Impaired Expression of Integrin -4 Subunit in Cultured Mast Cells Derived From Mutant Mice of mi/mi Genotype

The mi locus encodes a member of the basic-helix-loop-helix-leucine zipper protein family of transcription factors (hereafter called MITF). We have reported that expression of several genes was impaired in cultured mast cells (CMCs) ofmi/mi mice due to a defective transactivation ability of mutant MITF (mi-MITF). Because attachment of mi/mi CMCs to fibroblasts is impaired, we examined the expression of integrin genes in mi/mi CMCs in the present study. Among the integrin genes examined, the expression of integrin 4 subunit was barely detectable in mi/mi CMCs, and the 4 protein was not detected by flow cytometry either. The specific adhesion to vascular cell adhesion molecule-1 (VCAM-1), the ligand for 4 subunit, was observed in +/+ CMCs but not in mi/mi CMCs, indicating that the expression of integrin 4 subunit at a functional level did not occur in mi/mi CMCs. In the promoter region of the 4 subunit gene, there was a CACTTG motif to which normal MITF (+- MITF) bound. The coexpression of +-MITF but not of mi-MITF transactivated the promoter of the 4 subunit gene. The deletion or mutation of the CACTTG motif abolished the transactivation by +-MITF, suggesting that +-MITF directly transactivated the gene encoding 4 subunit of integrin. © 1998 by The American Society of Hematology.