Fibroblast activation protein, alpha explained

Fibroblast activation protein alpha (FAP-alpha) also known as prolyl endopeptidase FAP is an enzyme that in humans is encoded by the FAP gene.

Prolyl endopeptidase FAP is a 170 kDa membrane-bound gelatinase. It was independently identified as a surface glycoprotein recognized by the F19 monoclonal antibody in activated fibroblasts^[1] and a Surface Expressed Protease (seprase) in invasive melanoma cells.^{[2] [3]}

Structure and enzymatic activity

FAP is a 760 amino acid long type II transmembrane glycoprotein. It contains a very short cytoplasmic N terminal part (6 amino acids), a transmembrane region (amino acids 7–26), and a large extracellular part with an alpha/beta-hydrolase domain and an eight-bladed beta-propeller domain.^{[4] [5]}

A soluble form of FAP, which lacks the intracellular and transmembrane part, is present in blood plasma.^[6] FAP is a non-classical serine protease, which belongs to the S9B prolyl oligopeptidase subfamily. Other members of the S9B subfamily are DPPIV, DPP8 and DPP9.^[7] FAP is most closely related to DPPIV (approximately 50% of their amino acids are identical). The active site of FAP is localized in the extracellular part of the protein and contains a catalytic triad composed of Ser⁶²⁴ Asp⁷⁰² His⁷³⁴ in humans and mice. FAP is catalytically active as a 170kD homodimer and has a dipeptidase and an endopeptidase activity.

Several bioactive peptides and structural proteins were reported to be cleaved by FAP, such as neuropeptide Y (NPY), Peptide YY, Substance P (SP), and B-type natriuretic peptide (BNP),^[8] human fibroblast growth factor 21 (FGF-21), human alpha2 antiplasmin and denatured collagen I and III. NPY, FGF-21 and alpha2 antiplasmin are considered to be physiological FAP substrates.^{[9] [10]}

Expression and possible function

FAP expression under physiological conditions is very low in the majority of adult tissues. FAP is nevertheless expressed during embryonic development,^[11] and in adults in pancreatic alpha cells^[12] in multipotent bone marrow stromal cells (BM-MSC)^[13] and uterine stroma.^[14]

FAP expression is high in reactive stromal fibroblasts of epithelial cancers, granulation tissue of healing wounds, and malignant cells of bone and soft tissue sarcomas. FAP is thought to be involved in the control of fibroblast growth or epithelial-mesenchymal interactions during development, tissue repair, and epithelial carcinogenesis.^[15]

Clinical significance

FAP expression is seen on activated stromal fibroblasts of more than 90% of all human carcinomas. Stromal fibroblasts play an important role in the development, growth and metastasis of carcinomas. Several approaches of FAP targeting mainly in cancer treatment are currently being tested including the use of low molecular weight inhibitors, prodrugs activated by FAP, various anti-FAP antibodies and their conjugates, FAP-CAR T cells, and FAP vaccines.

By cleaving FGF-21, FAP is also thought to play a possible role in energy metabolism.^[16]

Talabostat is an inhibitor of FAP and related enzymes, for which clinical trials have been done, but further research is suspended.

Sibrotuzumab is a monoclonal antibody against FAP.

