Lamina-associated Polypeptide 2α Research Articles

Inhibition of long noncoding RNA Gm41724 alleviates pressure overload-induced cardiac fibrosis by regulating lamina-associated polypeptide 2α

Cardiac fibrosis is a pathological process underlying myocardial remodeling and is characterized by excessive deposition of the myocardial extracellular matrix. Long noncoding RNAs (lncRNAs) have emerged as critical regulators of various biological processes. In this study, we investigated the role of a novel lncRNA, Gm41724, in cardiac fibrosis induced by pressure overload. High-throughput whole transcriptome sequencing analysis was performed to detect differentially expressed lncRNAs in cardiac fibroblasts (CFs) with or without TGF-β1 treatment. Differential expression analysis and gene set enrichment analysis identified Gm41724 as a potential molecule targeting fibrosis. Gm41724 positively regulated the activation of CFs induced by TGF-β1 and pressure overload. Knocking down Gm41724 could inhibit the differentiation of CFs into myofibroblasts and alleviate cardiac fibrosis induced by pressure overload. Mechanistically, comprehensive identification of RNA-binding proteins by mass spectrometry (CHIRP-MS) and RNA immunoprecipitation (RIP) assay combined with other methods of molecular biological revealed the important role of Gm41724 binding to lamina-associated polypeptide 2α (lap2α) for the activation of CFs. Further mechanistic studies indicated that the regulator of G protein signaling 4 (Rgs4), as the downstream effector of Gm41724/lap2α, regulated CFs activation. Our results implicated the involvement of Gm41724 in cardiac fibrosis induced by pressure overload and it is expected to be a promising target for anti-fibrotic therapy.

SIRT7 Downregulation Promotes Breast Cancer Metastasis Via LAP2α-Induced Chromosomal Instability.

Chromosomal instability (CIN) plays an important role in the initiation and progression of carcinomas. However, the regulatory mechanism of metastasis mediated by CIN in breast cancer is not fully understood. Here, we aimed to demonstrate that the deregulation of SIRT7 and lamina-associated polypeptide 2α (LAP2α) critically contributes to CIN-induced metastasis in breast cancer. Expression of SIRT7 and chromosome stability-related genes was examined using western blotting, quantitative real-time PCR, immunohistochemistry, and immunofluorescence; functional significance of SIRT7 was examined using in vitro and in vivo models; and interaction between SIRT7 and LAP2α was assessed by co-inmunoprecipitation (Co-IP) assays. Doxorubicin (DOX) inhibited SIRT7 expression and enhanced CIN in breast cancer cells; SIRT7 deficiency led to CIN in breast cancer cells. Co-IP approach and immunohistochemistry demonstrated that SIRT7 interacted directly and positively with LAP2α and SIRT7 knockdown led to increased ubiquitination-dependent degradation of LAP2α and reduced protein levels of LAP2α, whereas LAP2α knockdown did not affect SIRT7 expression. In vitro and in vivo evidence revealed that SIRT7 promotes breast cancer metastasis through the SIRT7/LAP2α axis. In summary, SIRT7 interacts with LAP2α to regulate CIN and metastasis in breast cancer, and inhibition of SIRT7/LAP2α axis represents a potential therapeutic strategy for preventing breast cancer metastasis.

The Retinoblastoma Tumor Suppressor Is Required for the NUP98-HOXA9-Induced Aberrant Nuclear Envelope Phenotype.

Chromosomal translocations involving the nucleoporin NUP98 gene are recurrently identified in leukemia; yet, the cellular defects accompanying NUP98 fusion proteins are poorly characterized. NUP98 fusions cause changes in nuclear and nuclear envelope (NE) organization, in particular, in the nuclear lamina and the lamina associated polypeptide 2α (LAP2α), a regulator of the tumor suppressor retinoblastoma protein (RB). We demonstrate that, for NUP98-HOXA9 (NHA9), the best-studied NUP98 fusion protein, its effect(s) on nuclear architecture largely depend(s) on RB. Morphological alterations caused by the expression of NHA9 are largely diminished in the absence of RB, both in human cells expressing the human papillomavirus 16 E7 protein and in mouse embryonic fibroblasts lacking RB. We further show that NHA9 expression associates with distinct histone modification. Moreover, the pattern of trimethylation of histone H3 lysine-27 is affected by NHA9, again in an RB-dependent manner. Our results pinpoint to an unexpected interplay between NUP98 fusion proteins and RB, which may contribute to leukemogenesis.

