Down-regulation of E-cadherin expression in Madin Darby canine kidney (MDCK) cells inside tumors of nude mice.

The 120-kDa cell-cell adhesion molecule E-cadherin is localized at the epithelial junctional complex and participates in the organization and maintenance of epithelia. The Madin Darby canine kidney (MDCK) cell line expresses E-cadherin in a stable way and forms polarized epitheloid structures in vitro. Harvey-murine-sarcoma-virus-transformed derivatives (MDCK-ras) produce malignant (i.e., invasive and metastatic) tumors in nude mice. We obtained evidence that E-cadherin is down-regulated in nude mouse tumors and that this down-regulation is reversible. MDCK-ras-e cell lines were cloned in vitro from MDCK-ras cell cultures. They showed an epithelioid morphotype and expressed E-cadherin at homogeneously high level. This characteristic has been conserved for at least 60 passages in vitro. MDCK-ras-e cells were not invasive in vitro. When injected into nude mice, however, they produced invasive and metastatic tumors. Primary tumors as well as large metastases were heterogeneous, showing E-cadherin-positive well differentiated epithelial structures and E-cadherin-negative undifferentiated areas. Metastasis-derived cell cultures contained both E-cadherin-positive and E-cadherin-negative MDCK-ras-e cells during early passages in vitro. During further culture, however, they regained the homogeneous E-cadherin-positive characteristic of the original MDCK-ras-e cell line. The behavior of MDCK-ras-e cells in vitro, as compared with its in vivo behavior, points to the existence of host factors which are able to down-regulate E-cadherin expression. We hypothesize that this down-regulation plays a basic role in invasion.

Invasiveness and metastatic capability of rat fibroblast-like cells before and after transfection with immortalizing and transforming genes.

Invasion in vitro and in vivo and spontaneous metastasis was investigated in cell lines before and after introduction of immortalizing (polyoma large-T and activated myc) genes and of transforming (polyoma middle-T and activated ras) genes in Fischer rat cells. Invasion in vitro was tested by confrontation of rat cells with embryonic chick heart fragments in organ culture. Invasion in vivo and metastasis was evaluated in nude mice and in syngeneic rats after injection of cells i.p. or s.c. in the flank and after implantation of cell aggregates s.c. in the tail. Rat cells were also analyzed for the presence of myc oncogenes, and for the expression of ras oncogenes. Cells from primary or low passage rat embryo (REF) cells were not invasive in vitro and did not produce tumors in vivo. Cell lines (LTRAT1, LTaRAT1) derived from REF cultures after transfection with plasmids encoding polyoma large-T antigens, behaved like REF cells. Cell lines (REFpEJgpt4, REFpEJmycN7) established from REF cultures after transfection with either a plasmid encoding an activated human ras protein or with the latter plasmid plus one containing an activated myc gene, were invasive in vitro and in vivo and produced invasive and metastatic tumors in syngeneic rats. Cell lines (FR3T3) established in an apparently spontaneous way were invasive in vitro and produced invasive tumors in vivo without metastasis. Derivatives of FR3T3 (FRLT1, MTT4, MMC1, and PyT21) transfected with plasmids encoding one or more of the polyoma antigens, differed from FR3T3 cells by a shorter latency period of tumor formation (less than 1 versus 1 to 3 weeks). Like FR3T3 tumors, FRLT1, MTT4, MMC1, and PyT21 tumors were invasive but not metastatic. Other spontaneously established lines (Rat1) were invasive and metastatic. Cells (Rat1pEJ6.6) derived from Rat1 cultures after transfection with a plasmid encoding an activated ras protein, showed shorter tumor latency periods (less than 1 versus 7 weeks). A thymidine kinase deficient Rat1 derivative (Rat2) was not invasive in vitro but produced invasive and metastatic tumors in vivo with long (9 to 21 weeks) latency periods. Rat2pT24B4 cells derived by us from Rat2 cells after transfection with a plasmid containing a mutated human ras gene (pT24), were invasive in vitro and in vivo as were cells derived from Rat2 tumors. We conclude from our experiments that invasiveness and metastatic capability are often acquired by established REF-derived cell lines in an apparently spontaneous way.(ABSTRACT TRUNCATED AT 400 WORDS)