References

Further reading

• Rettig WJ, Su SL, Fortunato SR, Scanlan MJ, Raj BK, Garin-Chesa P, Healey JH, Old LJ . Fibroblast activation protein: purification, epitope mapping and induction by growth factors . International Journal of Cancer . 58 . 3 . 385–92 . August 1994 . 7519584 . 10.1002/ijc.2910580314 . 26488735 .
• Mathew S, Scanlan MJ, Mohan Raj BK, Murty VV, Garin-Chesa P, Old LJ, Rettig WJ, Chaganti RS . The gene for fibroblast activation protein alpha (FAP), a putative cell surface-bound serine protease expressed in cancer stroma and wound healing, maps to chromosome band 2q23 . Genomics . 25 . 1 . 335–7 . January 1995 . 7774951 . 10.1016/0888-7543(95)80157-H .
• Scanlan MJ, Raj BK, Calvo B, Garin-Chesa P, Sanz-Moncasi MP, Healey JH, Old LJ, Rettig WJ . Molecular cloning of fibroblast activation protein alpha, a member of the serine protease family selectively expressed in stromal fibroblasts of epithelial cancers . Proceedings of the National Academy of Sciences of the United States of America . 91 . 12 . 5657–61 . June 1994 . 7911242 . 44055 . 10.1073/pnas.91.12.5657 . 1994PNAS...91.5657S . free .
• Piñeiro-Sánchez ML, Goldstein LA, Dodt J, Howard L, Yeh Y, Tran H, Argraves WS, Chen WT . Identification of the 170-kDa melanoma membrane-bound gelatinase (seprase) as a serine integral membrane protease . The Journal of Biological Chemistry . 272 . 12 . 7595–601 . March 1997 . 9065413 . 10.1074/jbc.272.12.7595 . 27391619 . free .
• Goldstein LA, Ghersi G, Piñeiro-Sánchez ML, Salamone M, Yeh Y, Flessate D, Chen WT . Molecular cloning of seprase: a serine integral membrane protease from human melanoma . Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease . 1361 . 1 . 11–9 . July 1997 . 9247085 . 10.1016/s0925-4439(97)00032-x . free .
• Goldstein LA, Chen WT . Identification of an alternatively spliced seprase mRNA that encodes a novel intracellular isoform . The Journal of Biological Chemistry . 275 . 4 . 2554–9 . January 2000 . 10644713 . 10.1074/jbc.275.4.2554 . 45385101 . free .
• Ghersi G, Dong H, Goldstein LA, Yeh Y, Hakkinen L, Larjava HS, Chen WT . Regulation of fibroblast migration on collagenous matrix by a cell surface peptidase complex . The Journal of Biological Chemistry . 277 . 32 . 29231–41 . August 2002 . 12023964 . 10.1074/jbc.M202770200 . 23470018 . free .
• Levy MT, McCaughan GW, Marinos G, Gorrell MD . Intrahepatic expression of the hepatic stellate cell marker fibroblast activation protein correlates with the degree of fibrosis in hepatitis C virus infection . Liver . 22 . 2 . 93–101 . April 2002 . 12028401 . 10.1034/j.1600-0676.2002.01503.x .
• Artym VV, Kindzelskii AL, Chen WT, Petty HR . Molecular proximity of seprase and the urokinase-type plasminogen activator receptor on malignant melanoma cell membranes: dependence on beta1 integrins and the cytoskeleton . Carcinogenesis . 23 . 10 . 1593–601 . October 2002 . 12376466 . 10.1093/carcin/23.10.1593 . free .
• Book: Gorrell MD, Wang XM, Levy MT, Kable E, Marinos G, Cox G, McCaughan GW . Intrahepatic Expression of Collagen and Fibroblast Activation Protein (FAP) in Hepatitis C Virus Infection . Dipeptidyl Aminopeptidases in Health and Disease . 524 . 235–43 . 12675244 . 10.1007/0-306-47920-6_28 . 978-0-306-47717-1 . Advances in Experimental Medicine and Biology . 2004 . 10.1.1.535.3436 .
• Jin X, Iwasa S, Okada K, Mitsumata M, Ooi A . Expression patterns of seprase, a membrane serine protease, in cervical carcinoma and cervical intraepithelial neoplasm . Anticancer Research . 23 . 4 . 3195–8 . 2003 . 12926053 .
• Iwasa S, Jin X, Okada K, Mitsumata M, Ooi A . Increased expression of seprase, a membrane-type serine protease, is associated with lymph node metastasis in human colorectal cancer . Cancer Letters . 199 . 1 . 91–8 . September 2003 . 12963128 . 10.1016/S0304-3835(03)00315-X .
• Goodman JD, Rozypal TL, Kelly T . Seprase, a membrane-bound protease, alleviates the serum growth requirement of human breast cancer cells . Clinical & Experimental Metastasis . 20 . 5 . 459–70 . 2003 . 14524536 . 10.1023/A:1025493605850 . 1511984 .
• Okada K, Chen WT, Iwasa S, Jin X, Yamane T, Ooi A, Mitsumata M . Seprase, a membrane-type serine protease, has different expression patterns in intestinal- and diffuse-type gastric cancer . Oncology . 65 . 4 . 363–70 . 2004 . 14707457 . 10.1159/000074650 . 41823279 .
• Cheng JD, Valianou M, Canutescu AA, Jaffe EK, Lee HO, Wang H, Lai JH, Bachovchin WW, Weiner LM . Abrogation of fibroblast activation protein enzymatic activity attenuates tumor growth . Molecular Cancer Therapeutics . 4 . 3 . 351–60 . March 2005 . 15767544 . 10.1158/1535-7163.MCT-04-0269 . free .
• Aertgeerts K, Levin I, Shi L, Snell GP, Jennings A, Prasad GS, Zhang Y, Kraus ML, Salakian S, Sridhar V, Wijnands R, Tennant MG . Structural and kinetic analysis of the substrate specificity of human fibroblast activation protein alpha . The Journal of Biological Chemistry . 280 . 20 . 19441–4 . May 2005 . 15809306 . 10.1074/jbc.C500092200 . 25810686 . free .
• Fassnacht M, Lee J, Milazzo C, Boczkowski D, Su Z, Nair S, Gilboa E . Induction of CD4(+) and CD8(+) T-cell responses to the human stromal antigen, fibroblast activation protein: implication for cancer immunotherapy . Clinical Cancer Research . 11 . 15 . 5566–71 . August 2005 . 16061874 . 10.1158/1078-0432.CCR-05-0699 . 13455377 . free .