Physalin B attenuates liver fibrosis via suppressing LAP2α-HDAC1-mediated deacetylation of the transcription factor GLI1 and hepatic stellate cell activation.

Liver fibrosis is one of the leading causes of morbidity and mortality worldwide but lacks any acceptable therapy. The transcription factor glioma-associated oncogene homologue 1 (GLI1) is a potentially important therapeutic target in liver fibrosis. This study investigates the anti-fibrotic activities and potential mechanisms of the phytochemical, physalin B. Two mouse models (CCl4 challenge and bile duct ligation) were used to assess antifibrotic effects of physalin B in vivo. Mouse primary hepatic stellate cells (pHSCs) and human HSC line LX-2 also served as in vitro liver fibrosis models. Liver fibrogenic genes, GLI1 and GLI1 downstream genes were examined using Western blot and quantitative real-time PCR (qRT-PCR). GLI1 acetylation and LAP2α-HDAC1 interaction were analysed by co-immunoprecipitation. In vivo, physalin B administration attenuated hepatic histopathological injury and collagen accumulation and decreased expression of fibrogenic genes. Physalin B dose-dependently suppressed fibrotic marker expression in LX-2 cells and mouse pHSCs. Mechanistic studies showed that physalin B inhibited GLI activity by non-canonical Hedgehog signalling. Physalin B blocked formation of lamina-associated polypeptide 2α (LAP2α)/histone deacetylase 1 (HDAC1) complexes, thus inhibiting HDAC1-mediated GLI1 deacetylation. Physalin B up-regulated acetylation of GLI1, down-regulated expression of GLI1 and subsequently inhibited HSC activation. Physalin B exerted potent antifibrotic effects in vitro and in vivo by disrupting LAP2α/HDAC1 complexes, increasing GLI1 acetylation and inactivating GLI1. This indicates that the phytochemical physalin B may be a potential therapeutic candidate for the treatment of liver fibrosis.

PCA3 controls chromatin organization and p53 signal activation by regulating LAP2α-lamin A complexes.

Prostate cancer antigen 3 (PCA3) is a prostate cancer-specific long noncoding RNA (lncRNA). Here, we report that lncRNA PCA3 plays a role in prostate cancer progression that is mediated by nucleoplasmic lamins. PCA3 interacts with the C-terminal region of lamina-associated polypeptide (LAP) 2α. The C-terminal region of LAP2α includes tumor suppressor protein retinoblastoma (pRb)- and lamin-binding domains, and it is necessary for the regulation and stabilization of the nucleoplasmic pool of lamin A. PCA3 inhibits the interaction of LAP2α with lamin A through binding with the C-terminus of LAP2α. The level of nucleoplasmic lamin A/C is increased by knockdown of PCA3. Together, the level of LAP2α within the nucleus is increased by PCA3 knockdown. In PCA3 knockdown cells, the levels of HP1γ, trimethylation of Lys9 on histone H3 (H3K9me3), and trimethylation of Lys36 on histone H3 (H3K36me3) are upregulated. In contrast, trimethylation of Lys4 on histone H3 (H3K4me3) is downregulated. We further demonstrate that activation of the p53 signaling pathway and cell cycle arrest are promoted in the absence of PCA3. These findings support a unique mechanism in which prostate cancer-specific lncRNA controls chromatin organization via regulation of the nucleoplasmic pool of lamins. This proposed mechanism suggests that cancer progression may be mediated by nuclear lamins.

Depletion of A-type lamins and Lap2α reduces 53BP1 accumulation at UV-induced DNA lesions and Lap2α protein is responsible for compactness of irradiated chromatin.

