{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\nPIK3R5 encodes the regulatory subunit p101 of class IB phosphoinositide 3-kinase γ (PI3Kγ), a critical mediator of G protein-coupled receptor (GPCR) signaling. p101 is responsible for recruiting the catalytic p110γ subunit to the plasma membrane through its interaction with Gβγ dimers, thereby facilitating the generation of PtdIns-3,4,5-P3 and the subsequent activation of downstream effectors that control cellular processes including proliferation, survival, and chemotaxis. Detailed structure–function analyses have revealed that distinct domains within p101 mediate its binding to Gβγ and p110γ, underpinning its role as an adaptor that orchestrates PI3Kγ activation and spatiotemporal signaling."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "3"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nBeyond its central role in GPCR-mediated PI3Kγ activation, alterations in PIK3R5 have been implicated in diverse pathophysiological contexts. A homozygous missense mutation in PIK3R5 has been identified in a family with ataxia with oculomotor apraxia type 2, suggesting that proper p101 function is important for cerebellar development and vermis formation. Moreover, aberrant expression of p101 in T-cell line models can modulate apoptosis, with overexpression leading to protection from stimuli such as ultraviolet irradiation, thereby implicating changes in the PI3Kγ complex stoichiometry in malignant transformation."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "4"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nIn addition, genetic variants in PIK3R5 are emerging as predictors of drug response and disease progression. A specific single-nucleotide polymorphism in PIK3R5 has been associated with an increased risk of hypertension induced by VEGF-pathway inhibitors, highlighting its potential as a pharmacogenomic biomarker. Furthermore, in acute leukemia, p101 not only stabilizes the active PI3Kγ complex but also facilitates a noncanonical signaling cascade through PAK1 that impacts mitochondrial oxidative phosphorylation. These findings extend to the regulation of MAP kinase signaling via Golgi-associated Gβγ recruitment, ultimately influencing tumor cell migration, invasion, and metastasis."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "6", "end_ref": "9"}]}, {"type": "t", "text": "\n"}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Carsten Brock, Michael Schaefer, H Peter Reusch, et al. 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