The Effect Of Homo Selenoprotein SelK On The Ca²⁺ Home Ostasis And The Grow States Of Human Gastric Cancer BGC-823 Cells

Selenium is an essential mammalian trace element. Selenium has important roles in preventing cancer, cardiovascular diseases, viral infections, skin diseases and regulation of thyroid, immune and reproductive function. Selenoproteins are a class of proteins which use one of the stop codon UGA to mediate the inserting of selenocysteine （Sec） into the amino acid sequences of the proteins. Homo selenoprotein SelK has been verified to be located on the endoplasmic reticulum （ER） of the cells, but its biological functions are waiting for further elucidation. The researches on the biological functions of Homo selenoprotein SelK have important theoretical and medical significance.In earlier studies it has been found that the Drosophila seleonoprotein dSelK can induce apoptosis of human gastric cancer cells, and the apoptosis is due to increasing of the intracellular calcium concentration caused by the elevation of the expression of inositol （1.4,5）-trisphosphate receptor （IP3 receptor） after the over-expression of dSelK in human cells. Homo selenoprotein SelK is a homologue of Drosophila selenoprotein dSelK, studies on its biological functions has more important significance for elucidating its importance on human growth and development and revealing its significance on the pathogenesis of some human diseases. In this paper, the over-expression plasmid of selenoprotein SelK, p-SelK-Dsred2, was constructed and transfected into human gastric cancer cells. The changes of intracellular free Ca²⁺concentrations were detected by Ca²⁺ fluorescent prober Fluo-3/AM. The apoptosis of cancer cells was detected by Hoechst33342 staining and tunel test. It was concentrated on that if apoptosis of cancer cells could be induced by the over expression of selenoprotein SelK and if the apoptosis is related to the changes of intracellular free Ca²⁺concentrations.First, the over-expression plasmid in human cells of Homo selenoprotein SelK, p-SelK-Dsred2, was constructed, and the over-expression plasmid of endoplasmic reticulum-located ERp29 （negative control）, p-ERp29-Dsred2, was also constructed. Both of the plasmids were transfected into human gastric cancer cell BGC-823. The intracellular free Ca²⁺ was stained by free Ca²⁺ prober Fluo-3/AM and the changes of intracellular free Ca²⁺ concentrations were detected by laser cofocal microscope and analyzed by fluorescence intensity analysis software. It was showed that the intracellular free Ca²⁺ concentrations were increased 3.27 times （P<0.01） after the overexpression of Homo selenoprotein SelK in human gastric cancer BGC-823 cells, compared to blank control cells. And the intracellular free Ca²⁺ concentrations in the cells over-expressing negative control proteins, ERp29, were not significantly increased （P>0.01）. These indicated that the over expression of Homo selenoprotein SelK could significantly increase intracellular free Ca²⁺ concentrations.Then, the human gastric cancer cell BGC-823 transfected with the two plasmids, p-SelK-Dsred2 and p-ERp29-Dsred2 were stained with Hoechst33342 and tunel reagents. The cells were observed by laser scanning confocal microscope to detect the apoptosis of the cells. It was showed that SelK could induce the apoptosis of the transfected cancer cells, meanwhile the negative control ERp-29 could not induce. These showed that the over expression of human selenoprotein SelK has the function of inducing the apoptosis of human cancer cells.In summary, human selenoprotein SelK has the function of inducing apoptosis of human cancer cell BGC-823. And the apoptosis of cancer cells is mainly due to the imbalance of intracellular calcium concentration caused by the over-expression of Homo selenoprotein SelK. These researches lay a well foundation for systemically elucidating the biological functions of Homo selenoprotein SelK.