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Elevated expression of Ha-ras is an early event in two-stage skin carcinogenesis in SENCAR mice
Abstract:
Alterations in the expression of the Ha-ras oncogene were investigated in SENCAR mice epidermis at various stages of initiation and promotion during two-stage skin carcinogenesis in SENCAR mice. Adult SENCAR mice were treated with 200 nmol of the (+) enantiomer of benzo[a]pyrene 7,8-diol 9,10-epoxide-anti (BPDE-anti), a potent initiating agent, followed by repetitive treatments with the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). Other mice were 'sham'-initiated with the (-) enantiomer of BPDE-anti, which is inactive as a tumor initiator. Polyadenylated RNA was isolated from pre-tumor epidermis and tumors at eight different stages of tumorigenesis and analyzed for changes in Ha-ras expression using Northern blot hybridization. Significantly enhanced levels of Ha-ras RNA were observed in TPA-promoted papillomas as early as 7 weeks after initiation. Only trace amounts of Ha-ras RNA were present in untreated epidermis or epidermis treated with the (+) or (-) enantiomer followed by 2-12 treatments with TPA (pre-papilloma stage). Southern blot hybridization of tumor DNA indicated that the increased expression of the Ha-ras oncogene was not due to gene amplification. We conclude that elevated levels of Ha-ras expression can occur at an early stage of tumor development in mouse epidermis in vivo and may play a role in tumorigenesis.
Insights
Investigating Ha-ras oncogene expression in SENCAR mice during skin carcinogenesis revealed significantly enhanced Ha-ras RNA levels in tumors. This elevation occurred early in tumor development, suggesting a role in tumorigenesis.
Area of Science:
- Oncology
- Molecular Biology
- Carcinogenesis
Background:
- The Ha-ras oncogene is frequently implicated in various cancers.
- Understanding oncogene expression dynamics during carcinogenesis is crucial for identifying therapeutic targets.
Purpose of the Study:
- To investigate alterations in Ha-ras oncogene expression during two-stage skin carcinogenesis in SENCAR mice.
- To determine if Ha-ras gene amplification contributes to its increased expression.
Main Methods:
- SENCAR mice were subjected to chemical initiation with benzo[a]pyrene 7,8-diol 9,10-epoxide-anti (BPDE-anti) and promotion with 12-O-tetradecanoylphorbol-13-acetate (TPA).
- Polyadenylated RNA and DNA were isolated from epidermis and tumors at various stages.
- Northern and Southern blot hybridizations were used to analyze Ha-ras RNA expression and gene copy number.
Main Results:
- Significantly enhanced Ha-ras RNA levels were detected in TPA-promoted papillomas as early as 7 weeks post-initiation.
- Trace amounts of Ha-ras RNA were observed in pre-tumorigenic stages.
- Southern blot analysis excluded gene amplification as the cause for elevated Ha-ras expression.
Conclusions:
- Elevated Ha-ras expression occurs at an early stage of tumor development in mouse epidermis.
- Increased Ha-ras expression may play a significant role in the process of skin tumorigenesis.