Irene Diez‐Itza

A cDNA coding for a new human matrix metalloproteinase (MMP) has been cloned from a cDNA library derived from a breast tumor. The isolated cDNA contains an open reading frame coding for a polypeptide of 471 amino acids. The predicted protein sequence displays extensive similarity to the previously known MMPs and presents all the structural features characteristic of the members of this protein family, including the well conserved PRCGXPD motif, involved in the latency of the enzyme and the zinc-binding domain (HEXGHXXXXXHS). In addition, this novel human MMP contains in its amino acid sequence several residues specific to the collagenase subfamily (Tyr-214, Asp-235, and Gly-237) and lacks the 9-residue insertion present in the stromelysins. According to these structural characteristics, the MMP described herein has been tentatively called collagenase-3, since it represents the third member of this subfamily, composed at present of fibroblast and neutrophil collagenases. The collagenase-3 cDNA was expressed in a vaccinia virus system, and the recombinant protein was able to degrade fibrillar collagens, providing support to the hypothesis that the isolated cDNA codes for an authentic collagenase. Northern blot analysis of RNA from normal and pathological tissues demonstrated the existence in breast tumors of three different mRNA species, which seem to be the result of the utilization of different polyadenylation sites present in the 3'-noncoding region of the gene. By contrast, no collagenase-3 mRNA was detected either by Northern blot or RNA polymerase chain reaction analysis with RNA from other human tissues, including normal breast, mammary fibroadenomas, liver, placenta, ovary, uterus, prostate, and parotid gland. On the basis of the increased expression of collagenase-3 in breast carcinomas and the absence of detectable expression in normal tissues, a possible role for this metalloproteinase in the tumoral process is proposed.

Apolipoprotein D (apo D) is a glycoprotein involved in the human plasma lipid transport system and present at large amounts in cyst fluid from women with gross cystic disease of the breast. Apo D expression in breast carcinomas was examined by immunoperoxidase staining of a series of 163 tumors. A total of 60 (36.8%) tumors were negative for apo D immunostaining, 28 (17.2%) carcinomas were weakly positive, 33 (20.2%) were moderately stained, whereas the remaining 42 (25.8%) tumors were strongly stained with the specific antibodies. No significant correlation was found between apo D content and tumor size, lymph node involvement, or biochemical parameters such as estrogen receptors, cathepsin D, or pS2 protein. However, the finding of a significant association between apo D and menopausal status of patients or differentiation grade of tumors, with apo D values being lower in tumors from premenopausal women or in poorly differentiated carcinomas, suggested a potential value of this glycoprotein as a prognostic factor in breast cancer. Preliminary analysis of relapse-free survival and overall survival in a subgroup of 152 women with a mean follow-up of 42 months confirmed that low apo D values were significantly associated to a shorter relapse-free survival and poorer survival. According to these data, we propose that apo D in combination with other well-established prognostic factors may contribute to more accurately identify subgroups of breast cancer patients with low or high risk for relapse and death.

The protein composition of breast secretions from 99 premenopausal women with benign or malignant breast diseases and from 70 control women without breast pathologies has been studied by using polyacrylamide gel electrophoresis. These fluids have been classified into two types according to their major polypeptide components. Type I fluids are defined by three major distinctive bands at Mr 44,000, 24,000, and 17,000, while those designated Type II present distinctive bands at Mr 80,000, 15,000, and 14,000. Amino acid sequencing and immunoblotting analysis demonstrated that proteins in Type I secretions correspond to Zn-alpha 2-glycoprotein, apolipoprotein D, and gross cystic disease fluid protein-15, while those from Type II fluids have been identified as lactoferrin, lysozyme, and alpha-lactalbumin. Most women (93%) without breast pathology and most patients (88%) with benign diseases had secretions with a Type I polypeptide pattern. By contrast, a large percentage (57%) of secretions from women with breast carcinoma presented a Type II protein pattern. Further studies with a large number of women will be useful for corroborating the potential clinical interest of breast fluid protein analysis.