Inactivation of RB1 in mantle-cell lymphoma detected by nonsense-mediated mRNA decay pathway inhibition and microarray analysis

Abstract

Mantle-cell lymphoma (MCL) is genetically characterized by the translocation t(11;14)(q13;q32) and a high number of secondary chromosomal abnormalities. To identify genes inactivated in this lymphoma, we examined 5 MCL cell lines following a strategy previously described in tumors with microsatellite instability that is based on the combined inhibition of the nonsense-mediated mRNA decay pathway and gene-expression profiling. This approach, together with the design of a conservative algorithm for analysis of the results, allowed the identification of 3 genes carrying premature stop codons. These genes were p53 with a mutation previously described in JEKO-1, the leukocyte-derived arginine aminopeptidase (LRAP) gene in REC-1 that showed a new splicing isoform generating a premature stop codon, and RB1 in UPN-1 that contained an intragenic homozygous deletion resulting in a truncated transcript and total loss of protein expression. The new LRAP isoform was detected also in 2 primary MCLs, whereas inactivating intragenic deletions of RB1 were found in the primary tumor from which UPN-1 was derived and 1 additional blastoid MCL. These tumors carried a concomitant inactivation of p53, whereas p16INK4a was wild type. These results indicate for the first time that RB1 may be inactivated in aggressive MCL by intragenic deletions. IntroductionMantle-cell lymphoma (MCL) is as a distinct type of B-cell non-Hodgkin lymphoma genetically characterized by the t(11; 14)(q13;q32) translocation that leads to the dysregulation of cyclin D1. 1 In addition to the constitutive overexpression of cyclin D1, MCL shows frequent alterations of genes involved in the DNA damage response pathway and in the G1/S-phase checkpoint. 2 The dysregulation of the DNA damage response pathway may facilitate the chromosomal instability observed in these tumors. In that sense, inactivation of the tumor-suppressor genes (TSGs) p53 or ATM has been frequently observed in MCL with high number of chromosome abnormalities. [3][4][5] Oncogenic alterations in the cell cycle machinery include the inactivation of INK4a/ARF and the amplification of potential oncogenes such as BMI-1 or CDK4. [6][7][8] All these alterations play an important pathogenetic role in MCL, probably deregulating the cell cycle control by overcoming the suppressor effect that retinoblastoma 1 (RB1) performs in the G1/S-phase transition. In addition to these molecular oncogenic events, conventional cytogenetic and comparative genomic hybridization (CGH) studies have revealed a high number of secondary chromosomal abnormalities in MCL. However, only a few target genes of these genetic alterations have been identified. 9,10 The nonsense-mediated mRNA decay (NMD) pathway is an eukaryotic cellular mRNA surveillance mechanism that rapidly degrades mRNA transcripts containing premature termination codons (PTCs). 11,12 This mechanism of control prevents the accumulation of truncated proteins generated by translation of mRNAs that carry PTCs due to nonsense mutations, splicing errors, or inaccuracie...

Molecular pathogenesis of mantle cell lymphoma

“…These non-cell cycle-related functions of cyclin D1 have not been properly investigated in MCL. However, the complete inactivation of the RB1 by mutations and deletions in some MCLs (19), making cyclin D1 dispensable for cell cycle functions, would support the idea that cyclin D1 may play additional oncogenic roles in these tumors. Interestingly, the recent description of cyclin D1 as promoting cell survival in MCL by sequestering the proapoptotic BAX protein reinforces this concept (20).…”

“…Both pathways are connected through the CDKN2A locus (9p21), which encodes for both the CDK inhibitor INK4a and the positive p53 regulator ARF, and this locus is frequently deleted in MCL. Other key elements of these pathways, such as TP53 and RB1, are also frequently inactivated by point mutations or gene deletions (19,21). In addition, gene amplification events have been found to deregulate additional genes, including CDK4, polycomb ring finger gene BMI1, and MDM2 (19,22).…”

The EMT activator ZEB1 promotes tumor growth and determines differential response to chemotherapy in mantle cell lymphoma

“…Beyond the translocation of cyclin D1, cell cycle deregulation by secondary genetic alterations of components of the p16 INK4a /CDK4/Rb1 or p14 ARF /MDM2/p53 tumor suppressor pathways are frequent in MCLs. 1,40,43,44 ZEB1 is known to be repressed by Rb1 and in turn to repress several cyclin-dependent kinase inhibitors (for example, p15 INK4b , p19 ARF , and p21 CIP/WAF1 ). [45][46][47] In several hematological malignancies, including MCLs, Wnt signaling enhances cell viability, whereas its inhibition reduces it.…”

“…In addition to the translocation and overexpression of cyclin D1, a number of other genetic and nongenetic alterations resulting in deregulated cell cycle progression and/or reduced apoptosis have been reported in MCLs. 1,10,11,40,43,44,48,49 In that line, pharmacological inhibitors of Wnt signaling or knockdown of components of the pathway reduce proliferation and trigger apoptosis in MCL cells. 5,6 Our data show that ZEB1 could have a role in the regulation of proliferation and apoptosis in MCL.…”

Genomic aberrations in mantle cell lymphoma detected by interphase fluorescence in situ hybridization. Incidence and clinicopathological correlations

“…However, while in CLL genomic material from chromosome band 13q14.3 is lost distal to the retinoblastoma gene (RB), in some MCL cases RB might also be a potential candidate. 36 Furthermore, additional, as yet unidentified, tumor suppressors located in 13qter might play an important role in MCL, as this genomic region is more frequently deleted in MCL than in CLL.…”