Mitochondrial localization as a determinant of capacitative Ca2+ entry in HeLa cells.
Whether different subsets of mitochondria play distinct roles in shaping intracellular Ca2+ signals is presently unresolved. Here, we determine the role of mitochondria located beneath the plasma membrane in controlling (a) Ca2+ release from the endoplasmic reticulum (ER) and (b) capacitative Ca2+ entry. By over-expression of the dynactin subunit dynamitin, and consequent inhibition of the fission factor, dynamin-related protein (Drp-1), mitochondria were relocalised from the plasma membrane towards the nuclear periphery in HeLa cells. The impact of these changes on free calcium concentration in the cytosol ([Ca2+]c), mitochondria ([Ca2+]m) and ER ([Ca2+]ER) was then monitored with specifically-targeted aequorins. Whilst dynamitin over-expression increased the number of close contacts between the ER and mitochondria by >2.5-fold, assessed using organelle-targeted GFP variants, histamine-induced changes in organellar [Ca2+] were unaffected. By contrast, Ca2+ influx elicited significantly smaller increases in [Ca2+]c and [Ca2+]m in dynamitin-expressing than in control cells. These data suggest that the strategic localisation of a subset of mitochondria beneath the plasma membrane is required for normal Ca2+ influx, but that the transfer of Ca2+ ions between the ER and mitochondria is relatively insensitive to gross changes in the spatial relationship between these two organelles.
Varadi
Aniko
A
Henry Wellcome Laboratories for Integrated Cell Signalling and Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, Bristol BS8 1TD, UK.
Cirulli
Vincenzo
V
Rutter
Guy A
GA
D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D015220:Calcium Channels / Q000032:analysis / Q000378:metabolism*; D000072159:Dynactin Complex; D006367:HeLa Cells; D006801:Humans; D008869:Microtubule-Associated Proteins / Q000032:analysis / Q000096:biosynthesis; D008928:Mitochondria / Q000737:chemistry* / Q000378:metabolism*
D015220:Calcium Channels; C000606361:DCTN2 protein, human; D000072159:Dynactin Complex; D008869:Microtubule-Associated Proteins; D002118:Calcium