No Functional Role for microRNA-342 in a Mouse Model of Pancreatic Acinar Carcinoma

Abstract

The intronic microRNA (miR)-342 has been proposed as a potent tumor-suppressor gene. miR-342 is found to be downregulated or epigenetically silenced in multiple different tumor sites, and this loss of expression permits the upregulation of several key oncogenic pathways. In several different cell lines, lower miR-342 expression results in enhanced proliferation and metastasis potential, both in vitro and in xenogenic transplant conditions. Here, we sought to determine the function of miR-342 in an in vivo spontaneous cancer model, using the Ela1-TAg transgenic model of pancreatic acinar carcinoma. Through longitudinal magnetic resonance imaging monitoring of Ela1-TAg transgenic mice, either wild-type or knockout for miR-342, we found no role for miR-342 in the development, growth rate, or pathogenicity of pancreatic acinar carcinoma. These results indicate the importance of assessing miR function in the complex physiology of in vivo model systems and indicate that further functional testing of miR-342 is required before concluding it is a bona fide tumor-suppressor-miR.

Keywords: acinar carcinoma; in vivo; miR-342-5p; microRNAs; pancreatic cancer.

Figure 1

Pancreatic acinar carcinoma development in miR-342 knockout mice. Pancreatic tumors were dissected from TAg⁺, miR-342^+/0 TAg⁺, and miR-342^0/0 TAg⁺ mice at 21 weeks of age. (A) Representative histology of tumors from each genotype. Scale = 250 μm. (B) Expression of miR-342 in tumors from wild-type, heterozygous, and KO mice (n = 3/group). Individual values shown with mean and standard error.

Figure 2

Longitudinal monitoring of tumor growth in miR-342 knockout mice. TAg⁺, miR-342^+/0 TAg⁺, and miR-342^0/0 TAg⁺ mice were monitored longitudinally by magnetic resonance imaging (MRI) for tumor load and size, from 7 weeks of age until 21 weeks of age. (A) Representative MRI images for each genotype. (B) Individual total predicted tumor volume curves for TAg⁺ female mice (n = 10), (C) miR-342^+/0 TAg⁺ female mice (n = 8), (D) miR-342^0/0 TAg⁺ female mice (n = 6), (E) TAg⁺ male mice (n = 13), (F) miR-342^+/0 TAg⁺ male mice (n = 6), and (G) miR-342^0/0 TAg⁺ male mice (n = 4).

Figure 3

Normal tumor onset in miR-342 knockout mice. TAg⁺, miR-342^+/0 TAg⁺, and miR-342^0/0 TAg⁺ mice were monitored longitudinally by magnetic resonance imaging for tumor presence. (A) Violin plots showing the mean, standard deviation, and kernel probability density of age at tumor onset. Cumulative incidence of pancreatic cancer in (B) female (n = 10, 8, 6) and (C) male (n = 13, 6, 4) mice.

Figure 4

Tumor growth rates are unaffected in miR-342 knockout mice using a pancreatic cancer model. TAg⁺, miR-342^+/0 TAg⁺, and miR-342^0/0 TAg⁺ mice were monitored longitudinally by magnetic resonance imaging for tumor load and size, from 7 weeks of age until 21 weeks of age. Total tumor volumes were square root transformed, with plots showing individual growth in total tumor burden from point of first detection in (A) TAg⁺ female mice (n = 10), (B) miR-342^+/0 TAg⁺ female mice (n = 8), (C) miR-342^0/0 TAg⁺ female mice (n = 6), (D) TAg⁺ male mice (n = 13), (E) miR-342^+/0 TAg⁺ male mice (n = 6), and (F) miR-342^0/0 TAg⁺ male mice (n = 4). (G) Violin plots for the percentage tumor volume increase per 2 weeks, averaged from time of detection to death. Mean, standard deviation, and kernel probability density.

Figure 5

Tumor-induced mortality is unaffected in miR-342 knockout mice. TAg⁺, miR-342^+/0 TAg⁺, and miR-342^0/0 TAg⁺ mice were followed until 21 weeks of age. Kaplan–Meier analysis of survival in (A) female (n = 10, 8, 6) and (B) male (n = 13, 6, 4) mice.