2bgr

Structural highlights

Function

[DPP4_HUMAN] Cell surface glycoprotein receptor involved in the costimulatory signal essential for T-cell receptor (TCR)-mediated T-cell activation. Acts as a positive regulator of T-cell coactivation, by binding at least ADA, CAV1, IGF2R, and PTPRC. Its binding to CAV1 and CARD11 induces T-cell proliferation and NF-kappa-B activation in a T-cell receptor/CD3-dependent manner. Its interaction with ADA also regulates lymphocyte-epithelial cell adhesion. In association with FAP is involved in the pericellular proteolysis of the extracellular matrix (ECM), the migration and invasion of endothelial cells into the ECM. May be involved in the promotion of lymphatic endothelial cells adhesion, migration and tube formation. When overexpressed, enhanced cell proliferation, a process inhibited by GPC3. Acts also as a serine exopeptidase with a dipeptidyl peptidase activity that regulates various physiological processes by cleaving peptides in the circulation, including many chemokines, mitogenic growth factors, neuropeptides and peptide hormones. Removes N-terminal dipeptides sequentially from polypeptides having unsubstituted N-termini provided that the penultimate residue is proline.^{[1] [2] [3] [4] [5] [6] [7] [8] [9]} [TAT_HV1Z2] Nuclear transcriptional activator of viral gene expression, that is essential for viral transcription from the LTR promoter and replication. Acts as a sequence-specific molecular adapter, directing components of the cellular transcription machinery to the viral RNA to promote processive transcription elongation by the RNA polymerase II (RNA pol II) complex, thereby increasing the level of full-length transcripts. In the absence of Tat, the RNA Pol II generates short or non-processive transcripts that terminate at approximately 60 bp from the initiation site. Tat associates with the CCNT1/cyclin-T1 component of the P-TEFb complex (CDK9 and CCNT1), which promotes RNA chain elongation. This binding increases Tat's affinity for a hairpin structure at the 5'-end of all nascent viral mRNAs referred to as the transactivation responsive RNA element (TAR RNA) and allows Tat/P-TEFb complex to bind cooperatively to TAR RNA. The CDK9 component of P-TEFb and other Tat-activated kinases hyperphosphorylate the C-terminus of RNA Pol II that becomes stabilized and much more processive. Other factors such as HTATSF1/Tat-SF1, SUPT5H/SPT5, and HTATIP2 are also important for Tat's function. Besides its effect on RNA Pol II processivity, Tat induces chromatin remodeling of proviral genes by recruiting the histone acetyltransferases (HATs) CREBBP, EP300 and PCAF to the chromatin. This also contributes to the increase in proviral transcription rate, especially when the provirus integrates in transcriptionally silent region of the host genome. To ensure maximal activation of the LTR, Tat mediates nuclear translocation of NF-kappa-B. In this purpose, it activates EIF2AK2/PKR which, in turns, may phosphorylate and target to degradation the inhibitor IkappaB-alpha which normally retains NF-kappa-B in the cytoplasm of unstimulated cells. Through its interaction with TBP, Tat may be involved in transcription initiation as well. Interacts with the cellular capping enzyme RNGTT to mediate co-transcriptional capping of viral mRNAs. Tat protein exerts as well a positive feedback on the translation of its cognate mRNA. Tat can reactivate a latently infected cell by penetrating in it and transactivating its LTR promoter. In the cytoplasm, Tat is thought to act as a translational activator of HIV-1 mRNAs (By similarity). Extracellular circulating Tat can be endocytosed by surrounding uninfected cells via the binding to several surface receptors such as CD26, CXCR4, heparan sulfate proteoglycans (HSPG) or LDLR. Neurons are rarely infected, but they internalize Tat via their LDLR. Endosomal low pH allows Tat to cross the endosome membrane to enter the cytosol and eventually further translocate into the nucleus, thereby inducing severe cell dysfunctions ranging from cell activation to cell death. Through its interaction with nuclear HATs, Tat is potentially able to control the acetylation-dependent cellular gene expression. Tat seems to inhibit the HAT activity of KAT5/Tip60 and TAF1, and consequently modify the expression of specific cellular genes. Modulates the expression of many cellular genes involved in cell survival, proliferation or in coding for cytokines (such as IL10) or cytokine receptors. May be involved in the derepression of host interleukin IL2 expression. Mediates the activation of cyclin-dependent kinases and dysregulation of microtubule network. Tat plays a role in T-cell and neurons apoptosis. Tat induced neurotoxicity and apoptosis probably contribute to neuroAIDS. Host extracellular matrix metalloproteinase MMP1 cleaves Tat and decreases Tat's mediated neurotoxicity. Circulating Tat also acts as a chemokine-like and/or growth factor-like molecule that binds to specific receptors on the surface of the cells, affecting many cellular pathways. In the vascular system, Tat binds to ITGAV/ITGB3 and ITGA5/ITGB1 integrins dimers at the surface of endothelial cells and competes with bFGF for heparin-binding sites, leading to an excess of soluble bFGF. Binds to KDR/VEGFR-2. All these Tat-mediated effects enhance angiogenesis in Kaposi's sarcoma lesions (By similarity).

