טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentNovak Rostislav
SubjectThe B Cell Antigen Receptor Signaling Regulates Activation
Induced Cell Death and Expression of Recombination
Activating Genes in Transformed B Cells
DepartmentDepartment of Medicine
Supervisor Professor Doron Melamed
Full Thesis textFull thesis text - English Version


Abstract

V(D)J recombinase machinery constructs the B Cell Antigen Receptor through the formation of double strand breaks in DNA and therefore increases genomic instability and the propensity of B cells to undergo genetic alterations with a high frequency of oncogenic events and subsequent lymphomagenesis. Since B cell lymphoma is often resistant to traditional radiation therapy, alternative approaches to control B cell lymphoma fate are necessary. Earlier studies have shown that BCR tonic signals are vital for lymphoma B cells. Recently, two approaches to promote apoptosis of lymphoma B cells have been published. One is to inhibit tonic BCR signaling and the other is to promote Activation Induced Cell Death (AICD). Hence, elucidating survival mechanisms and unraveling general apoptotic pathways are important to understand how cell-fate decisions are made and may suggest new approaches for the treatment of leukemia patients. Earlier it was shown that the knockout of CD19 (a positive regulator of BCR signaling) alters fate decision of primary B cells through modification of intracellular signals. The major aim of this study is to define whether modification of intracellular signals, obtained by knockdown of CD19 co-receptor, will alter fate decision of transformed B cells in ligand dependent and ligand independent manner. For this propose, we have used siRNA technique to knockdown CD19 expression. We found that the knockdown of CD19 results in enhanced AICD in the transformed B cell lines. Ablation of CD19 in WEHI- 231 cell line resulted in an early drop in NFkB, c- MYC and serine/ threonine protein kinase AKT. However, co-ligation of CD40 maintained NFkB and c- MYC and efficiently rescued both the CD19- knockdown and the control cells from AICD. Thus, the increased AICD in CD19- knockdown cells may be the result of improper activation of survival signals. We also show here that Hematopoietic Progenitor Kinase 1 (HPK1) regulates NFkB activation upon BCR ligation and the consequential AICD rate. Moreover, we demonstrate that ablation of CD19 in 38c-13 cell line decreases the tonic BCR signaling with consequent elevation in RAG expression. Here we demonstrate that RAG expression is regulated by tonic ERK activity. Collectively, our results suggest that intervention in tonic BCR signaling combined with promoting of AICD in B cell lymphomas have a synergistic effect, which can contribute to the development of proper treatment to B cell lymphomas.