Store-operated calcium (Ca(2+)) entry (SOCE) is important for cellular activities such as gene transcription, cell cycle progression and proliferation in most non-excitable cells. Stromal interaction molecule 1 (STIM1), a newly identified Ca(2+)-sensing protein, monitors the depletion of endoplasmic reticulum (ER) Ca(2+) stores and activates store-operated Ca(2+) channels at the plasma membrane to induce SOCE. To investigate the possible roles of STIM1 in tumor growth in relation to SOCE, we established STIM1 knockdown (KD) clones of human epidermoid carcinoma A431 cells by RNA interference. Thapsigargin, an inhibitor of ER Ca(2+)-ATPase, -induced and phospholipase C-coupled receptor agonist-induced SOCEs were reduced in two STIM1 KD clones compared to a negative control clone. Re-expression of a KD-resistant full-length STIM1, but not a Ca(2+) release-activated Ca(2+) channel activation domain (CAD)-deleted STIM1 mutant, in the KD clone restored the amplitude of SOCE, suggesting the specificity of the STIM1 knockdown. The cell growth of the STIM1 KD clones was slower than that of the negative control clone. DNA synthesis assessed by BrdU incorporation, as well as EGF-stimulated EGF receptor activation, decreased in the STIM1 KD clones. Xenograft growth of the STIM1 KD clones was significantly retarded compared with that of the negative control. Cell migration was attenuated in the STIM1 KD clone and the STIM1 silencing effect was reversed by transient re-expression of the full-length STIM1 but not CAD-deletion mutant. These results indicate that STIM1 plays an important role in SOCE, cell-growth and tumorigenicity in human epidermoid carcinoma A431cells, suggesting the potential use of STIM1-targeting agents for treating epidermoid carcinoma.
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