StAR-related lipid transfer domain-containing protein 3 (STARD3)

StAR-related lipid transfer domain-containing protein 3 (STARD3) is a multi-domain integral membrane protein primarily located in the limiting membrane of late endosomes. It contains an N-terminal MENTAL domain (anchoring the protein and mediating cholesterol binding), a central phospho-FFAT motif (enabling interaction with ER-resident partners), and a C-terminal START domain (forming a hydrophobic pocket that binds and transfers cholesterol and, potentially, carotenoids). STARD3 facilitates cholesterol transport from the endoplasmic reticulum (ER) to endosomal compartments and maintains intracellular lipid distribution. It is ubiquitously expressed but shows high expression in certain cancer subtypes, especially HER2+ breast cancer, due to genomic co-amplification with the HER2 gene (ERBB2). Increasing evidence implicates STARD3 in oncogenic processes, as it stabilizes HER2, contributes to cancer cell proliferation and migration, and is considered a prognostic biomarker for aggressive breast cancer. No approved drugs directly target STARD3, but it may become a future target in oncology or metabolic disease due to its central role in intracellular lipid regulation.

Other names

Metastatic lymph node 64 protein (MLN64)MLN64StAR related lipid transfer domain containing 3Steroidogenic acute regulatory protein-related lipid transfer domain protein 3

Not a direct drug target yet; mechanisms involve modulation of HER2 stability in cancer by influencing lysosomal degradation, cholesterol binding and transfer between organelles (mechanisms for hypothetical future drugs may include inhibition of cholesterol transport or interfering with protein-protein interactions)