Authors: M. Danielle Bareford, Hossein A. Hamed, Jeremy Allegood, Nichola Cruickshanks, Andrew Poklepovic, Margaret A. Park, Besim Ogretmen, Sarah Spiegel, Steven Grant and Paul Dent

M. Danielle Bareford

Department of Neurosurgery; Virginia Commonwealth University; Richmond, VA USA

Hossein A. Hamed

Department of Neurosurgery; Virginia Commonwealth University; Richmond, VA USA

Jeremy Allegood

Department of Biochemistry and Molecular Biology; Virginia Commonwealth University; Richmond, VA USA

Nichola Cruickshanks

Department of Neurosurgery; Virginia Commonwealth University; Richmond, VA USA

Andrew Poklepovic

Department of Medicine; Virginia Commonwealth University; Richmond, VA USA

Margaret A. Park

Department of Biochemistry and Molecular Biology; Virginia Commonwealth University; Richmond, VA USA

Besim Ogretmen

Department of Biochemistry and Molecular Biology; Medical University of South Carolina; Charleston, SC USA

Sarah Spiegel

Department of Biochemistry and Molecular Biology; Virginia Commonwealth University; Richmond, VA USA

Steven Grant

Department of Medicine; Virginia Commonwealth University; Richmond, VA USA

Paul Dent

Corresponding author: pdent@vcu.edu
Department of Neurosurgery; Virginia Commonwealth University; Richmond, VA USA

Abstract:
The present studies sought to further understand how the anti-folate pemetrexed and the multi-kinase inhibitor sorafenib interact to kill tumor cells. Sorafenib activated SRC, and via SRC the drug combination activated ERK1/2. Expression of dominant negative SRC or dominant negative MEK1 abolished drug-induced ERK1/2 activation, together with drug-induced autophagy, acidic lysosome formation, and tumor cell killing. Protein phosphatase 2A is an important regulator of the ERK1/2 pathway. Fulvestrant resistant MCF7 cells expressed higher levels of the PP2A inhibitor SET/I2PP2A, had lower endogenous PP2A activity, and had elevated basal ERK1/2 activity compared with their estrogen dependent counterparts. Overexpression of I2PP2A blocked drug-induced activation of ERK1/2 and tumor cell killing. PP2A can be directly activated by ceramide and SET/I2PP2A can be inhibited by ceramide. Inhibition of the de novo ceramide synthase pathway blocked drug-induced ceramide generation, PP2A activation and tumor cell killing. Collectively these findings demonstrate that ERK1/2 plays an essential role downstream of SRC in pemetrexed and sorafenib lethality and that PP2A plays an important role in regulating this process.

Received: February 15, 2012; Accepted: April 29, 2012; Published Online: June 7, 2012

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