THEM6

THEM6 is an endoplasmic reticulum membrane-associated protein that links lipid homeostasis to stress signaling and cancer cell fate (PMID:35014179). It regulates intracellular ether lipid levels and is required for induction of the unfolded protein response, with its loss reducing de novo sterol biosynthesis and abrogating lipid-mediated activation of the transcription factor ATF4 in castration-resistant prostate cancer cells (PMID:35014179). THEM6 also stabilizes the cholesterol biosynthesis enzyme FDFT1 by inhibiting its K48-linked ubiquitination, thereby extending FDFT1 protein half-life; this axis shifts cells toward a ferroptosis-prone state—lowering GPX4 and SLC7A11 while raising ACSL4—and enhances carboplatin sensitivity in triple-negative breast cancer, with FDFT1 knockdown reversing the THEM6-driven sensitization (PMID:40619388). Beyond these two studies, the catalytic activity and structural basis of THEM6 function have not been characterized in the available corpus.

1. 2022 High

   Established THEM6 as an ER membrane-associated regulator coupling ether lipid and sterol metabolism to ER stress signaling, defining its role in cancer cell adaptation.

   Evidence THEM6 deletion in orthograft castration-resistant prostate cancer models with biochemical readouts of ether lipids, UPR markers, sterol biosynthesis, and ATF4 activation

   PMID:35014179

   Open questions at the time

   • The molecular/catalytic activity by which THEM6 controls ether lipid levels is not defined
   • The mechanism linking THEM6 to ATF4 activation and sterol biosynthesis is not resolved
   • No structural model or direct substrate identified
2. 2025 Medium

   Identified a post-translational mechanism in which THEM6 stabilizes FDFT1 to promote ferroptosis and chemosensitivity, connecting THEM6 lipid metabolism to redox-driven cell death.

   Evidence THEM6 overexpression in vitro and orthotopic xenografts, K48-linkage ubiquitination assays, protein half-life assays, FDFT1 knockdown epistasis, and ferroptosis marker/ROS/iron measurements in triple-negative breast cancer

   PMID:40619388

   Open questions at the time

   • Single-lab study not independently replicated
   • The mechanism by which THEM6 inhibits K48-linked ubiquitination of FDFT1 (direct binding vs. recruitment of a deubiquitinase) is not established
   • Whether THEM6 directly interacts with FDFT1 was not shown by reciprocal validation

• The biochemical activity of THEM6 itself remains undefined—whether it is an enzyme acting on lipids or an adaptor regulating other enzymes.
• No defined enzymatic activity or substrate for THEM6
• No structural characterization
• Direct physical interaction partners not validated