PTPRT Could Be a Treatment Predictive and Prognostic Biomarker for Breast Cancer

The role of PTPRT in breast cancer was not comprehensively explored and well analyzed. Our study comprehensively searched available databases to analyze the clinical role of PTPRT in breast cancer. We found PTPRT was an antioncogene and could be used to distinguish different stages, age groups, molecular types, and grades for breast cancer. PTPRT might be primary resistance biomarkers for taxane, anthracycline, and ixabepilone but not be acquired resistance biomarkers. Higher PTPRT expression levels were associated with longer overall survival and recurrence-free survival. PTPRT was negatively associated with Ki67 and CDK4/6 but positively associated with BCL-2. PTPRT might be associated with cell cycle and microtubule, and tumor infiltration in B cell and macrophage cell. PTPRT could predict chemotherapy effectiveness and prognosis for breast cancer patients. PTPRT might inhibit tumor growth via disrupting the microtubule dynamics and cell cycle in breast cancer.


Introduction
PTPRT belongs to the type IIB RPTP subfamily, which consisted of an extracellular domain (a meprin/A5/PTP μ domain, an Ig domain, and four fibronectin type III repeats), a transmembrane domain, a juxtamembrane region, and two phosphatase domains (D1 and D2) [1]. PTPRT plays in suppressing tumor growth and cell adhesion in various cancers, including colorectal cancer [2], hepatocellular carcinoma [3], prostate cancer [4], lung squamous cell carcinoma [5], esophageal squamous cell carcinoma [6], and glioma [7]. Previous review showed PTPRT as a tumor suppressor might be involved in cell cycle and cell adhesion [1]. Five missense mutations in the most commonly altered PTPRT were found to reduce phosphatase activity, and expression of wild-type but not a mutant PTPRT in human cancer cells inhibited cell growth [8]. Zhang et al. showed deletion of the fibronectin type III repeats (FNIII) of PTPRT result in defective cellcell aggregation, which suggest the inactivation of PTPRT might lead to cancer progression by disrupting cell-cell adhesion [9]. Available studies about the PTPRT were limited, and about 66 studies were found in Pubmed. Few studies were conducted about the PTPRT signaling pathway. Zhang et al. identified signal transducer and activator of transcription 3 (STAT3) as a substrate of PTPRT. They showed PTPRT specifically dephosphorylated STAT3 at a tyrosine at amino acid Y705 and overexpression of normal PTPRT in colorectal cancer cells reduced the expression of STAT3 target genes [10]. Other studies identified miR-532-3p [3], miR-218 [6], miR-215 [11], and miR-888 [12] might regulate and mediate the expression of PTPRT. Schettini et al. used a novel methodology to detect surface antigen to develop ADC and CAR-T against breast cancer already and identified PTPRT as a novel potential target for molecular Luminal A or immunohistochemical HR+/HER2-negative BC [13]. In order to analyze the clinical role of PTPRT in breast cancer, we comprehensively searched available databases to summarize the treatment predictive and prognostic values of PTPRT.

Materials and Methods
No Institutional Review Board (IRB) approval was needed for this study. Available databases based on TCGA and 3. Results 3.1. The Expression of PTPRT in Breast Cancer. Using TCGA data, the expression level of PTPRT in breast cancer tissue is lower than that in adjacent normal breast tissue (median 2.24 vs. 4.41 TPM (transcript per million), p < 0:001). The expression level of PTPRT in stage 1 to 4 breast cancer tissues was lower than that in adjacent normal breast tissue (stage 1 vs. stage 2 vs. stage 3 vs. stage 4: 3.68 vs. 2.01 vs. 1.92 vs. 0.83). The expression level of PTPRT decreased from stage 1 to stage 4, and there were statistical significances between stage 1 and 4, stage 2 and 4 (p < 0:05). Interestingly, the expression level of PTPRT increased with age from 1 Figure 1). Based on GEO data, the expression level of PTPRT decreased with the increase of Scarff-Bloom-Richardson (SBR) grade (SBR1 > SBR2 > SBR3, p < 0:001, 6810 patients). Those patients with lymph node metastases were of lower PTPRT levels (p < 0:0001, 7474 patients). The PTPRT expression levels in patients with different ages were similar to that in TCGA databases. The older the patients, the higher the PTPRT expressions (7434 patients, 70 − 97 > 40 − 70 > 21 − 40, p < 0:05). Luminal A breast cancer patients were of the highest level of PTPRT, which was higher than that in normal-like breast cancer (p < 0:05). HER2+ and basal-like breast cancer were of lower PTPRT level than that in normal-like breast cancer, and basal-like breast cancer was of the lowest PTPRT expression level. There was no statistical significance between luminal B and normal-like breast cancer ( Figure 2).

