Unique characteristics of Ca ²⁺ homeostasis of the trans -Golgi compartment

Abstract

Taking advantage of a fluorescent Ca 2+ indicator selectively targeted to the trans -Golgi lumen, we here demonstrate that its Ca 2+ homeostatic mechanisms are distinct from those of the other Golgi subcompartments: ( i ) Ca 2+ uptake depends exclusively on the activity of the secretory pathway Ca 2+ ATPase1 (SPCA1), whereas the sarco-endoplasmic reticulum Ca 2+ ATPase (SERCA) is excluded; ( ii ) IP 3 generated by receptor stimulation causes Ca 2+ uptake rather than release; ( iii ) Ca 2+ release can be triggered by activation of ryanodine receptors in cells endowed with robust expression of the latter channels (e.g., in neonatal cardiac myocyte). Finally, we show that, knocking down the SPCA1, and thus altering the trans -Golgi Ca 2+ content, specific functions associated with this subcompartment, such as sorting of proteins to the plasma membrane through the secretory pathway, and the structure of the entire Golgi apparatus are dramatically altered.

Lack of Evidence for Presenilins as Endoplasmic Reticulum Ca2+ Leak Channels

“…To determine whether PS influences resting [Ca 2ϩ ] Golgi or ionomycin-induced Ca 2ϩ release from the Golgi, we employed D1-Golgi-cameleon (41). Basal Golgi apparatus YFP/CFP ratios were not different (p Ͼ 0.1) between the PS DKO (2.45 Ϯ 0.07) and hPS1 (2.61 Ϯ 0.07) cells (Fig.…”

Genetically Encoded Fluorescent Indicators for Organellar Calcium Imaging

“…GT-YC3.3 was targeted to the Golgi by incorporating the N-terminal sequence of type II galactosyltransferase, and was used to successfully detect Ca 2þ release from the Golgi upon depletion of the luminal Ca 2þ with ionomycin, a Ca 2þ ionophore, although its affinity to Ca 2þ (K d ¼ 1.5 mM) appears rather high for Golgi Ca 2þ concentrations. Later, cameleon-type Golgi GECIs with lower Ca 2þ affinities were developed: Go-D1cpv and medial Go-D1cpv localized in the trans and medial Golgi through incorporation of the N-terminal sequence of sialyl-transferase I and 1,6 n-acetyl glucosaminyl transferase, respectively (42,43). These indicators showed that Ca 2þ uptake into the Golgi depends on both secretory pathway Ca 2þ ATPase1 and sarco/endoplasmic reticulum Ca 2þ ATPase, but their activities are differently regulated between the trans and medial Golgi.…”

The Golgi Apparatus: Panel Point of Cytosolic Ca2+Regulation

“…However, Cifuentes et al [10] argued that the RyR channel probably takes part in the Golgi Ca 2+ release in rat sympathetic neurons, and Lissandrona et al [11] proved that the trans -Golgi subcompartment is endowed with functional RyRs in neonatal cardiac myocytes. Therefore, it also can be confirmed that RyRs may locate on the GA; hitherto they have been discovered in trans -Golgi subcompartments.…”

“…Fluorescence microscopy of the endogenous expression of SPCA1 in HeLa [46] and PC12 cells [47] also revealed its Golgi-like distribution. Furthermore, SPCA1 was found to be present in the trans -Golgi stacks and networks from human keratinocytes using immunocytochemistry and sucrose gradient centrifugation [11,47]. …”