Molecular basis of tubulin transport within the cilium by IFT74 and IFT81.

Intraflagellar transport (IFT) of ciliary precursors such as tubulin from the cytoplasm to the ciliary tip is involved in the construction of the cilium, a hairlike organelle found on most eukaryotic cells. However, the molecular mechanisms of IFT are poorly understood. Here, we found that the two core IFT proteins IFT74 and IFT81 form a tubulin-binding module and mapped the interaction to a calponin homology domain of IFT81 and a highly basic domain in IFT74. Knockdown of IFT81 and rescue experiments with point mutants showed that tubulin binding by IFT81 was required for ciliogenesis in human cells.

Cep164, a novel centriole appendage protein required for primary cilium formation.

Primary cilia (PC) function as microtubule-based sensory antennae projecting from the surface of many eukaryotic cells. They play important roles in mechano- and chemosensory perception and their dysfunction is implicated in developmental disorders and severe diseases. The basal body that functions in PC assembly is derived from the mature centriole, a component of the centrosome. Through a small interfering RNA screen we found several centrosomal proteins (Ceps) to be involved in PC formation. One newly identified protein, Cep164, was indispensable for PC formation and hence characterized in detail. By immunogold electron microscopy, Cep164 could be localized to the distal appendages of mature centrioles. In contrast to ninein and Cep170, two components of subdistal appendages, Cep164 persisted at centrioles throughout mitosis. Moreover, the localizations of Cep164 and ninein/Cep170 were mutually independent during interphase. These data implicate distal appendages in PC formation and identify Cep164 as an excellent marker for these structures.

Centrosome-associated NDR kinase regulates centrosome duplication.

Human NDR kinases are upregulated in some cancer types, yet their functions still remain undefined. Here, we report the first known function of a mammalian NDR kinase by demonstrating that human NDR directly contributes to centrosome duplication. A subpopulation of endogenous NDR localizes to centrosomes in a cell-cycle-dependent manner. Overexpression of NDR resulted in centrosome overduplication in a kinase-activity-dependent manner, while expression of kinase-dead NDR or depletion of NDR by small interfering RNA (siRNA) negatively affected centrosome duplication. By targeting NDR to the centrosome, we show that the centrosomal pool of NDR is sufficient to generate supernumerary centrosomes. Furthermore, our data indicate that NDR-driven centrosome duplication requires Cdk2 activity and that Cdk2-induced centrosome amplification is affected upon reduction of NDR activity. Overall, considering that centrosome overduplication is linked to cellular transformation, our observations may also provide a molecular link between mammalian NDR kinases and cancer.

Dual activity of phosphorothioate CpG oligodeoxynucleotides on HIV: reactivation of latent provirus and inhibition of productive infection in human T cells.

CpG oligodeoxynucleotides (CpG ODNs) bind to toll-like receptor-9 (TLR-9) and activate immune cells with antigen-presenting activity, including B cells and dendritic cells. Here we show that treatment of the latently human immunodeficiency virus (HIV)-infected T cell line ACH-2 with the CpG ODNs 2006 or 2040 triggers activation of viral gene expression, demonstrating that CpG-signaling activity can also be found in T cells. The CpG ODNs g12AAC and g12GTC had no effect on virus reactivation. In contrast to the stimulating effects on viral gene expression in latently infected cells, CpG ODNs potently suppressed HIV replication in productively infected MT4 T cells or PBLs. Inhibition of virus replication was not related to the CpG motif but similarly occurred with non-CpG phosphorothioate (PTO)-ODNs. Thus, virus inhibition was likely caused by the PTO backbone of the CpG ODNs, probably by interfering with events prior to integration of the viral cDNA into the host genome. The ability of CpG PTO-ODNs to trigger reactivation of latent HIV in combination with their antiviral activity on productive infection makes this substance class an interesting candidate for further test to asses their potential as supplements in HIV therapy.

CpG oligodeoxynucleotides activate HIV replication in latently infected human T cells.

CpG oligodeoxynucleotides (CpG ODNs) stimulate immune cells via the Toll-like receptor 9 (TLR9). In this study, we have investigated the effects of CpG ODNs on latent human immunodeficiency virus (HIV) infection in human T cells. Treatment of the latently infected T cell line ACH-2 with CpG ODNs 2006 or 2040 stimulated HIV replication, whereas no effects were evident when ODNs without the CpG motif were used. CpG-induced virus reactivation was blocked by chloroquine, indicating the involvement of TLR9. In contrast to the responsiveness of ACH-2 cells, CpG ODNs failed to activate HIV provirus in the latently infected Jurkat clone J1.1. We also studied the effects of CpG ODNs on productive HIV infection and found enhancement of viral replication in A3.01 T cells, whereas again no stimulating effects were observed in Jurkat T cells. CpG ODN treatment activated NF-kappaB in ACH-2 cells, which was similarly triggered in uninfected A3.01 T cells following exposure to CpG ODNs, indicating that TLR9-induced signal transduction was not dependent on proviral infection. Our study demonstrates that CpG ODNs directly trigger the activation of NF-kappaB and reactivation of latent HIV in human T cells. Our results point to a novel role for CpG ODNs as stimulators of HIV replication and open new avenues to eradicate the latent viral reservoirs in HIV-infected patients treated with antiretroviral therapy.