A 5' PORTION OF THE ICAM-1 GENE CONFERS TISSUE-SPECIFIC DIFFERENTIAL EXPRESSION LEVELS AND CYTOKINE RESPONSIVENESS

Intercellular adhesion molecule-1 (ICAM-1), a cell-adhesion molecule c ritically involved in leukocyte trafficking and adherence, displays ti ssue-specific and cytokine-specific expression profiles. Although huma n dermal microvascular endothelial cells (HDMEC) constitutively expres s ICAM-1, keratinocytes (HK) do not. Interleukin-1 (IL-1) upregulates ICAM-1 expression in HDMEC, but fails to do so in either HK or A431, a human squamous carcinoma cell line, even though both have IL-1 recept ors and express ICAM-1 on exposure to other cytokines. We have previou sly characterized a human ICAM-1 genomic clone that contains the 5' fl anking transcriptional regulatory region. To test the hypothesis that tissue- and cytokine-specific ICAM-1 gene expression results from the interaction of constitutive and inducible tissue-specific trans-acting factors with distinct cis-elements of the ICAM-1 gene, various ICAM-1 -based reporter gene (CAT) plasmids were constructed. Transcriptional activity of these various constructs was assessed after transient tran sfection into HDMEC and A431. A critical ICAM-1 region was identified that conferred enhanced expression of CAT in HDMEC and suppressed expr ession of CAT in A431. This same region further enhanced CAT expressio n in transfected HDMEC treated with IL-1alpha, yet no such enhancement was seen with IL-1 treatment of identically transfected A431. However , treatment of A431 transfectants with IFNgamma did result in enhanced CAT expression, demonstrating reversal of A431 cell context suppressi on of the ICAM-1-based reporter gene construct. These data implicate t he existence of both tissue- and cytokine-specific responsive elements in the 5' flanking region of the ICAM- 1 gene and demonstrate that re gulatory effects directed by such elements are dependent upon their ce llular context. Moreover, they provide the basis for identification of specific cis-acting genetic elements, the trans-acting factors with w hich they interact, and the molecular mechanisms by which they regulat e transcription of the ICAM-1 gene.