Rotavirus Calcium Dysregulation Manifests as Dynamic Calcium Signaling in the Cytoplasm and Endoplasmic Reticulum

Abstract

28 Like many viruses, rotavirus (RV) dysregulates calcium homeostasis by elevating 29 cytosolic calcium ([Ca 2+ ]cyt) and decreasing endoplasmic reticulum (ER) stores. While 30 an overall, monophasic increase in [Ca 2+ ]cyt during RV infection has been shown, the 31 nature of the RV-induced aberrant calcium signals and how they manifest over time at 32 the single-cell level have not been characterized. Thus, we generated cell lines and 33 human intestinal enteroids (HIEs) stably expressing cytosolic and/or ER-targeted 34 genetically-encoded calcium indicators to characterize calcium signaling throughout RV 35 infection by time-lapse imaging. We found that RV induces highly dynamic [Ca 2+ ]cyt 36 signaling that manifest as hundreds of discrete [Ca 2+ ]cyt spikes, which increase during 37 peak infection. Knockdown of nonstructural protein 4 (NSP4) attenuates the [Ca 2+ ]cyt 38 spikes, consistent with its role in dysregulating calcium homeostasis. RV-induced 39 [Ca 2+ ]cyt spikes were primarily from ER calcium release and were attenuated by 40 inhibiting the store-operated calcium entry (SOCE) channel Orai1. RV-infected HIEs 41 also exhibited prominent [Ca 2+ ]cyt spikes that were attenuated by inhibiting SOCE, 42 underlining the relevance of these [Ca 2+ ]cyt spikes to gastrointestinal physiology and 43 role of SOCE in RV pathophysiology. Thus, our discovery that RV increases [Ca 2+ ]cyt 44 by dynamic Ca 2+ signaling, establishes a new, paradigm-shifting understanding of the 45 spatial and temporal complexity of virus-induced Ca 2+ signaling. 46 47 48 Eukaryotic signal transduction pathways employ a variety of signaling molecules 49 to regulate cellular processes. Calcium (Ca 2+ ) is one of the most ubiquitous secondary 50 messengers in the cell, which tightly regulates Ca 2+ movement through the coordinated 51 function of Ca 2+ channels, transporters, and pumps. Since Ca 2+ signaling modulates a 52 wide array of cellular processes, it is not surprising that many different viruses exploit 53 Ca 2+ signaling to facilitate their replication, and the resulting dysregulation of Ca 2+ 54 signaling causes pathogenesis. Rotavirus (RV), a member of the Reoviridae family, is 55 one of the first viruses shown to elevate cellular Ca 2+ levels and has become a widely-56 used model system to characterize mechanisms by which viruses dysregulate host Ca 2+ 57 homeostasis 1 . RV is a clinically important enteric virus that causes severe diarrhea and 58 vomiting in children, resulting in over approximately 258 million diarrhea episodes and 59 198,000 deaths in 2016 2 . Hyperactivation of cyclic nucleotide (e.g., cAMP/cGMP) and 60 Ca 2+ signaling pathways is a common strategy among enteric pathogens 3 . Thus, 61 understanding how RV exploits Ca 2+ signaling is key to understanding and combating 62 RV-induced diarrhea. 63 RV was first reported to elevate cytosolic [Ca 2+ ] by Michelangeli et al. (1991), 64 which stimulated subsequent research into how RV alters cellular Ca 2+ levels 4 . RV 65 causes a 2-fold steady-state increase in ...

Purinergic Signaling Drives Multiple Aspects of Rotavirus Pathophysiology

“…African green monkey kidney epithelial (MA104) cells were cultured in high glucose DMEM supplemented with 10% fetal bovine serum (FBS) at 37°C in 5% CO2. MA104 cells were engineered to stably express the GCaMP6s cytosolic calcium indicator (MA104-GCaMP6s) as previously described and maintained under 50 µg/mL hygromycin drug selection 20,21 . D6/2-rotavirus was propagated in MA104 cells in serum-free DMEM supplemented with 1 µg/mL Worthington's Trypsin (Worthington Biochemical).…”

“…Within virus-infected cells, intracellular NSP4 functions as a viral ion channel to release Ca 2+ from the endoplasmic reticulum, which initiates the reprogramming of cells for virus replication. Further, the NSP4-induced increase in Ca 2+ signaling in infected cells also induces the release of paracrine signals, which affect neighboring uninfected cells [15][16][17][18][19][20] . We recently showed that rotavirus infected cells exhibit robust Ca 2+ signaling, which drives increased extracellular purines that activate the purinergic receptor P2Y1 on neighboring cells, and results in a propagating "intercellular Ca 2+ wave" encompassing neighboring cells 21 .…”