We studied how deficiency in lamins A/C and lamina-associated polypeptide 2α (Lap2α) affects DNA repair after irradiation. A-type lamins and Lap2α were not recruited to local DNA lesions and did not accumulate to γ-irradiation-induced foci (IRIF), as it is generally observed for well-known marker of DNA lesions, 53BP1 protein. At micro-irradiated chromatin of lmna double knockout (dn) and Lap2α dn cells, 53BP1 protein levels were reduced, compared to locally irradiated wild-type counterpart. Decreased levels of 53BP1 we also observed in whole populations of lmna dn and Lap2α dn cells, irradiated by UV light. We also studied distribution pattern of 53BP1 protein in a genome outside micro-irradiated region. In Lap2α deficient cells, identical fluorescence of mCherry-tagged 53BP1 protein was found at both microirradiated region and surrounding chromatin. However, a well-known marker of double strand breaks, γH2AX, was highly abundant in the lesion-surrounding genome of Lap2α deficient cells. Described changes, induced by irradiation in Lap2α dn cells, were not accompanied by cell cycle changes. In Lap2α dn cells, we additionally performed analysis by FLIM (Fluorescence Lifetime Imaging Microscopy) that showed different dynamic behavior of mCherry-tagged 53BP1 protein pools when it was compared with wild-type (wt) fibroblasts. This analysis revealed three different fractions of mCherry-53BP1 protein. Two of them showed identical exponential decay times (τ1 and τ3), but the decay rate of τ2 and amplitudes of fluorescence decays (A1-A3) were statistically different in wt and Lap2α dn fibroblasts. Moreover, γ-irradiation weakened an interaction between A-type lamins and Lap2α. Together, our results demonstrate how depletion of Lap2α affects DNA damage response (DDR) and how chromatin compactness is changed in Lap2α deficient cells exposed to radiation.

E3 ubiquitin ligase RNF123 targets lamin B1 and lamin-binding proteins.

Lamins are key nuclear proteins which are important for maintaining nuclear structure and function. Mutations in lamins cause a spectrum of genetic diseases termed as laminopathies. RING finger containing E3 ubiquitin ligase, RNF123, is transcriptionally upregulated in cells expressing rod domain lamin A mutations. However, the functional relevance of RNF123 in laminopathic cells is not clear. Using a mass spectrometry-based approach, we identified lamins and lamin-binding proteins retinoblastoma protein (pRb), lamina-associated polypeptide 2α (LAP2α), and emerin as RNF123-interacting proteins. We determined that RNF123 mediated the ubiquitination of these proteins and caused the proteasomal degradation of pRb, LAP2α, and lamin B1. Furthermore, these proteins were also targeted for proteasomal degradation in cells expressing lamin A rod domain mutants G232E, Q294P, and R386K. Overexpression of RNF123 resulted in delayed transit through the S-phase which was alleviated by coexpression of pRb or LAP2α. Our findings imply that RNF123-mediated ubiquitination of lamin-binding proteins may contribute to disease-causing mechanisms in laminopathies by depletion of key nuclear proteins and defects in cell cycle kinetics.

First person – Sandra Vidak

ABSTRACT First Person is a series of interviews with the first authors of a selection of papers published in Journal of Cell Science, helping early-career researchers promote themselves alongside their papers. Sandra Vidak is the first author on ‘Nucleoplasmic lamins define growth-regulating functions of lamina-associated polypeptide 2α in progeria cells’, published in Journal of Cell Science. Sandra Vidak is a postdoctoral fellow in the lab of Tom Misteli at the National Cancer Institute, NIH, Bethesda, Maryland, USA, investigating how the impairment of protein quality control mechanisms contributes to the progression of the premature ageing disease Hutchinson–Gilford Progeria Syndrome (HGPS).

Lamins in the nuclear interior - life outside the lamina.

Nuclear lamins are components of the peripheral lamina that define the mechanical properties of nuclei and tether heterochromatin to the periphery. A-type lamins localize also to the nuclear interior, but the regulation and specific functions of this nucleoplasmic lamin pool are poorly understood. In this Commentary, we summarize known pathways that are potentially involved in the localization and dynamic behavior of intranuclear lamins, including their post-translational modifications and interactions with nucleoplasmic proteins, such as lamina-associated polypeptide 2α (LAP2α; encoded by TMPO). In addition, new data suggest that lamins in the nuclear interior have an important role in chromatin regulation and gene expression through dynamic binding to both hetero- and euchromatic genomic regions and promoter subdomains, thereby affecting epigenetic pathways and chromatin accessibility. Nucleoplasmic lamins also have a role in spatial chromatin organization and may be involved in mechanosignaling. In view of this newly emerging concept, we propose that the previously reported cellular phenotypes in lamin-linked diseases are, at least in part, rooted in an impaired regulation and/or function of the nucleoplasmic lamin A/C pool.

Nucleoplasmic lamins define growth-regulating functions of lamina-associated polypeptide 2α in progeria cells.

