The p85α regulatory subunit of PI3K mediates cAMP-PKA and retinoic acid biological effects on MCF7 cell growth and migration

Phosphoinositide-3-OH kinase (PI3K) signalling regulates various cellular processes, including cell survival, growth, proliferation and motility, and is among the most frequently mutated pathways in cancer. Although the involvement of p85 alpha(PI3K) SH2 domain in signal transduction has been extensively studied, the function of the SH3 domain at the N-terminus remains elusive. A serine (at codon 83) adjacent to the N-terminal SH3 domain in the PI3K regulatory subunit p85 alpha(PI3K) that is phosphorylated by protein kinase A (PKA) in vivo and in vitro has been identified. Virtually all receptors binding p85 alpha(PI3K) can cooperate with cAMP-PKA signals via phosphorylation of p85 alpha(PI3K)Ser83. To analyse the role of p85 alpha(PI3K)Ser83 in retinoic acid (RA) and cAMP signalling, in MCF7 cells, we used p85 alpha(PI3K) mutated forms, in which Ser83 has been substituted with alanine (p85A) to prevent phosphorytalon or with aspartic acid (p85D) to mimic the phosphorylated residue. We demonstrated that p85 alpha(PI3K)Ser83 is crucial for the synergistic enhancement of RAR alpha/p85 alpha(PI3K) binding induced by cAMP/RA co-treatment in MCF7 cells. Growth curves, colorimetric MTT assay and cell cycle analysis demonstrated that phosphorylation of p85 alpha(PI3K)Ser83 plays an important role in the control of MCF7 cell proliferation and in RA-induced inhibition of proliferation. Wound healing and transwell experiments demonstrated that p85 alpha(PI3K)Ser83 was also essential both for the control of migratory behaviour and for the reduction of motility induced by RA. This study points to p85 alpha(PI3K)Ser83 as the physical link between different pathways (cAMP-PKA, RA and FA K), and as an important regulator of MCF7 cell proliferation and migration.