Reduced expression of autophagy markers correlates with high-risk human papillomavirus infection in human cervical squamous cell carcinoma

Abstract

Infection by an oncogenic human papillomavirus (HPV), in particular HPV16 and 18, is a high risk factor for developing cervical cancer; however, viral infection alone is not sufficient for cancer progression. Autophagy is hypothesized to be an important process during carcinogenesis. The aim of the present study was to investigate the association between autophagy and high-risk HPV (hrHPV) infection in human cervical squamous cell carcinomas (SCCs), and to analyze the clinical significance of this association. Quantum dot (QD)-based immunofluorescence histochemistry was used to detect the expression of autophagy markers, Beclin-1 and microtubule-associated proteins 1A/1B light chain 3B (LC3B) proteins, in 104 cases of cervical cancer (including 80 SCCs and 24 adenocarcinomas) and 20 normal cervical tissues. hrHPV (HPV16/18) infection was detected by QDs based fluorescence in situ hybridization in cervical cancers. The results revealed that the expression levels of Beclin-1 and LC3B were significantly lower in cervical cancer cells when compared with those of normal cervical squamous epithelial cells, and were found to negatively correlate with hrHPV infection. The expression levels of Beclin-1 and LC3B were not associated with age, tumor grade, tumor stage, tumor node metastasis stage or lymph node metastasis. However, a positive correlation was identified between Beclin-1 and LC3B protein expression. In addition, the absence of autophagy in combination with hrHPV infection may accelerate the progression of cervical SCC. In conclusion, decreased expression of Beclin-1 and LC3B may be important in cervical carcinogenesis. The hrHPV-host cell interaction may inhibit autophagy, which may aid virus duplication and infection, as well as cervical cancer development.

Keywords: autophagy; beclin-1; cervical cancer; human papilloma virus; light chain 3B; quantum dots.

Figure 1

Expression of Beclin-1 and LC3B proteins in the normal cervical and cancerous tissues was analyzed by quantum dot immunofluorescence histochemistry. A positive signal for Beclin-1 was located (A) at the cytoplasm membrane of normal cervical squamous epithelial cells, (B) in the cervical adenocarcinoma cells and (C) in the cervical squamous cell cancer cells. A positive signal for LC3B was observed in the (D) normal cervical squamous epithelial cells, (E) cervical adenocarcinoma cells and (F) cervical squamous cell cancer cells; however, a negative signal for LC3B was detected in the stroma. (G) Beclin-1 and LC3B protein expression was negative in the same cervical SCC case. The expression of (H) Beclin-1 and (I) LC3B proteins were positive at the same cervical SCC case (A–F, H and I, magnification, ×200; G, magnification, ×100). LC3B, microtubule-associated proteins 1A/1B light chain 3B; SCC, squamous cell carcinoma.

Figure 2

hrHPV infection was detected by quantum dot fluorescence in situ hybridization in the normal cervical and cancerous tissues. (A) Positive controls revealed hrHPV located in the nuclei, which was detected by chromogenic in situ hybridization. hrHPV exhibited a positive signal in the (B) normal cervical tissues, (C) adenocarcinoma and (D) SCC. (E and F) In the same SCC case, hrHPV infection exhibited a positive signal (E); however, Beclin-1 exhibited a negative signal (F). (A, B and F, magnification, ×100; C–E, magnification, ×200). hrHPV, high risk human papillomavirus; SCC, squamous cell carcinoma.