The Paternally Expressed Gene 10 (PEG10) on Chromosome 7q21 Is Overexpressed and Imprinted in High-Risk B-CLL.

Introduction: To establish surrogate markers for IgV_H mutation status in B-CLL, we performed microarray analysis with mutated and unmutated patient samples. Among the most differentially expressed genes was PEG10, a maternally imprinted gene located on chromosome 7q21. PEG10 is known to be expressed during placental development and in hepatocellular carcinoma. Here we have investigated the association of PEG10 with B-CLL subtypes and risk factors as well as its transcriptional regulation. In addition, we studied its expression in other hematologic malignancies.

Methods and Results: In our microarray experiments, PEG10 was highly expressed (2.1-fold) in unmutated samples. We confirmed these results by real time PCR in 42 B-CLL patients and found a significant correlation between PEG10 expression and unmutated IgV_H status (P=0.007). High PEG10 expression was associated with chromosomal del(11q) (P=0.008), a shorter time to treatment (P=0.009) as well as a positive Coombs test (P=0.04). High expression was found in B-CLL and sorted CD19+ B-CLL cells, plasmoblastic DLBCL as well as in the Burkitt’s lymphoma cell line Ramos. In normal tissues, relatively high levels were seen in brain, liver, lung and kidney, but these expression levels were lower than in CD19+ B-CLL cells. Expression in sorted B cells from healthy donors was lower than two orders of magnitude. Intracellular expression of the PEG10 protein in B-CLL cells was confirmed by immunofluorescence studies using antibodies that recognize specifically PEG10-RF1. To address the question whether PEG10 overexpression results from loss of imprinting, we performed allele-specific as well as methylation-specific PCR. Imprinting was maintained in 6 patients with B-CLL. Analysis of a mother and son, both having B-CLL, confirmed that at least in this familial case the maternal PEG10 allele was silenced as expected. Interestingly, similar expression patterns were observed for the neighbouring gene sarcoglycan epsilon indicating a common mechanism of deregulation of the 7q21 locus in high risk B-CLL.

Conclusions: We show that PEG10 is differentially expressed in B-CLL and is associated with del(11q), a shorter time to treatment and unmutated IgV_H mutation status, suggesting its role as a marker for high risk B-CLL. PEG10 overexpression is unlikely to result from loss of imprinting. Further studies of the gene locus at 7q21 are in progress.