Reduced Expression of Multiple Gap Junction Proteins is a Feature of Cervical Dysplasia

Published 9 August 2005 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. Findings Connexins, a family of 20 trans-membrane proteins in humans, comprise the main subunits of gap junctions – specialised clusters of intercellular channels that allow adjacent cells to directly share ions and hydrophilic molecules of up to ~1 KDa in size [1]. Gap junctional intercellular communication (GJIC) is thought to control tissue homeostasis and to coordinate cellular processes such as proliferation, migration and differentiation. Disruption of GJIC or mutations in connexins is associated with several human diseases such as hearing loss, neuropathies and various skin conditions [2]. There is also substantial evidence that connexins have a tumour suppressor role [reviewed in [3]]. While reduced or aberrant GJIC or connexin expression has been found in some tumours and in many tumour cell lines [4-7], restoration of GJIC in tumour cell lines by connexin transfection can reduce growth and tumourigenicity [8-10]. However, the tumour suppressive effects may be tissue and connexin-specific [11,12] and also appear to involve non-gap junctional properties of connexins [13-15]. Moreover, it has been observed that connexin expression (especially connexin26) is often upregulated in hyperplastic tissues including psoriatic epidermis and viral warts [16], benign prostatic hyperplasia [17], and mouse papillomas [18]. While induction of connexin26 and connexin43 has also been observed in metastatic breast carcinomas [19], others have reported that connexin26 and connexin43 are downregulated in mammary carcinoma cell lines and re-expression of these connexins leads to repression of tumour-forming ability [20]. Although potent tumour promoters markedly downregulate GJIC in cultured cells [21], intact skin painted with tumour promoters such as 12-O-tetradecanoylphorbol 13-acetate (TPA) show a dramatic upregulation of connexin26 and connexin43 expression [22-24]. Moreover, several reports have shown a negative correlation between expression of connexins and cell diapedesis and or tumour metastasis, including brain tumours [25,26], melanoma [27], breast carcinoma [28] and lung squamous cell carcinomas [29]. Thus, although connexins act as tumour suppressor genes in several types of cancers, the role of connexins in metastasis are more conflicting. The association of certain "high risk" human papillomaviruses (HPVs) with the development of