A Switch of G Protein-Coupled Receptor Binding Preference from Phosphoinositide 3-Kinase (PI3K)–p85 to Filamin A Negatively Controls the PI3K Pathway

Abstract

Frequent oncogenic alterations occur in the phosphoinositide 3-kinase (PI3K) pathway, urging identification of novel negative controls. We previously reported an original mechanism for restraining PI3K activity, controlled by the somatostatin G proteincoupled receptor (GPCR) sst2 and involving a ligand-regulated interaction between sst2 with the PI3K regulatory p85 subunit. We here identify the scaffolding protein filamin A (FLNA) as a critical player regulating the dynamic of this complex. A preexisting sst2-p85 complex, which was shown to account for a significant basal PI3K activity in the absence of ligand, is disrupted upon sst2 activation. FLNA was here identified as a competitor of p85 for direct binding to two juxtaposed sites on sst2. Switching of GPCR binding preference from p85 toward FLNA is determined by changes in the tyrosine phosphorylation of p85-and FLNA-binding sites on sst2 upon activation. It results in the disruption of the sst2-p85 complex and the subsequent inhibition of PI3K. Knocking down FLNA expression, or abrogating FLNA recruitment to sst2, reversed the inhibition of PI3K and of tumor growth induced by sst2. Importantly, we report that this FLNA inhibitory control on PI3K can be generalized to another GPCR, the mu opioid receptor, thereby providing an unprecedented mechanism underlying GPCR-negative control on PI3K.

Contribution of HIF-1α in 4E-BP1 Gene Expression

“…These data suggest that 4E-BP1 phosphorylation at S65 is inversely correlated to cell density, and is severely impaired by sst2 signaling. This latter observation is consistent with our previous reports describing how sst2 inhibits the PI3K/mTOR axis (19,20), the major signaling pathway that impinges upon 4E-BP1 phosphorylation (2).…”

Filamin-A is required to mediate SST2 effects in pancreatic neuroendocrine tumours

“…grading), this finding being in contrast with other cancer types. In fact, it has been (Peverelli et al 2014) and on FLNA deficient melanoma cell lines M2 (Najib et al 2012). Although, further studies will be needed to fully understand how FLNA regulates SST2 stability, several evidences indicate that FLNA plays a crucial role in trafficking and stabilizing several GPCRs on plasma membrane (Liu et al 1997, Seck et al 2003, Thelin et al 2007.…”

“…In addition, the relevance of FLNA in pituitary tumour responsiveness to pharmacological treatment has been demonstrated in PRL-secreting pituitary tumours, where FLNA plays a key role in dopamine receptor type 2 signalling and cell surface expression (Peverelli et al 2012). Recently, FLNA/SST2 interaction has been found to play a critical role for SST2 stabilization and cell survival in human pancreatic tumour cells (BON) and in melanoma cell line (Najib et al 2012) as well as in tumourous pituitary GH-secreting cells (Peverelli et al 2014).…”

Filamin A Expression Negatively Regulates Sphingosine-1-Phosphate-Induced NF-κB Activation in Melanoma Cells by Inhibition of Akt Signaling

“…As a consequence, upon ligand treatment, the PI3K regulatory p85 subunit dissociates from the GPCR, which now associates with FLNA. This switch causes an inhibition of PI3K/Akt signaling (24). Interestingly, S1PR1 is the sole S1P receptor that contains both of these motifs (24) (Fig.…”

“…It was then important to determine how FLNA negatively regulates S1P-mediated signaling leading to NF-B activation. It was recently shown that FLNA can function as a negative regulator of the PI3K/Akt signaling of some GPCRs containing both a FLNA binding motif and the PI3K regulatory p85 subunit binding YXXM motif in close proximity in an intracellular loop sequence (24). As a consequence, upon ligand treatment, the PI3K regulatory p85 subunit dissociates from the GPCR, which now associates with FLNA.…”