Studies Highlight Role of bcl-2 Gene in Programmed Cell Death

SAN DIEGO--The bcl-2 gene, present in follicular-type B cell lymph-oma,serves as a critical checkpoint in the apoptosis pathway, and may be involvedin the development of ultraviolet-induced skin cancers, in combinationwith the tumor-suppressor gene p53, according to two reports presentedat the American Association for Cancer Research (AACR) annual meeting.

The bcl-2 apoptosis-suppressor gene is complemented by another gene,known as bax, which is involved in stimulating apoptosis, Stanley J. Korsmeyer,MD, said at the meeting in the 36th Annual Clowes Memorial Award lecture.When bax predominates, cells execute a programmed death command, but whenbcl-2 is excessive, the program is interrupted and cells survive.

In their studies of bcl-2-deficient mice, Dr. Korsmeyer and his colleaguesat the Howard Hughes Medical Institute at Washington University Schoolof Medicine, St. Louis, found that the mice embryos developed normally.However, when these bcl-2-deficient mice reached adulthood, the bax genepredominated, leading to massive death of lymphocytes and the disappearanceof lymphoid organs.

In contrast, in bax-deficient mice, bcl-2 predominated. These mice displayedcellular hyperplasia and aberrations in cell death during the developmentof the testes.

"Further study of the bcl-2 family holds the promise of improvingour understanding of the pathway of programmed cell death and the aberrationsin this process that result in malignancy," Dr. Korsmeyer said.

UV Radiation-Induced Apoptosis

In other research, investigators from the Department of Dermatologyat Mount Sinai School of Medicine, New York, hypothesized that ultravioletA (UVA) radiation and ultraviolet B (UVB) radiation could induce apoptosisby stimulating p53 or by downregulating the expression of bcl-2.

Using a cell line that expresses both p53 and bcl-2, the New York Cityinvestigators found that UVB radiation significantly induced the expressionof p53 in a dose-dependent and time-dependent manner. Exposure to an equallycytotoxic dose of UVA radiation, however, produced no effects on p53 expression.

In contrast, UVA radiation substantially down-regulated the expressionof bcl-2, whereas exposure to the same level of UVB radiation producedno change in bcl-2 expression.

Different Pathways Triggered

The researchers concluded that UVA and UVB radiation cause cell damageand induce apoptosis by triggering different signal transduction pathways,and that the balance between the expression of p53 and bcl-2 plays an importantrole in regulating ultraviolet radiation-induced apoptosis.

Said investigator Huachen Wei, MD, PhD: "Because mutations in p53and overexpression of bcl-2 can result in human cancers, our findings suggestthat ultraviolet radiation may provide a new approach for drug development."