Phosphoinositide 3-kinase regulatory subunit 1 (p85 alpha) (PIK3R1)

The Phosphoinositide 3-kinase regulatory subunit 1 (p85 alpha), encoded by the PIK3R1 gene, is a critical adapter protein that modulates the activity, stability, and localization of Class IA PI3K catalytic subunits (p110 alpha, beta, and delta) [UniProt: P27338, NCBI Gene: 5295]. It contains SH2 and SH3 domains that allow it to bind to phosphorylated tyrosine residues on activated receptor tyrosine kinases (RTKs), thereby recruiting the PI3K complex to the plasma membrane to initiate the conversion of PIP2 to PIP3 and subsequent AKT/mTOR signaling [PMID: 24651012, PMID: 22430204]. Under physiological conditions, p85 alpha maintains the catalytic subunit in an inactive state while simultaneously protecting it from proteasomal degradation [PMID: 22430204]. Somatic mutations in PIK3R1 are prevalent in various malignancies, such as endometrial, colorectal, and glioblastoma, where they disrupt the inhibitory interface and lead to constitutive pathway activation [PMID: 24651012, StatPearls: NBK535424]. Furthermore, germline mutations in this subunit are linked to rare clinical conditions, including the immunodeficiency APDS2 and the developmental disorder SHORT syndrome [UniProt: P27338]. Although most therapeutic agents like Alpelisib and Idelalisib directly inhibit the p110 catalytic subunit, the p85 subunit is essential for the functional integrity of the target complex and serves as a vital biomarker for predicting drug response and understanding resistance mechanisms [StatPearls: NBK535424].

Other names

p85p85-alphaGRB1Phosphatidylinositol 3-kinase 85 kDa regulatory subunit alphaPI3-kinase regulatory subunit alphaP85A_HUMAN

Inhibition of the PI3K catalytic activity by targeting the p110 subunit within the p85-p110 complex, or disruption of the p85-p110 regulatory interaction [PMID: 22430204, StatPearls: NBK535424].