Regulation of Autophagy and Its Associated Cell Death by “Sphingolipid Rheostat”

Makoto Taniguchi,Satoshi Asano,Hiroyuki Takeya,Toshiro Okazaki,Mayumi Hashimoto-Nishimura,Kazuyuki Kitatani,Akira Hayashi,Susumu Mitsutake,Yasuyuki Igarashi,Junzo Kigawa,Hisanori Umehara,Tadakazu Kondo

doi:10.1074/jbc.m112.416552

Abstract

The role of "sphingolipid rheostat" by ceramide and sphingosine 1-phosphate (S1P) in the regulation of autophagy remains unclear. In human leukemia HL-60 cells, amino acid deprivation (AA(-)) caused autophagy with an increase in acid sphingomyleinase (SMase) activity and ceramide, which serves as an autophagy inducing lipid. Knockdown of acid SMase significantly suppressed the autophagy induction. S1P treatment counteracted autophagy induction by AA(-) or C(2)-ceramide. AA(-) treatment promoted mammalian target of rapamycin (mTOR) dephosphorylation/inactivation, inducing autophagy. S1P treatment suppressed mTOR inactivation and autophagy induction by AA(-). S1P exerts biological actions via cell surface receptors, and S1P(3) among five S1P receptors was predominantly expressed in HL-60 cells. We evaluated the involvement of S1P(3) in suppressing autophagy induction. S1P treatment of CHO cells had no effects on mTOR inactivation and autophagy induction by AA(-) or C(2)-ceramide. Whereas S1P treatment of S1P(3) overexpressing CHO cells resulted in activation of the mTOR pathway, preventing cells from undergoing autophagy induced by AA(-) or C(2)-ceramide. These results indicate that S1P-S1P(3) plays a role in counteracting ceramide signals that mediate mTOR-controlled autophagy. In addition, we evaluated the involvement of ceramide-activated protein phosphatases (CAPPs) in ceramide-dependent inactivation of the mTOR pathway. Inhibition of CAPP by okadaic acid in AA(-)- or C(2)-ceramide-treated cells suppressed dephosphorylation/inactivation of mTOR, autophagy induction, and autophagy-associated cell death, indicating a novel role of ceramide-CAPPs in autophagy induction. Moreover, S1P(3) engagement by S1P counteracted cell death. Taken together, these results indicated that sphingolipid rheostat in ceramide-CAPPs and S1P-S1P(3) signaling modulates autophagy and its associated cell death through regulation of the mTOR pathway.

Highlights

The sphingolipids ceramide and sphingosine 1-phosphate (S1P) control various cellular functions, including proliferation, cell death, and autophagy
Sphingolipid rheostat between ceramide and S1P plays an important role in regulating mammalian target of rapamycin (mTOR)-controlled autophagy
In human leukemia HL-60 cells, amino acid deprivation (AA(؊)) caused autophagy with an increase in acid sphingomyleinase (SMase) activity and ceramide, which serves as an autophagy inducing lipid

Summary

Conclusion

Sphingolipid rheostat between ceramide and S1P plays an important role in regulating mTOR-controlled autophagy. S1P treatment of CHO cells had no effects on mTOR inactivation and autophagy induction by AA(؊) or C2-ceramide. S1P3 overexpressing CHO cells resulted in activation of the mTOR pathway, preventing cells from undergoing autophagy induced by AA(؊) or C2-ceramide. These results indicate that S1P-S1P3 plays a role in counteracting ceramide signals that mediate mTOR-controlled autophagy. Inhibition of CAPP by okadaic acid in AA(؊)- or C2-ceramide-treated cells suppressed dephosphorylation/inactivation of mTOR, autophagy induction, and autophagy-associated cell death, indicating a novel role of ceramide-CAPPs in autophagy induction. S1P3 engagement by S1P counteracted cell death Taken together, these results indicated that sphingolipid rheostat in ceramide-CAPPs and S1P-S1P3 signaling modulates autophagy and its associated cell death through regulation of the mTOR pathway.

The abbreviations used are

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION