Distinct roles of class IA PI3K isoforms in primary and immortalised macrophages

The class IA isoforms of phosphoinositide 3-kinase (p110 alpha, p110 beta and p110 delta) often have non-redundant functions in a given cell type. However, for reasons that are unclear, the role of a specific PI3K isoform can vary between cell types. Here, we compare the relative contributions of PI3K isoforms in primary and immortalised macrophages. In primary macrophages stimulated with the tyrosine kinase ligand colony-stimulating factor 1 (CSF1),all class IA PI3K isoforms participate in the regulation of Rac1, whereas p110 delta selectively controls the activities of Akt, RhoA and PTEN, in addition to controlling proliferation and chemotaxis. The prominent role of p110 delta in these cells correlates with it being the main PI3K isoform that is recruited to the activated CSF1 receptor (CSF1R). In immortalised BAC1.2F5 macrophages, however, the CSF1R also engages p110 alpha, which takes up a more prominent role in CSF1R signalling, in processes including Akt phosphorylation and regulation of DNA synthesis. Cell migration, however, remains dependent mainly on p110 delta. In other immortalised macrophage cell lines, such as IC-21 and J774.2, p110 alpha also becomes more prominently involved in CSF1-induced Akt phosphorylation, at the expense of p110 delta. These data show that PI3K isoforms can be differentially regulated in distinct cellular contexts, with the dominant role of the p110 delta isoform in Akt phosphorylation and proliferation being lost upon cell immortalisation. These findings suggest that p110 delta-selective PI3K inhibitors may be more effective in inflammation than in cancer.