Effect of diverse tumor promoters on the expression of gap-junctional proteins connexin (Cx) 26, Cx31.1, and Cx43 in SENCAR mouse epidermis

Abstract

The inhibition of gap-junctional intercellular communication (GJIC) between initiated and surrounding normal cells by tumor promoters is believed to be important in the promotion stage of carcinogenesis. Therefore, we examined the effect of skin-tumor promoters on the expression of the gap-junctional proteins connexin (Cx) 26, Cx43, and Cx31.1 in SENCAR mouse skin. Animals were treated with 12-0-tetradecanoylphorbol-13-acetate (TPA) (8.3 nmol), okadaic acid (OA) (2.5 nmol), chrysarobin (220 nmol), or benzoyl peroxide (BzPo) (83 micromol). Northern blot and immunofluorescence analyses revealed that keratinocytes in adult mouse skin expressed Cx31.1 and Cx43 but not Cx26. All four of the skin-tumor promoters switched on the Cx26 gene, transiently increased expression of Cx43, and significantly inhibited the expression of Cx31.1. The time courses for changes in Cx26, Cx3l. 1, and Cx43 mRNA levels coincided in most cases and in general corresponded well to the time-response curves for hyperplastic changes in mouse skin. The peaks of Cx26 and Cx43 expression and Cx31.1 inhibition appeared 12 h after TPA application and 24 h after OA and chrysarobin application. BzPo elevated the levels of Cx26 and Cx43 transcripts later (peak at 2-4 d). In tumor promoter-treated skin, Cx26 and Cx43 plaques were on the plasma membrane of most keratinocytes. Cx31.1 staining was much weaker than in untreated epidermis. Thus, tumor promoters induce a large change in the expression of several Cxs, which in turn may affect both the level of GJIC and the sensitivity of GJlC to regulatory factors.

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

“…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].…”

The relationship between connexins, gap junctions, tissue architecture and tumour invasion, as studied in a novel in vitro model of HPV-16-associated cervical cancer progression

“…Although potent tumour promoters markedly downregulate GJIC in cultured cells (Brissette et al, 1991), intact skin painted with tumour promoters such as 12-O-tetradecanoylphorbol 13-acetate (TPA) shows a dramatic upregulation of Cx26 and Cx43 expression (Budunova et al, 1995(Budunova et al, , 1996Risek et al, 1998). Another skin tumour promoter, ornithine decarboxylase (ODC), alters Cx43 distribution and increases GJIC in normal and h-Ras-transformed keratinocytes in vitro (Shore et al, 2001).…”

Epigenetic properties of the diarrhetic marine toxin okadaic acid: inhibition of the gap junctional intercellular communication in a human intestine epithelial cell line

“…Some connexins have been cloned from multiple species, and their sequences have turned out to be fairly conserved throughout the species, e.g., Cx 43 appears to be the most ubiquitous connexin, sharing 97% amino acid identity among mammals (Beyer 1993). Many tumor promoters have shown their capacity for inhibiting GJIC (Upham et al 1997;Kenne et al 1994;Ruch 1994); thus, the inhibition of GJIC between initiated and surrounded normal cells by tumor promoters is believed to be important in the promotion stage of carcinogenesis (Budunova et al 1996).…”