Cytoplasmic roles of HSATIII RNAs in RNA granule assembly and production of actin cytoskeleton-associated repeat-containing proteins

HSATIII architectural lncRNAs are nuclear short-tandem repeat ncRNAs induced upon thermal stress and serve as scaffolding molecules for nuclear stress bodies (nSBs), stress-induced membraneless organelles in the nucleus. We report that HSATIII lncRNAs are exported to the cytoplasm during stress recovery, where they form novel cytoplasmic bodies with nucleocytoplasmic RNA-binding proteins, including PURA, PURB, and m6A reader proteins. Recruitment of ALYREF to nSBs promotes HSATIII RNA export. These HSATIII-based granules, named HERALDs (Heat-removal-associated scaffolds), are transported along microtubules and accumulate at distal cellular regions. We further show that cytoplasmic HSATIII RNAs are translated into MEWNG-rich proteins, which interact with actin filaments and form complexes with HSPA8 and stress granule proteins such as ZC3HAV1 and ATXN2L. Together, these findings reveal previously unrecognized cytoplasmic roles of HSATIII RNAs, functioning both as lncRNAs to scaffold RNA granules and as mRNAs to produce proteins during the late phase of thermal stress recovery.