Interferon (IFN) exhibits a potent antiviral activity in vitro and plays a major role in the early defense against viruses. Like IFN, the proinflammatory chemokine, interleukin (IL)-8, is induced by viruses and appears in circulation during viral infections. In an in vitro cytopathic effect assay for IFN, we found that IL-8 can inhibit IFN-α activity in a dose-dependent manner. This action was reversed by specific monoclonal antibodies to IL-8. The chemokine was able to attenuate the IFN-mediated inhibition of viral replication as determined by measuring infectious virus yield. IL-8 also diminished the ability of IFN to inhibit an early stage of viral replication since IL-8 attenuated the inhibition of the formation of viral proteins. It appeared that IL-8 interfered with a late rather than an early step of IFN-mediated pathway such as early gene expression. The IL-8 inhibitory action on IFN-α antiviral activity was associated with reduced 2′,5′-A oligoadenylate synthetase activity, a pathway well correlative with the anti– encephalomyocarditis virus action of IFN-α. Understanding pathways that antagonize IFN action may lead to novel approaches to potentiate endogenous and therapeutic IFN.

SummaryPre-lamin A and progerin have been implicated in normal aging, and the pathogenesis of age-related degenerative diseases is termed 'laminopathies'. Here, we show that mature lamin A has an essential role in cellular fitness and that oxidative damage to lamin A is involved in cellular senescence. Primary human dermal fibroblasts (HDFs) aged replicatively or by pro-oxidants acquire a range of dysmorphic nuclear shapes. We observed that conserved cysteine residues in the lamin A tail domain become hyperoxidized in senescent fibroblasts, which inhibits the formation of lamin A inter-and intramolecular disulfide bonds. Both in the absence of lamin A and in the presence of a lamin A cysteine-toalanine mutant, which eliminates these cysteine residues (522, 588, and 591), mild oxidative stress induced nuclear disorganization and led to premature senescence as a result of decreased tolerance to ROS stimulators. Human dermal fibroblasts lacking lamin A or expressing the lamin A cysteine-to-alanine mutant displayed a gene expression profile of ROS-responsive genes characteristic of chronic ROS stimulation. Our findings suggest that the conserved C-terminal cysteine residues are essential for lamin A function and that loss or oxidative damage to these cysteine residues promotes cellular senescence.

(1) and mRNA turnover regulation by the AU-rich elements in the 3Ј-untranslated regions (2). The IFN antiviral response is a highly regulated process involving the transient inhibition of viral and cellular protein synthesis. The translational inhibition is mediated predominately by the activity of PKR, the double-stranded RNAdependent protein kinase. PKR is a serine/threonine protein kinase of 65 and 68 kDa in murine and human cells, respectively, that is induced by IFN treatment of cells and phosphorylates itself and other proteins, notably eIF2␣, in response to viral double-stranded RNA (3). DsRNA is produced as the replicative intermediates of many RNA viruses and also by annealing of complementary RNA strands transcribed from some DNA viruses (3). Phosphorylated eIF2␣ sequesters the guanine nucleotide exchange factor, eIF2B, which becomes trapped as inactive complex with GDP resulting in translational arrest (4, 5).Among the principal effectors of the IFN-induced antiviral state are the 2Ј,5Ј-oligoadenylate (2-5A) synthetases that convert ATP to 2-5A, activators of RNase L, in response to viral double-stranded RNA (6, 7). Thus, 2-5A is an alarmone that alerts the cells to the presence of virus by signaling to RNase L. Both RNase L and PKR have been implicated in the action of IFN-␣ against a variety of viruses (reviewed in Refs. 8 and 9). RNase L is widely distributed in different tissues, and it has been suggested that low levels of 2-5A lead to RNase L-mediated selective degradation of viral mRNA (10), whereas higher levels may lead to broader effects such as cleavage of 18 S and 28 S ribosomal RNAs (11). During the course of experiments on the role of RNase L in the inhibition of viral protein synthesis during acute infections, we observed that an absence of RNase L led to selective stabilization of PKR mRNA, extended kinetics of eIF2␣ phosphorylation, and potent inhibition of viral protein synthesis. Our findings suggest that RNase L truncates and limits the induction of PKR, possibly contributing to the transient nature of the IFN response against viral infections. Cell Culture, Viral Infections, and IFN Treatments-RNase L ϩ/ϩ and RNase L Ϫ/Ϫ mouse embryonic fibroblast (MEF) cell lines were of mixed or C57BL/6 genetic backgrounds. The cell lines are post-crisis derivatives of primary MEFs as described previously (12). MEFs were cultured in DMEM with high glucose supplemented with 10% FBS and antibiotics (Invitrogen, Gaithersburg, MD). Bone marrow macrophages collected from the femurs of RNase L ϩ/ϩ and RNase L Ϫ/Ϫ mice, both on a background of C57BL/6, were cultured in L-cell-conditioned medium for 8 days and plated at a density of 10 6 cells per 10-cm plate. WISH cell line (HeLa markers) was obtained from the American Type Culture Collection (ATCC, Rockville, MD) and cultured in RPMI 1640 supplemented with 10% FBS and antibiotics. EXPERIMENTAL PROCEDURES