Differential immunohistochemical staining for DNA topoisomerase II alpha and beta in human tissues and for DNA topoisomerase II beta in non-Hodgkin's lymphomas

Abstract

Topoisomerase II (Topo II) is the target for several chemotherapeutic agents, including doxorubicin and etoposide, termed Topo II poisons. Previous studies from cancer cell lines and clinical specimens attempted to correlate expression of Topo II with drug sensitivity. Mammalian cells, however, contain two isoforms of Topo II, termed Topo II alpha (subunit molecular weight, 170 kDa) and Topo II beta (subunit molecular weight, 180 kDa), both of which are sensitive to Topo II poisons. Studies of Topo II alpha in normal cells and tissues are limited, and few studies have begun to characterize the beta isoform. This study employed in situ immunohistochemical staining to characterize the tissue distribution of Topo II alpha in formalin-fixed, paraffin-embedded human tissues. A new antibody, confirmed by Western blot, specific to the beta isoform, was also used to characterize its distribution in non-neoplastic, formalin-fixed, paraffin-embedded human tissues and 33 cases of non-Hodgkin's lymphomas. Topo II alpha was identified in normal tissues with proliferating cells, especially in spermatocytes, germinal centers, and proliferative endometrium. Some terminally differentiated tissues, e.g., cerebral cortex, skeletal muscle, and nerve, showed no detectable Topo II alpha, whereas others, e.g., breast, salivary gland, and kidney, showed rare positive cells. In contrast, Topo II beta was present in all tissues, including fully differentiated tissues, e.g., cerebellum, myometrium, pancreas, as well as in tissues with cell turnover, e.g., endometrium, skin, and bowel mucosa. In non-Hodgkin's lymphomas, Topo II beta was uniformly present with no change in the intensity or staining pattern among the tumor subtypes. Topo II alpha may be distinguished from the beta isoform using immunohistochemical techniques, which permit precise localization of the enzyme in individual cells. Detection of this differential expression between the alpha and beta isoform of Topo II suggests distinct physiologic roles and might allow better therapeutic targeting for tumors.