Discussion
PTPRT is an antioncogene and plays important roles in various cancers, including colorectal cancer [2], hepatocellular carcinoma [3], prostate cancer [4], lung squamous cell carcinoma [5], and glioma [7]. Several studies showed overexpressed PTPRT might inhibit tumor cell growth acting as a putative tumor suppressor in cancer cell culture [2-5, 7, 8]. Animal studies showed PTPRT knockout increases the size of mouse colon tumors in the Apcmin+/-genetic background, suggesting that inactivation of PTPRT promotes tumor progression [14] Our study analyzed the role of PTPRT in breast cancer, and we found the PTPRT mRNA level could be biomarkers for different stages, age groups, molecular types, and grades for breast cancer, as well as prognostic biomarkers for breast cancer. Based on our analysis, it is obvious that a larger tumor was associated with a lower PTPRT expression level. Meanwhile, breast tumor with high PTPRT was associated with low proliferation rate (measured by Ki67) and high apoptotic rates (measured by BCL-2). All these data suggest PTPRT might inhibit tumor growth in breast cancer as a tumor suppressor. The signal transducer and activator of transcription 3 (STAT3) protein is a major

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BioMed Research International transcription factor involved in many cellular processes, such as cell growth and proliferation, differentiation, migration, and cell death or cell apoptosis [15]. Plenty of evidence suggested PTPRT might negatively regulate STAT3 activation by dephosphorylation of the tyrosine residue [15][16][17][18]. STAT3 may be activated by loss-of-function of negative regulators of STAT3, including by promoter hypermethylation of PTPRT [17]. This was confirmed in breast cancer, and PTPRT was negatively associated with STAT3, while the promoter methylation level of PTPRT was positively associated with STAT3 based on TCGA data. PTPRT might predict the effectiveness of primary resistance biomarkers for taxane, anthracycline, and ixabepilone, which all displayed better effectiveness in breast cancer disease control [19][20][21], but not be acquired resistance biomarkers. Taxane were potent cytotoxic microtubulestabilizing agents, and they exert their action through induction of apoptosis through phosphorylation of bcl-2 and inhibition of cell proliferation [22], as well as selectively disrupting the microtubule dynamics, inducing mitotic arrest that leads to cell death [23]. Anthracyclines, which belong to cell cycle nonspecific agents, are a class of potent and widely used cytotoxic drugs, derived from antibiotics that inhibit DNA and RNA synthesis by intercalating between base pairs of the DNA/RNA strand [24]. Ixabepilone bind to the βtubulin subunit of the α, β dimer of microtubules, inducing microtubule polymerization, stabilization, and formation of abnormal mitotic spindles, which in turn cause G2/M arrest and apoptosis [25,26]. The cell signaling pathways regulated by PTPRT largely remain to be elucidated. Based on our GO and KEGG analysis, we could find PTPRT might be associated with the cell cycle and microtubule-based process. It was reported that microtubules are cytoskeletal structures that play a pivotal role in cell division, locomotion, and intracellular transport [27]. During mitosis, microtubules, which consist of αand β-tubulin, represent a major structural component of the spindle apparatus, which is required for the separation of sister chromatids [28]. Our analysis indicated that PTPRT was significantly associated with several genes that were involved in microtubule motor activity. This might explain why PTPRT could be a primary resistance biomarker for taxane, anthracycline, and ixabepilone.
Acquired drug resistance to chemotherapy and targeted therapy treatment is unavoidable, creating a clinically challenging problem, which represents a major challenge in for various types of cancers [29,30]. Acquired resistance develops after a significant initial response over the course of several months [31]. Hammerlindl et al. [31] proposed that treatment will initially facilitate cellular reprogramming towards the slow-cycling drug-tolerant phenotype and continuous drug exposure will eventually lead to reactivation of transcriptional activity and regain of proliferative capacity. These will further stabilize their drugtolerant transcriptional profile to become permanent drug resistant. According to their theory, PTPRT stays stable during the acquired resistance process, which means the expression of PTPRT did not change during the long drug exposure. So PTPRT might be a good primary resistance biomarker for taxane, anthracycline, and ixabepilone without affecting by the drugs.
Based on our data, although PTPRT was coexpressed with ESR1 and ERBB2, the status of ESR1 and ERBB2 did not affect the expression of PTPRT. Whether PTPRT affects the expression of ESR1 and ERBB2 was unclear. Based on our study, higher PTPRT was associated with longer survival in different molecular types based on KMplot data, and this  Our study comprehensively analyzed the role of PTPRT in breast cancer. In our study, not only TCGA but also GEO data were included to explore the role of PTPRT in breast cancer. We found PTPRT might predict the effectiveness of taxane, anthracycline, ixabepilone, and the prognostic values. We confirmed that PTPRT might inhibit tumor growth in breast cancer, which might be due to microtubule dynamics. However, our study still has its own limitations: first, all of our analyses were based on RNA sequence data. Our study was based on RNA sequence, whether q-pcr or IHC results still have the predictive values for the effectiveness of taxane, anthracycline, and ixabepilone and prognosis or not. Second, population heterogeneity might exist in this study across different datasets, although we used GEO datasets to validate the results in TCGA data. Third, PTPRT might be an inhibitor of tumor growth via disrupting the microtubule dynamics and cell cycle in breast cancer. This lacked in vivo and in vitro experiments to validate our study results. Future studies are needed about how PTPRT affects the drug effectiveness and breast cancer prognosis, as well as microtubule dynamics and cell cycle.

Conclusion
PTPRT expression was not affected by ER or HER2 expression, but PTPRT could distinguish Luminal A and TNBC, HER2+ breast cancer. PTPRT could be used as biomarkers to predict taxane, anthracycline, and ixabepilone effectiveness and prognosis for breast cancer patients. PTPRT might be an inhibitor of tumor growth via disrupting the microtubule dynamics and cell cycle in breast cancer.

Data Availability
The data used to support the findings of this study are included within the article.