ABSTRACTA-type lamins are components of the peripheral nuclear lamina but also localize in the nuclear interior in a complex with lamina-associated polypeptide (LAP) 2α. Loss of LAP2α and nucleoplasmic lamins in wild-type cells increases cell proliferation, but in cells expressing progerin (a mutant lamin A that causes Hutchinson–Gilford progeria syndrome), low LAP2α levels result in proliferation defects. Here, the aim was to understand the molecular mechanism governing how relative levels of LAP2α, progerin and nucleoplasmic lamins affect cell proliferation. Cells from progeria patients and inducible progerin-expressing cells expressing low levels of progerin proliferate faster than wild-type or lamin A-expressing control cells, and ectopic expression of LAP2α impairs proliferation. In contrast, cells expressing high levels of progerin and lacking lamins in the nuclear interior proliferate more slowly, and ectopic LAP2α expression enhances proliferation. However, simultaneous expression of LAP2α and wild-type lamin A or an assembly-deficient lamin A mutant restored the nucleoplasmic lamin A pool in these cells and abolished the growth-promoting effect of LAP2α. Our data show that LAP2α promotes or inhibits proliferation of progeria cells depending on the level of A-type lamins in the nuclear interior.This article has an associated First Person interview with the first author of the paper.

Expression of Leukemia-Associated Nup98 Fusion Proteins Generates an Aberrant Nuclear Envelope Phenotype.

Chromosomal translocations involving the nucleoporin NUP98 have been described in several hematopoietic malignancies, in particular acute myeloid leukemia (AML). In the resulting chimeric proteins, Nup98's N-terminal region is fused to the C-terminal region of about 30 different partners, including homeodomain (HD) transcription factors. While transcriptional targets of distinct Nup98 chimeras related to immortalization are relatively well described, little is known about other potential cellular effects of these fusion proteins. By comparing the sub-nuclear localization of a large number of Nup98 fusions with HD and non-HD partners throughout the cell cycle we found that while all Nup98 chimeras were nuclear during interphase, only Nup98-HD fusion proteins exhibited a characteristic speckled appearance. During mitosis, only Nup98-HD fusions were concentrated on chromosomes. Despite the difference in localization, all tested Nup98 chimera provoked morphological alterations in the nuclear envelope (NE), in particular affecting the nuclear lamina and the lamina-associated polypeptide 2α (LAP2α). Importantly, such aberrations were not only observed in transiently transfected HeLa cells but also in mouse bone marrow cells immortalized by Nup98 fusions and in cells derived from leukemia patients harboring Nup98 fusions. Our findings unravel Nup98 fusion-associated NE alterations that may contribute to leukemogenesis.

Proliferation of progeria cells is enhanced by lamina-associated polypeptide 2α (LAP2α) through expression of extracellular matrix proteins.

Lamina-associated polypeptide 2α (LAP2α) localizes throughout the nucleoplasm and interacts with the fraction of lamins A/C that is not associated with the peripheral nuclear lamina. The LAP2α-lamin A/C complex negatively affects cell proliferation. Lamins A/C are encoded by LMNA, a single heterozygous mutation of which causes Hutchinson-Gilford progeria syndrome (HGPS). This mutation generates the lamin A variant progerin, which we show here leads to loss of LAP2α and nucleoplasmic lamins A/C, impaired proliferation, and down-regulation of extracellular matrix components. Surprisingly, contrary to wild-type cells, ectopic expression of LAP2α in cells expressing progerin restores proliferation and extracellular matrix expression but not the levels of nucleoplasmic lamins A/C. We conclude that, in addition to its cell cycle-inhibiting function with lamins A/C, LAP2α can also regulate extracellular matrix components independently of lamins A/C, which may help explain the proliferation-promoting function of LAP2α in cells expressing progerin.

High Mobility Group Protein N5 (HMGN5) and Lamina-associated Polypeptide 2α (LAP2α) Interact and Reciprocally Affect Their Genome-wide Chromatin Organization

The interactions of nuclear lamins with the chromatin fiber play an important role in regulating nuclear architecture and chromatin function; however, the full spectrum of these interactions is not known. We report that the N-terminal domain of the nucleosome-binding protein HMGN5 interacts with the C-terminal domain of the lamin-binding protein LAP2α and that these proteins reciprocally alter their interaction with chromatin. Chromatin immunoprecipitation analysis of cells lacking either HMGN5 or LAP2α reveals that loss of either protein affects the genome-wide distribution of the remaining partner. Our study identifies a new functional link between chromatin-binding and lamin-binding proteins.

