ARHGEF3 controls HDACi-induced differentiation via RhoA-dependent pathways in acute myeloid leukemias

Abstract

Altered expression and activity of histone deacetylases (HDACs) have been correlated with tumorigenesis. Inhibitors of HDACs (HDACi) induce acetylation of histone and non-histone proteins affecting gene expression, cell cycle progression, cell migration, terminal differentiation and cell death. Here, we analyzed the regulation of ARHGEF3, a RhoA-specific guanine nucleotide exchange factor, by the HDACi MS275 (entinostat). MS275 is a well-known benzamide-based HDACi, which induces differentiation of the monoblastic-like human histiocytic lymphoma cell line U937 to monocytes/macrophages. Incubation of U937 cells with MS275 resulted in an up regulation of ARHGEF3, followed by a significant enhancement of the marker of macrophage differentiation CD68. ARHGEF3 protein is primarily nuclear, but MS275 treatment rapidly induced its translocation into the cytoplasm. ARHGEF3 cytoplasmic localization is associated with activation of the RhoA/Rho-associated Kinase (ROCK) pathway. In addition to cytoskeletal rearrangements orchestrated by RhoA, we showed that ARHGEF3/RhoA-dependent signals involve activation of SAPK/JNK and then Elk1 transcription factor. Importantly, MS275-induced CD68 expression was blocked by exposure of U937 cells to exoenzyme C3 transferase and Y27632, inhibitors of Rho and ROCK respectively. Moreover, ARHGEF3 silencing prevented RhoA activation leading to a reduction in SAPK/JNK phosphorylation, Elk1 activation and CD68 expression, suggesting a crucial role for ARHGEF3 in myeloid differentiation. Taken together, our results demonstrate that ARHGEF3 modulates acute myeloid leukemia differentiation through activation of RhoA and pathways directly controlled by small GTPase family proteins. The finding that GEF protein modulation by HDAC inhibition impacts on cell differentiation may be important for understanding the antitumor mechanism(s) by which HDACi treatment stimulates differentiation in cancer.

ARHGEF3 regulates skeletal muscle regeneration and strength through autophagy

“…An alternative possibility is the regulation of ARHGEF3 activity by subcellular localization. A recent study has found that ARHGEF3 is normally enriched in the nucleus and it translocates into the cytoplasm upon inhibition of histone deacetylases, leading to activation of RhoA and actin cytoskeletal reorganization (D'Amato et al, 2015). Therefore, the RhoGEF activity of ARHGEF3 may be very low under normal conditions due to its nuclear sequestration, and it is switched on when specific conditions induce ARHGEF3 export from the nucleus.…”

Meta-Analysis of Transcriptomic Variation in T cell Populations Reveals Novel Signatures of Gene Expression and Splicing

“…A related Rho-GEF, ARHGEF3, is also somewhat differentially spliced between Treg and Th2 cells in that a proximal alternative first exon is favored in Tregs versus Th2 cells, thus altering the first 32-38 amino acids of the encoded protein. While functional differences have not been identified between the isoforms with distinct N-termini, ARHGEF3 has been linked to activation of RhoA in myeloid development (D'Amato et al, 2015).…”

Molecular strategies for modulating Wnt signaling

“…DVL interacts with Figure 3) (16). While several GEFs are involved, and it has been reported that Daam1 interaction may be non-essential, it is clear that both RhoA and Rac1 are activated by Wnt ligand/ROR-1/2/DVL signaling (17)(18)(19). RhoA can be initiated separately from Rac1, and vice versa; while in some cell types, it has been observed that non-canonical signaling can stimulate Rac1, but inhibit RhoA (20)(21)(22).…”

“…RhoA activates the Rho-associated kinase (ROCK), which induces actin filament assembly and cytoskeletal changes (16,19). Further, RhoA affects cell survival mechanisms through JNK signaling (18). Rac1 signals through MEK/ERK pathways and JNK/NF-κb pathways, resulting in a net proliferative/pro-survival stimulus (23)(24)(25).…”