Potential mechanism and prognostic value of promoter methylation of PRDM1 gene in diffuse large B cell lymphoma
Objective: To investigate PRDM1 gene methylation status, immune classification and their prognostic significance in diffuse large B cell lymphoma (DLBCL).
Methods: Immunohistochemical (IHC) staining for CD20, CD10, bcl-2, bcl-6, PRDM1/Blimp-1 and MUM1 was carried out in 100 cases of DLBCL specimens and 20 reactive lymphoid proliferation samples. All patients were classified into germinal center B cell-like (GCB) and activated B cell-like (ABC) subtype according to Hans' algorithmin. PRDM1 gene methylation was detected by methylation-specific PCR (MSP) and its relationship with clinicopathologic parameters was analyzed. OCI-Ly1 (GCB type) and OCI-Ly3 (ABC type) cell lines were transfected by Small interfering RNA(siRNA) with cationic lipid reagent transfection mediated, and the PRDM1/Blimp-1 expression in before and after transfected cell lines were detected with reverse transcription-PCR and Western blot methods. The relationship between PRDM1 gene methylation, clinicopathologic parameter and survival was analyzed using one-way analysis of variance.
Results: One hundred patients were classified into 73 (73%) cases of GCB subtypes and 27 (27%) cases of ABC. PRDM1/Blimp-1 was expressed in 21 DLBCL and highly expressed in 20 reactive lymphoid proliferation. PRDM1 gene methylation was detected in 23% (23/100) of DLBCL, while no methylation was detected in all 20 reactive lymphoid proliferation. The difference of the PRDM1 methylation status between DLBCL and the control samples was statistically significant (P=0.004). However, there was no significant correlation between the PRDM1 gene methylation and clinicopathologic parameters (P>0.05). Reverse transcription-PCR and Western blot showed that PRDM1 gene expression was reduced in siRNA-induced group compared with blank control group and negative control group. One-way analysis of variance revealed that aged ≥60 years, performance status score above 3, and the presence of general symptoms were associated with significantly lower overall survival rate.
Conclusions: PRDM1 gene silencing with aberrant CpG methylation is probably one of the critical events in the oncogenesis of DLBCL. This may have important implications as a candidate marker for diagnosis and targeted gene therapy. Meanwhile in vitro siRNA transfected OCI-Ly1 and OCI-Ly3 cell lines confirm that PRDM1 gene is a suppressor gene in DLBCL and may represent a novel therapeutic target.