Cytoplasmic SNHG1 is enriched in prostate cancer stress granules.

SNHG1 is a long non-coding RNA (lncRNA) with a variably reported subcellular localization to either the nucleus or cytoplasm. Its primary activity has been suggested as a competitive endogenous RNA (ceRNA), however, SNHG1 has also been shown to bind directly to proteins, including G3BP1, G3BP2, and DDX3X, all of which are associated with stress granules. Here we analyze the subcellular localization of SNHG1 in prostate cancer cells and determined the association with stress granules. Quantitation of individual SNHG1 transcripts by single molecule (sm)RNA-FISH showed that C4-2B and PC3 cells contained a median of 13 and 7.5 transcripts per cell, respectively. SNHG1 was predominantly nuclear, with most transcripts found in the nucleus of C4-2B and PC3 cells. The number of transcripts in individual cells varied greatly, from 0 to 36, indicating SNHG1 is expressed at low levels. We induced stress granule formation using thapsigargin to determine whether SNHG1 was localized in stress granules. Stress granules were visualized by G3BP1 immunofluorescence concurrently with SNHG1 RNA by smRNA-FISH. We found enrichment of SNHG1 in C4-2B and PC3 stress granules. Thapsigargin treatment also induced a shift in SNHG1 distribution to favor cytoplasmic localization. In C4-2B cells, the change was small, however, in PC3 cells, SNHG1 localization flipped to become predominantly cytoplasmic. These data show that SNHG1 is predominantly a nuclear RNA expressed at low levels, and stress induction induces an association with stress granules and a cell-dependent shift to the cytoplasm.