Orai1, a critical component of store-operated Ca²⁺ entry, is functionally associated with Na⁺/Ca²⁺ exchanger and plasma membrane Ca²⁺ pump in proliferating human arterial myocytes

Abstract

Ca(2+) entry through store-operated channels (SOCs) in the plasma membrane plays an important role in regulation of vascular smooth muscle contraction, tone, and cell proliferation. The C-type transient receptor potential (TRPC) channels have been proposed as major candidates for SOCs in vascular smooth muscle. Recently, two families of transmembrane proteins, Orai [also known as Ca(2+) release-activated Ca(2+) channel modulator (CRACM)] and stromal interacting molecule 1 (STIM1), were shown to be essential for the activation of SOCs mainly in nonexcitable cells. Here, using small interfering RNA, we show that Orai1 plays an essential role in activating store-operated Ca(2+) entry (SOCE) in primary cultured proliferating human aortic smooth muscle cells (hASMCs), whereas Orai2 and Orai3 do not contribute to SOCE. Knockdown of Orai1 protein expression significantly attenuated SOCE. Moreover, inhibition of Orai1 downregulated expression of Na(+)/Ca(2+) exchanger type 1 (NCX1) and plasma membrane Ca(2+) pump isoform 1 (PMCA1). The rate of cytosolic free Ca(2+) concentration decay after Ca(2+) transients in Ca(2+)-free medium was also greatly decreased under these conditions. This reduction of Ca(2+) extrusion, presumably via NCX1 and PMCA1, may be a compensation for the reduced SOCE. Immunocytochemical observations indicate that Orai1 and NCX1 are clustered in plasma membrane microdomains. Cell proliferation was attenuated in hASMCs with disrupted Orai1 expression and reduced SOCE. Thus Orai1 appears to be a critical component of SOCE in proliferating vascular smooth muscle cells, and may therefore be a key player during vascular growth and remodeling.

Ca 2 + signaling by plant Arabidopsis thaliana Pep peptides depends on AtPepR1, a receptor with guanylyl cyclase activity, and cGMP-activated Ca 2+ channels

“…Such microdomain signaling events occur in animal nucleotidyl cyclases and animal cell cyclic nucleotide signaling (39). Some Ca 2+ channels are present in multienzyme protein complexes with proteins that generate their activating ligands (1). It is intriguing to note that Ca 2+ signaling involving the Ca 2+ channel Orai1 that acts in animal immune signaling involves Orai1:adenylyl cyclase protein complexes and microdomains of cyclic nucleotide elevation (40,41).…”

“…In the case of multicellular animals, a two decade-long search for the identity of the protein facilitating immune-related cell membrane inward Ca 2+ channel currents ended recently in the cloning of a gene encoding Orai1 (1,2). The name of this immune portal refers to the keepers of Heaven's gate in Greek mythology and bespeaks the significance of the work (3).…”

STIM1/Orai1-mediated store-operated Ca2+ entry: the tip of the iceberg

“…Disruption of Orai1 expression resulted in reduced SOCE and attenuated cell proliferation in human VSMCs, demonstrating that Orai1 is critical to this process (34). Additionally, the STIM1/Orai1 pathway seems to play a role in the SOCE-induced proliferatory activity of endothelial cells (35) and STIM1 siRNA abrogated both proliferation and migration of endothelial progenitor cells (36).…”

STIM and ORAI proteins: crucial roles in hallmarks of cancer

“…Several publications suggest that ORAI2 mediates SOCE in immune cells with silenced ORAI1 (41,103). However, no effect of siRNA against ORAI2 on SOCE has been reported by other groups (8,97).…”