Metastasis is a major cause of cancer-related deaths. Evidence is accumulating for the role of various ion channels and ion pumps in metastatic activity of tumor cells. The plasma membrane Ca2+ ATPase (PMCA) has been identified as a metastasis suppressor, and an increased expression of voltage gated sodium channels (Nav) have been shown to promote metastasis among other membrane proteins.

The group of Rita Padanyi has described that increased expression of PMCA4b decreases motility and metastatic activity of melanoma cells. PIP2 and PIP3 lipids are one of the major modulators of actin cytoskeleton, cellular motility and metastatic activity in tumor cells. PMCA transporters have positively charged residues at the interface region of the membrane bilayer containing PIP2 binding pockets. Binding of PIP2 molecules can influence the conformational changes of PMCA during the enzyme cycle.

The expression of sodium channels in cancer cells has recently been observed, and Nav inhibitors have been found to reduce metastasis. The group of Arpad Mike identified specific mechanisms of action for different Nav inhibitors, and they found that therapeutic applicability corresponded with mechanisms of action. Understanding the mode of action in Nav inhibitors that are effective inhibitors of metastasis may help to identify novel potential Nav inhibitor anti-metastatics.

Both the pro-metastatic role of Nav-s, and the anti-metastatic role of PMCA-s may be related to calcium signaling, thus their effects may be supra-additive.

In this project we will study the combined effect of these two transmembrane proteins on the progression of tumors. We aim to integrate cell biology and electrophysiology methods as well as in silico molecular modeling. We will investigate the expression patterns of the two proteins in different tumor cell lines. We will study the effect of anti-tumor drugs on the expression patterns of these proteins and cell migration. We will investigate whether Nav inhibitors, which are effective against metastasis, possess a specific mode of action or bind to a specific binding site on these proteins. Our hypotheses will be tested by the group of Tamas Hegedus using in silico modeling methods. In addition, they will investigate conformational transitions of PMCA in the presence of PIP2 in molecular dynamics simulations, in order to understand atomic level interactions between this pump and lipid for drug target identification. Completion of the project will help developing novel, more effective drugs or drug-combinations against tumor metastasis.

Tamás Hegedűs - Árpád Mike - Rita Padányi

Report I. - 2017 June