Dipeptidyl peptidase IV (CD 26) gene expression in enterocyte-like colon cancer cell lines HT-29 and Caco-2. Cloning of the complete human coding sequence and changes of dipeptidyl peptidase IV mRNA levels during cell differentiation.
Résumé
A cDNA (DPCR1) specific for human intestinal dipeptidyl peptidase IV (DPP IV) has been isolated. This 1.7-kilobase cDNA, together with a previously published partial sequence, covers the entire open reading frame of human DPP IV plus 67 base pairs of the 3'-untranslated end. Human DPP IV is a 766-amino acid polypeptide with a high degree of homology with the rat liver protein. The characterization of this molecular probe allowed us to definitively confirm the identity of DPP IV with CD 26, a mouse thymocyte activation antigen, a conclusion strengthened by the fact that we observed identical patterns on Southern blot of human genomic DNA hybridized either with human DPP IV or mouse CD 26 cDNA probe. Using this new tool, we have investigated the expression of DPP IV during the onset of enterocytic differentiation of two cultured human colon cancer cell lines, HT-29 and Caco-2. Whatever the cell line and the culture conditions, DPP IV expression strictly correlates with the presence of a differentiated phenotype, as shown by enzyme activity and the steady state amount of the protein measured by indirect immunofluorescence and Western blot. Accordingly, DPP IV biosynthesis exclusively increases in cells that display an enterocytic differentiation. Neither the glycosylation nor the stability of the protein appear to be dependent on the state of enterocytic differentiation. The DPP IV mRNA level remains very low in undifferentiated cell populations and specifically increases in cells that undergo an enterocytic differentiation. These results strongly suggest that DPP IV gene expression is controlled at the transcriptional or posttranscriptional level during intestinal differentiation.