Phosphatidylinositol ether lipid analogues that inhibit AKT also independently activate the stress kinase, p38α, through MKK3/6-independent and -dependent mechanisms

Joell J. Gills, S. Sianna Castillo, Chunyu Zhang, Pavel A. Petukhov, Regan M. Memmott, Melinda Hollingshead, Noel Warfel, Jiahuai Han, Alan P. Kozikowski, Phillip A. Dennis

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Abstract

Previously, we identified five active phosphatidylinositol ether lipid analogues (PIAs) that target the pleckstrin homology domain of Akt and selectively induce apoptosis in cancer cells with high levels of Akt activity. To examine specificity, PIAs were screened against a panel of 29 purified kinases. No kinase was inhibited, but one isoform of p38, p38α, was uniformly activated 2-fold. Molecular modeling of p38α revealed the presence of two regions that could interact with PIAs, one in the activation loop and a heretofore unappreciated region in the upper lobe that resembles a pleckstrin homology domain. In cells, two phases of activation were observed, an early phase that was independent of the upstream kinase MKK3/6 and inhibited by the p38 inhibitor SB203580 and a latter phase that was coincident with MKK3/6 activation. In short term xenograft experiments that employed immunohistochemistry and immunoblotting, PIA administration increased phosphorylation of p38 but not MKK3/6 in tumors in a statistically significant manner. Although PIAs rapidly activated p38 with similar time and dose dependence as Akt inhibition, p38 activation and Akt inhibition were independent events induced by PIAs. Using SB203580 or p38α-/- cells, we showed that p38α is not required for PIA-induced apoptosis but is required for H2O2- and anisomycin-induced apoptosis. Nonetheless, activation of p38a contributes to PIA-induced apoptosis, because reconstitution of p38a into p38α-/- cells increased apoptosis. These studies indicate that p38α is activated by PIAs through a novel mechanism and show that p38α activation contributes to PIA-induced cell death. Independent modulation of Akt and p38α could account for the profound cytotoxicity of PIAs.

Original languageEnglish (US)
Pages (from-to)27020-27029
Number of pages10
JournalJournal of Biological Chemistry
Volume282
Issue number37
DOIs
StatePublished - Sep 14 2007

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ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

Cite this

Gills, J. J., Castillo, S. S., Zhang, C., Petukhov, P. A., Memmott, R. M., Hollingshead, M., Warfel, N., Han, J., Kozikowski, A. P., & Dennis, P. A. (2007). Phosphatidylinositol ether lipid analogues that inhibit AKT also independently activate the stress kinase, p38α, through MKK3/6-independent and -dependent mechanisms. Journal of Biological Chemistry, 282(37), 27020-27029. https://doi.org/10.1074/jbc.M701108200