title: Dipeptidyl peptidase IV (CD26) activity in the hematopoietic system: differences between the membrane-anchored and the released enzyme activity.
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.
authors.affiliation: Divisão de Farmacologia, Coordenação de Pesquisa, Instituto Nacional do Câncer, Rio de Janeiro, RJ, Brasil.
authors.forename: D A
authors.initials: DA
authors.lastname: Pereira
authors.forename: L
authors.initials: L
authors.lastname: Gomes
authors.forename: M C
authors.initials: MC
authors.lastname: El-Cheikh
authors.forename: R
authors.initials: R
authors.lastname: Borojevic
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells / Q000201:enzymology*; D002460:Cell Line; D018819:Dipeptidyl Peptidase 4 / Q000235:genetics / Q000502:physiology*; D015870:Gene Expression; D006413:Hematopoietic System / Q000201:enzymology; D015151:Immunoblotting; D008099:Liver / Q000166:cytology / Q000201:enzymology; D021962:Membrane Microdomains / Q000201:enzymology*; D051379:Mice; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017154:Stromal Cells / Q000201:enzymology*
chemical_list: D012333:RNA, Messenger; D018819:Dipeptidyl Peptidase 4