PTP1B phosphatase as a novel target of oleuropein activity in MCF-7 breast cancer model

Highlights

• Oleuropein, polyphenol of olive oil, is a potent anticancer agent towards breast cancer.

• Oleuropein induces both cytostatic and cytotoxic effect in MCF-7 breast cancer model.

• Non-receptor tyrosine phosphatase 1 (PTP1B) constitutes a target for oleuropein in MCF-7 breast cancer model.

• Oleurpein inhibits activity of PTP1B as confirmed by in vitro and computational modelling studies.

Abstract

Phosphatase PTP1B has become a therapeutic target for the treatment of type 2-diabetes, whereas recent studies have revealed that PTP1B plays a pivotal role in pathophysiology and development of breast cancer. Oleuropein is a natural, phenolic compound with anticancer activity. The aim of this study was to address the question whether PTP1B constitutes a target for oleuropein in breast cancer MCF-7 cells.

The cellular MCF-7 breast cancer model was used in the study. The experiments were performed using cellular viability tests, Elisa assays, immunoprecipitation, flow cytometry analyses and computer modelling.

Herein, we evidenced that the reduced activity of phosphatase PTP1B after treatment with oleuropein is strictly correlated with decreased MCF-7 cellular viability and cell cycle arrest. These results provide new insight into further research on oleuropein and possible role of the compound in adjuvant treatment of breast cancer.

Introduction

Both conventional medicine and phytotherapy use olive leaf extracts to treat and prevent various diseases, including cancer (Gryszczyńska et al., 2010; Omar et al., 2017; Elamin et al., 2013; Mahmoudi et al., 2018; Hamdi and Castellon, 2005; Zhao et al., 2009). A chemopreventive activity of olive oil has been mainly attributed to its unique phenolic compounds represented by i.e. phenolic alcohols (hydroxytyrosol, tyrosol) and their secoiridoid derivatives (oleuropein, ligstroside and oleocanthal) (Fabiani, 2016; Gorzynik-Dębicka et al., 2018). Oleuropein is a natural, phenolic compound found in olive oil from Olea europaea (Oleaceae) (Servili et al., 2009). It is an ester of hydroxytyrosol containing an oleosidic skeleton and carbohydrate group (Fig. 1).

Notably, oleuropein has valuable beneficial properties such as antioxidant, anti-inflammatory, cardioprotective or neuroprotective (Gorzynik-Dębicka et al., 2018). Interestingly, numerous studies evidenced also the anticancer activity of oleuropein in various malignant cells; breast cancer (MCF-7 and MDA cell lines) (Liao et al., 2017a; Han et al., 2009; Sirianni et al., 2010; Reboredo-Rodríguez et al., 2018), melanoma (A375 and BRAF cell lines) (Ruzzolini et al., 2018), urinary bladder carcinoma (T-24 cell line) (Goulas et al., 2009), colorectal adenocarcinoma (HT 29, Caco-2, and LoVo cell lines) (Cárdeno et al., 2013), prostate cancer (TF1 cell line) (Vanella et al., 2012), lung carcinoma (A549 cell line) (Cao et al., 2017) and glioma (U251 and A172 cell lines) (Liu et al., 2016a).

Especially, encouraging data were obtained on breast cancer cellular models. According to Sirianni et al., oleuropein plays an important chemo-preventive role in breast cancer via inhibition of estrogen-dependent tumor proliferation (Sirianni et al., 2010). Whereas, results obtained by Hassan et al., indicate that oleuropein induces apoptosis in breast cancer cells via a p53-dependent pathway mediated by Bax and Bcl2 genes (Hassan et al., 2013). Wide range of health beneficial effects of oleuropein strictly correlate with its antioxidant activity as phenolic structure of oleuropein is capable of scavenging free radicals and reactive oxygen species (Rizzo et al., 2017). Unfortunately, the limitation of the data reporting anticancer properties of oleuropein and other polyphenols of olive oil is the fact that they are mainly based on in vitro cellular models. Thus, in vivo experiments are needed to further investigate the anticancer potential of oleuropein and other polyphenols of olive oil.

Nonetheless, the preclinical studies searching for targets of oleuropein in different cancer models is an emerging issue (Isgut et al., 2018). Notably, protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs) are the crucial class of oncology drugs targets (He et al., 2014). They both control levels of cellular protein tyrosine phosphorylation, which is essential for most of the cellular processes such as growth, differentiation, migration, survival and apoptosis (Hunter, 1995). Dysregulation of protein tyrosine phosphorylation leads to development of cancers (Hunter, 1995). Due to above, PTPs are considered as promising targets of novel anticancer therapies (He et al., 2014). PTP1B (non-receptor tyrosine phosphatase 1, PTPN1) is one of the most significant anti-oncogenic phosphatase that belongs to the protein-tyrosine phosphatase family (Cho, 2013; Lou et al., 2008; Rivera Franco et al., 2016; Wu et al., 2006; Scott et al., 2010). The PTP1B gene is frequently amplified in ovarian, gastric, prostate and breast cancers, and correlates with poor prognosis (Liao et al., 2017a; Rivera Franco et al., 2016; Yu et al., 2019a; Liu et al., 2016b). Importantly, PTP1B is over-expressed in >70% of breast cancer tissues (Liao et al., 2017a; Yu et al., 2019a; Wiener et al., 1994). This tissue-specific over-expression of PTP1B plays a pivotal role in mammary tumorigenesis (Lou et al., 2008; Rivera Franco et al., 2016; Wu et al., 2006). In 2016 Liu et al. demonstrated that PTP1B is involved in carcinogenesis of estrogen receptor (ER)-positive breast cancer (Liu et al., 2016b). Moreover, PTP1B up-regulates the proliferation, and suppresses the apoptosis in both HER2-positive and triple-negative breast cancer cell lines (Yu et al., 2019a).

Numerous epidemiological studies reported a beneficial effect of intake of olive oil on the risk of breast cancer (Liu et al., 2019). However, the potential effect of oleuropein on estrogen receptor-positive breast cancer is not fully understood. Furthermore, up to date, they are no studies considering PTP1B as a target for oleuropein. Due to confirmed expression of PTP1B, we chose estrogen receptor-positive, MCF-7, cell line for our studies (Kuban-Jankowska et al., 2017a; Kuban-Jankowska et al., 2017b; Kostrzewa et al., 2019; An et al., 2016; Liao et al., 2017b). It was furthermore evidenced that knocking down the gene of PTP1B inhibits the proliferation and migration of MCF-7 cells (Liao et al., 2017b). Therefore, the aim of this study was to investigate whether PTP1B constitutes a target for oleuropein in breast adenocarcinoma MCF-7 cellular model.