Discovery and Pharmacological Evaluation of STEAP4 as a Novel Target for HER2 Overexpressing Breast Cancer

Abstract

Breast cancer (BC) is a highly heterogeneous disease encompassing multiple subtypes with different molecular and histopathological features, disease prognosis, and therapeutic responses. Among these, the Triple Negative BC form (TNBC) is an aggressive subtype with poor prognosis and therapeutic outcome. With respect to HER2 overexpressing BC, although advanced targeted therapies have improved the survival of patients, disease relapse and metastasis remains a challenge for therapeutic efficacy. In this study the aim was to identify key membrane-associated proteins which are overexpressed in these aggressive BC subtypes and can serve as potential biomarkers or drug targets. We leveraged on the development of a membrane enrichment protocol in combination with the global profiling GeLC-MS/MS technique, and compared the proteomic profiles of a HER2 overexpressing (HCC-1954) and a TNBC (MDA-MB-231) cell line with that of a benign control breast cell line (MCF-10A). An average of 2300 proteins were identified from each cell line, of which approximately 600 were membrane-associated proteins. Our global proteomic methodology in tandem with invigoration by Western blot and Immunofluorescence analysis, readily detected several previously-established BC receptors like HER2 and EPHA2, but importantly STEAP4 and CD97 emerged as novel potential candidate markers. This is the first time that the mitochondrial iron reductase STEAP4 protein up-regulation is linked to BC (HER2+ subtype), while for CD97, its role in BC has been previously described, but never before by a global proteomic technology in TNBC. STEAP4 was selected for further detailed evaluation by the employment of Immunohistochemical analysis of BC xenografts and clinical tissue microarray studies. Results showed that STEAP4 expression was evident only in malignant breast tissues whereas all the benign breast cases had no detectable levels. A functional role of STEAP4 intervention was established in HER2 overexpressing BC by pharmacological studies, where blockage of the STEAP4 pathway with an iron chelator (Deferiprone) in combination with the HER2 inhibitor Lapatinib led to a significant reduction in cell growth in vitro. Furthermore, siRNA mediated knockdown of STEAP4 also suppressed cell proliferation and enhanced the inhibition of Lapatinib in HER2 overexpressing BC, confirming its potential oncogenic role in BC. In conclusion, STEAP4 may represent a novel BC related biomarker and a potential pharmacological target for the treatment of HER2 overexpressing BC.

STAMP2 Attenuates Cardiac Dysfunction and Insulin Resistance in Diabetic Cardiomyopathy via NMRAL1-Mediated NF-κB Inhibition in Type 2 Diabetic Rats

“…Nevertheless, “NMRAL1-Mediated NF-κB Inhibition” might not be the only biological effect of the NADPH oxidoreductase motif of STAMP2. Previous research has also revealed that STAMP2 is involved in tumorigenesis 24 , 25 but functions as a proinflammatory oxidative stress promoter, indicating that it might have an opposite function under different circumstances. More research, including loss-of-function research, needs to be performed in the future for further confirmation.…”

The Role of STAMP2 in Pathogenesis of Chronic Diseases Focusing on Nonalcoholic Fatty Liver Disease: A Review

“…Previous studies indicate that STAMP2 performs all of these functions [ 16 , 30 , 41 ]. Furthermore, STAMP2 is associated with metabolic diseases [ 7 , 10 , 25 , 42 ] and is overexpressed in several human cancers [ 32 , 43 , 44 , 45 ], underlining its physiological function in the maintenance of cellular iron homeostasis [ 30 , 42 ].…”

“…Orfanou et al found that STEAP4 expression was obvious only in malignant breast tissues, whereas all benign breast cases had no detectable levels. Furthermore, knockdown of STEAP4 also suppressed cell proliferation and enhanced the pharmacological effect of lapatinib (HER2 inhibitor) in HER2-overexpressing breast cancer [ 45 ], confirming its potential oncogenic role in breast cancer. These results in various cancers demonstrate that the growth-inducing and anti-apoptotic roles of STAMP2 are needed for carcinogenesis.…”

Regulatory Roles of Six-Transmembrane Epithelial Antigen of the Prostate Family Members in the Occurrence and Development of Malignant Tumors

“…Jin et al (2015) reported that STEAP4 increases ROS in prostate cancer cells through its iron reductase activity, and subsequently affects proliferation, colony formation, anchorageindependent growth, and apoptosis, involving a mechanism at least partly mediated by activating transcription factor 4 (ATF4). Recently, Orfanou et al (2021) investigated the function of STEAP4 in breast cancer and demonstrated that knockdown of STEAP4 suppresses cell proliferation and enhances the inhibition of lapatinib in HER2-overexpressing breast cancer, predicting an oncogenic role for STEAP4 in breast cancer. On the contrary, STEAP4-mediated increases in intracellular copper levels result in activation of the E3 ligase X-linked inhibitor of apoptosis (XIAP), enhancing IL-17-induced NF-κB activation and inhibiting caspase-3 activity (Liao et al, 2020).…”