A study of the genetic alterations in the progression of plutonium-239-induced rat lung cancer

Bryan L Stegelmeier, Purdue University

Abstract

Specific molecular alterations have been detected in many neoplasms and their presence may be pivotal in neoplastic transformation. Our objective was to sequentially evaluate the molecular alterations in $\sp{239}$Pu-induced proliferative lesions in rat lungs. Three-hundred-sixty Fischer F344/N female rats were exposed by inhalation to a $\sp{239}$PuO$\sb2$ aerosol and one-hundred-forty control animals were exposed to a sham aerosol. Proliferative and neoplastic pulmonary lesions were evaluated by immunohistochemistry, in situ hybridization, Western blot immunochemistry, Northern and Southern hybridization, oligonucleotide hybridization, and direct nucleic acid sequencing for activation or altered expression of Ki-ras, TGF$\alpha$, EGFR, and p53. Specific Ki-ras point mutations were present in about 40% of the radiation-induced and spontaneous malignant neoplasms. We found similar mutation frequencies in adenomas and foci of epithelial hyperplasia. No Ki-ras mutations were identified in normal lung tissue. Ras expression in hyperplastic lesions and neoplasms was similar to that observed in normal pulmonary epithelia. Many pulmonary proliferative lesions and neoplasms had increased expression of TGF$\alpha$. Some of the same neoplasms also had increased expression of EGFR. TGF$\alpha$ was present in lavage fluid of normal and neoplastic lungs and normalized TGF$\alpha$ concentrations in lavages from lungs with squamous cell carcinomas were significantly higher than concentrations in lavages of normal lung. No alterations were found in expression or Southern blot analysis of p53. Preliminary sequence analysis suggests that 2-of-8 neoplasms examined have point mutations in the p53 gene. These findings suggest the following: (1) Ki-ras mutation, not alterations in ras expression, and increased TGF$\alpha$ expression are early lesions associated with many radiation-induced, proliferative pulmonary lesions. (2) Increased or concomitant expression of EGFR and TGF$\alpha$ may provide proliferative and neoplastic cells growth advantages and promote neoplastic progression. (3) Small numbers of neoplasms may have mutational alterations in the p53 gene. And (4) the frequency of these alterations suggests these are important components of radiation-induced pulmonary carcinogenesis. However, there were many neoplasms in which we did not detect altered expression or mutational activation of any of these genes, suggesting there are additional molecular lesions and transforming factors, that as yet, remain unidentified.

Degree

Ph.D.

Advisors

Rebar, Purdue University.

Subject Area

Radiology|Pathology|Radiation

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