The post-translational arginylation of proteins is the
covalent union of arginine to an acidic amino acid at the N-terminal position.
We characterized calreticulin (CRT) as substrate of this modification. This modified
protein (R-CRT) showed a sub-cellular localization in the cytosol different
from that known for CRT in the endoplasmic reticulum. We
determined that the decrease in cytosolic calcium concentration increases the
production of R-CRT, witch is associated with stress granules (SGs).
Furthermore, we found R-CRT associated to SGs in cells exposed to oxidative stress
and heat shock, similar to the calcium stress condition. However, in cells
treated with UV, R-CRT does not aggregate with SGs. In correlation with these
observations, cytosolic calcium decreases in both oxidative stress and heat
shock conditions, whereas after the UV, calcium levels are unchanged. After
withdrawal of the stressor, SGs rapidly disappear but the R-CRT remains
aggregated after 2 h. Thus, there are different rates of disassociation between
SGs and R-CRT aggregates after the environmental stress has ended. These
changes correlate with the restoration of calcium levels, which in itself
depend on the magnitude of the stress.
In conclusion, intracellular calcium changes promote the selective association
of R-CRT to SGs under particular stress conditions.
Supported by SECyT-UNC,
CONICET, ANPCyT-PICT.
