Phosphatidylinositol 3-Kinase-Binding Protein, PI3KAP/XB130, Is Required for cAMP-induced Amplification of IGF Mitogenic Activity in FRTL-5 Thyroid Cells

Abstract

We previously demonstrated that long-term pretreatment of rat FRTL-5 thyroid cells with TSH or cAMP-generating reagents potentiated IGF-I-dependent DNA synthesis. Under these conditions, cAMP treatment increased tyrosine phosphorylation of a 125-kDa protein (p125) and its association with a p85 regulatory subunit of phosphatidylinositol 3-kinase (p85 PI3K), which were suggested to mediate potentiation of DNA synthesis. This study was undertaken to identify p125 and to elucidate its roles in potentiation of DNA synthesis induced by IGF-I. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) analysis revealed p125 to be a rat ortholog of human XB130, which we named PI3K-associated protein (PI3KAP). cAMP treatment elevated PI3KAP/XB130 mRNA and protein levels as well as tyrosine phosphorylation and interaction with p85 PI3K leading to increased PI3K activities associated with PI3KAP/XB130, supporting the role of PI3KAP/XB130 in DNA synthesis potentiation. Importantly, PI3KAP/XB130 knockdown attenuated cAMP-dependent potentiation of IGF-I-induced DNA synthesis. Furthermore, c-Src was associated with PI3KAP/XB130 and was activated in response to cAMP. Addition of Src family kinase inhibitors, PP1 or PP2, during cAMP treatment abolished tyrosine phosphorylation of PI3KAP/XB130 and its interaction with p85 PI3K. Finally, introduction of PI3KAP/XB130 into NIH3T3 fibroblasts lacking endogenous PI3KAP/XB130 enhanced IGF-I-induced DNA synthesis; however, a mutant Y72F incapable of binding to p85 PI3K did not show this response. Together, these data indicate that cAMP-dependent induction of PI3KAP/XB130, which is associated with PI3K, is required for enhancement of IGF mitogenic activities.

XB130 Mediates Cancer Cell Proliferation and Survival through Multiple Signaling Events Downstream of Akt

“…In a recent study, Yamanaka et al found rat XB130 was associated with p85 subunit of PI3K, and they named it as PI3KAP. This interaction is essential to enhance cAMP-induced amplification of IGF mitogenic activity in FRTL-5 thyroid cells [27]. In the present study, interaction between XB130 and p85 was found in both thyroid and lung cancer cells.…”

Advances in targeting cyclic nucleotide phosphodiesterases

“…Re-expression of PDE4D inhibited cell death, which suggests that PDE4D might be both a tumour promoter and a therapeutic target in certain cancers. These beneficial effects of reducing PDE-mediated cAMP hydrolysis should, however, be tempered, given that cAMP can promote the growth of certain carcinomas and that apparently inactivating mutations in some PDEs (for example, PDE8 and PDE11 ) can predispose to endocrine tumours 88,89 . The effects of PDE inhibitors on the permeability of the blood–brain barrier may also alter the effects of other therapeutic agents 90 .…”

XB130, a New Adaptor Protein, Regulates Expression of Tumor Suppressive MicroRNAs in Cancer Cells

“…It includes AFAP [1], AFAP1L1 (actin filament associate protein 1 like 1) [2], and XB130 (also known as actin filament associated protein 1-like 2, AFAP1L2) [3]. They have been demonstrated to participate in the regulation of various signaling pathways by forming protein-protein and/or protein-lipid complexes [1], [4], and under certain circumstances these adaptor proteins can be involved in tumorigenesis [5], [6].…”