Constitutive expression of NF-kappa B 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 sw itching, cellular differentiation, and apoptosis. Recently, members of the NF-kappaB family, including p65(Rel A), have been implicated in promoting s urvival of various hematopoeitic neoplasms, including T cell malignancies s uch as adult T cell leukemia-lymphoma. We investigated the expression of ac tive 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 lymph oma (CTCL) cell lines. Paraffin-embedded tissues from 23 cutaneous lesions and a single lymph node biopsy from patients diagnosed with MF were evaluat ed for p65(RelA) expression by using a monoclonal mouse antibody that detec ts 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 quanti tatively 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)) populati on and by determination of increased Annexin V/7-amino-actinomycin D (7-AAD ) expression. Nuclear extracts from CTCL cells before and after chemical in hibition were analyzed for NF-kappaB nuclear DNA-binding activity by electr ophoretic mobility shift assay (EMSA) with quantitative densitometry Nuclea r expression of p65(RelA) before and after treatment with the various inhib itory compounds was measured by immunofluorescence staining in each CTCL ce ll line. Neoplastic T lymphocytes from 22 of 24 cases of MF showed strong n uclear and cytoplasmic expression of active p65(Rel A). Compared with untre ated control cells, a marked increase in apoptosis, a significant decrease in NF-KB DNA-binding activity, and a marked decrease in nuclear p65(RelA) e xpression were seen in cells from both CTCL cell lines after chemical NF-ka ppaB 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-kapp aB inhibition suggest a critical role for NF-kappaB in the pathogenesis and tumor cell maintenance of CTCLs. Copyright (C) 2000 by W.B. Saunders Compa ny.