Expression of Cereblon (CRBN) Is Associated with Disease Stage, Genetic Subgroups and Specific Micro-RNAs in Multiple Myeloma

Since the introduction of thalidomide into the treatment of multiple myeloma (MM) immunomodulatory drugs (IMiDs) have become an essential treatment modality for the management of MM. Recently, cereblon (CRBN) has been identified as the thalidomide binding protein disrupting the E3 ubiquitin ligase complex composed by CRBN, DDB1 and Cul4 (Ito et al., Science 2010). Moreover, CRBN is essential for the antimyeloma activity of lenalidomide and pomalidomide (Zhu et al.; Blood 2011). However, the genetic and epigenetic mechanisms by which CRBN is regulated are not understood so far. Therefore, we aimed to determine if CRBN expression associates with clinically relevant subgroups and response to therapy with lenalidomide. In addition, we investigated additional regulatory layers by identifying key microRNAs (miRNAs) correlated with CRBN expression.

CRBN expression was measured by real-time PCR (qPCR) using CD138 purified plasma cells from 17 patients with a monoclonal gammopathy of undetermined significance (MGUS) and 139 patients with MM. CRBN expression was normalized to GUSB (used as internal control) and to the expression levels of CRBN in normal plasma cells (n=4). MiRNA expression profiles were generated using Agilent mirRNA-arrays on patients with the highest and lowest CRBN mRNA expression levels, respectively (n=42). All patients were characterized by a comprehensive set of FISH probes for the presence of recurring cytogenetic abnormalities.

CRBN expression was variable in the investigated samples (median: 0.717; range: 0.078 – 5.285). In patients with MGUS (median: 0.833) CRBN expression was significantly (p=0.01) lower as compared to patients with a MM (median: 0.673). CRBN expression was associated with cytogenetic subgroups (p<0.05), with patients harboring a translocation t(11;14) and gains at 9q34 presenting with the highest CRBN expression levels and patients with a deletion(del) 17p13 or gains at 1q21 with the lowest CRBN expression levels. Out of 526 miRNAs that passed the detection threshold, 28 miRNAs were significantly associated with CRBN expression (p<0.005; >2-fold change). A total of 21 miRNAs were positively correlated and seven miRNAs were negatively correlated with high CRBN expression levels. Of particular interest, miRNAs with conserved target sites in the CRBN 3′-UTR (miRNA -23a and let-7g) were represented in the signature.

The expression of CRBN is variable in plasma cell disorders with decreasing CRBN expression levels in MM compared to the precursor state MGUS and normal plasma cells. Moreover, CRBN is lower expressed in poor cytogenetic subgroups (in particular del17p13 and gains at 1q21). This might provide a novel mechanism underlying the adverse clinic outcome in this patient group. Finally, the differential expression of miRNAs with putative CRBN target sites may uncover an important regulatory mechanism.

No relevant conflicts of interest to declare.