Muscle dystrophy-causing ΔK32 lamin A/C mutant does not impair functions of nucleoplasmic LAP2α - lamin A/C complexes in mice

A-type lamins are components of the nuclear lamina, a filamentous network of the nuclear envelope in metazoans that supports nuclear architecture. In addition, lamin A/C can also be found in the interior of the nucleus. This nucleoplasmic lamin pool is soluble in physiological buffer, depends on the presence of the lamin-binding protein, lamina-associated polypeptide 2α (LAP2α) and regulates cell cycle progression in tissue progenitor cells. ΔK32 mutations in A-type lamins cause severe congenital muscle disease in humans and a muscle maturation defect in Lmna(ΔK32/ΔK32) knock-in mice. Mutant ΔK32 lamin A/C protein levels were reduced and all mutant lamin A/C was soluble and mislocalized to the nucleoplasm. To test the role of LAP2α in nucleoplasmic ΔK32 lamin A/C regulation and functions, we deleted LAP2α in Lmna(ΔK32/ΔK32) knock-in mice. In double mutant mice the Lmna(ΔK32/ΔK32)-linked muscle defect was unaffected. LAP2α interacted with mutant lamin A/C, but unlike wild-type lamin A/C, the intranuclear localization of ΔK32 lamin A/C was not affected by loss of LAP2α. In contrast, loss of LAP2α in Lmna(ΔK32/ΔK32) mice impaired the regulation of tissue progenitor cells as in lamin A/C wild-type animals. These data indicate that a LAP2α-independent assembly defect of ΔK32 lamin A/C is the predominant cause of the mouse pathology, whereas the LAP2α-linked functions of nucleoplasmic lamin A/C in the regulation of tissue progenitor cells are not affected in Lmna(ΔK32/ΔK32) mice.

Wnt-4 protects thymic epithelial cells against dexamethasone-induced senescence.

Glucocorticoids are widely used immunosuppressive drugs in treatment of autoimmune diseases and hematological malignancies. Glucocorticoids are particularly effective immune suppressants, because they induce rapid peripheral T cell and thymocyte apoptosis resulting in impaired T cell-dependent immune responses. Although glucocorticoids can induce apoptotic cell death directly in developing thymocytes, how exogenous glucocorticoids affect the thymic epithelial network that provides the microenvironment for T cell development is still largely unknown. In the present work, we show that primary thymic epithelial cells (TECs) express glucocorticoid receptors and that high-dosage dexamethasone induces degeneration of the thymic epithelium within 24 h of treatment. Changes in organ morphology are accompanied by a decrease in the TEC transcription factor FoxN1 and its regulator Wnt-4 parallel with upregulation of lamina-associated polypeptide 2α and peroxisome proliferator activator receptor γ, two characteristic molecular markers for adipose thymic involution. Overexpression of Wnt-4, however, can prevent upregulation of adipose differentiation-related aging markers, suggesting an important role of Wnt-4 in thymic senescence.

Lamina-Associated Polypeptide 2α Loss Impairs Heart Function and Stress Response in Mice

Lamina-associated polypeptide (LAP)2alpha is a mammalian chromatin-binding protein that interacts with a fraction of A-type lamins in the nuclear interior. Because mutations in lamins and LAP2alpha lead to cardiac disorders in humans, we hypothesized that these factors may play important roles in heart development and adult tissue homeostasis. We asked whether the presence of LAP2alpha was required for normal cardiac function. To study the molecular mechanisms of the disease, we analyzed heart structure and function in complete and conditional Lap2alpha(-/-) mice as well as Lap2alpha(-/-)/Mdx mutants. Unlike conditional deletion of LAP2alpha in late embryonic striated muscle, its complete knockout caused systolic dysfunction in young mice, accompanied by sporadic fibrosis in old animals, as well as deregulation of major cardiac transcription factors GATA4 and myocyte enhancer factor 2c. Activation of compensatory pathways, including downregulation of beta-adrenergic receptor signaling, resulted in reduced responsiveness of the myocardium to chronic beta-adrenergic stimulation and stalled the progression of LAP2alpha-deficient hearts from hypertrophy toward cardiac failure. Dystrophin deficiency in an Mdx background resulted in a transient rescue of the Lap2alpha(-/-) phenotype. Our data suggest a novel role of LAP2alpha in the maintenance of cardiac function under normal and stress conditions.

