title: Calcium-Oxidant Signaling Network Regulates AMP-activated Protein Kinase (AMPK) Activation upon Matrix Deprivation.
abstract: The AMP-activated protein kinase (AMPK) has recently been implicated in anoikis resistance. However, the molecular mechanisms that activate AMPK upon matrix detachment remain unexplored. In this study, we show that AMPK activation is a rapid and sustained phenomenon upon matrix deprivation, whereas re-attachment to the matrix leads to its dephosphorylation and inactivation. Because matrix detachment leads to loss of integrin signaling, we investigated whether integrin signaling negatively regulates AMPK activation. However, modulation of focal adhesion kinase or Src, the major downstream components of integrin signaling, failed to cause a corresponding change in AMPK signaling. Further investigations revealed that the upstream AMPK kinases liver kinase B1 (LKB1) and Ca(2+)/calmodulin-dependent protein kinase kinase β (CaMKKβ) contribute to AMPK activation upon detachment. In LKB1-deficient cells, we found AMPK activation to be predominantly dependent on CaMKKβ. We observed no change in ATP levels under detached conditions at early time points suggesting that rapid AMPK activation upon detachment was not triggered by energy stress. We demonstrate that matrix deprivation leads to a spike in intracellular calcium as well as oxidant signaling, and both these intracellular messengers contribute to rapid AMPK activation upon detachment. We further show that endoplasmic reticulum calcium release-induced store-operated calcium entry contributes to intracellular calcium increase, leading to reactive oxygen species production, and AMPK activation. We additionally show that the LKB1/CaMKK-AMPK axis and intracellular calcium levels play a critical role in anchorage-independent cancer sphere formation. Thus, the Ca(2+)/reactive oxygen species-triggered LKB1/CaMKK-AMPK signaling cascade may provide a quick, adaptable switch to promote survival of metastasizing cancer cells.
authors.affiliation: From the Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore-560012 and.
authors.forename: Ananthalakshmy
authors.initials: A
authors.lastname: Sundararaman
authors.affiliation: the Department of Pathology, Kidwai Memorial Institute of Oncology, Bangalore-560030, India.
authors.forename: Usha
authors.initials: U
authors.lastname: Amirtham
authors.affiliation: From the Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore-560012 and anu@mrdg.iisc.ernet.in.
authors.forename: Annapoorni
authors.initials: A
authors.lastname: Rangarajan
mesh_terms: D000263:Adenylate Kinase / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D045744:Cell Line, Tumor; D004789:Enzyme Activation; D005109:Extracellular Matrix / Q000378:metabolism*; D006801:Humans; D016877:Oxidants / Q000378:metabolism*; D010766:Phosphorylation
chemical_list: D016877:Oxidants; D000263:Adenylate Kinase; D002118:Calcium
keywords: AMP-activated kinase (AMPK); anoikis; calcium; cancer biology; matrix deprivation; reactive oxygen species (ROS)