Differential calcium handling by the cis and trans regions of the Golgi apparatus

High Ca2+ content in the Golgi apparatus (Go) is essential for protein processing and sorting. Additionally, Go can shape the cytosolic Ca2+ signals by releasing or sequestering Ca2+. We generated two new aequorin-based Ca2+ probes to specifically measure Ca2+ in the cis-/cis to medial Golgi (cGo) or the trans-Golgi (tGo). Ca2+ homeostasis in these compartments and in the ER has been studied and compared. Moreover, the relative size of each subcompartment was estimated from aequorin consumption. We find that the cGo accumulates Ca2+ to high concentrations (150-300 µM) through the sarco-endoplasmic reticulum Ca2+ ATPase (SERCA). The tGo, in turn, is divided into two subcompartments, tGo1 and tGo2. The subcompartment tGo1 contains 20% of the aequorin and has a high [Ca2+] inside; Ca2+ is accumulated in this subcompartment via the Secretory Pathway Ca2+-ATPase 1 (SPCA1) at very high affinity (K50 = 30 nM). The subcompartment tGo2 contains 80% of aequorin, has a lower [Ca2+] and no SPCA1 activity; Ca2+ uptake happens through SERCA and is slower than in tGo1. The two tGo subcompartments, tGo1 and tGo2, are diffusionally isolated. Inositol-trisphosphate mobilizes Ca2+ from cGo and tGo2, but not from tGo1, whereas caffeine releases Ca2+ from all the Golgi regions, and NAADP and cADPR from none.

Source: BJ Cell - December 16, 2014 Category: Biochemistry Authors: F J Aulestia, M Teresa Alonso, J Garcia-Sancho Tags: BJ Signal Source Type: research