Phosphorylation at S1288 of leukemia associated RhoGEF (LARG/ARHGEF12) induces plasma membrane localization and promotes binding and activation of RhoA.

Leukemia-associated RhoGEF (LARG) is a guanine nucleotide exchange factor (GEF) known for its specificity toward Ras homolog family member A (RhoA). LARG plays a crucial regulatory role in various cellular processes such as migration, proliferation, invasion, and metastasis by facilitating the exchange of GDP to GTP on RhoA. Phosphorylation of LARG at S1288 by ribosomal S6 kinase 2 (RSK2) promotes RhoA activation. However, the precise mechanism remains unclear. Here, we demonstrate the essential role and mechanism by which S1288 phosphorylation facilitates LARG-mediated invasiveness in response to epidermal growth factor (EGF). Upon EGF stimulation, RSK2 phosphorylates LARG at S1288, thereby promoting the membrane translocation of LARG. Furthermore, phosphorylation of LARG at S1288 markedly enhances the assembly of the LARG-RhoA complex and subsequent activation of RhoA through GTP loading. Analysis of patient-derived glioblastoma (GBM) cell lines revealed a correlation between RSK activation and LARG S1288 phosphorylation. Moreover, GBM tissue samples showed LARG S1288 phosphorylation and RhoA-GTP-bound RhoA. Elucidating the regulatory mechanisms governing this process is crucial for the development of LARG-targeted therapeutic interventions.