ABSTRACT
The most common PIK3CA mutation, producing the H1047R mutant of p110α, arises in myriad malignancies and is typically observed in low-grade breast tumours. In contrast, amplification is observed for wild-type PIK3CB, encoding p110ß, and occurs at low frequency but in aggressive, high-grade metastatic tumours. We hypothesized that mutant p110αH1047R and wild-type p110ß give rise to distinct transformed phenotypes. We show that p110αH1047R and wild-type p110ß, but not wild-type p110α, transform MCF-10A cells and constitutively stimulate phosphoinositide 3-kinase (PI3K)-AKT pathway signalling. However, their resultant morphological transformed phenotypes are distinct. p110αH1047R induced an epithelial-to-mesenchymal transition (EMT) commensurate with SNAIL (also known as SNAI1) induction and loss of E-cadherin. Upon p110ß expression, however, E-cadherin expression was maintained despite cells readily delaminating from epithelial sheets. Distinct from the prominent filopodia in p110αH1047R-expressing cells, p110ß induced formation of lamellipodia, and these cells migrated with significantly greater velocity and decreased directionality. p110ß-induced phenotypic alterations were accompanied by hyperactivation of RAC1; the dependency of transformation of p110ß-binding to Rac1 revealed using a Rac1-binding mutant of p110ß. Thus, PIK3CB amplification induces a transformed phenotype that is dependent upon a p110ß-Rac1 signalling loop and is distinct from the transformed phenotype induced by p110αH1047R.
Subject(s)
Phosphatidylinositol 3-Kinase , Phosphatidylinositol 3-Kinases , Class I Phosphatidylinositol 3-Kinases/genetics , Epithelial-Mesenchymal Transition/genetics , Humans , Phosphatidylinositol 3-Kinases/genetics , Phosphatidylinositol 3-Kinases/metabolism , Signal TransductionABSTRACT
Tumors are intrinsically heterogeneous and it is well established that this directs their evolution, hinders their classification and frustrates therapy1-3. Consequently, spatially resolved omics-level analyses are gaining traction4-9. Despite considerable therapeutic interest, tumor metabolism has been lagging behind this development and there is a paucity of data regarding its spatial organization. To address this shortcoming, we set out to study the local metabolic effects of the oncogene c-MYC, a pleiotropic transcription factor that accumulates with tumor progression and influences metabolism10,11. Through correlative mass spectrometry imaging, we show that pantothenic acid (vitamin B5) associates with MYC-high areas within both human and murine mammary tumors, where its conversion to coenzyme A fuels Krebs cycle activity. Mechanistically, we show that this is accomplished by MYC-mediated upregulation of its multivitamin transporter SLC5A6. Notably, we show that SLC5A6 over-expression alone can induce increased cell growth and a shift toward biosynthesis, whereas conversely, dietary restriction of pantothenic acid leads to a reversal of many MYC-mediated metabolic changes and results in hampered tumor growth. Our work thus establishes the availability of vitamins and cofactors as a potential bottleneck in tumor progression, which can be exploited therapeutically. Overall, we show that a spatial understanding of local metabolism facilitates the identification of clinically relevant, tractable metabolic targets.