Abstract 5289: Proteomic profile of breast carcinomas with unbalanced levels of progesterone receptor isoforms

Abstract Preclinical studies indicate that progesterone receptors (PR) play a relevant role in breast carcinogenesis. Even more, a misbalanced expression of PR isoforms A (PRA) and B (PRB) differentially affect breast cancer progression and only tumors with higher levels of PRA than PRB (PRA-H) respond to an antiprogestin treatment. There are controversial results regarding the prognosis of PRA-H luminal tumors compared with those with the opposite ratio (PRB-H tumors) highlighting the necessity to further understand the role of PR isoforms in tumor progression and to develop novel methods to discriminate these tumors without performing western blot studies. Along this line we have previously studied the transcriptome of PRA-H or PRB-H breast cancer samples, thus our aim is to expand these results and compare the proteome profile of PRA-H and PRB-H samples obtained from postmenopausal breast cancer patients. Nuclear (Nuc) and cytosolic (Cyt) protein fractions were obtained from 18 breast cancer samples classified as PRA-H or PRB-H and they were studied by LC-MS/MS (UltiMate 3000 LC system - Q Exactive HF-X mass spectrometer - Thermo). We observed 289 differentially deregulated proteins in Cyt (164 down and 125 up) and 301 in Nuc extracts (131 down and 170 up; logFC > 1, pval < 0.05). Gene set enrichment analysis of the Nuc fractions showed biological processes related to Cell junction organization (pval = 8,87e-05), Collagen formation (pval = 0,0005), and Cell-Cell communication processes (pval = 0,0035) in PRB-H tumors; while in PRA-H tumors, pathways related to Innate Immune System (pval = 8,8e-05), Class I MHC mediated antigen processing & presentation (pval = 8e-05) and Stabilization of p53 (pval = 0,0051) processes were enriched. Similar trends were observed in Cyt fractions. Individual candidates that were overrepresented in both fractions in PRB-H tumors are BAG3 and GH3, related to cell proliferation, and VWF, related to the activation of the Akt pathway. Overrepresented proteins in both fractions of PRA-H tumors are BST2, IFT27 related to invasion, and MIF associated with poor prognosis. As we were interested in looking for differential expressed proteins that could be tested in plasma samples to discriminate both tumor types, using the Vertebrate Secretome Database we focused on those that might be secreted. Noteworthy is CBP1 which was overrepresented in the PRB-H tumors and this was in agreement with the RNA-Seq data and with results obtained using preclinical models, repurposing this protein as one candidate of concern in the search for biomarkers. Other secretory proteins of interest are SFRP2 and SERPIND1, both highly expressed in PRA-H Cyt fractions. In conclusion, this study underscores the biological differences between PRA-H and PRB-H breast carcinomas and provides candidates that deserve to be tested as surrogate markers in plasma to discriminate patients that may benefit from an antiprogestin treatment. Citation Format: Andres M. Elia, Jana Sanchez, Rui Vitorino, Leo Saldain, Paula Martinez Vazquez, Javier Burruchaga, Eunice Spengler, Javier Muñoz, Paola Rojas, Luisa Helguero, Claudia Lanari. Proteomic profile of breast carcinomas with unbalanced levels of progesterone receptor isoforms. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5289.