Human coronaviruses (HCoVs) modify host proteins to evade the antiviral defense and sustain viral expansion. Here, we report tonicity-responsive enhancer (TonE) binding protein (TonEBP) as a cellular target of HCoVs. TonEBP was cleaved into N-terminal and C-terminal fragments (TonEBP NT and TonEBP CT, respectively) by NSP5 from all the HCoVs tested. This cleavage resulted in the loss of TonEBP’s ability to stimulate the TonE-driven transcription. On the other hand, TonEBP NT promoted viral expansion in association with the suppression of IFN-β expression. TonEBP NT competed away NF-κB binding to the PRD II domain on the IFN-β promoter. A TonEBP mutant resistant to the cleavage by NSP5 did not promote the viral expansion nor suppress the IFN-β expression. These results demonstrate that HCoVs use a common strategy of targeting TonEBP to suppress the host immune defense.

Intracellular Ca²⁺ is crucial in the regulation of adipocyte lipid metabolism and adipogenesis. In this study, we aimed to investigate the regulation mechanism of intracellular Ca²⁺ levels ([Ca²⁺]_i) during adipocyte differentiation. We found that the expression of stromal interaction molecule 2 beta (STIM2β), which is the inhibitor of store‐operated Ca²⁺ entry (SOCE), is upregulated throughout the differentiation process. Evaluation of [Ca²⁺]_i in 3 T3‐L1 and primary stromal vascular fraction (SVF) cells revealed that the basal Ca²⁺ level is downregulated after differentiation. Knockout (KO) of STIM2β in 3T3‐L1 and primary SVF cells showed increased [Ca²⁺]_i, indicating the involvement of STIM2β in the regulation of [Ca²⁺]_i during adipogenesis. We further evaluated the function of STIM2β‐mediated [Ca²⁺]_i in early and terminal differentiation of adipogenesis. Analysis of cell proliferation rate during mitotic clonal expansion (MCE) in wild‐type and STIM2β KO 3T3‐L1 cell lines revealed that a larger population of KO cells underwent G1 arrest, suggesting that reduced [Ca²⁺]_i by STIM2β induces MCE. Additionally, ablation of STIM2β increased differentiation efficiency, with more lipid accumulation and rapid transcriptional activation of adipogenic genes, especially proliferator‐activator receptor γ2 (PPARG2). We found that PPARG2 transcription is regulated by store‐operated calcium entry (SOCE) downstream transcription factors, confirming that increased [Ca²⁺]_i by STIM2β ablation promotes PPARG2 transcription during adipogenesis. Additionally, STIM2β KO mice showed hypertrophic adipose tissue development. Our data suggest that STIM2β‐mediated [Ca²⁺]_i plays a pivotal role in the regulation of mitotic clonal expansion and PPARG2 gene activation and provides evidence that MCE is not a prerequisite process for terminal differentiation during adipogenesis.