Depletion of L-arginine induces autophagy as a cytoprotective response to endoplasmic reticulum stress in human T lymphocytes

Abstract

L-arginine (L-Arg) deficiency results in decreased T-cell proliferation and impaired T-cell function. Here we have found that L-Arg depletion inhibited expression of different membrane antigens, including CD247 (CD3ζ), and led to an ER stress response, as well as cell cycle arrest at G₀/G₁ in both human Jurkat and peripheral blood mitogen-activated T cells, without undergoing apoptosis. By genetic and biochemical approaches, we found that L-Arg depletion also induced autophagy. Deprivation of L-Arg induced EIF2S1 (eIF2α), MAPK8 (JNK), BCL2 (Bcl-2) phosphorylation, and displacement of BECN1 (Beclin 1) binding to BCL2, leading to autophagosome formation. Silencing of ERN1 (IRE1α) prevented the induction of autophagy as well as MAPK8 activation, BCL2 phosphorylation and XBP1 splicing, whereas led T lymphocytes to apoptosis under L-Arg starvation, suggesting that the ERN1-MAPK8 pathway plays a major role in the activation of autophagy following L-Arg depletion. Autophagy was required for survival of T lymphocytes in the absence of L-Arg, and resulted in a reversible process. Replenishment of L-Arg made T lymphocytes to regain the normal cell cycle profile and proliferate, whereas autophagy was inhibited. Inhibition of autophagy by ERN1, BECN1 and ATG7 silencing, or by pharmacological inhibitors, promoted cell death of T lymphocytes incubated in the absence of L-Arg. Our data indicate for the first time that depletion of L-Arg in T lymphocytes leads to a reversible response that preserves T lymphocytes through ER stress and autophagy, while remaining arrested at G₀/G₁. Our data also show that the L-Arg depletion-induced ER stress response could lead to apoptosis when autophagy is blocked.

Keywords: :

• autophagy
• endoplasmic reticulum stress
• L-arginine
• arginine depletion
• survival
• apoptosis
• signaling
• T cell
• Jurkat cell

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Acknowledgement

We thank M. Modolell (Max-Planck-Institut für Immunbiologie, Freiburg, Germany) for critical reading the manuscript and helpful suggestions. We also thank the blood bank of the University Hospital of Salamanca for blood supply. This work was supported by the Spanish Ministerio de Ciencia e Innovación (SAF2008-02251, SAF2011-30518 and RD06/0020/1037 from Red Temática de Investigación Cooperativa en Cáncer, Instituto de Salud Carlos III, cofunded by the Fondo Europeo de Desarrollo Regional of the European Union), European Community’s Seventh Framework Programme FP7-2007-2013 (grant HEALTH-F2-2011-256986), Junta de Castilla y León (CSI052A11-2, CSI221A12-2, GR15-Experimental Therapeutics and Translational Oncology Program, Biomedicine Project 2009) and Acciones Integradas Spain-Germany (HA2007-0080).

Supplemental Materials

Supplemental materials may be found here: www.landesbioscience.com/journals/autophagy/article/21315