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Specific viral oncogenes cause differential effects on cell-to-cell communication, relevant to the suppression of the
1Laboratorio di Tossicologia Applicata, Istituto Superiore di Sanitá, Roma, Italy.
Abstract:
We have studied growth regulation in mixed cultures of normal and oncogene-transformed 3T3 cells. The NIH 3T3 cells transformed by myc, src, and ras showed comparable cloning efficiency in semisolid medium. However, when they were plated on plastic with an excess of normal mouse embryo fibroblasts, BALB/c 3T3 ClA31-1-1, ras- and src-transformed cells were able to form distinct foci on the layer of density-arrested normal cells, whereas myc-transformed cells lacked this ability. In order to determine whether suppression or expression of the transformed phenotype could be correlated with the ability of the different cell populations to communicate, gap-junctional intercellular communication (IC) was measured by the Lucifer yellow dye transfer assay in coculture of normal and transformed cells. The dye was observed to spread from BALB/c 3T3 to myc-NIH 3T3 cells, indicating the presence of IC between these two cell types. In contrast no passage of Lucifer yellow was observed between src-NIH 3T3 or ras-NIH 3T3 and BALB/c 3T3. Addition of a phorbol ester tumor promoter, phorbol-12,13-didecanoate, efficiently rescued proliferation and focus formation by myc-transformed cells. The tumor promoter was able to inhibit IC in BALB/c 3T3 cells, although this response greatly varied among the different oncogene transformed clones. Tumorigenicity in nude mice strongly correlated with growth behavior in vitro: myc-transformed cells were either nontumorigenic or slowly tumorigenic, and src- and ras-transformed cells were highly tumorigenic. These data suggest an important role of IC in modulating abnormal growth behavior in vitro and in vivo.
Insights
Intercellular communication (IC) regulates cell growth. Myc-transformed cells formed foci and tumors only when IC was rescued by tumor promoters, unlike src- and ras-transformed cells.
Area of Science:
- Cell Biology
- Oncology
- Cancer Research
Background:
- Oncogene-transformed cells exhibit altered growth regulation.
- Different oncogenes (myc, src, ras) can induce distinct cellular phenotypes.
- Intercellular communication (IC) plays a role in coordinating cell behavior.
Purpose of the Study:
- To investigate the role of gap-junctional IC in growth regulation of oncogene-transformed 3T3 cells.
- To correlate IC status with transformed cell behavior in vitro and tumorigenicity in vivo.
- To determine if tumor promoters can modulate IC and rescue transformed phenotypes.
Main Methods:
- Coculture of normal BALB/c 3T3 cells with NIH 3T3 cells transformed by myc, src, or ras.
- Measurement of IC using the Lucifer yellow dye transfer assay.
- Assessment of focus formation in vitro and tumorigenicity in nude mice.
- Treatment with phorbol ester tumor promoter (phorbol-12,13-didecanoate).
Main Results:
- Myc-transformed cells showed IC with normal cells and lacked focus formation, unlike src- and ras-transformed cells.
- Tumor promoters rescued proliferation and focus formation in myc-transformed cells by inhibiting IC.
- Src- and ras-transformed cells exhibited high tumorigenicity, correlating with lack of IC.
- IC was present between normal BALB/c 3T3 and myc-NIH 3T3 cells, but not with src- or ras-NIH 3T3 cells.
Conclusions:
- Gap-junctional IC is a critical factor in suppressing abnormal growth of certain oncogene-transformed cells.
- Modulation of IC by tumor promoters can restore transformed phenotypes and tumorigenicity.
- IC plays a significant role in regulating cell growth and behavior both in vitro and in vivo.