Evolutionary Conservation

Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf.

See Also

• Dipeptidyl peptidase
• Tat protein

References

1. ↑ Durinx C, Lambeir AM, Bosmans E, Falmagne JB, Berghmans R, Haemers A, Scharpe S, De Meester I. Molecular characterization of dipeptidyl peptidase activity in serum: soluble CD26/dipeptidyl peptidase IV is responsible for the release of X-Pro dipeptides. Eur J Biochem. 2000 Sep;267(17):5608-13. PMID:10951221
2. ↑ Davoodi J, Kelly J, Gendron NH, MacKenzie AE. The Simpson-Golabi-Behmel syndrome causative glypican-3, binds to and inhibits the dipeptidyl peptidase activity of CD26. Proteomics. 2007 Jun;7(13):2300-10. PMID:17549790 doi:10.1002/pmic.200600654
3. ↑ Abbott CA, McCaughan GW, Gorrell MD. Two highly conserved glutamic acid residues in the predicted beta propeller domain of dipeptidyl peptidase IV are required for its enzyme activity. FEBS Lett. 1999 Sep 24;458(3):278-84. PMID:10570924
4. ↑ Ikushima H, Munakata Y, Ishii T, Iwata S, Terashima M, Tanaka H, Schlossman SF, Morimoto C. Internalization of CD26 by mannose 6-phosphate/insulin-like growth factor II receptor contributes to T cell activation. Proc Natl Acad Sci U S A. 2000 Jul 18;97(15):8439-44. PMID:10900005
5. ↑ Gines S, Marino M, Mallol J, Canela EI, Morimoto C, Callebaut C, Hovanessian A, Casado V, Lluis C, Franco R. Regulation of epithelial and lymphocyte cell adhesion by adenosine deaminase-CD26 interaction. Biochem J. 2002 Jan 15;361(Pt 2):203-9. PMID:11772392
6. ↑ Aertgeerts K, Ye S, Shi L, Prasad SG, Witmer D, Chi E, Sang BC, Wijnands RA, Webb DR, Swanson RV. N-linked glycosylation of dipeptidyl peptidase IV (CD26): effects on enzyme activity, homodimer formation, and adenosine deaminase binding. Protein Sci. 2004 Jan;13(1):145-54. PMID:14691230 doi:10.1110/ps.03352504
7. ↑ Ghersi G, Zhao Q, Salamone M, Yeh Y, Zucker S, Chen WT. The protease complex consisting of dipeptidyl peptidase IV and seprase plays a role in the migration and invasion of human endothelial cells in collagenous matrices. Cancer Res. 2006 May 1;66(9):4652-61. PMID:16651416 doi:10.1158/0008-5472.CAN-05-1245
8. ↑ Ohnuma K, Uchiyama M, Yamochi T, Nishibashi K, Hosono O, Takahashi N, Kina S, Tanaka H, Lin X, Dang NH, Morimoto C. Caveolin-1 triggers T-cell activation via CD26 in association with CARMA1. J Biol Chem. 2007 Mar 30;282(13):10117-31. Epub 2007 Feb 6. PMID:17287217 doi:10.1074/jbc.M609157200
9. ↑ Shin JW, Jurisic G, Detmar M. Lymphatic-specific expression of dipeptidyl peptidase IV and its dual role in lymphatic endothelial function. Exp Cell Res. 2008 Oct 1;314(16):3048-56. doi: 10.1016/j.yexcr.2008.07.024. Epub , 2008 Aug 3. PMID:18708048 doi:10.1016/j.yexcr.2008.07.024
10. ↑ Weihofen WA, Liu J, Reutter W, Saenger W, Fan H. Crystal structures of HIV-1 Tat-derived nonapeptides Tat-(1-9) and Trp2-Tat-(1-9) bound to the active site of dipeptidyl-peptidase IV (CD26). J Biol Chem. 2005 Apr 15;280(15):14911-7. Epub 2005 Jan 28. PMID:15695814 doi:10.1074/jbc.M413400200