The presence of plasmin receptors on three mammary carcinoma MCF‐7 sublines

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Abstract
We studied plasmin receptors on 3 MCF-7 sublines: MCF7, MCF7R which was derived by transfection with v-Ha-ras oncogene, and MCF7MF which has been studied for the secretion of procathepsin D in the presence of estrogen. All 3 sublines bound plasmin (Pli) with a much higher affinity than plasminogen (Pg). The number of binding sites was increased about 4-fold by weak proteolytic pretreatment of tumor cells. Transfection by v-Ha-ras oncogene did not apparently change the affinity of Pli binding sites (KD 27-26 nM) and increased their number very slightly (3,800 against 3,200 fmoles/mg protein). However, this number was 5 times higher for MCF7MF (15,000 fmoles/mg protein) and the affinity was 4 times lower (106 nM). MCF7 and MCF7R sublines have previously been reported to be non-invasive in the in vitro invasion assay system (embryo chick heart muscle) but tumorigenic and metastatic in nude mice. In contrast, the MCF7MF subline has been shown to be invasive in both in vivo and in vitro invasion systems. Thus, the number of Pli binding sites at the MCF7 tumor-cell surface may be associated directly or indirectly with tumor-cell invasiveness.