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

Abstract

Like many viruses, rotavirus (RV) dysregulates calcium homeostasis by elevating cytosolic calcium ([Ca2+]cyt) and decreasing endoplasmic reticulum (ER) stores. While an overall, monophasic increase in [Ca2+]cyt during RV infection has been shown, the nature of the RV-induced aberrant calcium signals and how they manifest over time at the single-cell level have not been characterized. Thus, we generated cell lines and human intestinal enteroids (HIEs) stably expressing cytosolic and/or ER-targeted genetically-encoded calcium indicators to characterize calcium signaling throughout RV infection by time-lapse imaging. We found that RV induces highly dynamic [Ca2+]cyt signaling that manifest as hundreds of discrete [Ca2+]cyt spikes, which increase during peak infection. Knockdown of nonstructural protein 4 (NSP4) attenuates the [Ca2+]cyt spikes, consistent with its role in dysregulating calcium homeostasis. RV-induced [Ca2+]cyt spikes were primarily from ER calcium release and were attenuated by inhibiting the store-operated calcium entry (SOCE) channel Orai1. RV-infected HIEs also exhibited prominent [Ca2+]cyt spikes that were attenuated by inhibiting SOCE, underlining the relevance of these [Ca2+]cyt spikes to gastrointestinal physiology and role of SOCE in RV pathophysiology. Thus, our discovery that RV increases [Ca2+]cyt by dynamic Ca2+ signaling, establishes a new, paradigm-shifting understanding of the spatial and temporal complexity of virus-induced Ca2+ signaling.