The LEM Domain Proteins Emerin and LAP2α Are Dispensable for Human Immunodeficiency Virus Type 1 and Murine Leukemia Virus Infections

The human nuclear envelope proteins emerin and lamina-associated polypeptide 2alpha (LAP2alpha) have been proposed to aid in the early replication steps of human immunodeficiency virus type 1 (HIV-1) and murine leukemia virus (MLV). However, whether these factors are essential for HIV-1 or MLV infection has been questioned. Prior studies in which conflicting results were obtained were highly dependent on RNA interference-mediated gene silencing. To shed light on these contradictory results, we examined whether HIV-1 or MLV could infect primary cells from mice deficient for emerin, LAP2alpha, or both emerin and LAP2alpha. We observed HIV-1 and MLV infectivity in mouse embryonic fibroblasts (MEFs) from emerin knockout, LAP2alpha knockout, or emerin and LAP2alpha double knockout mice to be comparable in infectivity to wild-type littermate-derived MEFs, indicating that both emerin and LAP2alpha were dispensable for HIV-1 and MLV infection of dividing, primary mouse cells. Because emerin has been suggested to be important for infection of human macrophages by HIV-1, we also examined HIV-1 transduction of macrophages from wild-type mice or knockout mice, but again we did not observe a difference in susceptibility. These findings prompted us to reexamine the role of human emerin in supporting HIV-1 and MLV infection. Notably, both viruses efficiently infected human cells expressing high levels of dominant-negative emerin. We thus conclude that emerin and LAP2alpha are not required for the early replication of HIV-1 and MLV in mouse or human cells.

Lamina-associated polypeptide 2α forms complexes with heat shock proteins Hsp70 and Hsc70 in vivo

Lamina-associated polypeptide 2α (LAP2α), one of the alternatively spliced isoforms of the LAP2 gene, is a nucleoplasmic protein which forms oligomers and presumably associates to chromosomes via the LEM- and LEM-like regions. To characterize components of the LAP2α-containing complexes, we have expressed the α-specific C-terminal domain of LAP2α in HeLa cells and, after immunopurification, found that the heat shock proteins Hsp70 and Hsc70 reproducibly co-purified with this domain. Association between endogenous LAP2α and Hsp70 in non-transfected cells was confirmed by co-immunoprecipitation. The association was not mediated by the retinoblastoma protein.

LAP2α-binding protein LINT-25 is a novel chromatin-associated protein involved in cell cycle exit

Lamina-associated polypeptide 2alpha (LAP2alpha) is a nuclear protein dynamically associating with chromatin during the cell cycle. In addition, LAP2alpha interacts with A-type lamins and retinoblastoma protein and regulates cell cycle progression via the E2F-Rb pathway. Using yeast two-hybrid analysis and three independent in vitro binding assays we identified a new LAP2alpha interaction partner of hitherto unknown functions, which we termed LINT-25. LINT-25 protein levels were upregulated during G1 phase in proliferating cells and upon cell cycle exit in quiescence, senescence and differentiation. Upon cell cycle exit LINT-25 accumulated in heterochromatin foci, and LAP2alpha protein levels were downregulated by proteasomal degradation. Although LAP2alpha was not required for the upregulation and reorganization of LINT-25 during cell cycle exit, transient expression of LINT-25 in proliferating cells caused loss of LAP2alpha and subsequent cell death. Our data show a role of LINT-25 and LAP2alpha during cell cycle exit, in which LINT-25 acts upstream of LAP2alpha.

Wild-Type Levels of Human Immunodeficiency Virus Type 1 Infectivity in the Absence of Cellular Emerin Protein

Preintegration complexes (PICs) mediate retroviral integration, and recent results indicate an important role for the inner nuclear membrane protein emerin in orienting human immunodeficiency virus type 1 (HIV-1) PICs to chromatin for integration. Two other host cell proteins, the barrier-to-autointegration factor (BAF) and lamina-associated polypeptide 2alpha (LAP2alpha), seemed to play a similar preintegrative role for Moloney murine leukemia virus (MMLV) in addition to HIV-1. In contrast, we determined efficient HIV-1 and MMLV infection of HeLa-P4 cells following potent down-regulation of emerin, BAF, or LAP2alpha protein by using short interfering RNA. Mouse embryo fibroblasts ablated for emerin protein through gene knockout support the same level of HIV-1 infection as cells derived from wild-type littermate control animals. As the expression of human emerin in mouse knockout cells fails to affect the level of infectivity achieved in its absence, we conclude that HIV-1 efficiently infects cells in the absence of emerin protein and, by extension, that emerin is not a universally important regulator of HIV-1 infectivity.