The small GTPase RhoA regulates the expression and function of the sodium channel Nav1.5 in breast cancer cells

Our plain-English summary of The small GTPase RhoA regulates the expression and function of the sodium channel Nav1.5 in breast cancer cells, by C. Dulong, Y.J. Fang, C. Gest, et al (International Journal of Oncology, 2014).

The study

• Authors: C. Dulong, Y.J. Fang, C. Gest, M.H. Zhou, C. Patte-Mensah, A.G. Mensah-Nyagan, J.P. Vannier, H. Lu, C. Soria, L. Cazin, Y.A. Mei, R. Varin, H. Li
• Journal: International Journal of Oncology
• Published: 2014;44(2):539-47
• Cited by: 21 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Voltage-gated Na+ channels (VGSCs) are highly expressed in several types of carcinomas including breast, prostate and lung cancers as well as in mesothelioma and cervical cancers. Although the VGSCs activity is considered crucial for the potentiation of cancer cell migration and invasion, the mechanisms responsible for their functional expression and regulation in cancer cells remain unclear. In the present study, the role of the small GTPase RhoA in the regulation of expression and function of the Nav1.5 channel in the breast cancer cell lines MDA-MB 231 and MCF-7 was investigated. RhoA silencing significantly reduced both Nav1.5 channel expression and sodium current indicating that RhoA exerts a stimulatory effect on the synthesis of an active form of Nav1.5 channel in cancer cells. The inhibition of Nav1.5 expression dramatically reduced both cell invasion and proliferation. In addition, a decrease of RhoA protein levels induced by Nav1.5 silencing was observed. Altogether, these findings revealed: i) the key role of the small GTPase RhoA in upregulation of Nav1.5 channel expression and tumor aggressiveness, and ii) the existence of a positive feedback of Nav1.5 channels on RhoA protein levels.

In plain English

This laboratory study did not involve asbestos; mesothelioma is mentioned only as background. The authors worked with two human breast cancer cell lines grown in dishes, MDA-MB-231 (described as invasive) and MCF-7 (less invasive). They used small interfering RNAs to switch down either a protein called RhoA or a sodium channel called Nav1.5. In MDA-MB-231 cells, silencing RhoA cut the peak sodium current by 50.5% (1016.1 pA in 20 treated cells versus 2054.7 pA in 16 control cells). Silencing Nav1.5 reduced it to 288.0 pA in 25 cells. Silencing RhoA lowered Nav1.5 gene activity in both cell lines. Silencing Nav1.5 did not change RhoA gene activity but reduced RhoA protein by more than 50%. Silencing Nav1.5 inhibited growth of MDA-MB-231 cells after 72 hours, while RhoA silencing failed to exert any effect on their growth. In MCF-7 cells, no significant effect of either treatment on growth was detected. Both treatments reduced invasion by MDA-MB-231 cells in a chamber test. The authors concluded that RhoA plays a key role in sodium current, most probably through the level of Nav1.5 channels.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: laboratory (in vitro) experiment on human breast cancer cell lines, using gene silencing (siRNA), patch-clamp electrical recording, real-time RT-PCR, western blot, and proliferation and invasion assays
• Who was studied: two human breast cancer cell lines, MDA-MB-231 (invasive) and MCF-7 (less invasive), obtained from ECACC; no human subjects
• Exposure: no asbestos exposure; cells were treated with siRNAs (10 nM) targeting RhoA or the Nav1.5 sodium channel, compared with a negative control siRNA
• Main results:
  • In MDA-MB-231 cells, RhoA silencing reduced peak sodium current by 50.5% (1016.1±163.2 pA, n=20 treated cells) compared with control cells (2054.7±380.5 pA, n=16), p<0.05
  • In MDA-MB-231 cells, RhoA silencing did not significantly change the voltage at which the sodium channels inactivate (half-inactivation -85.8±0.6 mV in treated cells, n=16, and -86.1±0.4 mV in untreated cells, n=13)
  • In MDA-MB-231 cells, Nav1.5 silencing reduced peak sodium current to 288.0±53.5 pA (n=25), compared with control 2054.7±380.5 pA (n=16)
  • RhoA silencing significantly decreased Nav1.5 mRNA levels in both cell lines (MDA-MB-231: p<0.001, n=4; MCF-7: p<0.05, n=3)
  • Nav1.5 silencing did not change RhoA mRNA, but after 48 hours it reduced RhoA protein by more than 50% (MDA-MB-231: p<0.01, n=4; MCF-7: n=2, no p-value given)
  • Nav1.5 silencing inhibited proliferation of MDA-MB-231 cells (p<0.0001, n=7 after 72 hours), while RhoA silencing failed to exert any effect on their proliferation. In MCF-7 cells, no significant effect on proliferation was detected after either treatment (n=8).
  • Both RhoA and Nav1.5 silencing significantly inhibited invasion by MDA-MB-231 cells (p<0.0001, n=6 at 48 hours; p<0.001, n=4 at 72 hours). RhoA silencing appeared to have a more pronounced effect. MCF-7 cells were not invasive in this test.
• The authors' conclusion: The authors concluded that RhoA plays a key role in sodium current, most probably by modulating the level of Nav1.5 channels. They also reported a positive feedback of Nav1.5 on RhoA protein levels.
• Limitations the authors state:
  • The authors state it remains to be studied in other normal and tumor cell types whether this effect of RhoA is a general physiological mechanism or specific to tumors.

Topics

Medical terms in this study, explained in our Lexicon: Carcinoma, Lung Cancer, Mesothelioma.

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