Functional proteomics is a powerful approach for studying breast cancer that focuses on analyzing protein expression, interactions, and functions. Key aspects include identifying biomarker panels for prognosis and treatment prediction, profiling protein expression in large cohorts of breast cancer specimens to link proteomic data with clinical outcomes and exploring the complexity of breast cancer proteomes to identify potential therapeutic targets and improve patient stratification [27–29]. Functional proteomics has significant potential to enhance breast cancer management by providing insights into disease mechanisms, identifying novel biomarkers, and guiding personalized treatment strategies.
NGS, coupled with matched treatment, has shown to enhance clinical outcomes [30].
NGS testing allows for molecular-guided treatment decisions, offering new targeted therapy options. With identification of actionable mutations, NGS helps detect mutations that can be targeted with specific therapies. Combining NGS with functional proteomics offers several benefits for breast cancer research and clinical applications such as comprehensive molecular profiling, enhanced heterogeneity analysis as both genomic and proteomic levels are deciphered.
In current study, we took advantage of 61 Taiwanese breast cancers who underwent functional proteomics coupled with either WES or targeted sequencing. A couple of pathogenic mutations were identified and were clinically relevant: namely BRCA1/2, PTEN and PIK3CA. Both BRCA1 and BRCA2 are well-known tumor suppressors while Poly (ADP-ribose) polymerase (PARP) inhibitors are FDA-approved for patients with germline BRCA1/2 mutant ovarian and breast cancers [31]. PTEN is a tumor suppressor that is one of the most frequently mutated genes in human cancer, and the pan-AKT kinase inhibitor capivasertib in combination with the selective estrogen receptor degrader (SERD) fulvestrant is FDA-approved for the treatment of patients with PTEN-mutant HR+/HER2- metastatic breast cancer [32]. PIK3CA, the catalytic subunit of PI3-kinase, is frequently mutated in a diverse range of cancers including breast, endometrial and cervical cancers, and the alpha-isoform selective PI(3)-kinase inhibitor alpelisib and the pan-AKT kinase inhibitor capivasertib, each in combination with fulvestrant, are FDA-approved for the treatment of patients with PIK3CA mutant ER+/HER2- metastatic breast cancer [32–33]. Other pathogenic mutations are currently not actionable for breast cancer treatment.
Five genes, including FANCA, HRAS, PIK3CA, MAP2K1 and JAK2, were shown to impact distant (trans) protein expressions, with most being negatively correlated. FANCA is a tumor suppressor and DNA repair protein with germline mutations of FANCA associated with the cancer predisposition syndrome Fanconi Anemia. HRAS, a GTPase, is commonly mutant in head and neck, thyroid, and bladder cancer. The Ras proto-oncogene family (HRAS, NRAS and KRAS) is the upstream of pro-proliferative and anti-apoptotic signal transduction pathways, including the mitogen activated protein kinase (MAPK) and PI3 kinase (PI3K) pathways [34]. MAP2K1 (MEK1), which is infrequently mutated in melanoma, colon and lung cancer, is involved in the RAS/MAPK signaling pathway, influencing various cellular processes such as growth, proliferation, and survival [35]. JAK2, a non-receptor tyrosine kinase, is commonly mutant in hematologic malignancies such as myeloproliferative neoplasm [36]. Except PIK3CA, none of these impacting genes were breast cancer actionable.
