KBF1 (P50 NF-KAPPA-B HOMODIMER) ACTS AS A REPRESSOR OF H-2K(B) GENE-EXPRESSION IN METASTATIC TUMOR-CELLS

Downregulation of major histocompatibility complex class I expression is causally related to high malignancy and low immunogenicity of certain murine tumors. In this study, we have analyzed the roles of the nuclear factors KBF1/p50 and p65 in regulation of class I expression in high and low metastatic tumor cells. Low class I-expressing cells show at higher levels of KBF1/p50 and NF-kappaB (p50/p65) binding activity than high class I-expressing cells. However, an excess of KBF1 over NF-kappaB is observed in low expressing cells, while an excess of NF-kappaB over KBF1 is observed in high expressing cells. Stable transfection of a p65 expression vector into low class I-expressing cells activated H-2 transcription and cell surface expression, while stable transfection of p50 expression vector into high expressing cells suppressed H-2K(b) transcription and cell surface expression. Our studies suggest that KBF1 has the potential of downregulating class I gene expression, whereas dimers containing the p65 subunit are activators of class I gene expression.