BCR is a multifunctional regulatory protein with opposing activities toward Rho GTPases, containing three distinct functional domains. Its C-terminal GTPase-activating protein (GAP) domain stimulates GTP hydrolysis by RAC1, RAC2, and CDC42, thereby inactivating these proteins 1. Conversely, its central Dbl homology (DH) domain functions as a guanine nucleotide exchange factor (GEF), promoting conversion of CDC42, RHOA, and RAC1 from GDP-bound to GTP-bound active forms 2. The N-terminal region possesses intrinsic kinase activity 3. BCR serves as a critical negative regulator of neuronal RAC1 activity and regulates macrophage functions including CSF1-directed motility and phagocytosis through RAC1 modulation 1. In keratinocytes, BCR functions primarily as a RHOA GEF, playing a major role in focal adhesion formation and keratinocyte differentiation 2. This dual regulatory capacity allows BCR to fine-tune GTPase signaling across multiple cell types and processes. Clinically, BCR is associated with chr22 myeloid leukemia, though the provided abstracts do not contain specific information regarding BCR's role in this disease or other cancer pathways.