TRIM28-mediated SUMOylation of G3BP1/2 regulates stress granule dynamics.

Stress granules (SGs) are stress-induced membraneless organelles whose dynamics are tightly regulated by protein interactions and modifications. However, whether SUMOylation directly targets SG core proteins G3BP1/2 and which ligase is involved remains unclear, partly due to their transient and membraneless nature. To investigate this SUMOylation and its ligase, we applied our low-concentration formaldehyde crosslinking (lcFAX) method to stabilize SGs and enhance analysis. Using lcFAX-MS, we identified TRIM28 as a previously undefined SG-associated protein and showed that it SUMOylates G3BP1 at K287 and G3BP2 at K281, establishing a critical mechanism regulating SG dynamics that ultimately impacts cellular ROS and apoptosis. In addition, lcFAX-seq provides insights into SG RNA composition. Altogether, our study uncovers an essential role for TRIM28-mediated SUMOylation in modulating SG dynamics. TRIM28 may act as a versatile regulator, and with the aid of lcFAX, this mechanism could be further explored across diverse membraneless organelles and regulatory pathways.