Targeting of Kruppel-associated box-containing zinc finger proteins to centromeric heterochromatin - Implication for the gene silencing mechanisms

Kruppel-associated box-containing zinc finger proteins (KRAB-ZFPs) repress transcription via functional interaction with the corepressor KRAB-associat ed protein-1 (KAP-1). KAP-1 directly interacts with heterochromatin protein 1 (HP1), a dose-dependent regulator of heterochromatin-mediated silencing. Here we show that two KRAB-ZFPs that we previously identified, KRAZ1 and K RAZ2, are targeted to foci of centromeric heterochromatin containing HP1 al pha through the interaction with KAP-1, Centromeric targeting potential of KRAZ1 and KAP-1 is strictly correlated with their silencing activities; a K RAB mutant of KRAZ1 that is unable to bind KAP-1 and KAP-1 deletions unable to bind HP1 cannot localize to centromeric foci nor repress transcription. We provide evidence that this correlation is likely to be functionally rel evant, First, overexpression of the VP16 transactivation domain fused with the KAP-1 deletion that binds to KRAB but not to HP1 leads to dramatic redi stribution of KRAZ1 from centromeric foci and simultaneously converts KRAZ1 -mediated silencing into strong transcriptional activation. Second, a speci fic inhibitor of histone deacetylases, trichostatin A, effectively redistri butes KRAZ1 and KAP-1 from centromeric foci and partially relieves their si lencing activities. These data strongly suggest that KRAB-ZFPs/KAP-1 silenc e transcription by dynamic recruitment of the target locus to the specific gene silencing compartment, centromeric heterochromatin, in a histone deace tylase-dependent manner.