Modulation of Gene Expression by Substrate Stiffness via Ubiquitination of Histone H2B by Ubiquitin-Conjugating Enzyme E2A/B

Animal cells adapt to the stiffness of their environment
through
mechanotransduction, a process in which mechanical signals are converted
into biochemical responses, influencing key cellular processes such
as growth and differentiation. We identified ubiquitin-conjugating
enzymes E2 A and B (UBE2A/B) as mechanosensitive proteins that translocate
between the nucleus and cytoplasm depending on force and substrate
stiffness. Here, we hypothesized that UBE2A/B nuclear translocation
on stiff substrates triggers gene expression via UBE2A/B-mediated
ubiquitination of histone H2B lysine 120 (H2BK120). Chromatin immunoprecipitation
sequencing (ChIP-seq) revealed distinct DNA fragments bound to monoubiquitinated
H2B in cells cultured on soft (0.2 kPa) versus stiff (64 kPa) substrates.
We identified 2245 gene regions binding to ubiquitinated histones
on stiff substrates and 294 on soft substrates and further integrated
RNA-seq and UBE2A/B knockdown data to pinpoint 179 stiff-specific
and 18 soft-specific genes. Among these, filamin C (FLNC), leucine
zipper protein 1 (LUZP1), and glutamate-rich WD repeat-containing
protein 1 (GRWD1) showed higher expression on stiff substrates, with
GRWD1 known for its role in cancer progression through cell cycle
and gene regulation. These findings highlight how substrate stiffness
modulates gene expression via UBE2A/B-mediated H2B ubiquitination.