Richter's and prolymphocytic transformation of chronic lymphocytic leukemia are associated with high mRNA expression of activation-induced cytidine deaminase and aberrant somatic hypermutation

Abstract

Chronic lymphocytic leukemia (CLL) is an indolent B-cell nonHodgkin's lymphoma that may transform into higher-grade lymphoma. The transformation involves an increased number of prolymphocytic cells, termed prolymphocytic transformation (PLT) or the development of diffuse large B-cell lymphoma (DLBL), also referred to as Richter's transformation (RT). To analyze whether activation-induced cytidine deaminase (AID), which is essential for somatic hypermutation (SHM) of normal B-cells, and malfunction of SHM termed aberrant somatic hypermutation (ASHM) are associated with higher-grade transformation of CLL, AID mRNA expression and the mutation pattern of c-MYC, PAX-5 and RhoH genes were analyzed in eight cases of CLL without transformation and in 21 cases that showed RT or PLT. Chronic lymphocytic leukemia cases, which showed no transformation or eventually transformed into higher-grade lymphoma, showed low levels of AID mRNA expression and low frequency of mutations of c-MYC, PAX-5 and RhoH genes. In both RT and PLT, high-levels of AID mRNA expression and high-frequency mutations of c-MYC, PAX-5 and RhoH genes were detected. These results indicate that AID expression and ASHM are associated with higher-grade transformation of CLL and provide further evidences that AID expression and ASHM may be activated during the clonal history of B-cell lymphomas.

MALT lymphoma and extranodal diffuse large B-cell lymphoma are targeted by aberrant somatic hypermutation

“…Because frequency of mutations and AID protein/RNA expression are both lower in MALT lymphomas, one might speculate an active involvement of ASHM in the high-grade transformation process of MALT lymphoma to overt DLBCL, resembling that described for Richter and prolymphocytic transformation in chronic lymphocytic leukemia. 25 By mutating regulatory and coding sequences of the targeted genes, ASHM may represent a major contributor to their pathogenesis. Images were captured with a Leica DMLB microscope (Leica, Bensheim, Germany) using a Leica PL FLUOTAR objective lens (40ϫ/0.70) and a Leica DC200 camera.…”

AID protein expression in chronic lymphocytic leukemia/small lymphocytic lymphoma is associated with poor prognosis and complex genetic alterations

“…Here, it might trigger disease progression and even transformation into aggressive lymphoma. Therefore, PC B cells might represent the initiator cells of prolymphocytic or Richter transformation as Reiniger et al 35 indeed found an elevated AID mRNA level in such patients.…”

Genetics of Chronic Lymphocytic Leukemia: Practical Aspects and Prognostic Significance

“…It has been suggested that AID may have a dual role; initiating chromosomal translocations on one hand and generating secondary hits by mutagenesis on the other (Perez-Duran et al, 2007). Aberrant SHM and involvement of AID were reported to be involved in mutations of TP53 (Malcikova et al, 2008), MYC, PAX5 and RhoH (Reiniger et al, 2006). Moreover, AID activity has been linked to the generation of DSBs involved in translocations in both IG and non-IG loci (Gostissa et al, 2011).…”