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Association of viral oncogene-induced changes in gap junctional intercellular communication and morphological
F Katoh1, J L Klein, M Bignami
1Unit of Multistage Carcinogenesis, International Agency for Research on Cancer, Lyon, France.
Abstract:
In order to study the relationship between altered gap junctional intercellular communication (GJIC) and induction of cell transformation by oncogenes, we transfected six viral oncogenes into BALB/c3T3 A31-1-1 cells. BALB/c3T3 cells with v-src, v-ras or polyoma middle T (PyMT) genes grew in soft agar and formed distinct transformed foci in the absence or presence of a vast excess of non-transfected cells. On the other hand, those with v-myc, v-fos or polyoma large T (PyLT) genes expressed less distinctly transformed phenotypes (less transformed morphology, higher saturation density than non-transfected counterparts and less growth in soft agar), and did not form distinct foci in coculture with non-transformed cells. When their homologous GJIC capacities were examined by the microinjection/dye transfer assay, no decrease in GJIC was observed in any of the v-onc-transformed cells. Non-transformed and all v-onc-transformed cell lines expressed similar levels of connexin 43 mRNA. v-myc-, v-fos- and PyLT-transformed cells, but not v-ras-, v-src- and PyMT-transformed cells were able to communicate heterologously with non-transformed cells. Tumor promoting phorbol esters strongly inhibited GJIC of non-transformed and all v-onc-transformed BALB/c3T3 cell lines. In cocultures of v-myc-, v-fos- or PyLT-transformed cells with non-transformed BALB/c3T3 A31-1-1 cells, 12-O-tetradecanoylphorbol-13-acetate (TPA) increased the number of transformed foci. However, when these v-onc-transformed cells were co-cultured with non-transformed BALB/c3T3 A31-1-13 cells (which lose GJIC at growth confluence, as if TPA had been added), no morphologically transformed foci appeared. These results suggest that factors other than GJIC are involved in the suppression of oncogene-transformed cells by surrounding normal counterparts.
Insights
Altered gap junctional intercellular communication (GJIC) does not directly correlate with oncogene-induced cell transformation. Other factors likely suppress oncogene-transformed cells by normal counterparts.
Area of Science:
- Cell Biology
- Molecular Oncology
- Cancer Research
Background:
- Gap junctional intercellular communication (GJIC) plays a role in cell growth regulation.
- The relationship between oncogene-induced cell transformation and GJIC is not fully understood.
Purpose of the Study:
- To investigate the link between altered GJIC and cell transformation induced by viral oncogenes.
- To determine if GJIC modulation is a key factor in oncogene-driven cancer development.
Main Methods:
- Transfection of six viral oncogenes into BALB/c3T3 cells.
- Assessing cell transformation phenotypes (soft agar growth, foci formation).
- Evaluating GJIC capacity using microinjection/dye transfer assays and analyzing connexin 43 mRNA levels.
Main Results:
- Cells transfected with v-src, v-ras, or polyoma middle T (PyMT) showed distinct transformed phenotypes.
- Cells with v-myc, v-fos, or polyoma large T (PyLT) exhibited less distinct transformation.
- No decrease in homologous GJIC was observed in any oncogene-transformed cells, with similar connexin 43 mRNA levels.
- Heterologous communication varied, with v-myc, v-fos, and PyLT cells communicating with non-transformed cells.
- Tumor-promoting phorbol esters inhibited GJIC in all cell lines.
- TPA treatment increased transformed foci in co-cultures of v-myc, v-fos, or PyLT cells, but only when GJIC was functional.
Conclusions:
- GJIC does not appear to be the primary mechanism suppressing oncogene-transformed cells by normal cells.
- Factors beyond GJIC are involved in the suppression of oncogene-transformed cells by their normal counterparts.
- The study highlights the complex interplay of cellular communication and oncogenic transformation.