PROS1 and cytomegalovirus infection: Upon HCMV infection, the antiapoptotic viral protein pUL37x1 (also known as the viral mitochondrion-localized inhibitor of apoptosis, vMIA) [16] targets the mitochondria and promotes fission [14] by inducing the release of Ca2+ from the ER into the cytosol [17], which subsequently elevates Ca2+ levels in the mitochondria [18].