Cx43 suppresses mammary tumor metastasis to the lung in a Cx43 mutant mouse model of human disease

Abstract

Gap junctions, the channels formed by the connexin (Cx) family of proteins, are responsible for direct intercellular communication. Although connexins are considered as tumor suppressors, their overall role in cancer onset, progression and metastasis is somewhat controversial. This study uses a novel Cx43 mutant mouse model (G60S mice) and cross-breeding strategies to determine the role of Cx43 in all stages of breast tumorigenesis. G60S mice were cross-bred with ErbB2 overexpressing mice, and spontaneous and 7,12-dimethylbenz[a]anthracene (DMBA)-induced tumor development was evaluated. Mice were killed when tumors reached B1 cm 3 or when mice showed signs of critical illness. In both spontaneous and DMBA studies, onset of palpable tumors was delayed in G60S mice compared with mice in control groups. Moreover, while tumors from control mice reached the size threshold, most DMBA-exposed Cx43 mutant mice were killed prematurely because of labored breathing, independent of the presence of a palpable tumor. Reduced Cx43 levels in Cx43 mutant mice were accompanied by extensive mammary gland hyperplasia. Lung histology revealed that all Cx43 mutant mice exhibited mammaglobin-positive mammary gland metastases to the lung, and the number of metastases was increased by threefold in Cx43 mutant mice on treatment with DMBA. Thus, while reduced levels of Cx43 delayed the onset of palpable tumors, normal Cx43 levels inhibited mammary gland tumor metastasis to the lungs. Understanding the mechanisms of how Cx43, which is expressed primarily in myoepithelial cells, inhibits mammary gland tumor metastasis is critical as Cx43 is assessed as a candidate for therapeutic intervention.

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).…”

Connexin 43: Key roles in the skin

“…On days 1 and 2 subsequent to injury, the mRNA and protein expression levels of Cx43 were significantly decreased at the wound edge, and readjusted to normal levels (like those in non-injured skin) from day 3 onwards in mice (10). By contrast, the level of Cx43 expression remains at a low level throughout the entire healing process in humans (29). Cx43 reduction has been shown to be associated with: i) Remodeling of the extracellular matrix (ECM) (38); ii) proliferation and migration of keratinocytes and fibroblasts (10,39,40); and iii) regulation of inflammatory responses through certain cytokines, chemokines or growth factors (38,40).…”

“…Increasing evidence indicates that Cx43 directly affects the proliferation and migration of keratinocytes and fibroblasts (29). Cx43 also participates in wound healing (30), hyperkeratosis (31) and tumor development of skin (32,33).…”

Role of connexins in metastatic breast cancer and melanoma brain colonization

“…Also, mice with Cx43 inactivating mutations when crossed with the ErbB2 overexpressing mice show delayed onset of palpable mammary tumors while displaying increased pulmonary metastases (Plante et al, 2011). On the other hand, in melanoma, breast, and gastric cancers connexin 43 (Cx43) and 26 (Cx26) are upregulated in invasive lesions and in cells that disseminate to the lymph nodes (Naoi et al, 2007;Haass et al, 2010;Saito-Katsuragi et al, 2007;Elzarrad et al, 2008;Chao et al, 2012).…”