AMPK-independent induction of autophagy by cytosolic Ca2+ increase.

Autophagy is a eukaryotic lysosomal bulk degradation system initiated by cytosolic cargo sequestration in autophagosomes. The Ser/Thr kinase mTOR has been shown to constitute a central role in controlling the initiation of autophagy by integrating multiple nutrient-dependent signaling pathways that crucially involves the activity of PI3K class III to generate the phosphoinositide PI(3)P. Recent reports demonstrate that the increase in cytosolic Ca(2+) can induce autophagy by inhibition of mTOR via the CaMKK-alpha/beta-mediated activation of AMPK. Here we demonstrate that Ca(2+) signaling can additionally induce autophagy independently of the Ca(2+)-mediated activation of AMPK. First, by LC3-II protein monitoring in the absence or presence of lysosomal inhibitors we confirm that the elevation of cytosolic Ca(2+) induces autophagosome generation and does not merely block autophagosome degradation. Further, we demonstrate that Ca(2+)-chelation strongly inhibits autophagy in human, mouse and chicken cells. Strikingly, we found that the PI(3)P-binding protein WIPI-1 (Atg18) responds to the increase of cytosolic Ca(2+) by localizing to autophagosomal membranes (WIPI-1 puncta) and that Ca(2+)-chelation inhibits WIPI-1 puncta formation, although PI(3)P-generation is not generally affected by these Ca(2+) flux modifications. Importantly, using AMPK-alpha1(-/-)alpha2(-/-) MEFs we show that thapsigargin application triggers autophagy in the absence of AMPK and does not involve complete mTOR inhibition, as detected by p70S6K phosphorylation. In addition, STO-609-mediated CaMKK-alpha/beta inhibition decreased the level of thapsigargin-induced autophagy only in AMPK-positive cells. We suggest that apart from reported AMPK-dependent regulation of autophagic degradation, an AMPK-independent pathway triggers Ca(2+)-mediated autophagy, involving the PI(3)P-effector protein WIPI-1 and LC3.

Grotemeier A ，Alers S ，Pfisterer SG ，Paasch F ，Daubrawa M ，Dieterle A ，Viollet B ，Wesselborg S ，Proikas-Cezanne T ，Stork B ... -  《-》

Ca2+/calmodulin-dependent kinase (CaMK) signaling via CaMKI and AMP-activated protein kinase contributes to the regulation of WIPI-1 at the onset of autophagy.

Pfisterer SG ，Mauthe M ，Codogno P ，Proikas-Cezanne T ... -  《-》

Possible CaMKK-dependent regulation of AMPK phosphorylation and glucose uptake at the onset of mild tetanic skeletal muscle contraction.

Jensen TE ，Rose AJ ，Jørgensen SB ，Brandt N ，Schjerling P ，Wojtaszewski JF ，Richter EA ... -  《AMERICAN JOURNAL OF PHYSIOLOGY-ENDOCRINOLOGY AND METABOLISM》

Ca2+/calmodulin-dependent protein kinase kinase-alpha regulates skeletal muscle glucose uptake independent of AMP-activated protein kinase and Akt activation.

Witczak CA ，Fujii N ，Hirshman MF ，Goodyear LJ ... -  《-》

Caffeine-induced Ca(2+) release increases AMPK-dependent glucose uptake in rodent soleus muscle.

Jensen TE ，Rose AJ ，Hellsten Y ，Wojtaszewski JF ，Richter EA ... -  《AMERICAN JOURNAL OF PHYSIOLOGY-ENDOCRINOLOGY AND METABOLISM》