STX16

STX16 encodes a syntaxin family SNARE protein that functions in autophagolysosome biogenesis; its deficiency blocks autophagolysosome formation and causes accumulation of autophagosomes that can be exported via extracellular vesicles (PMID:41731604). STX16 transcription is regulated by histone lactylation (H3K9/H3K18) at its promoter downstream of ALDOB-mediated lactate production (PMID:41731604). The STX16 genomic locus harbors a cis-acting imprinting control element required for maintaining methylation at the GNAS exon A/B differentially methylated region; maternally inherited microdeletions within this locus cause autosomal dominant pseudohypoparathyroidism type Ib (AD-PHP-Ib), though STX16 itself is biallelically expressed and the disease mechanism is disruption of GNAS imprinting regulation rather than loss of STX16 protein (PMID:15800843).

1. 2005 High

   Overlapping microdeletions within the STX16 locus were shown to cause AD-PHP-Ib when maternally inherited, establishing that this region contains a cis-acting imprinting control element for GNAS exon A/B methylation — not that STX16 protein loss causes disease, since STX16 is biallelically expressed.

   Evidence Deletion mapping across multiple AD-PHP-Ib kindreds combined with STX16 mRNA expression analysis in lymphoblastoid cells from deletion carriers versus controls

   PMID:15800843

   Open questions at the time

   • The precise regulatory element within the deleted region has not been molecularly defined
   • The mechanism by which this element controls methylation at the GNAS exon A/B DMR in trans is unknown
   • No direct functional rescue of imprinting by reinsertion of the deleted region has been performed
2. 2026 Medium

   STX16 was established as required for autophagolysosome biogenesis, revealing that its deficiency causes autophagosome accumulation and their export via extracellular vesicles, linking STX16 protein function to membrane fusion in the autophagy pathway and to intercellular signaling in the tumor microenvironment.

   Evidence STX16 gene editing, LC3-based autophagy tracing, extracellular vesicle isolation, Transwell cocultures, and orthotopic xenografts in hepatocellular carcinoma models

   PMID:41731604

   Open questions at the time

   • The specific SNARE complex partners through which STX16 mediates autophagolysosome fusion have not been identified in this system
   • Findings derive from a single lab study in hepatocellular carcinoma cells and await independent confirmation in other cell types
   • No structural or biochemical reconstitution of STX16-dependent membrane fusion in autophagy has been performed

• The precise SNARE partners and membrane fusion mechanism by which STX16 promotes autophagolysosome formation, and the identity of the cis-regulatory element within the STX16 locus that controls GNAS imprinting, remain unresolved.
• No reconstituted SNARE complex containing STX16 has been demonstrated for autophagolysosome fusion
• The minimal cis-acting imprinting control element within the STX16 deletion region is not defined
• Whether STX16 protein function contributes to autophagy in non-cancer physiological contexts is untested