Investigating the Context-Dependent Phase Separation of Human HOX
Transcription Factors
Abstract
Homeobox (HOX) transcription factors are essential for gene expression
during embryonic development and hematopoiesis, and their dysregulation
is potentially linked to several types of cancer. Recently,
liquid-liquid phase separation (LLPS) has been proposed as a key
mechanism in various physiological processes. Using computational tools
and molecular dynamics (MD) simulations, we found that the human HOX
transcription factors have a strong potential to undergo phase
separation. The large disordered regions of the HOX factors drive phase
separation via a fly-casting mechanism, where the terminal segments of
the disordered regions extend out to interact with and draw in
neighboring molecules. Interestingly, formation of transient secondary
structures in the short linear motifs (SliMs) of the disordered regions
was observed in the simulations of both isolated molecules and their
clustered states. This suggests that HOX transcription factors may act
as scaffold proteins and recruit partner molecules, such as TALE
proteins, in the biomolecular co-condensates, via interaction with these
preformed structural elements. Furthermore, a total of 352 SLiMs were
mapped with the droplet-promoting disordered regions of the human HOX
transcription factors, which indicated an abundance of possible binding
sites. These results have been curated in an interactive webpage
([https://sdelab-hoxverse.netlify.app/](https://sdelab-hoxverse.netlify.app/))
that generates motif maps, indicating the location of the motifs in the
disordered regions of the HOX transcription factors. Overall, this work
highlights the potential of phase separation of the human HOX factors
particularly through the lens of context-dependent interactions, which
may lead to novel insights into HOX-related processes.