The Tumor-Suppressive Function of Connexin43 in Keratinocytes Is Mediated in Part via Interaction with Caveolin-1

Abstract

Connexin43 (Cx43) is known to have tumor-suppressive effects, but the underlying mechanisms are still poorly understood. In keratinocytes, we previously showed that the COOH-terminal domain of Cx43 directly interacts with the tumor suppressor Cav-1. We now show that rat epidermal keratinocytes (REK) that are reduced in Cx43 present features of epithelial-to-mesenchymal transition and are more invasive than their control counterparts, whereas overexpression of Cx43 inhibited the 12-O-tetradecanoyl-phorbol-13-acetate (TPA)-and epidermal growth factor (EGF)-induced invasive properties. Carbenoxolone did not alter the inhibitory effect of Cx43 against TPA-and EGF-induced cell invasion, indicating the involvement of a gap junctional intercellular communication-independent mechanism. Interestingly, the association of Cx43 with Cav-1 was found to be reduced after TPA and EGF treatment. Accordingly, the colocalization of Cx43 with Cav-1 was diminished in cells from a human epidermal squamous cell carcinoma, as well as in sections from human keratinocyte tumors, suggesting that Cx43/Cav-1 interaction plays a protective role against keratinocyte transformation. As opposed to cells that overexpress Cx43-GFP, invasion could be induced in rat epidermal keratinocytes that overexpressed a GFP-tagged truncated mutant of Cx43 (Δ244-GFP) that we previously showed not to interact with Cav-1, as well as in cells that overexpressed Cx43-GFP but were reduced in Cav-1. Our data show that Cx43 possesses tumor-suppressive properties in keratinocytes and provide the first evidence that the Cx43/Cav-1 interaction is altered in keratinocyte transformation processes, as well as in human keratinocyte tumors, and that this association might play a role in Cx43-mediated tumor suppression. Cancer Res; (70)10; 4222-32. ©2010 AACR.

Pannexin1 and Pannexin3 Exhibit Distinct Localization Patterns in Human Skin Appendages and are Regulated during Keratinocyte Differentiation and Carcinogenesis

“…As we previously reported (Penuela et al, 2007, Langlois et al, 2008, Langlois et al, 2010, both proteins were expressed in human epidermis ( Figure 1A and C). A high level of intracellular Panx1 was found in hair follicles ( Figure 1D), while Cx43 was detected as punctate structures ( Figure 1F) (Salomon et al, 1994).…”

Smad ubiquitination regulatory factor-2 controls gap junction intercellular communication by modulating endocytosis and degradation of connexin43

“…Overexpression of Smurf2 has also been found to be associated with more aggressive metastasic properties of breast cancers (Jin et al, 2009). Importantly, loss of Cx43 expression in breast cancer cells has been shown to be associated with EMT and enhanced migration and invasion (Langlois et al, 2010;McLachlan et al, 2006;Plante et al, 2010). The present study establishes a direct functional link between Smurf2 and Cx43 gap junctions, and may have important implications for understanding the molecular basis underlying the loss of Cx43 gap junctions during EMT.…”

“…Dysfunctional gap junction intercellular communication has been causally implicated in a variety of diseases, such as deafness, peripheral neuropathies, skin disorders, cataracts and cardiovascular diseases (Saez et al, 2003). There is also significant evidence that aberrant regulation of gap junction intercellular communication is involved in carcinogenesis, and several connexin isoforms, including Cx43, act as tumor suppressors (King and Lampe, 2004;Langlois et al, 2010;McLachlan et al, 2006;Mesnil et al, 2005;Naus and Laird, 2010;Plante et al, 2010;Sirnes et al, 2012;Zhang et al, 2003).…”

Role of connexins in metastatic breast cancer and melanoma brain colonization

“…It is possible that the loss of GJ expression in primary tumor cells might be important for cells to physically detach from each other. During tumor progression, this could contribute to the local cell invasion into the surrounding stroma and vasculature, which are early steps in the metastatic process (Laird, 2006;Naus and Laird, 2010;Langlois et al, 2010). On the other hand, Cx43 and 26 were found to be upregulated in established breast cancer and melanoma metastatic lesions suggesting that connexins play roles in late metastatic steps involving vascular penetration and tissue colonization (Elzarrad et al, 2008;Ito et al, 2002;Naoi et al, 2007;Haass et al, 2010;Saito-Katsuragi et al, 2007;Chao et al, 2012).…”