TRPM7 kinase domain rather than the channel regulates breast cancer cell migration and tumor metastasis

Abstract

The channel‐kinase TRPM7 (transient receptor potential melastatin 7) is a bifunctional protein consisting of a cation channel that is permeable to Mg2+, Ca2+ and Mn2+ ions fused to a C‐terminal kinase domain. A growing number of studies with clinical significance suggest that TRPM7 is linked to adhesion and migration of breast cancer cells and promotes breast tumor metastasis. While the channel properties of TRPM7 have been studied extensively, little is known about its kinase activity and how it is linked to the control of actomyosin contractility. To understand the functions of the kinase domain we identified the first cell‐permeable inhibitor of the kinase domain (TRPM7‐IN‐1) and developed MDA‐MB‐231 cell lines in which TRPM7 is knocked out by CRISPR/Cas9 (KO), and in which various forms of TRPM7 were stably re‐expressed. These were wild type TRPM7 (WT), a kinase‐inactive mutant of TRPM7 (KD), and TRPM7 containing a truncated kinase domain (KT). TRPM7 KO significantly inhibited MDA‐MB‐231 cells migration. Only expression of the wild type TRPM7 (WT) rescued the migration phenotype, supporting a role for the kinase domain and not the channel in the regulation of cell migration. TRPM7‐IN‐1 decreased the binding of Myosin IIB to TRPM7 in HEK293 and MDA‐MB‐231 cells. And when MDA‐MB‐231 cells were treated with increasing doses of TRPM7‐IN‐1, TRPM7 phosphorylation at Ser‐1569 and its downstream Myosin IIa phosphorylation at Ser1943 were completely abrogated at a concentration of 5 μM. TRPM7‐IN‐1 inhibited MDA‐MB‐231 and BT 549 cell migration and invasion, while treatment of the KO cells with TRPM7‐IN‐1 showed no further inhibition of migration. Electrophysiological assessment of the TRPM7 channel revealed that the inhibitor did not affect the channel function in MD‐MB‐231 cells, supporting the notion that the inhibitor affects the migration exclusively through the inhibition of the TRPM7 kinase domain. Finally, in an experimental metastasis model, TRPM7‐IN‐1 significantly impeded metastasis to the lung. In conclusion, inhibition of TRPM7 kinase activity may reduce or block breast tumor progression and/or metastasis.Support or Funding InformationFinancial support by grants from the National Institute of General Medical Sciences (R01GM059802), the Welch Foundation (F‐1390) and Cancer Prevention and Research Institute of Texas to KND.