Inhibition of Integrin-linked Kinase/Protein Kinase B/Akt Signaling: MECHANISM FOR GANGLIOSIDE-INDUCED APOPTOSIS

Xiao-Qi Wang,Ping Sun,Amy S Paller

doi:10.1074/jbc.m106563200

Xiao-Qi Wang, Ping Sun + Show 1 more

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https://doi.org/10.1074/jbc.m106563200

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Abstract

Ganglioside GT1b inhibits keratinocyte attachment to and migration on a fibronectin matrix by binding to alpha(5)beta(1) and preventing alpha(5)beta(1) interaction with fibronectin. The role of gangliosides in triggering keratinocyte apoptosis, however, is unknown. Addition of GT1b to keratinocyte-derived SCC12 cells, grown in serum-free medium but exposed to fibronectin, suppressed Bad phosphorylation, activated caspase-9, and inhibited cyclin D and E expression, resulting in cell cycle arrest at G(1) phase and initiation of apoptosis. The mechanism of GT1b activation of caspase-9 involved inhibition of beta(1) integrin serine/threonine phosphorylation and decreased phosphorylation of both integrin-linked kinase and protein kinase B/Akt at its Ser-473 site, leading to cytochrome c release from mitochondria. Consistently, blockade of GT1b function with anti-GT1b antibody specifically activated the Ser-473 site of Akt, markedly suppressing apoptosis. The ganglioside-induced inhibition of Akt phosphorylation was GT1b-specific and was not observed when cells were treated with other keratinocyte gangliosides, including GD3. These studies suggest that the modulation of keratinocyte cell cycle and survival by GT1b is mediated by its direct interaction with alpha(5)beta(1) and resultant inhibition of the integrin/integrin-linked kinase/protein kinase B/Akt signaling pathway.

Highlights

Ganglioside GT1b inhibits keratinocyte attachment to and migration on a fibronectin matrix by binding to ␣5␤1 and preventing ␣5␤1 interaction with fibronectin
This paper is available on line at http://www.jbc.org addition of gangliosides and specific blockade of ganglioside function with anti-ganglioside antibodies, we investigated the ability of gangliosides to trigger keratinocyte apoptosis in the presence of FN and the mechanism of the induction of this apoptosis
Our studies show that ganglioside GT1b is a potent stimulant of apoptosis when keratinocyte-derived cells are exposed to FN via a mechanism that involves inhibition of Ser/ Thr phosphorylation of ILK and inhibition of phosphorylation of protein kinase B (PKB)/Akt at its Ser-473 site; consistently, blockade of GT1b function by anti-GT1b antibodies suppresses the induction of cell apoptosis, increasing phosphorylation of PKB/Akt at the Ser-473 but not at the Thr-308 phosphorylation site

Summary

Introduction

Ganglioside GT1b inhibits keratinocyte attachment to and migration on a fibronectin matrix by binding to ␣5␤1 and preventing ␣5␤1 interaction with fibronectin. Addition of GT1b to keratinocyte-derived SCC12 cells, grown in serum-free medium but exposed to fibronectin, suppressed Bad phosphorylation, activated caspase-9, and inhibited cyclin D and E expression, resulting in cell cycle arrest at G1 phase and initiation of apoptosis.

Results

Conclusion