Malignant T-cell-amplified sequence 1 (MCTS1)

MCTS1, also known as MCT-1, is a 181-amino-acid translation regulator that functions as part of the MCTS1/DENR complex to promote translation reinitiation (UniProt: Q9ULC4). This complex enables the small ribosomal subunit to resume translation scanning after upstream open reading frame (uORF) termination, facilitating downstream open reading frame (mORF) initiation in an EIF2-independent manner. The MCTS1/DENR complex regulates the translation of over 150 genes, thereby influencing cell cycle regulation, DNA damage signaling and repair, and interferon gamma immunity—notably enhancing JAK2 translation (UniProt: Q9ULC4).

In the UniProt disease database, MCTS1 is associated with Immunodeficiency 118 (IMD118), an X-linked recessive disorder characterized by susceptibility to disseminated mycobacterial infections following BCG vaccination (UniProt: Q9ULC4). Beyond this primary association, the protein's role in translational control implicates it in broader cellular stress responses.

MCTS1 is upregulated in Alzheimer's Disease brain tissue relative to age-matched controls, with a mean log2 fold-change of 0.58 across post-mortem AD samples analyzed by TMT-labeled quantitative proteomics (Chaparral AD proteomics). This elevation suggests potential involvement in AD-associated translational dysregulation, though the functional consequence of increased MCTS1 in AD neuropathology requires further investigation.