Alterations of the p53, Rb and p27 Tumor Suppressor Pathways in Diffuse Large B-cell Lymphomas

Abstract

Diffuse large B-cell lymphomas (DLBCL) display defects in cell cycle and apoptosis regulation. Therefore, the immunohistochemical expression patterns of the proteins p14, p21, Hdm2 and cyclin D2 were analyzed in relation to the previously reported expression of other major cell cycle proteins (p53, Rb, p16, p27, Ki-67 and cyclins A, B1, D2, D3 and E), apoptosis-associated proteins (bcl2, bcl-xl, bax, bak, bad and bid) and the B-cell differentiation immunophenotypes. Expression of the proteins p14, p21, Hdm2 and cyclin D2 was observed in 62/71 (87%), 22/76 (29%), 35/74 (47%) and 11/77 (14%) cases, respectively. Immunohistochemical alterations of the p53 (p53-Hdm2-p21-p14), Rb (Rb-p16-cyclin D [D2 or D3]) and p27 (p27-cyclin E) pathways were found in 56/77 (73%), 53/79 (67%) and 54/79 (68%) cases, respectively. Concomitant alterations of the p53-Rb, p53-p27 and Rb-p27 pathways were found in 40/77 (52%), 38/77 (50%) and 36/79 (46%) cases, respectively. Three concomitant alterations of the p53-Rb-p27 pathways were found in 28/79 (35%) cases. The main findings of the present study were the following: alterations of the p27 pathway were associated with higher expression of Ki-67 (p=0.023); concomitant alterations of the p53-Rb pathways and the p53-p27 pathways were associated with higher expression of cyclin A (p=0.015 and p=0.021, respectively) and concomitant alterations of the p53, Rb and p27 pathways were associated with higher expression of cyclin A (p=0.013). Since cyclin A supports DNA replication, centrosome duplication and mitosis, these findings indicate that concomitant alterations of the p53, Rb and p27 pathways in DLBCL may have cooperative effects resulting in increased neoplastic cell proliferation. This might explain, at least partially, the association between concurrent aberrations of the p53, Rb and p27 pathways and aggressive clinical behavior in DLBCL.