The Effect of Increased Intracellular Calcium on the Localization of the Catabolic Subunit of Telomerase, hTERT, in HeLa Cells

Abstract

In cancer cells, telomeres are constantly repaired by telomerase allowing them to avoid reaching a critical length where the cell becomes senescent.  Overtime, aerobic respiration in the mitochondria can create an increase in intracellular reactive oxygen species (ROS) that causes telomerase reverse transcriptase (hTERT), the catabolic subunit of telomerase, to exit the nucleus.  Without hTERT in the nucleus, telomerase cannot function to repair telomere ends, inducing senescence.  One effect of increased ROS production is the activation of calcium channels leading to an increase in intracellular calcium.  We attempted to mimic this ROS induced increase in intracellular calcium levels by administering  0.5uM of Thapsigargin to HeLa cells in order to determine if an increase in calcium levels alone would be sufficient to cause hTERT to exit the nucleus.  Immunofluorescene was used to visualize fluorescent intensities of hTERT in the nucleus after administration of the drug in conjunction with visualization of Ran as an indicator of functional nuclear transport.  We predicted thapsigargin would disrupt nuclear transport and cause hTERT to exit the nucleus.  Image J software was used to compare nuclear fluorescence intensities between treated and control cells.  Our results indicated that administration of thapsigargin caused a significant decrease in nuclear levels of hTERT in conjunction with decreased nuclear levels of Ran.  Our findings could provide a potential method to induce cellular senescence in cancer cells by inducing mislocalization of hTERT and Ran.