The Phospho-PAK1/2/3 (S144+S141+S139) antibody detects endogenous levels of PAK1. PAK2. and PAK3 when phosphorylated at specific regulatory sites: Ser144 (PAK1), Ser141 (PAK2), and Ser139 (PAK3). These p21-activated kinases (PAKs) are critical regulators of cytoskeletal dynamics, cell motility, survival, and proliferation. Their activation is tightly controlled by Rho GTPases (e.g., Cdc42. Rac1), which bind to the autoinhibitory domain, triggering autophosphorylation at these conserved serine residues. This phosphorylation event relieves autoinhibition, enabling kinase activation and downstream signaling. The antibody is particularly useful for studying PAK activation states in cellular pathways, such as MAPK, PI3K/Akt, and Wnt, which are often dysregulated in cancer, neurological disorders, and immune responses. Researchers employ this tool in techniques like Western blotting, immunofluorescence, or immunoprecipitation to explore PAK-related mechanisms in cell migration, invasion, and metastasis. Specificity validation is essential, as cross-reactivity with unrelated phospho-serine motifs may occur. Its application spans cancer research (e.g., breast, glioblastoma), neurodevelopmental studies, and investigations into PAK inhibitors' therapeutic potential. Proper controls, including knockout cells or phosphatase treatment, should confirm phosphorylation-dependent signals.