Phosphatidylinositol 3-Kinase Requirement in Activation of the ras/C-raf-1/MEK/ERK and p70^s6kSignaling Cascade by the Insulinomimetic Agent Vanadyl Sulfate

Abstract

The mechanisms by which inorganic salts of the trace element vanadium mediate their insulinomimetic effects are not clearly understood and were investigated. We have shown previously that vanadium salts activate mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase activities (PI3-K) via a pathway that does not involve the insulin receptor (IR) tyrosine kinase function [Pandey, S. K., Anand-Srivastava, M. B., and Srivastava, A. K. (1998) Biochemistry 37, 7006-7014]. Herein, we have examined a possible role of PI3-K in the vanadyl sulfate (VS)-mediated increase in the level of ras-MAPK activation as well as the contribution of signaling components upstream to MAPK in this VS response. Treatment of IR-overexpressing cells with VS resulted in an increased level of tyrosine phosphorylation of p44(mapk) (ERK-1) and p42(mapk) (ERK-2) along with stimulation of MAPK, MAPK kinase (MEK), and C-raf-1 activities, and ras activation. Preincubation with wortmannin and LY294002, two structurally and mechanistically different inhibitors of PI3-K, blocked the VS-mediated increase in MAPK activity and phosphorylation of ERK-1 and ERK-2. Furthermore, wortmannin inhibited activation of ras, C-raf-1, and MEK in response to VS. The addition of a farnesyltransferase inhibitor, B581, to cells reduced the level of MAPK activation as well as ERK-1 and ERK-2 phosphorylation stimulated by VS. Finally, VS increased PI3-K activity in ras immunoprecipitates. A VS-mediated increase in p70(s6k) activity was also found to be inhibited by wortmannin. Taken together, these results demonstrate that the insulinomimetic effects of VS may be mediated, in part, by PI3-K-dependent stimulation of the ras-MAPK and p70(s6k) pathways.

RAF antisense oligonucleotide as a tumor radiosensitizer

“…This appears to be in agreement with the involvement of PI3K in RAF-1-mediated ERK activation via p21-activated serine-threonine kinase (PAK) (King et al, 1997;Pandey et al, 1999;Wennstrom and Downward, 1999;Chaudhary et al, 2000;Kolch, 2000;Sun et al, 2000;Ballif and Blenis, 2001). RAF-1 also activates the transcription factor NF-kB in a PAK1-dependent manner .…”

Lower Phosphoinositide 3-Kinase (PI 3-kinase) Activity and Differential Expression Levels of Selective Catalytic and Regulatory PI 3-Kinase Subunit Isoforms in Prefrontal Cortex and Hippocampus of Suicide Subjects

“…It has been shown that PI 3-kinase through its protein kinase activity, regulates Ras, Raf, or ERK kinase (MEK) (Hu et al, 1995;Pandey et al, 1999;Bondeva et al, 1998). PI 3-kinase can directly activate MEK through protein phosphorylation Bondeva et al, 1998), or PDK-1 can directly bind and activate MEK (Sato et al, 2004).…”

Aldosterone Regulates Vascular Reactivity

“…34 Aldosteronemediated ERK activation (previously demonstrated in MadinDarby canine kidney cells 35 ) appears to be PI3K dependent, consistent with a role for PKB-mediated regulation of ERK activation. 36 Notably, the short-term effects of aldosterone to regulate MAPK activation might be expected to be synergistic with both (1) the short-term effects of angiotensin II to activate MAPK pathways 37 and (2) in a more general sense, the classic "transcriptional" effects of aldosterone. The implications of these synergies on vascular and endothelial hypertrophic mechanisms remain to be elucidated.…”