A rare variant in human fibroblast activation protein associated with ER stress, loss of enzymatic function and loss of cell surface localisation

Osborne B., Yao T., Wang X. M., Chen Y., KOTAN L. D., Nadvi N. A., ...More

BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS, vol.1844, no.7, pp.1248-1259, 2014 (SCI-Expanded) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 1844 Issue: 7
  • Publication Date: 2014
  • Doi Number: 10.1016/j.bbapap.2014.03.015
  • Journal Name: BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.1248-1259
  • Keywords: Dipeptidyl peptidase, Endoplasmic reticulum stress, Endoplasmic reticulum associated degradation, Fibroblast activation protein, Polymorphism, Unfolded protein response, DIPEPTIDYL PEPTIDASE-IV, ENDOPLASMIC-RETICULUM STRESS, REACTIVE STROMAL FIBROBLASTS, BETA PROPELLER DOMAIN, PROLYL OLIGOPEPTIDASE, ACTIVE-SITE, QUALITY-CONTROL, EXPRESSION, LIVER, DEGRADATION
  • Çukurova University Affiliated: Yes

Abstract

Fibroblast activation protein (FAP) is a focus of interest as a potential cancer therapy target. This membrane bound protease possesses the unique catalytic activity of hydrolysis of the post-proline bond two or more residues from the N-terminus of substrates. FAP is highly expressed in activated fibroblastic cells in tumours, arthritis and fibrosis. A rare, novel, human polymorphism, C1088T, encoding Ser363 to Leu, occurring in the sixth blade of the 3 propeller domain, was identified in a family. Both in primary human fibroblasts and in Ser363LeuFAP transfected cells, we showed that this single substitution ablates FAP dimerisation and causes loss of enzyme activity. Ser363LeuFAP was detectable only in endoplasmic reticulum (ER), in contrast to the distribution of wild-type FAP on the cell surface. The variant FAP showed decreased conformational antibody binding, consistent with an altered tertiary structure. Ser363LeuFAP expression was associated with upregulation of the ER chaperone BiP/GRP78, ER stress sensor ATF6, and the ER stress response target phospho-eIF2 alpha, all indicators of ER stress. Proteasomal inhibition resulted in accumulation of Ser363LeuFAP, indicating the involvement of ER associated degradation (ERAD). Neither CHOP expression nor apoptosis was elevated, so ERAD is probably important for protecting Ser363LeuFAP expressing cells. These data on the first loss of function human PAP gene variant indicates that although the protein is vulnerable to an amino acid substitution in the beta-propeller domain, inactive, unfolded FAP can be tolerated by cells. (C) 2014 Elsevier B.V. All rights reserved.