PSC is characterized by poorly differentiated carcinoma with an inferior survival outcome because of a high rate of resistance to conventional first-line platinum-based chemotherapy . Surgical resection, when feasible, remains the most important approach to systematic treatment. A clinical staging system is now being used widely to predict the prognosis of patients with PSC worldwide; however, patients still have worse outcomes across all stages of the disease, because they present with many adverse features, such as higher grade, larger volume, and more advanced clinical stage . Therefore, it remains necessary to develop new objective strategies that can effectively distinguish between patients with relatively better or worse prognosis. Previous studies demonstrated several aberrantly mutated genes in PSC, including the MET exon 14 skipping mutation, which causes increased oncogenic signaling of the MET receptor, leading to tumor growth and proliferation , and a dramatic response to MET inhibition has been noted [22, 28]. Two recent studies found that 30–40% of PSC cases harbored KRAS mutations that are associated with poor prognosis [29, 43]. However, patients with neither of these deleterious molecular changes were proven to be insensitive to targeted therapy in the clinic. Novel molecular markers that could identify tumor recurrence and/or risk assessment are urgently needed to select new treatments.
TROAP is a cytoplasmic protein regulated by the microtubular cytoskeleton that plays a prominent role in early embryo implantation, in which it mediates the process of cell mitosis and tumor progression [12, 50]. TROAP is a crucial regulator that controls cell proliferation, invasion, and migration via multiple signaling pathways. Recently, TROAP was observed to enhance the invasion of human colorectal cells via a mechanism involving high mobility group box 1 (HMGB1)/ receptor for advanced glycosylation end products (RAGE) , and seemed to be able to control the proliferation of prostate cancer cells through the Wnt family member 3 (WNT3)/survivin signaling pathway . In addition, increased expression of TROAP correlated with the development and progression of diverse human cancers, including ovarian cancer , gastric cancer , breast cancer , and hepatocellular carcinoma . These studies also showed that silencing of TROAP inhibited the proliferation and migration ability of gastric cancer and prostate cancer cells. Nevertheless, the expression of TROAP and its prognostic value in PSC remain unclear. In addition, the underlying mechanism by which TROAP affects prognosis requires further investigation. The results of the present study form the basis for further exploration of the in-depth mechanisms for the progression and metastasis of PSC mediated by TROAP, by identifying the receptors, adapters, target proteins, and pathways.
Meanwhile, previous NGS-based studies showed that in PSC, the highest rate of TP53 mutation ranged from 57.1 to 74% [27–29, 39, 43]. The examination of P53 status has used inexpensive IHC staining as a surrogate marker in many studies of human cancers [3, 23, 52]. In view of this, the expression of P53 in PSC and its prognostic value remain to be investigated. Moreover, the correlation between TROAP expression and P53 status based on IHC staining in PSC should also be evaluated.
In the present study, we investigated TROAP and P53 protein expression in 168 PSC tissues. The results revealed that 65 patients with PSC were classified as having high expression of TROAP, and aberrant expression rate of P53 was 66.7% (112/168). Although we examined P53 status using IHC as a surrogate marker, the rate of 66.7% is still located within the range 57.1–74% reported previously. It also showed that our results are credible to detect P53 mutation using IHC staining in PSC. Further NGS experiments should be done using our samples to confirm the IHC-based assessment of P53 status. We demonstrated that TROAP protein expression is significantly associated with P53 status. cBioPortal for Cancer Genomics identified a significant negative relationship between TROAP mRNA expression and P53 status. Online analysis using iBioSci Tools v5.0 predicted that TROAP’s function is closely related to the signaling pathways involving P53. GeneMANIA software predicted that the interaction of P53-ERBB4-TROAP or P53-MKI67-TROAP could play an important role in the regulation of TROAP expression, indicating the important function of P53. Therefore, we speculated that P53 status could serve as a candidate predictive marker for the response to targeted therapies involving TROAP.
Further correlation analyses showed that high expression of TROAP correlated strongly with clinical stage, indicating that TROAP might promote the proliferation and differentiation of PSC. Moreover, association analysis of TROAP expression with clinicopathological parameters suggested that high expression of TROAP was significantly linked to lymph node metastasis, which agreed with the results of previous research . Our findings support the view that TROAP acts as an oncogene in the progression and development of PSC, probably dependent on P53 status. Collectively, the data showed that TROAP functions to promoter malignant transformation and might be activated in human cancers, possibly through P53 signaling pathways. In addition, high TROAP expression was closely related to the poor prognosis of patients with PSC as an independent prognostic factor, which was similar to the results of previous studies [9, 17], in which high TROAP expression correlated with adverse survival in lung adenocarcinoma and liver cancer. This suggested that activated TROAP might lead to the aggressive biological behavior of cancers and could be considered as a critical biomarker to assess prognosis in various human cancers. Univariate analysis showed that patients with aberrant expression of P53 had shortened survival compared with that of patients with wild-type P53 expression. This was consistent with the results of previous studies in which the presence of any P53 mutation resulted in worse survival in patients with squamous cell carcinoma of the head and neck . In patients with ovarian cancer, the prognostic significance of aberrant P53 status, assessed using IHC or mutational analysis, was related to poor prognosis . These observations suggested that P53 mutations might be the critical drivers in the progression of squamous cell carcinoma of the head and neck, ovarian cancer, and PSC. However, the predictive value of aberrant P53 aberrant lacked significance in terms of clinical outcome in patients with colon cancer . This indicated that other gene mutations, such as KRAS mutations, might be the drivers leading to the development of colon cancer.
From the results mentioned above, an explanation is required as to why aberrant P53 expression or high expression of TROAP are strongly associated with worse prognosis in patients with PSC, whereas aberrant P53 expression is significantly associated with low expression of TROAP. In our study, aberrant P53 expression presumably results from the presence of P53 mutations. Previous studies reported that several types of P53 mutation led to the accumulation of mutated P53 protein in the nuclei of tumor cells that still exerted their function as a tumor suppressor [2, 32]. Therefore, the mutation type that promotes tumorigenesis and its relationship with TROAP expression requires further exploration in patients with aberrant P53 expression.
Risk stratified analysis demonstrated that high TROAP expression was significantly related to unfavorable OS in patients with PSC with aberrant P53 expression. Thus, identification of this subset of patients with aberrant P53 expression and high TROAP expression, might allow more accurate prediction of their prognosis and provide opportunities for improved individual treatment, including recovery of P53 gene function and/or targeted therapy associated with TROAP. Furthermore, there were significant statistical differences for OS and DFS for patients with PSC among the three risk groups, including the low risk group (low TROAP expression and wild-type P53 expression, the intermediate risk group (either high TROAP expression or aberrant expression of P53), and the high risk group (both high TROAP expression and aberrant P53 expression). Patients in the high risk group had a worse prognosis than the other two groups. These data suggested that patients harboring high expression of TROAP and aberrant expression of P53 might require more radical treatment, especially targeted therapy for TROAP protein and/or the recovery of P53 gene function.