Truncation in CCND1 mRNA alters miR-16-1 regulation in mantle cell lymphoma

Abstract

Cyclin D1 (CCND1) is a well-known regulator of cell-cycle progression. It is overexpressed in several types of cancer including breast, lung, squamous, neuroblastoma, and lymphomas. The most well-known mechanism of overexpression is the t(11;14)(q13;q32) translocation found in mantle cell lymphoma (MCL). It has previously been shown that truncated CCND1 mRNA in MCL correlates with poor prognosis. We hypothesized that truncations of the CCND1 mRNA alter its ability to be downregulated by microRNAs in MCL. MicroRNAs are a new class of abundant small RNAs that play important regulatory roles at the posttranscriptional level by binding to the 3 untranslated region (UTR) of mRNAs blocking either their translation or initiating their degradation. In this study, we have identified the truncation in CCND1 mRNA in MCL cell lines. We also found that truncated CCND1 mRNA leads to increased CCND1 protein expression and increased S-phase cell fraction. Furthermore, we demonstrated that this truncation alters miR-16-1 binding sites, and through the use of reporter constructs, we were able to show that miR-16-1 regulates CCND1 mRNA expression. This study introduces the role of miR-16-1 in the regulation of CCND1 in MCL. (Blood. 2008; 112:822-829) IntroductionMantle cell lymphoma (MCL) represents 5% to 10% of all nonHodgkin lymphomas. 1,2 It is a relatively uncommon but particularly difficult form of lymphoma to treat. It has the worst prognosis among the B-cell lymphomas, with median survival of 3 years with no standard effective therapy. 3 The genetic hallmark of MCL is the t(11;14)(q13; q32) translocation that displaces the CCND1 gene on chromosome 11 downstream to the enhancer region of the IgH gene on chromosome 14 and causes its overexpression. 4 CCND1 is a well-known cell-cycle regulator and promotes G1 to S-phase cell-cycle progression. 5,6 Although CCND1 overexpression has unified and simplified the diagnostic approach to MCL, no therapeutic advances have been made to target this particular pathway. In fact, controversy remains regarding the oncogenic potential of CCND1. Some have speculated that wild-type CCND1 requires another cooperating oncogenic event such as Ras activation to cause tumorigenesis. 7 Others such as Diehl et al 8 and Lu et al 9 have reported a CCND1 variant (cyclin D1b), the nuclear localization of which represents a critical step in oncogenesis. The most recent finding reported by Wiestner et al 10 showed that point mutations and genomic deletions in CCND1 created a truncated mRNA and result in increased proliferation and shorter survival. Although this report associates important clinical outcomes with the truncated mRNA, it does not delineate a definitive molecular mechanism or rationale. In their discussion, Wiestner et al alluded to the possibility of microRNAs as regulators of CCND1. 10 We hypothesize that CCND1 mRNA is normally under the regulation of microRNAs, and that truncated CCND1 mRNA escapes this regulation by deletion of the microRNA target binding sequences.MicroRNAs (miRNAs) are sm...

The impact of cyclin D1 mRNA isoforms, morphology and p53 in mantle cell lymphoma: p53 alterations and blastoid morphology are strong predictors of a high proliferation index

“…37 In addition, truncation of the 3'UTR of the CyD1 mRNA results in loss of miR-16-1 binding sites and may change regulation of CyD1 protein expression. 38 Although the predominance of the short CyD1 isoform in MCL is common -23% in our series, similar to the 18% observed by Wiestner et al -the reasons for this are evident only in a minority of cases. 19 Only 6% of MCL lacked the long canonical transcript completely, and in only half of these cases were we able to demonstrate a genomic deletion of the 3'UTR explaining the complete loss of expression.…”

3’UTR mediated regulation of the cyclin D1 proto-oncogene

“…Our demonstration of microRNA targeting of the cyclin D1 transcripts confirms recent reports showing microRNA mediated regulation of cyclin D1 in MCL and breast cancer. 32,33 Furthermore, our study shows the regulation of endogenous cyclin D1 levels by microRNAs only in cells with an intact 3'UTR but not in 3'UTR deleted breast cancer cells. Although such 3'UTR deletions have been detected in MCL patients, it remains to be seen whether solid tumors such as cyclin D1 without 3'UTR but not with full length cyclin D1 probably reflecting the different levels of overexpression in the respective cell lines.…”

Correcting miR-15a/16 genetic defect in New Zealand Black mouse model of CLL enhances drug sensitivity

“…Our New Zealand Black-derived malignant B-1 cell line, LNC, mimics late-stage aggressive CLL (27). Deletions in the 3′ UTR of cyclin D1 have been reported in CLL and are associated with overexpression of cyclin D1 (46,47).…”