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Office of Biological and Environmental Research

DOE Lowdose Radiation Program Workshop III

Abstract

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Title: Radiation Alters Epithelial Interactions with the Microenvironment.

Authors: S. Tamou and M. H. Barcellos-Hoff.

Figure 1 Schematic of extracellular signaling in the organization of multicellular functional units.

Recent studies (Figure 1) have shown that cell adhesion systems are fundamental pathways for cell signaling (1, 2), and play an important role during neoplasia (3-5). Radiation has been shown to alter the expression of endothelial and tumor cell integrins (6, 7). Our second objective was to compare patterns of radiation-proteins in sensitive versus resistant mouse strains. BALB/c mice have been used extensively in both chemical and hormonal mammary carcinogenesis studies. Ullrich and colleagues have characterized the C57BL/6 as resistant to mammary carcinogenesis versus the sensitive BALB/c (8) and have demonstrated that BALB/c epithelial cells irradiated In vivo give rise to a greater frequency of delayed genomic changes during long term culture compared to epithelial cells from C57BL/6 (9). To further characterize the phenotype of a carcinognesis sensitive and resistant genetic strain, we studied cell adhesion proteins, "3, "6, and $1 integrins in these mouse strains as a function of radiation dose and time using quantitative digital fluorescence microscopy. Typical integrin immunolocalization in mouse mammary gland is shown in Figure 2.

Figure 3 Relative immunoreactivity of a6 integrin (A), a3 integrin (B) and b1 integrin (C) in Balb/c as a function of dose 24 hour post irradiation. Figure 4 Relative immunoreactivity of a6 integrin (D), a3 integrin (E) and b1 integrin (F) in C57bl/6 as a function of dose 24 hr post irradiation.

Localization was similar in both mouse strains. A time course from 1 to 7 days post irradiation with 5 Gy was conducted to determine the period of greatest response (not shown). Based on these, we chose to conduct a dose response and collect tissue at 24 hrs. In dose response experiments, mice were irradiated in estrus to eliminate any confounding influence of hormonal status.Balb/c mice showed a complex response for all three antigens, suggestive of hypersensitivity in the low dose (<0.5 Gy) range and a plateau at doses greater than 2 Gy. In contrast C57bl/6 mice irradiated at estrus lacked any dose response in regards to "6 or $1 integrin. "3 showed a dose response similar to that found for Balb/c. A possible role of TGF-b1 in regulating the expression and/or localization of integrins in the mammary gland of C57BL/6 mice was investigated using Tgf$1 null heterozygotes compared to wildtype littemates. We found no significant difference either with expression or localization of three integrins in the mammary gland in both genotypes either irradiated or non-irradiated.

These data indicate that epithelial integrins are modulated in the irradiated mammary gland and that such responses are modulated further by the genetic background of the individual.

REFERENCES

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