Bcl-2 and c-Myc co-operate in the Epstein – Barr virus-immortalized human B-cell line GM607 but do not confer tumorigenicity

Abstract

Eighty-five percent of follicular lymphomas possess a characteristic t(14;18) translocation that results in the deregulated expression of the proto-oncogene BCL-2. BCL-2 overexpression alone is insufficient for full cellular transformation and at least 1 other genetic event is believed to be necessary for follicular lymphoma development. Deregulated c-Myc expression has previously been shown to cooperate with Bcl-2 to transform murine fibroblast cell lines and lead to tumor development in mice. We have developed a human model system to study early transformation in lymphoid cells using immortalized lymphoblastoid cells. We sequentially introduced BCL-2 and c-MYC, 2 proto-oncogenes known to be involved in the transformation of B cells into Epstein-Barr virus (EBV)-immortalized human B cells. We show that the c-Myc and Bcl-2 overexpression, together with EBV immortalization were insufficient to cause full cellular transformation as measured by cell proliferation rates, soft agar and tumorigenicity assays. These results show that more than 3 genetic hits (EBV infection, Bcl-2 and c-Myc overexpression) were required for the full cellular transformation of human lymphoblastoid cells. However, subtle changes in cellular proliferation and sensitivity to apoptosis were documented, at non-limiting dilutions. These changes may confer a susceptibility to the modified cells such that they are more susceptible to the acquisition of additional genetic changes and evolve towards a fully transformed state. In addition, the model system developed may be suitable for the identification of further known and novel oncogenic events involved in the full transformation of B cells.

c-Myc induction of programmed cell death may contribute to carcinogenesis

“…Tomlin et al report that co-expression of Bcl-2 does not promote transformation of human B-cell lines by c-myc. 64 More surprisingly, Bcl-2 actually inhibits c-myc-induced liver carcinogenesis in L-PK-Bcl-2/L-PK-c-myc double transgenic mice. 65 Bcl-2 overexpression also inhibits liver carcinogenesis induced by transforming growth factorα (TGFα), with and without a concomitant treatment with a chemical carcinogen, in a Bcl-2/ tgfα double transgenic model.…”