Confocal maximum Z projections of MEFs in metaphase, immunostained for α-tubulin (violet), γ- tubulin (yellow) and DAPI (blue). Casimiro et al. show that in contrast to Cyclin D1-/- cells (left), those overexpressing Cyclin D (right) develop multiple centrosomes and abnormal spindle architecture, resulting in chromosomal instability. Cyclin D1 is overexpressed in many human tumors, and Casimiro and colleagues investigate its role in driving a transcriptional program that promotes chromosome instability.
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–/– 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.
Mathew C. Casimiro, Marco Crosariol, Emanuele Loro, Adam Ertel, Zuoren Yu, William Dampier, Elizabeth A. Saria, Alex Papanikolaou, Timothy J. Stanek, Zhiping Li, Chenguang Wang, Paolo Fortina, Sankar Addya, Aydin Tozeren, Erik S. Knudsen, Andrew Arnold, Richard G. Pestell