The trans-golgi compartment: A new distinct intracellular Ca store.
The Golgi apparatus (GA) is an intracellular organelle that plays a central role in lipid and protein posttranslational modification and sorting. In addition, the GA has been also shown to be involved in Ca(2+) signalling, as: (i) it accumulates Ca(2+) within its lumen in an ATP-dependent process catalyzed by two enzymes, the sarco-endoplasmic reticulum Ca(2+) ATPase (SERCA) and the secretory pathway Ca(2+) ATPase1 (SPCA1), and (ii) it releases Ca(2+) during cell stimulation in response to inositol 1,4,5-trisphosphate (IP(3)) receptor activation. Therefore, on this aspect, the GA appears to behave similarly to the major intracellular Ca(2+) store, the endoplasmic reticulum (ER). By using a new FRET-based Ca(2+) probe, specifically targeted to the trans-compartment of the GA, we demonstrate that the organelle is heterogeneous in terms of Ca(2+) handling, the trans-Golgi being insensitive to IP(3) and capable of accumulating Ca(2+) solely through the activity of SPCA1. The SERCA and the IP(3) receptor appear to be restricted to the cis- and intermediate GA compartments. Moreover, selective reduction of Ca(2+) concentration within the trans-Golgi, obtained by reducing the level of SPCA1 by RNAi, results in major alterations of protein trafficking within the secretory pathway and induces the collapse of the entire GA morphology.
Dept Biomedical Sciences; University of Padova and CNR Institute of Neuroscience; Padova, Italy.
Paola
P
Pizzo
Valentina
V
Lissandron
Tullio
T
Pozzan