Adapter protein for SORL1, but not SORT1. Delays SORL1 internalization and affects SORL1 subcellular localization. Interacts with SORL1 (via cytosolic C-terminus); this interaction affects SORL1 internalization and subcellular localization. Expressed most strongly in brain, kidney and heart with little or no expression in other tissues (PubMed:12552099). In the brain, expressed in glial cells, including astrocytes (at protein level) (PubMed:30679749). In the aorta, preferentially expressed in lesions (PubMed:12552099). Belongs to the heat shock protein 70 family.