An interesting new field in cancer research is the role of voltage-gated Na+ channels (VGSCs) in cancer cell invasion. Expression of these ion channels is normally restricted to excitable cells; however functional expression has been demonstrated in multiple cancer cell types where channel activity leads to changes in invasion potential in vitro. This study investigated the consequences of functional expression of Na v1.5, a protein encoded by SCN5A, in colon cancer cell lines. Pharmacological inhibition of channel activity led to a decrease in invasion potential, whereas activation led to an increase in invasion potential. Moreover, upon examination of patient samples we found that protein expression was restricted to malignant tissue. What has remained largely uncharacterized is the mechanism by which these channels promote oncogenic behavior. We explored the mechanism of VGSC-mediated invasion potential on the basis of reported links between VGSC activity and gene expression in excitable cells. Probabilistic modeling of loss-of-function screens and microarray data established a clear role of VGSC SCN5A as a key regulator of a colon cancer invasion network. Coincidentally, many genes regulated by SCN5A have binding sites for transcription factors phosphorylated by ERK1/2. We hypothesized that VGSC activity promotes MAPK activation, a pathway activated during neurogenesis and deregulated in cancer. Using pharmacological inhibition of MAPK, we demonstrated the requirement of this molecule for colon cancer invasion in vitro. Furthermore, we showed that MAPK activity is reduced when colon cancer cells are treated with the VGSC blocker, lidocaine, and persistently enhanced when treated with the VGSC activator, veratridine. This persistent activation and the increase in invasion potential were lost when veratridine was used in the presence of a PKA inhibitor or with a siRNA directed against Rap1. Lastly, we demonstrated increased Src activity after treatment with veratridine. Taken together our data suggest that VGSC activation increases MAPK activity through activation of PKA, Rap1 and Src in colon cancer cells. This is the first study demonstrating functional expression of VGSCs in colon cancer cells and the first to illustrate both genomic and molecular signaling pathways activated in response to VGSC activity to promote oncogenesis in colon cancer cells.
|Advisor:||Lee, Norman H., Hales, Tim G.|
|Commitee:||Ceryak, Susan, Chiappinelli, Vincent, O'Brien, Travis, Patel, Vyomesh|
|School:||The George Washington University|
|School Location:||United States -- District of Columbia|
|Source:||DAI-B 72/05, Dissertation Abstracts International|
|Subjects:||Molecular biology, Cellular biology, Oncology|
|Keywords:||Colon cancer, Gene network, Invasion, Metastatic potential, Sodium ion channels, Voltage-gate|
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