EC is a tumor with high invasive ability. It is usually diagnosed in the late stage due to the lack of specific initial symptoms. For late-stage EC, the main treatment is surgery combined with chemotherapy [17, 18]. However, the cure and survival rates of patients are still very low, and other methods are needed to help predict the survival rate and identify potential responders of a given treatment.
HPV is a kind of DNA virus with small size and no envelope. HPV DNA is often dissociated from chromosome. In malignant tumor, HPV DNA is integrated into host cell DNA, resulting in the loss of negative regulation of HPV E2 gene on HPV E6 and HPV E7 gene initiation, resulting in abnormal expression of E6 and E7 genes, leading to malignant cell proliferation. In 1982, syrjanen et al. Proposed for the first time that HPV infection may be related to the occurrence of esophageal squamous cell carcinoma. In recent years, some scholars suggested that HPV could be a prognostic indicator of esophageal squamous cell carcinoma[20–22]. In head and neck cancer, patients with HPV-positive cancer have better therapeutic outcome and higher survival rate than patients with HPV-negative cancer [23–25]. A similar correlation possibly exists, because the esophagus may also be infected with HPV. HPV-infected tumors are characterized by a high expression of p16, which is widely considered as an alternative marker for HPV infection [10, 12]. In the present study, the expression rate of p16 in ESCC was 30.8%, which was significantly higher than in normal esophageal mucosa. In the correlation analysis with clinical pathological factors, p16 expression was significantly correlated with esophageal location, and the expression rate of p16 in the cervical/upper part was significantly higher than in the middle and lower parts. In addition, p16 expression was negatively correlated with the degree of differentiation, invasion depth, and lymph node metastasis of ESCC. Thus, p16 was highly expressed in patients with a high degree of differentiation, shallow invasion depth, and no lymph node metastasis. Prognosis analysis showed that the 5-year survival rate of p16-positive group was 39.6%, whereas that of p16-negative group was 23.1%. Cox regression analysis of OS and PFS showed that p16 status was an independent prognostic factor for OS and PFS in patients with ESCC. The present study clearly showed that p16-positive tumor was related to high differentiation, TNM stage, and lymph node metastasis. These three differences may have enhanced the prognosis in patients with p16-positive tumor. Another hypothesis was that HPV infection leads to the high expression of tumor protein E6/E7, which weakens the functions of p53 and RB proteins and promotes genome rearrangement and DNA rearrangement is theoretically more sensitive to radiotherapy and chemotherapy [26–27]. This hypothesis explains the indications of increased survival rate in patients with HPV-positive tumors.
As one of the important signal transduction pathways in cells, the PI3K/Akt signaling pathway is closely related to the occurrence and development of various human tumors. Its abnormal activation promotes the normal development of cells to cancer cells. An abnormal PI3K/Akt signal transduction is present in many human malignant tumors [28–31]. As a catalytic subunit of PI3K, PI3Kp110 has four members, namely, P110α, P110β, P110δand P110γ. P110α and P110β, which are encoded by PIK3CA and PIK3CB, respectively, are widely found in cells. They can regulate DNA synthesis and promote normal cell development with normal expression; moreover, they are closely related to the occurrence and development of tumors with abnormal expression . The mutation of PIK3CA gene can increase the expression of p110α, which receives the EGF signal. In addition, p110α is activated by Ras protein, phosphorylates downstream Akt proteinand continuously activates the PI3K/Akt signal pathway, leading to cell overproliferation. The role of p110β in tumorigenesis and its mechanism are unclear. In the present study, the positive rates of PIK3CA and PIK3CB in ESCC were significantly higher than those in the normal mucosa, suggesting the abnormal PIK3CA and PIK3CB expression levels in ESCC. High PIK3CA and PIK3CB expression levels were related to the malignant potential of EC. PIK3CA overexpression resulted in the abnormal activation of the PI3K/Akt pathway. This abnormal activation could promote the growth and proliferation of tumor cells, inhibit apoptosis, promote invasion and metastasis, regulate endothelial growth and angiogenesisand affect the efficacy of chemotherapy by catalyzing a series of protein phosphorylation.
The expression of HPV E6/E7 oncoprotein induces the carcinogenesis of HPV-transformed cells, changing various cell and molecular events by activating the PI3K/Akt signaling pathway. Xie J et al. demonstrated that ALA-PDT treatment inhibits the proliferation of HeLa cells in a dose-dependent manner and effectively reduces HPV viral load via autophagy and apoptosis by regulating the Ras/Raf/MEK/ERK and PI3K/AKT/mTOR pathways . Madera D et al. suggested that inhibiting PIK3CA expression and HPV can slow down the further growth of OSCC . In our study, p16 expression was positively correlated with PIK3CA expression but was not correlated with PIK3CB expression. We believe that the PI3K/Akt/mTOR signaling pathway in HPV-infected cells was activated by mutations in pathway components and the activation of upstream signaling molecules. Activating this pathway contributes to the dysregulation of proliferation and changes in anti-apoptosis and metabolic characteristics and ultimately leads to the malignant transformation of infected cells. This signaling pathway may be a huge therapeutic opportunity and practical challenge for the treatment of HPV-induced cancer. The PI3K/Akt pathway plays a key role in many HPV-related human cancersand the HPV infection expressed in E6/E7 activates the PI3K/Akt signaling pathway by changing various cell and molecular events that lead to cancer.
The differential expression of tumor suppressor protein p53 is one of the most common abnormal expressions in cancer. Mutation is mainly related to cell invasion, metastasisand late-stage tumor. The expression of HPV E6/E7 oncoprotein can induce the transformation of HPV transformed cells, which leads to the degradation and instability of p53 and pRB. In this study, the positive expression rate of p53 protein in esophageal squamous cell carcinoma was 41.1%, which was significantly higher than that in normal tissuesand expression of p53 protein was related to the poor prognosis of ESCC. As a tumor suppressor gene, wild-type p53 can regulate cell cycle and avoid cell carcinogenesis. After p53 gene mutates, it loses its regulatory effect on cell growth, apoptosisand DNA repair and increases the tumor’s adaptability to hypoxic microenvironment due to the change in its spatial conformation [35, 36]. However, in the present study, no correlation was found between p53 and p16 expression levels, possibly due to the insufficient number of samples.
In conclusion, this study confirmed that HPV infection is associated with high differentiation, TNM stage and lymph node metastasis. HPV infection is a good prognostic indicator of esophageal squamous cell carcinoma. At the same time, our study showed that the increased expression levels of PIK3CA and PIK3CB were related to the occurrence of ESCC. The imbalance of PI3K/Akt signaling pathway is closely related to HPV infection and prognosis. In ESCC, PIK3CA and p53 are markers of poor prognosis. The combined detection of PIK3CA and p16 is of great significance for the prognosis evaluation and treatment optimization of esophageal squamous cell carcinoma.