NF-kB-regulated expression of the MHC class I related chain A gene (MICA) on activated T lymphocytes.

LUCIANA LORENA MOLINERO; MERCEDES BEATRIZ FUERTES; MARÍA VICTORIA GIRART; LEONARDO FAINBOIM; GABRIEL ADRIÁN RABINOVICH; MÓNICA COSTAS; NORBERTO WALTER ZWIRNER

JOURNAL OF IMMUNOLOGY

The American Association of Immunology

Lugar: Bethesda; Año: 2004 vol. 173 p. 5583 - 5590

0022-1767

MICA is a stress-regulated, HLA-related molecule which exhibits a restricted pattern of expression. MICA protein is upregulated on different tumor cells, and is recognized by the lectin-like NKG2D molecule expressed by cytotoxic gd T lymphocytes, CD8+ ab T lymphocytes and NK cells. Although MICA is not expressed on resting lymphocytes, we demonstrated that it is induced on activated T cells. Since NF-kB is actively involved in T-cell activation, and is constitutively activated in many tumors, here we investigated whether NF-kB may modulate MICA expression. Treatment with the NF-kB inhibitor sulfasalazine resulted in a dose-dependent inhibition of MICA expression in anti-CD3- and anti-CD28/PMA-activated T lymphocytes, as assessed by Western blot and RT-PCR analysis. Moreover, sulfasalazine also down-regulated MICA expression on epithelial tumor HeLa cells. MICA expression was accompanied by a sulfasalazine-sensitive IkBa degradation. EMSA with nuclear extracts from anti-CD3- and anti-CD28/PMA-stimulated T lymphocytes demonstrated the binding of a potential NF-kB family transcription factor to a MICA gene intron 1-derived oligonucleotide that contains a putative kB binding site. Supershift assays demonstrated the presence of p65(RelA)/p50 heterodimers and p50/p50 homodimers in the NF-kB complexes bound to the kB-MICA oligonucleotide. Transient transfection of HeLa cells with p65(RelA) upregulated MICA expression, as assessed by Western blot and flow cytometry analysis. Hence, we conclude that NF-kB regulates MICA expression on activated T lymphocytes and HeLa tumor cells, by binding to a specific sequence in the long intron 1 of the MICA gene. This constitutes the first description of a transcription factor that regulates MICA gene expression.