Autocrine expression of the epidermal growth factor receptor ligand heparin-binding EGF-like growth factor in cervical cancer

Abstract

In cervical cancer, the epidermal growth factor receptor (EGFR) is overexpressed in 70-90% of the cases and has been associated with poor prognosis. EGFR-based therapy is currently being explored in cervical cancer. We investigated which EGFR ligand is primarily expressed in cervical cancer and which cell type functions as the major source of this ligand. We hypothesized that macrophages are the main source of EGFR ligands and that a paracrine loop between tumor cells and macrophages is responsible for ligand expression. mRNA expression analysis was performed on 32 cervical cancer cases to determine the expression of the EGFR ligands amphiregulin, β-cellulin, epidermal growth factor (EGF), epiregulin, heparin-binding EGF-like growth factor (HB‑EGF) and transforming growth factor α (TGFα). Subsequently, protein expression was determined immunohistochemically on 36 additional cases. To assess whether macrophages are the major source of EGFR ligands, immunohistochemical double staining was performed on four representative tissue slides. Expression of the chemokines granulocyte-macrophage colony-stimulating factor (GM-CSF) and C-C motif ligand 2 (CCL2) was determined by mRNA in situ hybridization. Of the known EGFR ligands, HB‑EGF had the highest mRNA expression and HB‑EGF and EGFR protein expression were highly correlated. Tumor specimens with high EGFR expression showed higher numbers of macrophages, and higher expression of GM-CSF and CCL2, but only a small subset (9%) of macrophages was found to be HB‑EGF-positive. Strikingly, 78% of cervical cancer specimens were found to express HB‑EGF. Standardized assessment of staining intensity, using spectral imaging analysis, showed that HB‑EGF expression was higher in the tumor compartment than in the stromal compartment. These results suggest that HB‑EGF is an important EGFR ligand in cervical cancer and that cervical cancer cells are the predominant source of HB‑EGF. Therefore, we propose an autocrine EGFR stimulation model in cervical carcinomas.

Figure 1

Representative examples of heparin-binding EGF-like growth factor [(HB-EGF); (A) strong, (B) weak], amphiregulin [(AREG)/0; (C) strong, (D) weak] and transforming growth factor-α staining [(TGFα); (E) strong, (F) weak)] immunohistochemical staining in the epithelial compartment (asterisk) of squamous cell carcinoma of the cervix.

Figure 2

Immunohistochemical double staining of heparin-binding EGF-like growth factor (HB-EGF, DAB) and macrophages (CD68, PermaBlue), without nuclear counterstaining (A), and the simulated fluorescence composite image obtained through spectral imaging (B), showing not only macrophages (arrow), but also other cells in the stroma and tumor cells strongly expressing HB-EGF in cervical cancer.

Figure 3

Representative example of epidermal growth factor receptor (EGFR) (A) and heparin-binding EGF-like growth factor (HB-EGF) (B) immunohistochemical staining within the same squamous cell carcinoma tumor specimen, showing membranous staining of EGFR and cytoplasmic staining of HB-EGF.

Figure 4

Average staining intensities for heparin-binding EGF-like growth factor (HB-EGF) for each subgroup in the tumor and stromal compartment.

Figure 5

Proposed mechanism of heparin-binding EGF-like growth factor (HB-EGF) expression and macrophage recruitment in cervical cancer.