Stress granules (SGs) are dynamic, microscopically visible, cytoplasmic bodies that play a major role in mRNA metabolism (e.g. sorting, storage, decay) and induced in cells during stress conditions like starvation, oxidative strain or growth. With substantial role in cancer and neurodegenerative diseases, these granules have never been studied during cardiac hypertrophy, or in the heart in general. Several studies have identified independent proteins, mostly mRNA binding proteins that are part of these granules, some of which are sufficient to nucleate the assembly in quiescent cells even without stress. One such mRNA binding protein is Ras GTPase-activating protein SH3 domain binding protein 1 (G3BP1), which increases during cardiac hypertrophy via posttranscriptional regulation. Thus, we hypothesized that G3BP1 might be involved in the induction of SGs during hypertrophy and hence in regulating mRNA processing and gene expression. Our aim was to investigate, 1) if these SGs appear in hypertrophied hearts and 2) if G3BP1 is necessary and sufficient to induce them during hypertrophic stimuli. In vivo staining of TIA-1/TIAR (SG marker) in mouse hearts subjected to sham or transaortic coarctation (TAC) surgeries showed accumulation of these granules with cardiac hypertrophy. Similar induction was seen in isolated, cultured, rat neonatal cardiac myocytes with hypertrophic stimulation (Endothelin1) or overexpression of G3BP1 alone (>60% of myocytes stained for SG). Conversely, switch to growth-inhibited conditions or knockdown of G3BP1 in hypertrophying myocytes was sufficient to prevent the assembly of these structures. Co-staining with other components of these granules like TIA-1/TIAR or proteins specific to P bodies, like decapping enzyme 1 validated these structures as SGs in cardiac myocytes. Interestingly, a long non-coding RNA, Gas5 (Growth Arrest Specific 5) that is validated binding partner of G3BP1 sequestered to perinuclear focal locations in myocytes stimulated with ET1, suggesting growth-induced recruitment to SGs. While we are still in process of examining G3BP1 targets that are recruited to SGs and their role in hypertrophy development, we have concluded that G3BP1 is required for the induction of SGs during cardiac hypertrophy
Tyrosine phosphorylation of Ras GTPase-activating protein stabilizes its association with p62 at membranes of v-Src transformed cells.