Submitted on November 14, 2008
Revised on May 22, 2009
Accepted on May 27, 2009
S1P5 is required for sphingosine 1-phosphate-induced autophagy in human prostate cancer PC-3 cells
Chi-Lun Chang1, Ming-Chih Ho1, Po-Huang Lee1, Chi-Yen Hsu1, Wei-Pang Huang1, and Hsinyu Lee1*
1 National Taiwan University
* To whom correspondence should be addressed. E-mail: hsinyu{at}ntu.edu.tw.
Sphingosine 1-phosphate (S1P) is a platelet- and endothelial cell-released lysophospholipid which regulates various cellular functions through activating a specific family of G protein-coupled receptors. Both platelet activation and angiogenesis play important roles in cancer development, implying that cancer cells might encounter large amount of S1P during these processes. Cancer cells, in the mean time, may experience nutrient deprivation and rely on autophagy for early development. Whether extracellular S1P regulates autophagy remains to be tested. In the present work, we investigated whether autophagy is regulated by S1P in PC-3 cells. Through monitoring the modification patterns of LC3 by Western blotting, we demonstrated that autophagy was induced by exogenously applied S1P in PC-3 cells. This observation was further confirmed by fluorescent microscopy using PC-3 cells stably expressing EGFP-LC3. By applying siRNA and dihydro-S1P (DiH S1P), S1P5 activation was found involved in this process. Besides, mammalian target of rapamycin (mTOR) signaling was inhibited upon S1P treatment. Taken together, our results suggest that under serum-starved conditions, S1P further up-regulates autophagic activity through S1P5-dependent pathways in PC-3 cells.
