Dipeptidyl peptidase 8 and 9
Originally detected as expressed sequence tags of the human genome, dipeptidyl peptidase 8 and 9 gained considerable interest during the development of antidiabetic drugs targeting dipeptidyl peptidase 4. Since then considerable efforts have been made towards discovering the function of these peptidases and their potential as drug targets.
DPP9 and inflammation
The dipeptidyl peptidases are a family of proline-specific serine proteases capable of cleaving off a dipeptide from the amino-terminus. In contrast to its best known member, DPP4, the related enzymes DPP8 and DPP9 are poorly studied and their biological function remains largely unknown.
The lack of selective DPP8 or DPP9 inhibitors complicates the study of their individual functions (1). Our lab was the first to purify DPP9 from a natural source (2, 3) and to show DPP9 protein expression and DPP8/9 activity in male reproductive tissues (4), human leukocytes (5), and endothelial cells of conduct vessels and capillaries (6).
In the past years, there has been increasing evidence pointing towards involvement in inflammation. At present, our efforts are aimed at elaborating on this, with emphasis on DPP9’s role in monocytes, macrophages and dendritic cells. We mainly want to do this by tackling two key questions.
Where exactly do we find DPP9?
It is important to know where DPP9 resides within the cell and whether it moves upon cellular activation. We use immunofluorescent staining and subcellular fractionations in combination with Western blot and enzyme activity assays. Immunofluorescent staining of DPP9 has already been optimized in a neuroblastoma cell line, enabling us to apply this technique in isolated primary leukocytes, along with a number of compartment-specific markers. These data are complemented by performing subcellular fractionations of cells and detecting DPP9 protein by Western blot and DPP8/9 activity by using an enzyme activity assay.
Can we change cellular functions by changing the expression and/or enzyme activity of DPP9?
On the one hand, we have DPP8/9 inhibitors available that can penetrate the cell, interfering with their role at the activity level. On the other hand, we have optimized conditions for the silencing of DPP9 with siRNAs in primary cells, allowing us to study DPP9’s individual role at the protein level.
1. Van Goethem, S., Matheeussen, V., Joossens, J., Lambeir, A.-M., Chen, X., De Meester, I., Haemers, A., Augustyns, K., and Van Der Veken, P. (2011) Journal of Medicinal Chemistry 54, 5737–5746
2. Dubois, V., Lambeir, A.-M., Van der Veken, P., Augustyns, K., Creemers, J., Chen, X., Scharpé, S., and De Meester, I. (2008) Frontiers in Bioscience 13, 3558–3568
3. Dubois, V., Lambeir, A.-M., Vandamme, S., Matheeussen, V., Guisez, Y., Scharpé, S., and De Meester, I. (2010) Biochimica et biophysica acta 1804, 781–8
4. Dubois, V., Van Ginneken, C., De Cock, H., Lambeir, A.-M., Van der Veken, P., Augustyns, K., Chen, X., Scharpé, S., and De Meester, I. (2009) The journal of histochemistry and cytochemistry 57, 531–41
5. Maes, M.-B., Dubois, V., Brandt, I., Lambeir, A.-M., Van der Veken, P., Augustyns, K., Cheng, J. D., Chen, X., Scharpé, S., and De Meester, I. (2007) Journal of leukocyte biology 81, 1252–7
6. Matheeussen, V., Baerts, L., De Meyer, G., De Keulenaer, G., Van der Veken, P., Augustyns, K., Dubois, V., Scharpé, S., and De Meester, I. (2011) Biological chemistry 392, 189–98