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Effect of myogenic determination on tumorigenicity of chemically transformed 10T1/2 cells
1Kenneth Norris Jr. Comprehensive Cancer Center, University of Southern California, Los Angeles 90033.
Abstract:
Transforming agents have been postulated to interfere with cellular differentiation programs, thus causing uncontrolled growth. Inducing transformed cells to differentiate can result in loss of the transformed phenotype since many end-stage differentiated cells are unable to divide. We attempted to bypass or suppress the tumorigenic phenotype of 3-methylcholanthrene (MCA)-transformed 10T1/2 cells (MCA Cl 15C1) by induction of myogenic determination. MCA Cl 15C1 cells were either treated with the hypomethylating drug 5-azacytidine (5-aza-CR) or were transfected with the muscle determination gene MyoD1, both of which induce a myogenic phenotype in 10T1/2 cells. Colonies containing myoblast-like cells were isolated and examined. Muscle markers were detected both in 5-aza-CR-treated and in MyoD1-transfected myogenic clones by immunofluorescence and northern analyses. The myogenic clones did not show decreased tumorigenicities relative to that of the parental cells upon subcutaneous injection in nude mice. Some of the resulting tumors, however, were classified as rhabdomyosarcomas rather than fibrosarcomas. Although induction of myogenic determination was not sufficient to abolish the tumorigenic phenotype of MCA Cl 15C1 cells, several tumors showed decreased levels of MyoD1 mRNA, suggesting that growth in vivo either selected for or caused decreased determination gene expression.
Insights
Inducing myogenic differentiation in cancer cells did not eliminate tumors. However, some tumors changed type, and in vivo growth suggested reduced muscle gene expression.
Area of Science:
- Cellular Biology
- Cancer Research
- Developmental Biology
Background:
- Transforming agents can disrupt cellular differentiation, leading to uncontrolled growth.
- Inducing differentiation in transformed cells may suppress their tumorigenic potential.
- Differentiated cells often lose the ability to divide, potentially halting tumor progression.
Purpose of the Study:
- To investigate if inducing myogenic determination can suppress the tumorigenic phenotype of 3-methylcholanthrene (MCA)-transformed 10T1/2 cells.
- To assess the effect of 5-azacytidine (5-aza-CR) and MyoD1 gene transfection on the tumorigenicity of MCA-transformed cells.
Main Methods:
- MCA-transformed 10T1/2 cells were treated with 5-azacytidine or transfected with the MyoD1 gene to induce myogenic determination.
- Myogenic clones were isolated and analyzed for muscle markers using immunofluorescence and northern analyses.
- Tumorigenicity was assessed by subcutaneous injection into nude mice.
Main Results:
- Myogenic markers were detected in both 5-aza-CR-treated and MyoD1-transfected myogenic clones.
- Myogenic clones did not exhibit decreased tumorigenicity compared to parental cells.
- Some tumors derived from these clones were classified as rhabdomyosarcomas, and several showed reduced MyoD1 mRNA levels in vivo.
Conclusions:
- Induction of myogenic determination alone is insufficient to abolish the tumorigenic phenotype of MCA-transformed 10T1/2 cells.
- Tumor growth in vivo may select for or induce decreased expression of determination genes like MyoD1.
- Further research is needed to understand the complex interplay between differentiation and tumorigenesis.