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Presensitization of human cells with extrinsic signals to induced chemical carcinogenesis
Abstract:
Foreskin-derived low-passage human cell populations were reproducibly transformed with chemical carcinogens when the cells were blocked in G1, released from the block, and treated with either the carcinogen N-methyl-N-nitro-N-nitrosoguanidine (MNNG) or with Aflatoxin B1 in the S period of the cell cycle. Arginine- and glutamine-deficient medium was required to effectively block the cells in the G1 period. Estradiol, insulin, anthralin or phorbol myristate acetate sensitized the cell population to carcinogen treatment when added 10 h before the carcinogen in early S period. Presensitized cells kept blocked in G1 period for 48 h or longer, released and treated in S period with MNNG or Aflatoxin B1 were not transformed; nor did transformation occur in presensitized cell populations treated in G2 (4.5 h), M (1.5 h) or G1 (8.2 h). Cells derived from carcinogen-treated presensitized cells grew as colonies in soft agar at 16-20 PDL. When cells derived from colonies isolated from the soft agar were injected subcutaneously into nude mice, tumors developed.
Insights
Human foreskin cells transformed with carcinogens when treated in S phase after G1 arrest. Sensitizing agents enhanced transformation, but prolonged G1 arrest prevented it, indicating cell cycle-specific carcinogen susceptibility.
Area of Science:
- Cell biology
- Carcinogenesis
- Human cell culture
Background:
- Chemical carcinogens can induce cell transformation.
- Cell cycle phase influences susceptibility to DNA damage and mutation.
Purpose of the Study:
- To investigate the role of cell cycle phase in chemical carcinogen-induced transformation of human foreskin cells.
- To identify factors that sensitize cells to carcinogen treatment.
Main Methods:
- Human foreskin cells were cultured and arrested in G1 phase using nutrient-deficient media.
- Cells were treated with N-methyl-N-nitro-N-nitrosoguanidine (MNNG) or Aflatoxin B1 during the S phase.
- Sensitizing agents (estradiol, insulin, anthralin, phorbol myristate acetate) were administered prior to carcinogen exposure.
- Transformed cells were assessed by colony formation in soft agar and tumor development in nude mice.
Main Results:
- Reproducible transformation occurred when cells were treated with MNNG or Aflatoxin B1 in the S phase after release from G1 arrest.
- Sensitizing agents increased transformation rates.
- Prolonged G1 arrest (≥48 hours) or treatment in G2, M, or G1 phases prevented transformation.
- Transformed cells formed colonies in soft agar and induced tumors in vivo.
Conclusions:
- Cell cycle-dependent susceptibility to chemical carcinogens is demonstrated in human foreskin cells.
- The S phase is a critical window for transformation by MNNG and Aflatoxin B1.
- Specific pre-treatments can sensitize cells to carcinogens, but cell cycle arrest modulates this effect.