Inhibition of protein tyrosine phosphatase 1B by reactive oxygen species leads to maintenance of Ca2+ influx following store depletion in HEK 293 cells

Depletion of inositol 1,4,5 trisphosphate-sensitive Ca2+ stores generates a yet unknown signal, which leads to increase in Ca2+ influx in different cell types [J.W. Putney Jr., A model for receptor-regulated Calcium entry, Cell Calcium 7 (1986) 1-12]. Here, we describe a mechanism that modulates this store-operated Ca2+ entry (SOC). Ca2+ influx leads to inhibition of protein tyrosine phosphatase 1B (PTPIB) activity in HEK 293 cells [L. Sternfeld, er al., Tyrosine phosphatase PTP1B interacts with TRPV6 in vivo and plays a role in TRPV6-mediated calcium influx in HEK293 cells, Cell Signal 17 (2005) 951-960]. Since Ca2+ does not directly inhibit PTPlB. we assumed an intermediate signal, which links the rise in cytosolic Ca2+ concentration and PTP1B inhibition. We now show that Ca2+ influx is followed by generation of reactive oxygen species (ROS) and that it is reduced in cells preincubated with catalase. Furthermore. Ca2+-dependent inhibition of PTP1B can be abolished in the presence of catalase. H2O2 (100 mu M) directly added to cells inhibits PTP1B and leads to increase in Ca2+ influx after store depletion. PP1, an inhibitor of the Src family tyrosine kinases. prevents HO-indUced Ca2+ influx influx channel or a protein involved influx. Our results show that ROS act as fine tuning modulators of Ca2+ entry. We assume that the Ca2+ its regulation remains tyrosine phosphorylated as a consequence of PTP1B inhibition by ROS. This leads to maintained Ca2+ influx in the manner of a positive feedback loop. (c) 2006 Elsevier Ltd. All rights reserved.