Tumor-specific transcript variants of cyclin D1 in mantle cell lymphoma and multiple myeloma with chromosome 11q13 abnormalities

•Mantle cell lymphoma and multiple myeloma with 11q13 abnormalities express Cyclin D1 transcript variants with longer 5′-UTRs.•Cyclin D1 transcript variants with longer 5′-UTRs encode normal-sized cyclin D1 protein.•Protein expression of the CCND1 transcript variants with longer 5′-UTRs is regulated by the mTOR/EIF4E pathway. Cyclin D1 (CCND1) overexpression is an early and unifying oncogenic event in mantle cell lymphoma (MCL) and multiple myeloma (MM) with chromosome 11q13 abnormalities. Herein, we report newly discovered transcript variants of the CCND1 gene in MCL and MM cells with chromosome 11q13 abnormalities. These transcript variants, designated CCND1.tv., covered the full-length coding region of CCND1 with longer 5′-untranslated regions (5′-UTRs) of CCND1 and occasionally contained a novel exon. CCND1.tv. was specifically detectable in patient-derived primary MCL or MM cells with chromosomal translocation t(11;14)(q13;q32), but not in t(11;14)-negative cells. The lengths of the 5′-UTR sequences of CCND1.tv. differed among patients and cell lines. Introduction of CCND1.tv. led to increased expression of normal-sized CCND1 protein in HEK293 cells. Furthermore, mTOR inhibition by rapamycin or serum starvation reduced ectopic expression of CCND1.tv.-derived CCND1 protein, but not 5′-UTR less CCND1-derived CCND1 protein in HEK293 cells, suggesting that the protein expression of CCND1.tv. is regulated by the mTOR pathway. Our results suggest that the aberrant expression of CCND1.tv. may contribute to the understanding of the pathogenesis of MCL and MM with 11q13 abnormalities.