abstract

We have reported that SV40-transformed human lung fibroblasts secrete a 92-kDa metalloprotease which is not detectable in the parental cell line IMR-90. We now present the complete structure of this enzyme along with the evidence that it is identical to the 92-kDa metalloprotease secreted by normal human alveolar macrophages, phorbol ester-differentiated monocytic leukemia U937 cells, fibrosarcoma HT1080 cells, and cultured human keratinocytes. A similar, perhaps identical, enzyme can be released by polymorphonuclear cells. The preproenzyme is synthesized as a polypeptide of predicted Mr 78,426 containing a 19 amino-acid-long signal peptide and secreted as a single 92,000 glycosylated proenzyme. The purified proenzyme complexes noncovalently with the tissue inhibitor of metalloproteases (TIMP) and can be activated by organomercurials. Activation with phenylmercuric chloride results in removal of 73 amino acids from the NH2 terminus of the proenzyme, yielding an active form capable of digesting native types IV and V collagen. The in vitro substrate specificity of the enzyme using these substrates was indistinguishable from that of the 72-kDa type IV collagenase. The 92-kDa type IV collagenase consists of five domains; the amino-terminal and zinc-binding domains shared by all members of the secreted metalloprotease gene family, the collagen-binding fibronectin-like domain also present in the 72-kDa type IV collagenase, a carboxyl-terminal hemopexin-like domain shared by all known enzymes of this family with the exception of PUMP-1, and a unique 54-amino-acid-long proline-rich domain homologous to the alpha 2 chain of type V collagen.