KLHDC8B Is a Novel, Mitotically-Regulated Classical Hodgkin’s Lymphoma Candidate Susceptibility Gene.

Classical Hodgkin’s lymphoma (HL) is a B-cell malignancy associated with exposure to Epstein-Barr virus (EBV). Heritable factors also strongly contribute to its risk in the general population, but, except for rare immunodeficiency syndromes, susceptibility genes remain unidentified. We ascertained a family in which multiple individuals carrying a constitutional translocation between chromosomes 2 and 3 (t(2;3)(q11.2;p21.31)) have developed HL. The translocation is especially intriguing, because genetic linkage analysis had previously mapped a predisposition locus for another EBV-associated malignancy, nasopharyngeal carcinoma, to the vicinity of the breakpoint at 3p21.31, and this region is also frequently deleted or rearranged in sporadic B-cell lymphomas and other malignancies, suggesting that it may be the location of a tumor suppressor gene with broad cancer relevance. In order to identify the gene likely responsible for HL in this family, we molecularly cloned both translocation breakpoints. The chromosome 2 breakpoint is intergenic, but the chromosome 3 breakpoint disrupts the first intron of a previously uncharacterized gene, KLHDC8B (Kelch domain-containing 8B). The translocation separates the non-coding first exon from the remainder of the gene and appears to result in haploinsufficiency for the gene product, as demonstrated by the fact that lymphoblastoid cells from the translocation carriers have approximately half the level of KLHDC8B mRNA as found in controls (and there is no evidence supporting fusion transcript formation). In order to assess KLHDC8B’s broader significance in familial HL, we sequenced all six of its exons and flanking intronic sequence in affected probands from 52 families with two or more cases of HL. We detected no coding region variants. However, we did identify a 5′-UTR variant (+42CtoT) at a conserved position within a predicted exonic splice enhancer sequence that was present in 3 of 52 familial HL probands (5.8%) as compared to 4 of 307 controls (1.3%; Odds Ratio [95% C.I.] = 4.64 [1.01–21.4]) and that may be associated with decreased allele-specific expression. To investigate the functional role of KLHDC8B in the cell, we raised a polyclonal chicken IgY antibody against a KLHDC8B-derived peptide and have characterized the expression of KLHDC8B at the protein level in HeLa cells. The gene product locates to the cytoplasm. Interestingly, by both immunofluorescence and flow cytometry, KLHDC8B protein levels are significantly upregulated in cells undergoing mitosis. Given the dysregulation of normal mitotic processes that is well known to occur in Hodgkin and Reed-Sternberg cells, this protein may play an important role in HL pathogenesis. Although further studies will be necessary to replicate the genetic association, this study suggests that a SNP present in >1% of the Caucasian population may influence HL risk.