Molecular mechanisms of PI3K isoform dependence in embryonic growth

Abstract

Objective The phosphoinositide 3-kinase (PI3K) pathway is an important signaling mechanism for cell proliferation and metabolism. Mutations that activate PIK3CA may make cells p110a dependent, but when phosphatase tensin homolog (PTEN) is lost, the p110b isoform of PI3Ks becomes more important. However, the exact mechanism underlying the prevalence of p110s remains unclear. In this study, our aim was to elucidate the processes behind PI3K isoform dependency in a cellular model of embryonic development. Material and Methods In order to understand PI3K isoform prevalence, mouse embryonic fibroblasts (MEFs) were used and p110b, PTEN and Rac1 activity was modulated using retroviral plasmids. Expression levels and cellular growth were assessed by performing immunoblots and crystal violet assays. Results The levels of PTEN had only a partial effect on the prevalence of PI3K isoforms in MEFs. The dependency on p110a diminished when PTEN was depleted. Of note, when PTEN expression was repressed, there was no full transition in dependency from one PI3K isoform to the other. Interestingly, the viability of PTEN-depleted MEFs became less dependent on p110a and more dependent on p110b when p110b was overexpressed. Nevertheless, the overexpression of p110b in conjunction with PTEN knock-downs did not result in a complete shift of isoforms in PI3Ks. Finally, we investigated Rac1 activation with a mutant allele and determined a more potent increase in p110b prominence in MEFs. Conclusion These findings suggest that multiple cellular parameters, including PTEN status, PI3K isoform levels, and Rac1 activity, combine to influence PI3K isoform prevalence, rather than a single determinant.