Abstract 4478: The tumor suppressive function of HPP1 is mediated by its EGF-like domain

Abstract

Abstract Introduction: HPP1 is a putative tumor suppressor gene that has had significant interest as a potential serum- and stool-based biomarker in colorectal cancer. It is an Epidermal Growth Factor (EGF)-like ligand that we have previously demonstrated to mediate its effects via an erbB4-JAK-STAT signaling cascade. HPP1 is a secreted transmembrane protein comprised of two follistatin modules, a cytosolic tail with a potential G - protein-activating motif and an EGF-like domain which differs from EGF by replacement of arginine (R) by a histidine (H) residue at the critical 299 position. The exact component of HPP1 responsible for its biologic function has yet to be elucidated. We sought to examine the specific role of the EGF-like domain and the contribution of the H299R alteration. Methods: Synthetic wild-type (WT; H299) and mutant (R299) peptides were prepared at our crystallographic core facility. The change in amino acid did not alter the predicted 3D structure of the peptide. A total of 50ng/ml of each peptide per well (6-well plate) were used to treat the HPP1 non-expressing HCT116 colon cancer cell line. Cells were starved for 24 hours with a peptide exposure time of 7 minutes. Using immunoblot analyses, we examined alterations in the expression and activation status of erbB4, and STAT family proteins. Results: Delivery of the WT peptide into the HCT116 cell line resulted in increased activation/phosphorylation of erbB4, STAT1 and STAT2 with a concomitant downregulation of STAT3 activation as compared to controls. These findings are identical to the signaling profile that we have previously described for full length HPP1 and required for its tumor suppressive activity. The mutant peptide did not result in any change in the phosphorylation status of erbB4, STAT1 or STAT2 but was associated with an increase in STAT3 activation as compared to controls. Conclusion: The EGF-like domain of HPP1 is the key moiety responsible for triggering its tumor suppressive erbB -STAT signaling cascade. Furthermore, the histidine residue at position 299 is critical and differentiates it from the oncogenic function of EGF. Our findings may have implications for the further understanding of EGF-related signaling in cancer progression. Citation Format: Abul Elahi, Abidemi Ajidahun, Leah Hendrick, S. Mazher Husain, Irina Getun, Andreas Becker, Evan S. Glazer, David Shibata. The tumor suppressive function of HPP1 is mediated by its EGF-like domain [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4478.