Notes and References

1. Garin-Chesa P, Old LJ, Rettig WJ . Cell surface glycoprotein of reactive stromal fibroblasts as a potential antibody target in human epithelial cancers . Proceedings of the National Academy of Sciences of the United States of America . 87 . 18 . 7235–9 . September 1990 . 2402505 . 54718 . 10.1073/pnas.87.18.7235 . 1990PNAS...87.7235G . free .
2. Monsky WL, Lin CY, Aoyama A, Kelly T, Akiyama SK, Mueller SC, Chen WT . A potential marker protease of invasiveness, seprase, is localized on invadopodia of human malignant melanoma cells . Cancer Research . 54 . 21 . 5702–10 . November 1994 . 7923219 .
3. Aoyama A, Chen WT . A 170-kDa membrane-bound protease is associated with the expression of invasiveness by human malignant melanoma cells . Proceedings of the National Academy of Sciences of the United States of America . 87 . 21 . 8296–300 . November 1990 . 2172980 . 54942 . 10.1073/pnas.87.21.8296 . 1990PNAS...87.8296A . free .

4. Aertgeerts K, Levin I, Shi L, Snell GP, Jennings A, Prasad GS, Zhang Y, Kraus ML, Salakian S, Sridhar V, Wijnands R, Tennant MG . Structural and kinetic analysis of the substrate specificity of human fibroblast activation protein alpha . The Journal of Biological Chemistry . 280 . 20 . 19441–4 . May 2005 . 15809306 . 10.1074/jbc.C500092200 . 25810686 . free .

5. Goldstein LA, Ghersi G, Piñeiro-Sánchez ML, Salamone M, Yeh Y, Flessate D, Chen WT . Molecular cloning of seprase: a serine integral membrane protease from human melanoma . Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease . 1361 . 1 . 11–9 . July 1997 . 9247085 . 10.1016/S0925-4439(97)00032-X . free .
6. Lee KN, Jackson KW, Christiansen VJ, Lee CS, Chun JG, McKee PA . 17654245 . Antiplasmin-cleaving enzyme is a soluble form of fibroblast activation protein . Blood . 107 . 4 . 1397–404 . February 2006 . 16223769 . 10.1182/blood-2005-08-3452 . free .
7. Web site: Merops: the peptidase database. 2009-10-05. 2006-11-14. https://web.archive.org/web/20061114180435/http://merops.sanger.ac.uk/. dead.
8. Keane FM, Nadvi NA, Yao TW, Gorrell MD . Neuropeptide Y, B-type natriuretic peptide, substance P and peptide YY are novel substrates of fibroblast activation protein-α . The FEBS Journal . 278 . 8 . 1316–32 . April 2011 . 21314817 . 10.1111/j.1742-4658.2011.08051.x . 33826473 . free .
9. Puré E, Blomberg R . Pro-tumorigenic roles of fibroblast activation protein in cancer: back to the basics . Oncogene . 37 . 32 . 4343–4357 . August 2018 . 29720723 . 6092565 . 10.1038/s41388-018-0275-3 .
10. Busek P, Mateu R, Zubal M, Kotackova L, Sedo A . Targeting fibroblast activation protein in cancer - Prospects and caveats . Frontiers in Bioscience . 23 . 1933–1968 . June 2018 . 10 . 29772538 . 10.2741/4682 .
11. Niedermeyer J, Garin-Chesa P, Kriz M, Hilberg F, Mueller E, Bamberger U, Rettig WJ, Schnapp A . Expression of the fibroblast activation protein during mouse embryo development . The International Journal of Developmental Biology . 45 . 2 . 445–7 . April 2001 . 11330865 .
12. Busek P, Hrabal P, Fric P, Sedo A . Co-expression of the homologous proteases fibroblast activation protein and dipeptidyl peptidase-IV in the adult human Langerhans islets . Histochemistry and Cell Biology . 143 . 5 . 497–504 . May 2015 . 25361590 . 10.1007/s00418-014-1292-0 . 788806 .
13. Bae S, Park CW, Son HK, Ju HK, Paik D, Jeon CJ, Koh GY, Kim J, Kim H . Fibroblast activation protein alpha identifies mesenchymal stromal cells from human bone marrow . British Journal of Haematology . 142 . 5 . 827–30 . September 2008 . 18510677 . 10.1111/j.1365-2141.2008.07241.x . 40643695 . free .
14. Dolznig H, Schweifer N, Puri C, Kraut N, Rettig WJ, Kerjaschki D, Garin-Chesa P . Characterization of cancer stroma markers: in silico analysis of an mRNA expression database for fibroblast activation protein and endosialin . Cancer Immunity . 5 . 10 . August 2005 . 16076089 .
15. Web site: Entrez Gene: fibroblast activation protein, alpha.
16. Sánchez-Garrido MA, Habegger KM, Clemmensen C, Holleman C, Müller TD, Perez-Tilve D, Li P, Agrawal AS, Finan B, Drucker DJ, Tschöp MH, DiMarchi RD, Kharitonenkov A . Fibroblast activation protein (FAP) as a novel metabolic target . Molecular Metabolism . 5 . 10 . 1015–1024 . October 2016 . 27689014 . 5034526 . 10.1016/j.molmet.2016.07.003 .