The leukocyte integrin p150,95 (CD11c/CD18) is involved in a number of cell-cell 
and cell-extracellular matrix interactions and mediates signal transduction into 
the cytoplasm. p150,95 is expressed on cells of the myeloid lineage as well as 
on certain activated T and B lymphocytes, and its expression is regulated during 
cell activation and differentiation. Since CD18 is expressed on all leukocyte 
lineages, the restricted expression of p150,95 must be controlled at the level 
of CD11c gene transcription. To understand the mechanisms that direct the 
constitutive and regulated leukocyte expression of p150,95 we have structurally 
characterized the CD11c promoter region and initiated its functional dissection. 
The CD11c promoter lacks TATA- and CCAAT-boxes, directs the synthesis of 
transcripts with heterogeneous 5'-ends, and contains an initiator-like sequence 
at the major transcription initiation site. Several putative binding sequences 
for ubiquitous (Sp1, AP-1, AP-2, and NF-kB) and leukocyte-specific (PU.1) 
transcription factors have been identified in the proximal region of the CD11c 
promoter which may participate in the regulation of the expression of p150,95. 
Transient expression of CD11c-based reporter gene constructs indicates that the 
CD11c promoter dictates the tissue-specific expression of p150,95 and that 
sequences contained within 160 base pairs 5' from the major transcriptional 
start site are involved in the tissue-specific and regulated expression of 
p150,95. DNase I protection analysis on the promoter region spanning from -160 
to +40 revealed four regions of DNA-protein interactions (FPI-FPIV), two of 
which (FPII and FPIV) correlate with the cell type-specific and regulated 
expression of the CD11c gene.