The Potential Impact of Connexin 43 Expression on Bcl-2 Protein Level and Taxane Sensitivity in Head and Neck Cancers–In Vitro Studies

Abstract

The poor prognosis of head and neck squamous cell carcinoma (HNSCC) is partly due to the lack of reliable predictive markers. Connexin 43 (Cx43) protein and its cell-communication channels have been assigned tumor suppressor functions while the anti-apoptotic Bcl-2 (B-cell lymphoma-2) protein has been associated with negative prognostic significance in cancer. This study aimed to test the role of Cx43 protein on Bcl-2 expression, tumor progression and response to taxane-based treatment in HNSCC. Human papillomavirus (HPV) negative HNSCC cell lines were tested for paclitaxel sensitivity through measuring apoptosis induction, cell viability and changes in Cx43 and Bcl-2 levels using flow cytometry, cell viability assay, immunocytochemistry and western blot. Inhibition of Cx43 expression using siRNA increased Bcl-2 protein levels in SCC25 (tongue squamous cell carcinoma) cells, while forced Cx43 expression reduced Bcl-2 levels and supported paclitaxel cytotoxicity in FaDu (hypopharynx squamous cell carcinoma) cells. In vitro results were in line with protein expression and clinicopathological features tested in tissue microarray samples of HNSCC patients. Our data demonstrate that elevated Cx43 and reduced Bcl-2 levels may indicate HNSCC sensitivity to taxane-based treatments. On the contrary, silencing of the Cx43 gene GJA1 (gap junction protein alpha-1) can result in increased Bcl-2 expression and reduced paclitaxel efficiency. Clinical tumor-based analysis also confirmed the inverse correlation between Cx43 and Bcl-2 expression.

18-α-glycyrrhetinic acid alleviates oxidative damage in periodontal tissue by modulating the interaction of Cx43 and JNK/NF-κB pathways

“…Cx43 may control cell “fate” by delivering pro- and anti-apoptotic signals. Gurbi et al (2010) found that Bcl-2 is an important target of Cx43-mediated apoptosis. In addition, Sun et al (2012) suggested that Cx43 interacts directly with Bax and thus initiates the intrinsic apoptotic pathway.…”

The important role of connexin 43 in subarachnoid hemorrhage-induced cerebral vasospasm

“…Knockdown of Cx43 was performed by using an HVJ envelope (HVJ-E) transfection kit (GenomONE™, Cosmo Bio Co., Ltd., Tokyo, Japan), which is widely used for in vivo siRNA transfer [32, 33]. Cx43 siRNA (siGENOME SMARTpool, mouse GJA1, Thermo Scientific) [34, 35] was incorporated into the HVJ-E according to the manufacturer’s instructions. Two days prior to SAH induction, siRNA (5 pg in 10 μl sterile saline) was slowly injected into the cisterna magna as pretreatment, similar to the induction of SAH described above.…”

Taxanes in the Treatment of Head and Neck Squamous Cell Carcinoma

“…These kinases phosphorylate and activate c-Jun and ATF-2, which induce the pro-apoptotic signaling [51]. In addition, taxanes disrupt the function of anti-apoptotic proteins, such as Bcl-2 and Bcl-xL, which normally prevent apoptosis by inhibiting the release of cytochrome c from the mitochondria [52]. Taxanes modulate the expression or activity of these anti-apoptotic proteins, promoting the release of cytochrome c and the activation of the caspase cascade.…”