High Cyclin D1 Expression Is Associated with Increased Proliferation Rate and Decreased Survival in Mantle Cell Lymphoma (MCL) and Is Caused by Genomic Deletions and Mutations that Enhance Stability of Cyclin D1 mRNA.

Most MCLs harbor the t(11;14) translocation resulting in overexpression of cyclin D1 that promotes tumor proliferation. Gene expression profiling of 92 cyclin D1 positive MCL biopsy samples defined a gene expression signature of tumor proliferation that provided strong prognostic information: the quartile of patients with the highest proliferation gene expression signature had a 0.8 year median survival whereas the quartile with the lowest expression had a 6.7 year median survival (Cancer Cell 2003, 3:185). Sixteen of the 23 MCL samples in the highest proliferation quartile displayed exceptionally high cyclin D1 levels and preferentially expressed short cyclin D1 mRNA forms that lacked parts of the 3′UTR known to harbor RNA-destabilizing elements. To test whether expression of short cyclin D1 mRNA is due to genomic deletions, we screened DNA from all samples in the highest proliferation quartile by quantitative genomic PCR. We found genomic deletions of the 3′UTR region in 6 of the 10 samples that expressed short mRNAs. We next sequenced the proximal 400bp region of the 3′UTR in those samples with high expression of short mRNAs that did not have genomic deletions. In 2 samples, we found 2 distinct mutations: a 3bp deletion and an A insertion. Both of these mutations created a premature polyadenylation signal (AATAAA) about 300bp 3′ of the stop codon, giving rise to a predicted mRNA of 1.5kb that lacks the destabilizing elements present in the full-length form. We identified two MCL cell lines, Jeko-1 and Z138, that also showed high-level expression of the short cyclin D1 form. In Jeko-1 we found a deletion of the 3′UTR similar to that observed in the MCL patient samples, whereas the mechanism responsible for expression of the short cyclin D1 mRNA in Z138 remains unclear. In both lines, we confirmed that the half-life of the short cyclin D1 mRNA is longer than that of the full length mRNA. Our results demonstrate that MCLs increase cyclin D1 expression not only through the t(11;14), but also by the additional mechanisms of genomic deletions and mutations that create alternative polyadenylation sites that yield more stable mRNAs. Higher cyclin D1 expression increases proliferation and decreases survival, suggesting that strategies aimed at reducing cyclin D1 expression in MCL could have therapeutic promise.