Reduced expression of multiple gap junction proteins is a feature of cervical dysplasia

Abstract

Cervical dysplasia is a premalignant lesion associated with human papillomavirus (HPV) infection which, over time, can turn cancerous. Previous studies have indicated that loss of gap junctions may be a feature of cervical cancer and premalignant dysplasia. Loss of the gap junction protein connexin43 has been demonstrated in dysplastic cervix, but other connexins have not been investigated. In contrast we previously showed that HPV-associated cutaneous warts--and other hyperproliferative skin conditions--display a dramatic upregulation of certain connexins, in particular connexin26. By performing immunofluorescence staining after antigen retrieval of paraffin-embedded cervical tissue samples, this study reports for the first time that connexin26 and connexin30, in addition to connexin43, are expressed in differentiating cells of normal human cervical epithelia. Moreover, in dysplastic ectocervix, all connexins studied display a dramatic loss of expression compared to adjacent normal epithelia. The role of connexins in keratinocyte differentiation and carcinogenesis is discussed.

Figure 1

Connexin expression in normal and dysplastic human cervical epithelium. All nuclei are stained with DAPI (blue). A: All normal ectocervical tissue sections revealed positive staining of connexin43 gap junctions (red) particularly in the spinous layers. Connexin26 was also positive (green), particularly in upper spinous and more superficial layers. Overlapping expression of connexin43 and connexin26 was observed (yellow) and these areas displayed particularly large gap junction plaques (arrow). B: Connexin30 (red) displayed a similar staining pattern to Connexin26 although gap junction plaques were more frequently observed in lower spinous layers (arrow). In these normal sections, the proliferation marker Ki-67 was detected (turquoise) in basal and immediate suprabasal layers only, as expected. (C) In all premalignant CIN III sections there was complete absence of connexin26 (green) and connexin30 (red). D: In one CIN III lesion, small amounts of connexin43 (red) were present, mainly as diffuse cytoplasmic staining, but no positive connexin26 staining was detectable (green). E: In CIN I/II lesions no clear connexin26 gap junctions were present (green) whereas several connexin43 plaques were visible (arrow), but in a less homogenous fashion compared to normal ectocervix. F: Connexin30 gap junctions were clearly detected in areas of low grade CIN I lesions, although they tended to occur in stratified regions of cell differentiation (arrow) rather than areas of abnormal cellular proliferation (Ki-67, turquoise) and atypical cellular crowding.