Transcriptional control of the invariant chain gene involves promoter and enhancer elements common to and distinct from major histocompatibility complex class II genes.

Abstract

The invariant chain (Ii) is a glycoprotein coexpressed with the major histocompatibility complex (MHC) class II antigens. Although Ii is encoded by a single gene unlinked to the MHC gene complex, Ii and MHC class II appear to have similar patterns of tissue specific expression and generally are coordinately regulated by cytokines. Here we present evidence that transcription of the murine Ii gene is controlled by multiple cis-acting elements. The 5' regulatory region of the Ii gene appears to be combined of conserved class II regulatory elements with promoter elements commonly found in other eucaryotic genes. A region containing characteristic class II promoter elements (H box, X box, and a modified Y box) serves as an upstream enhancer in the Ii gene and might contribute to the coexpression of MHC class II and Ii genes. A series of positive control elements, the kappa B element, Sp1-binding site, and CCAAT box, are present in the Ii promoter and apparently serve distinct regulatory functions. The kappa B site in the Ii gene is a cell type-specific element, contributing to expression in a B-cell line but not in a fibroblast cell line, and the Sp1 site is required by the H-X-Y' enhancer element to stimulate promoter activity. In addition, an Ii enhancer in the first intron that specifically stimulates its own promoter has been identified. Our results suggest that a sequence match between enhancers and certain promoter elements is critical.