Intracellular interactions between APOBEC3G, RNA, and HIV-1 Gag: APOBEC3G multimerization is dependent on its association with RNA

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ERα-LBD, an isoform of estrogen receptor alpha, promotes breast cancer proliferation and endocrine resistance

Estrogen receptor alpha (ER alpha) drives mammary gland development and breast cancer (BC) growth through an evolutionarily conserved linkage of DNA binding and hormone activation functions. Therapeutic targeting of the hormone binding pocket is a widely utilized and successful strategy for breast cancer prevention and treatment. However, resistance to this endocrine therapy is frequently encountered and may occur through bypass or reactivation of ER-regulated transcriptional programs. We now identify the induction of an ER alpha isoform, ER alpha-LBD, that is encoded by an alternative ESR1 transcript and lacks the activation function and DNA binding domains. Despite lacking the transcriptional activity, ER alpha-LBD is found to promote breast cancer growth and resistance to the ER alpha antagonist fulvestrant. ER alpha-LBD is predominantly localized to the cytoplasm and mitochondria of BC cells and leads to enhanced glycolysis, respiration and stem-like features. Intriguingly, ER alpha-LBD expression and function does not appear to be restricted to cancers that express full length ER alpha but also promotes growth of triple-negative breast cancers and ER alpha-LBD transcript (ESR1-LBD) is also present in BC samples from both ER alpha(+) and ER alpha(-) human tumors. These findings point to ER alpha-LBD as a potential mediator of breast cancer progression and therapy resistance

ANK, a Host Cytoplasmic Receptor for the Tobacco mosaic virus Cell-to-Cell Movement Protein, Facilitates Intercellular Transport through Plasmodesmata

Plasmodesma (PD) is a channel structure that spans the cell wall and provides symplastic connection between adjacent cells. Various macromolecules are known to be transported through PD in a highly regulated manner, and plant viruses utilize their movement proteins (MPs) to gate the PD to spread cell-to-cell. The mechanism by which MP modifies PD to enable intercelluar traffic remains obscure, due to the lack of knowledge about the host factors that mediate the process. Here, we describe the functional interaction between Tobacco mosaic virus (TMV) MP and a plant factor, an ankyrin repeat containing protein (ANK), during the viral cell-to-cell movement. We utilized a reverse genetics approach to gain insight into the possible involvement of ANK in viral movement. To this end, ANK overexpressor and suppressor lines were generated, and the movement of MP was tested. MP movement was facilitated in the ANK-overexpressing plants, and reduced in the ANK-suppressing plants, demonstrating that ANK is a host factor that facilitates MP cell-to-cell movement. Also, the TMV local infection was largely delayed in the ANK-suppressing lines, while enhanced in the ANK-overexpressing lines, showing that ANK is crucially involved in the infection process. Importantly, MP interacted with ANK at PD. Finally, simultaneous expression of MP and ANK markedly decreased the PD levels of callose, β-1,3-glucan, which is known to act as a molecular sphincter for PD. Thus, the MP-ANK interaction results in the downregulation of callose and increased cell-to-cell movement of the viral protein. These findings suggest that ANK represents a host cellular receptor exploited by MP to aid viral movement by gating PD through relaxation of their callose sphincters

Validation of microtubule-associated Tobacco mosaic virus RNA movement and involvement of microtubule-aligned particle trafficking

Functional studies of Tobacco mosaic virus (TMV) infection using virus derivatives expressing functional,dysfunctional, and temperature-sensitive movement protein (MP) mutants indicated that the cell-to-celltransport of TMV RNA is functionally correlated with the association of MP with microtubules. However, therole of microtubules in the movement process during early infection remains unclear, since MP accumulates onmicrotubules rather late in infection and treatment of plants with microtubule-disrupting agents fails tostrongly interfere with cell-to-cell movement of TMV RNA. To further test the role of microtubules in TMV cellto-cell movement, we investigated TMV strain Ni2519, which is temperature-sensitive for movement. Wedemonstrate that the temperature-sensitive defect in movement is correlated with temperature-sensitivechanges in the localization of MP to microtubules. Furthermore, we show that during early phases of recoveryfrom non-permissive conditions, the MP localizes to microtubule-associated particles. Similar particles arefound in cells at the leading front of spreading TMV infection sites. Initially mobile, the particles becomeimmobile when MP starts to accumulate along the length of the particle-associated microtubules. Ourobservations confirm a role for microtubules in the spread of TMV infection and associate this role withmicrotubule-associated trafficking of MP-containing particles in cells engaged in the cell-to-cell movement ofthe TMV genome

Disruption of microtubule organization and centrosome function by expression of Tobacco mosaic virus movement protein

The movement protein (MP) of Tobacco mosaic virus mediates the cell-to-cell transport of viral RNA throughplasmodesmata, cytoplasmic cell wall channels for direct cell-to-cell communication between adjacent cells.Previous in vivo studies demonstrated that the RNA transport function of the protein correlates with itsassociation with microtubules, although the exact role of microtubules in the movement process remainsunknown. Since the binding of MP to microtubules is conserved in transfected mammalian cells, we tookadvantage of available mammalian cell biology reagents and tools to further address the interaction inflat-growing and transparent COS-7 cells. We demonstrate that neither actin, nor endoplasmic reticulum (ER),nor dynein motor complexes are involved in the apparent alignment of MP with microtubules. Together withresults of in vitro coprecipitation experiments, these findings indicate that MP binds microtubules directly.Unlike microtubules associated with neuronal MAP2c, MP-associated microtubules are resistant to disruptionby microtubule-disrupting agents or cold, suggesting that MP is a specialized microtubule binding protein thatforms unusually stable complexes with microtubules. MP-associated microtubules accumulate ER membranes,which is consistent with a proposed role for MP in the recruitment of membranes in infected plant cells andmay suggest that microtubules are involved in this process. The ability of MP to interfere with centrosomal-tubulin is independent of microtubule association with MP, does not involve the removal of other testedcentrosomal markers, and correlates with inhibition of centrosomal microtubule nucleation activity. Theseobservations suggest that the function of MP in viral movement may involve interaction with the microtubulenucleatingmachinery