Phosphatidylinositol ether lipid analogues that inhibit AKT also independently activate the stress kinase, p38alpha, through MKK3/6-independent and -dependent mechanisms.
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, p38alpha, was uniformly activated 2-fold. Molecular modeling of p38alpha 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 p38alpha(-/-) cells, we showed that p38alpha is not required for PIA-induced apoptosis but is required for H(2)O(2)- and anisomycin-induced apoptosis. Nonetheless, activation of p38a contributes to PIA-induced apoptosis, because reconstitution of p38a into p38alpha(-/-) cells increased apoptosis. These studies indicate that p38alpha is activated by PIAs through a novel mechanism and show that p38alpha activation contributes to PIA-induced cell death. Independent modulation of Akt and p38alpha could account for the profound cytotoxicity of PIAs.
Gills
Joell J
JJ
Medical Oncology Branch, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20889.
Castillo
S Sianna
SS
Medical Oncology Branch, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20889.
Zhang
Chunyu
C
Medical Oncology Branch, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20889.
Petukhov
Pavel A
PA
Department of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, University of Illinois, Chicago, Illinois 60612.
Memmott
Regan M
RM
Medical Oncology Branch, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20889.
Hollingshead
Melinda
M
Developmental Therapeutics Program, Division of Cancer Treatment and Diagnosis, NCI-Frederick, National Institutes of Health, Frederick, Maryland 21701.
Warfel
Noel
N
Medical Oncology Branch, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20889.
Han
Jiahuai
J
Department of Immunology, Scripps Research Institute, La Jolla, California 94080.
Kozikowski
Alan P
AP
Department of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, University of Illinois, Chicago, Illinois 60612.
Dennis
Phillip A
PA
Medical Oncology Branch, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20889. Electronic address: pdennis@nih.gov.
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D048371:MAP Kinase Kinase 3 / Q000502:physiology*; D048669:MAP Kinase Kinase 6 / Q000502:physiology*; D051379:Mice; D048308:Mitogen-Activated Protein Kinase 14 / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D010716:Phosphatidylinositols / Q000494:pharmacology*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors*
D010716:Phosphatidylinositols; D006861:Hydrogen Peroxide; D051057:Proto-Oncogene Proteins c-akt; D048308:Mitogen-Activated Protein Kinase 14; D048371:MAP Kinase Kinase 3; D048669:MAP Kinase Kinase 6; C482530:MAP2K3 protein, human; C482566:MAP2K6 protein, human