The endoplasmic reticulum (ER) operates in adaptive responses to various stresses, dictating cell fate. Here we show that knockdown of the ER protein mitsugumin23 (MG23) enhances cell death induced by ultraviolet C (UVC), which causes DNA damage. The small heat shock protein αB-crystallin (αBC) is identified as a MG23 binding molecule and its knockdown facilitates death of UVC-exposed cells. Conversely, αBC lowered UVC sensitivity when expressed as an ER-anchored form. Taken together, the results suggest that MG23 plays a protective role against UVC by accumulating αBC in the close vicinity of the ER.
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