The ShcA locus encodes 3 protein isoforms that differ in tissue specificity, subcellular localization, and function. Among these, p66Shc inhibits TCR coupling to the Ras/MAPK pathway and primes T cells to undergo apoptotic death. We have investigated the outcome of p66Shc deficiency on lymphocyte development and homeostasis. We show that p66Shc ؊/؊ mice develop an age-related lupus-like autoimmune disease characterized by spontaneous peripheral T-and B-cell activation and proliferation, autoantibody production, and immune complex deposition in kidney and skin, resulting in autoimmune glomerulonephritis and alopecia. IntroductionThe Shc protein family includes 4 members, ShcA, ShcB, ShcC, and RaLP. 1,2 ShcA is expressed as 3 isoforms of 52, 46, and 66 kDa, which display the PTB-CH1-SH2 Shc family signature, preceded in p66Shc by a CH2 domain containing a phosphorylatable serine (Ser36) 3 and a cytochrome c-binding region within the CH2-PTB domains. 4 In addition to structural differences, p52Shc/p46Shc differ from p66Shc in expression and function. The shorter isoforms are constitutively and ubiquitously expressed, whereas p66Shc expression is regulated by an alternative promoter 5 and is tissue restricted. 6 ShcA isoforms differ also in their subcellular localization and function. p52Shc is a cytosolic protein acting as adaptor in pathways triggered by surface receptors controlling proliferation, chemotaxis, and survival. 7,8 p46Shc localizes to mitochondria, where it subserves an unknown function. 9 On the other hand, p66Shc is expressed as 2 pools, one cytosolic and the other mitochondrial, and is endowed with antimitogenic and proapoptotic activities. Indeed, p66Shc inhibits activation of the Ras/MAPK pathway by tyrosine kinase receptors and the T-cell antigen receptor (TCR) by competing with p52Shc. Furthermore, in fibroblasts, p66Shc participates in oxidative stress-induced apoptosis by triggering the mitochondrial pathway as a p53 target. 10 p66Shc-mediated apoptosis is dependent on Ser36 phosphorylation, which is mediated by PKC␤ and required for p66Shc translocation from the cytosol to mitochondria by the prolylisomerase Pin1. 11 In mitochondria, p66Shc is maintained in an inactive state within a high-molecular-mass complex, which includes the TIM-TOM import complex and Hsp70. Following proapoptotic stimulation, p66Shc is released and acquires the capacity to oxidize cytochrome c and catalyze H 2 O 2 production, leading to mitochondrial dysfunction, opening of the permeability transition pore (PTP), and apoptosis. 4,12 Moreover, p66Shc modulates the levels of reactive oxygen species (ROSs) by suppressing activation of FKHRL1, a forkhead transcription factor that controls catalase expression and is implicated as such in H 2 O 2 scavenging. 13 Alterations in oxidative metabolism in p66Shc Ϫ/Ϫ fibroblasts, characterized by decreased mitochondriadependent energy generation and increased aerobic glycolysis, 14 also contribute to the reduction in ROS levels observed in these cells. In agreement with the capac...

The Shc adapter family includes four members that are expressed as multiple isoforms and participate in signaling by a variety of cell-surface receptors. The biological relevance of Shc proteins as well as their variegated function, which relies on their highly conserved modular structure, is underscored by the distinct and dramatic phenotypic alterations resulting from deletion of individual Shc isoforms both in the mouse and in two model organisms, Drosophila melanogaster and Caenorhabditis elegans. The p52 isoform of ShcA couples antigen and cytokine receptors to Ras activation in both lymphoid and myeloid cells. However, the recognition of the spectrum of activities of p52ShcA in the immune system has been steadily expanding in recent years to other fundamental processes both at the cell and organism levels. Two other Shc family members, p66ShcA and p52ShcC/Rai, have been identified recently in T and B lymphocytes, where they antagonize survival and attenuate antigen receptor signaling. These developments reveal an unexpected and complex interplay of multiple Shc proteins in lymphocytes.

Rai (ShcC) belongs to the family of Shc adaptor proteins and is expressed in neuronal cells, where it acts as a survival factor activating the PI3K/Akt survival pathway. In vivo, Rai protects the brain from ischemic damage. In this study, we show that Rai is expressed in T and B lymphocytes. Based on the finding that Rai−/− mice consistently develop splenomegaly, the role of Rai in lymphocyte homeostasis and proliferation was addressed. Surprisingly, as opposed to neurons, Rai was found to impair lymphocyte survival. Furthermore, Rai deficiency results in a reduction in the frequency of peripheral T cells with a concomitant increase in the frequency of B cells. Rai−/− lymphocytes display enhanced proliferative responses to Ag receptor engagement in vitro, which correlates with enhanced signaling by the TCR and BCR, and more robust responses to allergen sensitization in vivo. A high proportion of Rai−/− mice develop a lupus-like autoimmune syndrome characterized by splenomegaly, spontaneous peripheral T and B cell activation, autoantibody production, and deposition of immune complexes in the kidney glomeruli, resulting in autoimmune glomerulonephritis. The data identify Rai as a negative regulator of lymphocyte survival and activation and show that loss of this protein results in breaking of immunological tolerance and development of systemic autoimmunity.

Shc proteins participate in a variety of processes regulating cell proliferation, survival and apoptosis. The two ubiquitously expressed isoforms, p52Shc/p46Shc, couple tyrosine kinase receptors to Ras by recruiting Grb2/Sos complexes to a membrane-proximal localization. Tyrosine residues 239/240 and 317 become phosphorylated following receptor engagement and, as such, form two Grb2 binding sites, which have been proposed to be differentially coupled to Myc-dependent survival and to fos-dependent proliferation, respectively. Here, we have addressed the individual function of YY239/240 and Y317 in T-cell antigen receptor (TCR) signaling. We show that p52Shc is phosphorylated on both YY239/240 and Y317 following TCR engagement. Mutation of either YY239/ 240 or Y317 results in impaired interaction with Grb2 and inhibition of Ras/MAP kinase activation and CD69 induction, supporting a role for both Grb2 binding sites in this function. Substitution of either YY239/240 or Y317 also results in a defective activation of Rac and the coupled stress kinases JNK and p38. Furthermore, mutation of Y317 or, to a larger extent, of YY239/240, results in increased activation-induced cell death, which in cells expressing the FF239/240 mutant is accompanied by impaired TCR-dependent c-myc transcription. The data underline a pleiotropic and nonredundant role of Shc, mediated by both YY239/240 and Y317, in T-cell activation and survival.

Besides lowering circulating cholesterol, statins act as immunomodulators. Although the effects of statins on lymphocyte activation and differentiation have been clearly defined, there is no consensus as to effects of these drugs on phagocytes. We have addressed the outcome of simvastatin treatment on the activation and effector function of human macrophages in the pathophysiologically relevant context of challenge with an opportunistic pathogen. We provide evidence that: simvastatin blocks the biological effects rapidly triggered by IgG-opsonized bacteria (phagocytosis and oxidative burst) while enhancing the delayed effects elicited by FcgammaR stimulation (production of proinflammatory mediators); these opposite effects of simvastatin result from enhancement of the JNK pathway and concomitant impairment of other signaling modules activated by FcgammaR engagement; and these activities are dependent on the capacity of simvastatin to block protein prenylation. The results provide novel mechanistic insight into the activities of statins on phagocytes and are of relevance to the assessment of potential side-effects in patients undergoing long-term hypocholesterolemic therapy.