Twenty-two proteins were impacted by 5 altered genes, with most being negatively. GBAS (NIPSNAP2) a positive regulator of L-type calcium channels, belonging to the NipSnap family. SFXN3 is a mitochondrial protein that functions as a serine transporter, facilitating the transport of serine into the mitochondria, and is also involved in iron transport [37]. NEB is involved in maintaining the structural integrity of sarcomeres and the membrane system associated with the myofibrils. SAMM50 maintains the structure of mitochondrial cristae and the proper assembly of the mitochondrial respiratory chain complexes. TPM3 gene encodes the slow muscle alpha (α)-tropomyosin protein, which belongs to the tropomyosin family, a group of actin-binding proteins [38]. ANXA6 is associated with CD21 and regulates the release of Ca2+ from intracellular stores [39]. As a subunit of elongation factor-1 complex (EEF1), EEF1D is essential for protein synthesis, delivering aminoacyl tRNAs to ribosome, and short isoforms through alternative splicing may be pathogenic [40]. TWF1 gene encodes an actin monomer-binding protein, which is essential for cytoskeletal remodeling, myogenic differentiation and cancer progression [41]. CPPED1 belongs to the calcineurin-like phosphoesterase domain family and has protein phosphatase activity, specifically targeting serine and threonine residues. FLNC gene encodes Filamin-C, a protein that plays a key role in the structure and function of muscles. Protein phosphatase 1 catalytic subunit gamma (PP1-gamma), encoded by PPP1CC, opposes the action of kinases and phosphorylases and is involved in signal transduction. SSR3 gene encodes the gamma subunit of the signal sequence receptor (SSR), which is a protein complex involved in the recognition and targeting of proteins to the endoplasmic reticulum for further processing and secretion. Eukaryotic translation initiation factor 3 (eIF-3) complex is encoded by EIF3L, while this complex is essential for protein synthesis. COPE gene encodes a a subunit of the coatomer protein complex, which plays a vital role in intracellular protein transport, specifically in the retrograde transport of proteins from the Golgi apparatus back to the endoplasmic reticulum. Low-density lipoprotein receptor-related protein 1, encoded by LRP1 gene, is a large endocytic cell surface receptor involved in cell adhesion, signaling, trafficking and degradation of ligands. ITGA11 gene encodes integrin subunit alpha 11, a protein that forms part of the integrin, which is a cell adhesion molecule. RANGAP1 associates with the nuclear pore complex and acts as a GTPase activator for Ran, a small GTPase that plays a crucial role in nucleo-cytoplasmic transport converts GTP-bound Ran to GDP-bound Ran, which is essential for the directionality and fidelity of nuclear transport [42]. Phosphoribosyl pyrophosphate synthetase 1 (PRPP synthetase 1), encoded by PRPS1 gene, plays a crucial role in the production of phosphoribosyl pyrophosphate (PRPP), a molecule involved in the synthesis of purine and pyrimidine nucleotides, which are the building blocks of DNA and RNA. Prohibitin protein (encoded by PHB) plays a role in cellular senescence and tumor suppression in humans [43]. High Mobility Group Box 1 is a protein encoded by HMGB1 gene and is a non-histone chromosomal protein, functioning in DNA binding and chromatin architecture, inflammatory response, and autophagy. A diverse set of proteins were correlated with altered genes, and most of which were negatively correlated. Despite this, we could still categorize these proteins into cellular processes and signaling (SFXN3, SAMM50, EEF1D, TWF1, CPPED1, PPP1CC, SSR3, EIF3L, COPE, RANGAP1, PRPS1, PHB, HMGB1), muscle and structure proteins (NEB, TPM3, FLNC, ITGA11) and others (GBAS, ANXA6, LRP1, PRPS1L1, HMGB1P1).
It deserves notice that several studies evaluating the association between PHB expression and breast cancer [44–45]. In our study, altered FANCA was associated with a reduced PHB protein expression. TWF1 has also been linked to breast cancer progression, while our study indicated that FANCA alterations negatively impacted TWF1 expression [46]. SFXN3 and ANXA6 had also been reported to be over-expressed in breast cancer [37, 39]. To ascertain that our findings were not spurious, public domain GDC TCGA Breast Cancer (BRCA) database was consulted and elevated TWF1 mRNA expression did show a trend toward poor overall survival (Supplementary Fig. 1) while PIK3CA alterations did impact ANXA6 mRNA expression (Supplementary Fig. 2).
By combining NGS and functional proteomics, researchers and clinicians can gain a more holistic view of breast cancer, potentially improving diagnosis, prognosis, and treatment outcomes.
There were some limitations of the study. First, limited sample size might compromise the generalizability and external validation of the findings, and more samples in future studies are warranted. Second, NGS was performed with either WES or targeted sequencing, and the discrepancy in sequencing technologies and genomic regions inevitable introduced bias. Third, distinct molecular aberrations might exist across breast cancer subtypes, future studies should focus on subtype-specific proteogenomic interplays with more samples assayed.