Abstract
Dipeptidyl peptidase IV (DPP-IV; CD26) (EC 3.4.14.5) is a membrane-anchored ectoenzyme with N-terminal exopeptidase activity that preferentially cleaves X-Pro-dipeptides. It can also be spontaneously released to act in the extracellular environment or associated with the extracellular matrix. Many hematopoietic cytokines and chemokines contain DPP-IV-susceptible N-terminal sequences. We monitored DPP-IV expression and activity in murine bone marrow and liver stroma cells which sustain hematopoiesis, myeloid precursors, skin fibroblasts, and myoblasts. RT-PCR analysis showed that all these cells produced mRNA for DPP-IV. Partially purified protein reacted with a commercial antibody to CD26. The K M values for Gly-Pro-p-nitroanilide ranged from 0.43 to 0.98 mM for the membrane-associated enzyme of connective tissue stromas, and from 6.76 to 8.86 mM for the enzyme released from the membrane, corresponding to a ten-fold difference, but only a two-fold difference in K M was found in myoblasts. K M of the released soluble enzyme decreased in the presence of glycosaminoglycans, nonsulfated polysaccharide polymers (0.8-10 micro g/ml) or simple sugars (320-350 micro g/ml). Purified membrane lipid rafts contained nearly 3/4 of the total cell enzyme activity, whose K M was three-fold decreased as compared to the total cell membrane pool, indicating that, in the hematopoietic environment, DPP-IV activity is essentially located in the lipid rafts. This is compatible with membrane-associated events and direct cell-cell interactions, whilst the long-range activity depending upon soluble enzyme is less probable in view of the low affinity of this form.
Highlights
Dipeptidyl peptidase IV (DPP-IV) (EC 3.4.14.5) is a member of the serine peptidase family, which cleaves N-terminal X-Prodipeptides from peptides and proteins
In view of the fact that CD26 can both potentially act as a membrane ectoenzyme and be released in a soluble form into the intercellular biological fluids, we have addressed the question of the relative importance and activity of the two forms of DPP-IV in the hematopoietic environment
The expression of the DPP-IV gene was studied by RT-PCR in connective stroma cells that sustain hematopoiesis or myelopoiesis, i.e., S17, FF18 and GR, those that do not sustain hematopoiesis, i.e., SF, and an unrelated cell line C2C12, as well as in the established myeloid precursor cell lineage FDC-P1
Summary
Dipeptidyl peptidase IV (DPP-IV) (EC 3.4.14.5) is a member of the serine peptidase family, which cleaves N-terminal X-Prodipeptides from peptides and proteins. It is expressed in several tissues, with the highest levels being in kidney and small intestine, and lower ones in lungs, liver and spleen [1]. Binding to adenosine deaminase does not require the DPP-IV enzymatic activity and is involved in immunoregulatory mechanisms through the control of adenosine-mediated inhibition of lymphocyte interleukin-2 (IL-2) production and proliferation [8]
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