Ceramide inhibits PKCθ by regulating its phosphorylation and translocation to lipid rafts in Jurkat cells

Abstract

Protein kinase C theta (PKCθ) is a novel, calcium-independent member of the PKC family of kinases that was identified as a central player in T cell signaling and proliferation. Upon T cell activation by antigen-presenting cells, PKCθ gets phosphorylated and activated prior to its translocation to the immunological synapse where it couples with downstream effectors. PKCθ may be regulated by ceramide, a crucial sphingolipid that is known to promote differentiation, growth arrest, and apoptosis. To further investigate the mechanism, we stimulated human Jurkat T cells with either PMA or anti-CD3/anti-CD28 antibodies following induction of ceramide accumulation by adding exogenous ceramide, bacterial sphingomyelinase, or Fas ligation. Our results suggest that ceramide regulates the PKCθ pathway through preventing its critical threonine 538 (Thr538) phosphorylation and subsequent activation, thereby inhibiting the kinase's translocation to lipid rafts. Moreover, this inhibition is not likely to be a generic effect of ceramide on membrane reorganization. Other lipids, namely dihydroceramide, palmitate, and sphingosine, did not produce similar effects on PKCθ. Addition of the phosphatase inhibitors okadaic acid and calyculin A reversed the inhibition exerted by ceramide, and this suggests involvement of a ceramide-activated protein phosphatase. Such previously undescribed mechanism of regulation of PKCθ raises the possibility that ceramide, or one of its derivatives, and may prove valuable in novel therapeutic approaches for disorders involving autoimmunity or excessive inflammation-where PKCθ plays a critical role.

Cardiolipin Regulates Mitophagy through the Protein Kinase C Pathway

“…Similarly, mitochondria-associated neutral sphingomyelinase, the mammalian orthologue of Isc1, was shown to be activated by anionic phospholipids, especially phosphatidylserine and mitochondrial CL (42). In mammals, ceramide activates PKC-(43, 44) but inhibits PKC-and PKC-␦ in mammals (45,46). Yeast has only one PKC (Pkc1) isozyme, and its regulation by ceramide has not been studied.…”

Regulation ofStaphylococcus aureusInfection of Macrophages by CD44, Reactive Oxygen Species, and Acid Sphingomyelinase

“…These platforms form a unique microenvironment with biophysical properties that allow them to trap and cluster receptor molecules and intracellular signaling molecules, thereby permitting and amplifying signal transduction (3,13,(15)(16)(17). Ceramide also directly interacts with cathepsin D, phospholipase A 2 , kinase suppressor of Ras, and protein kinase C isoforms (21,24,27,68). Recent studies have indicated that the Asm-ceramide system has an important role in regulation of macrophage functions, such as phagosome maturation (64a), cytokine release (28), and apoptosis (53,69).…”

Expression of HERG in musculoskeletal tumors with different degrees of malignancy*

“…Human Ether-a-go-go Related Gene (HERG) potassium channels play an important role in repolarization in cardiac action potentials. However, recent evidence has suggested a role for HERG in the proliferation and progression of multiple types of cancers, which may make it an attractive target for cancer therapy [1] . It has been confirmed that the existence of encoded potassium ion channels within tumor cell membranes has the ability to control the communication current of the cells.…”