BACKGROUND

Voltage-gated sodium (Na) channels are heteromeric proteins consisting of a single pore forming α-subunit associated with one or two auxiliary β-subunits. These channels are classically known for being responsible of action potential generation and propagation in excitable cells; but lately they have been reported as widely expressed and regulated in several human cancer types. We have previously demonstrated the overexpression of Na1.6 channel in cervical cancer (CeCa) biopsies and primary cultures, and its contribution to cell migration and invasiveness. Here, we investigated the expression of Na channels β-subunits (Naβs) in the CeCa cell lines HeLa, SiHa and CaSki, and determined their contribution to cell proliferation, migration and invasiveness.

METHODS

We assessed the expression of Naβs in CeCa cell lines by performing RT-PCR and western blotting experiments. We also evaluated CeCa cell lines proliferation, migration, and invasion by in vitro assays, both in basal conditions and after inducing changes in Naβs levels by transfecting specific cDNAs or siRNAs. The potential role of Naβs in modulating the expression of Na α-subunits in the plasma membrane of CeCa cells was examined by the patch-clamp whole-cell technique. Furthermore, we investigated the role of Naβ1 on cell cycle in SiHa cells by flow cytometry.

RESULTS

We found that the four Naβs are expressed in the three CeCa cell lines, even in the absence of functional Na α-subunit expression in the plasma membrane. Functional in vitro assays showed differential roles for Naβ1 and Naβ4, the latter as a cell invasiveness repressor and the former as a migration abolisher in CeCa cells. In silico analysis of Naβ4 expression in cervical tissues corroborated the downregulation of this protein expression in CeCa vs normal cervix, supporting the evidence of Naβ4's role as a cell invasiveness repressor.

CONCLUSIONS

Our results contribute to the recent conception about Naβs as multifunctional proteins involved in cell processes like ion channel regulation, cell adhesion and motility, and even in metastatic cell behaviors. These non-canonical functions of Naβs are independent of the presence of functional Na α-subunits in the plasma membrane and might represent a new therapeutic target for the treatment of cervical cancer.