Constitutive expression of NF-κB is a characteristic feature of mycosis fungoides:: Implications for apoptosis resistance and pathogenesis

The NF-kappaB family of transcription factors is an important regulator of genes expressed during inflammatory responses, immunoglobulin (Ig) class switching, cellular differentiation, and apoptosis. Recently, members of the NF-kappaB family, including p65(Rel A), have been implicated in promoting survival of various hematopoeitic neoplasms, including T cell malignancies such as adult T cell leukemia-lymphoma. We investigated the expression of active NF-kappaB p65(Rel A) in cases of mycosis fungoides (MF) and the effect of chemical inhibitors of NF-kappaB on apoptosis in cutaneous T cell lymphoma (CTCL) cell lines. Paraffin-embedded tissues from 23 cutaneous lesions and a single lymph node biopsy from patients diagnosed with MF were evaluated for p65(RelA) expression by using a monoclonal mouse antibody that detects the activated form of p65(Rel A). Apoptosis after treatment with the NF-kappaB inhibitors gliotoxin, MG132, BAY 11-7082, and BAY 11-7085 was quantitatively measured in the CTCL cell lines HuT-78 and HH by propidium iodide (PI)/cell cycle analysis for detection of a hypodiploid (sub-G(0)) population and by determination of increased Annexin V/7-amino-actinomycin D (7-AAD) expression. Nuclear extracts from CTCL cells before and after chemical inhibition were analyzed for NF-kappaB nuclear DNA-binding activity by electrophoretic mobility shift assay (EMSA) with quantitative densitometry Nuclear expression of p65(RelA) before and after treatment with the various inhibitory compounds was measured by immunofluorescence staining in each CTCL cell line. Neoplastic T lymphocytes from 22 of 24 cases of MF showed strong nuclear and cytoplasmic expression of active p65(Rel A). Compared with untreated control cells, a marked increase in apoptosis, a significant decrease in NF-KB DNA-binding activity, and a marked decrease in nuclear p65(RelA) expression were seen in cells from both CTCL cell lines after chemical NF-kappaB inhibition. These data show that the active form of NF-kappaB p65(RelA) is commonly expressed in neoplastic T lymphocytes in patients with MF. In CTCL cell lines, the significant decrease in nuclear NF-kappaB expression and the marked increase in spontaneous apoptosis caused by chemical NF-kappaB inhibition suggest a critical role for NF-kappaB in the pathogenesis and tumor cell maintenance of CTCLs. Copyright (C) 2000 by W.B. Saunders Company.