A single transcript in its unspliced and spliced forms directs the synthesis of all HIV-1 proteins. Although nuclear export of intron-containing cellular transcripts is restricted in mammalian cells, HIV-1 has evolved the viral Rev protein to overcome this restriction for viral transcripts. Previously, CRM1 was identified as a cellular cofactor for Rev-dependent export of intron-containing HIV-1 RNA. Here, we present evidence that Rev/CRM1 activity utilizes the ATP-dependent DEAD box RNA helicase, DDX3. We show that DDX3 is a nucleo-cytoplasmic shuttling protein, which binds CRM1 and localizes to nuclear membrane pores. Knockdown of DDX3 using either antisense vector or dominant-negative mutants suppressed Rev-RRE-function in the export of incompletely spliced HIV-1 RNAs. Plausibly, DDX3 is the human RNA helicase which functions in the CRM1 RNA export pathway analogously to the postulated role for Dbp5p in yeast mRNA export.

SUMMARY Human LMNA gene mutations result in laminopathies that include Emery-Dreifuss Muscular Dystrophy (AD-EDMD) and Hutchinson-Gilford Progeria, the premature aging syndrome (HGPS). The Lmna null (Lmna−/−) and progeroid LmnaΔ9 mutant mice are models for AD-EDMD and HGPS respectively. Both animals develop severe tissue pathologies with abbreviated life spans. Like HGPS cells, Lmna−/− and LmnaΔ9 fibroblasts have typically misshapen nuclei. Unexpectedly, Lmna−/− or LmnaΔ9 mice that are also deficient for the inner nuclear membrane protein Sun1 show markedly reduced tissue pathologies and enhanced longevity. Concordantly, reduction of SUN1 over-accumulation in LMNA mutant fibroblasts and in HGPS cells corrected nuclear defects and cellular senescence. Collectively, these findings implicate Sun1 protein accumulation as a common pathogenic event in Lmna−/−, LmnaΔ9, and HGPS disorders.

Mitotic arrest-deficient protein 1 (MAD1) is a component of the mitotic spindle assembly checkpoint. We have created a knockout mouse model to examine the physiologic consequence of reduced MAD1 function. Mad1 +/À mice were successfully generated, but repeated paired mating of Mad1 +/À with Mad1 +/À mice failed to produce a single Mad1 À/À animal, suggesting that the latter genotype is embryonic lethal. In aging studies conducted for >18 months, Mad1 +/À mice compared with control wild-type (wt) littermates showed a 2-fold higher incidence of constitutive tumors. Moreover, 42% of Mad1 +/À (P < 0.03), but 0% of wt, mice developed neoplasia after treatment with vincristine, a microtubule depolymerization agent. Mad1 +/À mouse embryonic fibroblasts (MEF) were found to be more prone than wt cells to become aneuploid; Mad1 +/À , but not wt, MEFs produced fibrosarcomas when explanted into nude mice. Our results indicate an essential MAD1 function in mouse development and correlate Mad1 haploinsufficiency with increased constitutive tumors. [Cancer Res 2007;67(1):160-6]

The inner nuclear envelope (NE) proteins interact with the nuclear lamina and participate in the architectural compartmentalization of chromosomes. The association of NE proteins with DNA contributes to the spatial rearrangement of chromosomes and their gene expression. Sun1 is an inner nuclear membrane (INM) protein that locates to telomeres and anchors chromosome movement in the prophase of meiosis. Here, we have created Sun1 -/-mice and have found that these mice are born and grow normally but are reproductively infertile. Detailed molecular analyses showed that Sun1 -/-P14 testes are repressed for the expression of reproductive genes and have no detectable piRNA. These findings raise a heretofore unrecognized role of Sun1 in the selective gene expression of coding and non-coding RNAs needed for gametogenesis.