Dihydrosphingomyelin Impairs HIV-1 Infection by Rigidifying Liquid-Ordered Membrane Domains
´ ´ Catarina R. Vieira,1,7 Jose M. Munoz-Olaya,2,7 Jesus Sot,3,7 Sonia Jimenez-Baranda,1 Nuria Izquierdo-Useros,4 ´ Jose Luis Abad,2 Beatriz Apellaniz,3 Rafael Delgado,5 Javier Martinez-Picado,4,6 Alicia Alonso,3 Joseﬁna Casas,2 ´ ´ ´ ˜ ˜ Jose L. Nieva,3 Gemma Fabrias,2,8Santos Manes,1,8,* and Felix M. Goni3,8,*
´ of Immunology and Oncology, Centro Nacional de Biotecnologıa/CSIC, Darwin 3, E-28049 Madrid, Spain of Biomedicinal Chemistry, Institute of Advanced Chemistry of Catalonia (IQAC)/CSIC, Jordi Girona 18, 08034 Barcelona, Spain 3Unidad de Biofısica (Centro Mixto CSIC-UPV/EHU) and Departamento de Bioquımica, Universidad del Paıs Vasco, P.O. Box 644, ´ ´ ´E-48080 Bilbao, Spain 4irsiCaixa Foundation, Hospital Universitari Germans Trias i Pujol, E-08916 Badalona, Spain 5Hospital Universitario 12 de Octubre, Avenida. Andalucıa s/n, E-28049 Madrid, Spain ´ 6ICREA, Barcelona, Spain 7These authors contributed equally to this work 8These authors contributed equally to the design and direction of this work *Correspondence: email@example.com (F.M.G.),firstname.lastname@example.org (S.M.) DOI 10.1016/j.chembiol.2010.05.023
The lateral organization of lipids in cell membranes is thought to regulate numerous cell processes. Most studies focus on the coexistence of two ﬂuid phases, the liquid crystalline (ld) and the liquid-ordered (lo); the putative presence of gel domains (so) is not usually taken into account. We show that inphospholipid:sphingolipid:cholesterol mixtures, in which sphingomyelin (SM) promoted ﬂuid lo domains, dihydrosphingomyelin (DHSM) tended to form rigid domains. Genetic and pharmacological blockade of the dihydroceramide desaturase (Des1), which replaced SM with DHSM in cultured cells, inhibited cell infection by replication-competent and -deﬁcient HIV-1. Increased DHSM levels gave rise to morerigid membranes, resistant to the insertion of the gp41 fusion peptide, thus inhibiting viral-cell membrane fusion. These results clarify the function of dihydrosphingolipids in biological membranes and identify Des1 as a potential target in HIV-1 infection.
INTRODUCTION Biological membranes show lateral heterogeneity due to the presence of lipid domains (Mukherjee and Maxﬁeld, 2004), which isproposed to be central to cell physiology by spatially and temporally regulating the formation of multimolecular complexes ˜ at the cell surface (Goni et al., 2008). Identiﬁcation of factors that regulate phase formation in living cells would thus be relevant in pathophysiological processes, including cell infection by many ˜ intracellular pathogens (Manes et al., 2003). Two lamellar phases havebeen classically deﬁned in model membranes: the gel or solid-ordered (so) and the liquid-crystalline or disordered (ld) phase. Saturated and unsaturated phospholipids partition preferentially into the so and ld phases,
respectively. A liquid-ordered (lo) phase has also been described in the presence of cholesterol (Chol) (Ipsen et al., 1987). In the lo phase, acyl chains are in a highly orderedconformation but lateral lipid diffusion is allowed. The so-called lipid rafts, enriched in sphingomyelin (SM) and Chol, appear to exist in the lo phase (Edidin, 2003). A variety of physical techniques applied to liposomes containing mixtures of SM:PC (phosphatidylcholine) and/or Chol have shown the coexistence of gel and ﬂuid, gel and lo, and lo and ld domains (Almeida et al., 1993; Collado et al.,2005). Coexistence of the three so, lo and ld phases has been visualized directly in giant unilamellar vesicles (GUV) containing SM:PC: Chol:Ceramide (Cer) and SM:PC:PE (phosphatidylethanolamine):Chol (Chiantia et al., 2006; de Almeida et al., 2007; Sot et al., 2008). Segregation of lo- and ld-like domains in the micrometer range is reported for vesicles isolated from the plasma membrane of...