METASTATIC ABILITY OF MXT MOUSE MAMMARY SUBPOPULATIONS CORRELATES WITH CLONAL EXPRESSION AND OR MEMBRANE-ASSOCIATION OF GELATINASE-A/

We have developed a novel murine mammary tumor system with Variants re presenting different stages of tumor progression. The MXT-s parental c ell line was established from a urethane-induced and hormone-sensitive mammary tumor. MXT-s parental cells are highly tumorigenic but poorly metastatic. MXT clones and variants were selected by either in vitro or in vivo procedures, and they differ in metastatic ability and 17 be ta-estradiol dependency for tumor growth. The MXT-c1.1 and MXT-B2 cell lines produced lung metastasis after intravenous injection into 100% of syngenic mice, but only MXT-c1.1 cells were highly metastatic from intramammary tumors. The fingerprints obtained by arbitrarily primed-p olymerase chain reaction demonstrated that the metastatic variants and clones had a common genetic background and resulted from clonal selec tion from the parental cell line. We studied whether the matrix metall oproteinase (MMP) profile is correlated with tumor progression and met astatic ability in the MXT tumor system. Gelatinases A and Ei were ass ayed in the cells, both by enzyme activity and mRNA expression. Gelati nase A was expressed in MXT-c1.1 cells, whereas MXT-B2 cells did not e xpress either MMP. In contrast, the mammary fat pad tumors expressed b oth gelatinases. Membrane Type 1-MMP transcripts were also detected in MXT cells and tumors. Because the mRNA levels of gelatinase A were la w in MXT-B2 tumors, we suggested that exogenous gelatinase A bound the cell membranes of MXT-B2 cells in vivo. Indirect evidence was obtaine d in vitro by treatment of MXT-B2 cells with NIH/3T3 fibroblast-condit ioned medium. After this treatment, we detected a gelatinolytic activi ty at M-r 68 000 in the cell-membrane extract of MXT-B2 cells and an i ncrease in migratory ability through type IV collagen matrices. On the other hand, Ha-ras gene dosage correlated positively with metastatic ability but not with either gelatinase A or gelatinase B expression. N o significant differences were observed in the expression of stromelys in-l and tissue inhibitors of MMP. Thus, in the MXT tumor system, the expression of gelatinase A or its cell association and Ha-ras gene dos age independently contribute to the metastatic phenotype. (C) 1997 Wil ey-Liss, Inc.