With the spread of vaccination and screening programmes, the mortality associated with cervical cancer has fallen sharply in developed countries in recent years but remains high in developing regions, where nearly 90 percent of cervical cancer deaths occur[1, 13]. If the prognosis of patients can be known in time, it will sound the alarm for treatment and follow-up. As we mentioned above, advances in high-throughput sequencing and large-scale databases have facilitated to excavate large amounts of molecular data on diseases, thus providing a better understanding of the relationship between biomarkers and cancer. We presented the details of building a protein prediction model and analyzed the results in this study. Computationally, survival prediction was often attributed to regression of patient survival time. Cox regression model is the most commonly used method[14, 15].We identified 29 PRPs and further screened 11 as key proteins. Finally, we established an optimized signature consisting of BCL2, SMAD3 and 4EBP1-pT70 as a prediction signature for the prognosis of common cervical cancer. The model contains a small number of molecules that contribute to practical clinical applications.
The GO analysis of 29 PRPs revealed a high correlation with apoptosis in terms of biological processes and related to chromosome, DNA damage and some membrane structures in the terms of cellular components. Apoptosis is a manifestation of programmed cell death, a normal biological process, and its disorder is a hallmark of cancer. The dysregulation of apoptosis is not only related to the occurrence and development of tumor, but also related to drug resistance[16, 17]. The molecular regulatory mechanism of apoptosis is very complex and can be divided into the extrinsic pathway and intrinsic pathway. In the intrinsic pathway, mitochondrial outer membrane permeabilization is a trigger of apoptosis regulated by the B-cell lymphoma 2 (BCL-2) family [18, 19], which will be discussed in detail later. Under the set of molecular functions, the ubiquitin-protein ligase binding plays a regulatory role in extrinsic apoptotic signaling pathway[20, 21]. In addition, in KEGG analysis, enrichment of important pathways is not only closely related to apoptosis, but also cell senescence and autophagy.
SMAD3 is known to act as a signaling intermediate for transforming growth factor β (TGF-β), and high levels of TGF-β often predict poor prognosis[22]. Biological processes such as cell proliferation, apoptosis, differentiation, and motility have been shown to be regulated by the TGF-β/SMAD3 signaling pathway[23]. Some biomarkers, LncRNA PVT1 and Twist, have been proved to promote proliferation, invasion, and metastasis by enhancing the expression of SMAD3 in the cell trial of cervical cancer[24, 25]. These biomarkers are potential therapeutic targets. Enhanced phosphorylation of SMAD3 inhibits cell invasions, while inhibition of phosphorylation of SMAD3 promotes cancer cell invasions[26, 27].
4EBP1 has been shown to promote tumorigenesis, which is encoded by EIF4EBP1 and affects the mTOR signaling pathway by inhibiting eukaryotic translation initiation factor 4e (EIF4E)[28]. In general, phosphorylated 4EBP1 is believed to indicate a poor tumor prognosis[29]. It is worth emphasizing that 4EBP1-pT70, a high-risk protein, was included in our panel. Interestingly, E6 and E7 of human papillomavirus were found to induce the expression and enhance the activity of eIF4E[30, 31],which indicated that 4EBP1 may be more expressed in cervical cancer associated with HPV infection. Drugs that act on the Akt /mTOR/4EBP1 pathway were being discovered. Britannin indirectly suppressed the expression of PD-L1 through this pathway, thus stabilizing the activity of T cells and inhibiting proliferation and angiogenesis to complete the anti-tumor effect[32]. Some synthetic drugs[33, 34] that could inhibit mTOR/4EBP1 pathway showed superior anti-tumor activity, which suggested that 4EBP1 was a new anticancer drug target for specific anticancer therapy and a promising method to overcome drug resistance and enhance the anti-tumor efficacy of chemotherapy.
BCL2 is not only an effective anti-apoptotic molecule but also a carcinogenic protein[35], which can enhance the sensitivity to carcinogenesis via DNA replication stress[36]. Counter-intuitively, low expression of the BCL2 indicated worse prognosis. Of course, we were not alone in having counterintuitive results [37], and the research of Yang F et al. might provide us with ideas. They believe that miR-7-5p reduces the expression level of BCL2 in platinum-resistant cells, promotes autophagy, and increases energy generation to maintain the survival of platinum-resistant cells[38]. In addition, we speculate that BCL2 is an effective target for the treatment of common CC. In several studies, BCL2 has been reported as a target gene for some miRNAs to inhibit tumor cells, such as miR-449a, miR-136 and miR-365[39–41]. Therefore, we believed that the elusive molecular mechanism was responsible for the better prognosis of patients with high expression, and the phenomenon needs to be explained in the context of specific diseases. It could be a therapeutic opportunity for patients with high BCL2 expression.
Given the complexity of molecular mechanisms, we should realize the necessity of establishing a multi-molecular signature. Due to the complex role of protein signaling pathways, many proteins play a bifunctional role in tumors. Understanding these specific patterns can help screen high-risk biomarkers for potential therapeutic targets. For this purpose, we also screened the co-expressed proteins related to the establishment of the signature in the database as potential research targets. However, we were unable to examine a causal relationship between risk score and prognostic status in patients with CC. And more prospective studies are needed to validate the predictive performance of our model.
In summary, the expression of 29 PRPs, and the enrichment of their functions was mainly related to apoptosis. Based on the optimized model of a three-protein signature, a promising method for predicting the prognosis of patients with cervical cancer was proposed, and several potential therapeutic targets for cervical cancer were pointed out. These results could provide additional reflection and improvement for treatment decision making and further research.