RASGRP1 (RAS guanyl releasing protein 1) functions as a calcium- and diacylglycerol (DAG)-regulated guanine nucleotide exchange factor that specifically activates RAS proteins by catalyzing the exchange of bound GDP for GTP 1. This activation triggers the ERK/MAPK kinase cascade, which is crucial for cellular signaling 1. RASGRP1 plays essential roles in immune cell development and function, governing B-cell and T-cell differentiation, activation, and proliferation 1. The protein operates through compartmentalized signaling mechanisms, with activity detected on both plasma membrane and Golgi apparatus, involving PLCgamma-dependent pathways 2. In T-lymphocytes, RASGRP1 expression is regulated by transcriptional enhancer elements, where variants like rs11631591 interact with hnRNP-K protein to modulate expression levels 1. Disease relevance includes association with systemic lupus erythematosus, where increased RASGRP1 expression and ERK activity correlate with disease risk 1. RASGRP1 deficiency causes primary immunodeficiency with autoimmune lymphoproliferative syndrome-like phenotypes 3. The protein also shows involvement in cancer biology, particularly in glioblastoma where it promotes temozolomide resistance through RAS-GTP transformation 4, and in cutaneous squamous cell carcinoma where elevated expression triggers oncogenic changes in keratinocytes 5. Additionally, fine-mapping studies have implicated RASGRP1 variants in bipolar disorder susceptibility 6.