Role of JNK in a Trp53-dependent mouse model of breast cancer

Abstract

The cJun NH2-terminal kinase (JNK) signal transduction pathway has been implicated in mammary carcinogenesis. To test the role of JNK, we examined the effect of ablation of the Jnk1 and Jnk2 genes in a Trp53-dependent model of breast cancer using BALB/c mice. We detected no defects in mammary gland development in virgin mice or during lactation and involution in control studies of Jnk1(-/-) and Jnk2(-/-) mice. In a Trp53(-/+) genetic background, mammary carcinomas were detected in 43% of control mice, 70% of Jnk1(-/-) mice, and 53% of Jnk2(-/-) mice. These data indicate that JNK1 and JNK2 are not essential for mammary carcinoma development in the Trp53(-/+) BALB/c model of breast cancer. In contrast, this analysis suggests that JNK may partially contribute to tumor suppression. This conclusion is consistent with the finding that tumor-free survival of JNK-deficient Trp53(-/+) mice was significantly reduced compared with control Trp53(-/+) mice. We conclude that JNK1 and JNK2 can act as suppressors of mammary tumor development.

Figure 1. Effect of JNK-deficiency in virgin mice on breast development.

A) Whole mount preparations of the fourth inguinal mammary gland of 10 week-old female virgin mice were stained with carmine red. Representative images are presented. Scale bar: 5 mm (upper panel); 800 µm (lower panel). B) Sections of the breast tissue were stained with hematoxylin and eosin. Representative images are presented. Scale bar: 100 µm.

Figure 2. Effect of JNK-deficiency on breast development during lactation.

Sections of the fourth inguinal mammary gland of female mice at day 7 post-partum were examined by staining with hematoxylin and eosin (upper panels). Sections were also stained with an antibody to the proliferation marker PCNA (red) and the DNA stain DAPI (blue) (lower panels). Scale bar: 200 µm (upper panel); 50 µm (lower panel).

Figure 3. Effect of JNK-deficiency on mammary gland involution.

The pups were removed from female mice at day 7 post-partum to induce mammary gland involution. Sections of the fourth inguinal mammary gland were examined at two days or three days post-weaning by staining with hematoxylin and eosin. Scale bar: 200 µm.

Figure 4. Effect of JNK-deficiency on Trp53^−/− mouse survival.

A) Kaplan-Meier analysis of the tumor-free survival of wild-type (WT), Jnk1 ^−/−, Jnk2 ^−/−, Trp53 ^−/−, Jnk1 ^−/− Trp53 ^−/−, and Jnk2 ^−/− Trp53 ^−/− mice is presented. No statistically significant differences between Trp53 ^−/−, Jnk1 ^−/− Trp53 ^−/−, and Jnk2 ^−/− Trp53 ^−/− mice were detected (Log-rank test, p>0.05). The data represent groups of 44–62 mice. These groups include equal numbers of male and female mice. B) The spectrum of tumors detected in Trp53 ^−/−, Jnk1 ^−/− Trp53 ^−/−, and Jnk2 ^−/− Trp53 ^−/− mice following euthanasia is presented. No statistically significant differences in the tumor profiles between genotypes were detected using Fisher's exact test.

Figure 5. Effect of JNK-deficiency on Trp53^−/+ mouse survival.

A) Kaplan-Meier analysis of the tumor-free survival of wild-type (WT), Jnk1 ^−/−, Jnk2 ^−/−, Trp53 ^−/+, Jnk1 ^−/− Trp53 ^−/+, and Jnk2 ^−/− Trp53 ^−/+ mice is presented. The survival of Jnk1 ^−/− Trp53 ^−/+ mice and Jnk2 ^−/− Trp53 ^−/+ mice was reduced compared with Trp53 ^−/+ mice (Log-rank test, p = 0.026 and 0.012, respectively). The data represent groups of 14 - 20 female mice. B) The spectrum of tumors detected in Trp53 ^−/+, Jnk1 ^−/− Trp53 ^−/+, and Jnk2 ^−/− Trp53 ^−/+ female mice following euthanasia is presented. No statistically significant differences in the tumor profiles between genotypes were detected using Fisher's exact test. C) Kaplan-Meier analysis of the mammary carcinoma-free survival of Trp53 ^−/+, Jnk1 ^−/− Trp53 ^−/+, and Jnk2 ^−/− Trp53 ^−/+ mice is presented. Cohorts of Trp53 ^−/+ mice (n = 6), Jnk1 ^−/− Trp53 ^−/+ mice (n = 14), and Jnk2 ^−/− Trp53 ^−/+ mice (n = 8) with mammary carcinoma were examined. JNK1-deficiency and JNK2-deficiency caused reduced mammary carcinoma-free survival compared with Trp53 ^−/+ mice (Log-rank test, p = 0.018 and 0.039, respectively).