A thymocyte factor SATB1 suppresses transcription of stably integrated matrix-attachment region-linked reporter genes.

SATB1 specifically recognizes and binds to specialized genomic regions with an ATC sequence context with high base-unpairing propensity. Such base-unpairing regions (BURs) are typically identified within nuclear scaffold- or matrix-attachment regions (S/MARs). SATB1 is a homeodomain protein and is predominantly expressed in thymocytes. We obtained BHK cell lines expressing low levels of SATB1 by stable transfection and investigated its effect on stably integrated MAR-linked SV40 enhancer/promoter-driven luciferase reporter genes. For this study, both naturally occurring and synthetic MARs, as well as an AT-rich non-MAR control, were tested. Previous studies demonstrated that MAR sequences augment transcription of the linked reporter luciferase gene. Here, we show that SATB1 dramatically reduces the high levels of MAR-linked luciferase gene transcription. Transcription was virtually abolished for a reporter gene surrounded by two MARs at the 5' and 3' ends of the gene, which otherwise confer the highest level of transcriptional augmentation. On the other hand, SATB1 did not affect expression of an AT-rich non-MAR-linked luciferase gene or of endogenous housekeeping genes. This study shows that SATB1 acts as a strong transcriptional suppressor on a reporter gene linked to MARs when it is stably integrated into chromatin.