Search

PurposeWe sought to develop and characterize a model of human vitamin D nutritional insufficiency/deficiency in the adult mouse, which could have broad utility in examining health consequences of this common condition.MethodsAdult mice were fed diets containing cholecalciferol contents of 0.05 IU/g, 0.25 IU/g, 0.5 IU/g or 1.5 IU/g for four months. We studied induction of steady-state vitamin D insufficiency, and its consequences on primary cholecalciferol metabolite levels, calcium homeostasis, parathyroid physiology, and bone morphology.ResultsAll diets were well tolerated, without adverse effects on body weight. Diets containing 0.05 IU/g and 0.25 IU/g cholecalciferol significantly lowered serum 25-hydroxyvitamin D levels (median 25OHD, 10.5 ng/ml, and 21.6 ng/ml, respectively), starting as early as one month following initiation of the diets, maintained through the four-month experimental period. The 0.05 IU/g diet significantly decreased 1,25-dihydroxyvitamin D (1,25OH2D) levels (median, 78 pg/ml). Despite these decreased 25OHD and 1,25OH2D levels, the diets did not alter parathyroid gland morphology or parathyroid cell proliferation. There were no statistical differences in the serum total calcium and serum PTH levels among the various dietary groups. Furthermore, the 0.05 IU/g diet did not cause any alterations in the cortical and trabecular bone morphology, as determined by microCT.ConclusionsThe dietary manipulations yielded states of vitamin D insufficiency or modest deficiency in adult mice, with no overtly detectable impact on parathyroid and bone physiology, and calcium homeostasis. This model system may be of value to study health effects of vitamin D insufficiency/deficiency especially on extraskeletal phenotypes such as cancer susceptibility or immune function.

Cyclin D1 is an important molecular driver of human breast cancer but better understanding of its oncogenic mechanisms is needed, especially to enhance efforts in targeted therapeutics. Currently, pharmaceutical initiatives to inhibit cyclin D1 are focused on the catalytic component since the transforming capacity is thought to reside in the cyclin D1/CDK activity. We initiated the following study to directly test the oncogenic potential of catalytically inactive cyclin D1 in an in vivo mouse model that is relevant to breast cancer. Herein, transduction of cyclin D1(-/-) mouse embryonic fibroblasts (MEFs) with the kinase dead KE mutant of cyclin D1 led to aneuploidy, abnormalities in mitotic spindle formation, autosome amplification, and chromosomal instability (CIN) by gene expression profiling. Acute transgenic expression of either cyclin D1(WT) or cyclin D1(KE) in the mammary gland was sufficient to induce a high CIN score within 7 days. Sustained expression of cyclin D1(KE) induced mammary adenocarcinoma with similar kinetics to that of the wild-type cyclin D1. ChIP-Seq studies demonstrated recruitment of cyclin D1(WT) and cyclin D1(KE) to the genes governing CIN. We conclude that the CDK-activating function of cyclin D1 is not necessary to induce either chromosomal instability or mammary tumorigenesis.

Chromosomal instability (CIN) in tumors is characterized by chromosomal abnormalities and an altered gene expression signature; however, the mechanism of CIN is poorly understood. CCND1 (which encodes cyclin D1) is overexpressed in human malignancies and has been shown to play a direct role in transcriptional regulation. Here, we used genome - wide ChIP sequencing and found that the DNA - bound form of cyclin D1 occupied the regulatory region of genes governing chromosomal integrity and mitochondrial biogenesis. Adding cyclin D1 back to [Ccnd1.sup.-/-] mouse embryonic fibroblasts resulted in CIN gene regulatory region occupancy by the DNA - bound form of cyclin D1 and induction of CIN gene expression. Furthermore, increased chromosomal aberrations, aneuploidy, and centrosome abnormalities were observed in the cyclin D1 - rescued cells by spectral karyotyping and immunofluorescence. To assess cyclin D1 effects in vivo, we generated transgenic mice with acute and continuous mammary gland - targeted cyclin D1 expression. These transgenic mice presented with increased tumor prevalence and signature CIN gene profiles. Additionally, interrogation of gene expression from 2,254 human breast tumors revealed that cyclin D1 expression correlated with CIN in luminal B breast cancer. These data suggest that cyclin D1 contributes to CIN and tumorigenesis by directly regulating a transcriptional program that governs chromosomal stability., Introduction Chromosomal instability (CIN) in tumors (1-3) is characterized by an elevated rate of gain or loss of whole chromosomes (i.e., aneuploidy) and/or as structural chromosomal aberrations (i.e., translocations, deletions, [...]