KNOP1

KNOP1 (TSG118) is a nucleolar protein that undergoes cell-cycle-dependent redistribution, occupying the dense fibrillar component of the nucleolus in interphase—where it co-localizes with fibrillarin—and relocating to the surface of condensed chromosomes during mitosis (PMID:10430019). Within the nucleolus it serves as a retention factor for ZFP106, binding the C-terminal WD40 repeat domain of ZFP106 and being required for its nucleolar localization (PMID:15833274). Beyond this structural role, KNOP1 has a metabolic function in breast cancer cells, where it directly interacts with NMNAT1 to sustain intracellular NAD+ levels; this NAD+ homeostasis suppresses FoxO1 phosphorylation and promotes FoxO1 nuclear retention, driving GPX4 transcription and thereby suppressing ferroptosis (PMID:40784594). KNOP1 loss reduces NAD+, drives FoxO1 nuclear export, downregulates GPX4, and sensitizes cells to ferroptosis (PMID:40784594).

1. 1999 Medium

   Established KNOP1 as a nucleolar protein with a dynamic, cell-cycle-coupled localization, raising the possibility of distinct interphase and mitotic functions.

   Evidence Indirect immunofluorescence with affinity-purified antibody, co-localization with fibrillarin in interphase and with condensed chromosomes in mitosis

   PMID:10430019

   Open questions at the time

   • Molecular function within the nucleolus not defined
   • Mechanism driving chromosome surface relocalization at mitosis unknown
   • Single lab, antibody-based localization only
2. 2005 Medium

   Assigned KNOP1 a concrete molecular role as a nucleolar retention factor for ZFP106, answering what protein partner it acts upon in the nucleolus.

   Evidence Yeast two-hybrid, ZFP106 domain deletion mapping, co-localization, and an in vitro differentiation assay linking KNOP1 loss to loss of nucleolar ZFP106

   PMID:15833274

   Open questions at the time

   • Functional consequence of ZFP106 nucleolar retention not defined
   • Interaction not confirmed by reciprocal endogenous co-IP or structure
   • Biological role of the differentiation-coupled downregulation unresolved
3. 2025 Medium

   Revealed a metabolic axis linking KNOP1 to NAD+ homeostasis and ferroptosis resistance, defining a disease-relevant function distinct from its nucleolar role.

   Evidence Co-IP, ChIP, NAD+ quantification, ROS detection, proliferation/migration assays, xenografts, and rescue/epistasis with Ferrostatin-1 and NMNAT1 in breast cancer cells

   PMID:40784594

   Open questions at the time

   • Single lab, not independently replicated
   • Whether the NMNAT1 axis connects to the nucleolar/ZFP106 functions is unknown
   • Direct biochemical basis for how KNOP1 sustains NMNAT1-dependent NAD+ output not resolved

• How KNOP1's nucleolar structural role relates to its metabolic NAD+/ferroptosis function, and whether either represents a unified molecular activity, remains unresolved.
• No structural or enzymatic activity defined for KNOP1
• No mechanism connecting the ZFP106 and NMNAT1 interactions
• Physiological role outside cancer cells uncharacterized