Breaking Down Microtubule Formation: Characterizing the Biochemical and Cellular Functions of the γ-Tubulin Ring Complex

The γ-Tubulin ring complex (γ-TuRC) is an essential regulator of the microtubule cytoskeleton. It is composed of\u3e30 individual proteins that include the major component,γ-tubulin, as well as γ-tubulin complex proteins 2-6 (GCP2-6), mitotic-spindle organizing proteins associated with a ring of γ-tubulin proteins 1 and 2 (MOZART, or MZT1 andMZT2), and an actin molecule. This ~2.2MDa assembly regulates microtubule dynamics by facilitating the nucleation of new microtubules, modulating microtubule minus-end dynamics by acting as a minus-end cap, and anchoring microtubules to specify their cellular localization. These three major activities of the γ-TuRC, nucleation, capping, and anchoring, contribute to the dynamic nature of individual microtubules and of larger microtubule networks that are critical for cellular activities, including cell motility, intrace have spurred biochemical and cellular characterization of its nucleation activity. However,it remains unclear how the remaining major γ-TuRC activities contribute to microtubule dynamics

Evolutionary Modeling of Rate Shifts Reveals Specificity Determinants in HIV-1 Subtypes

A hallmark of the human immunodeficiency virus 1 (HIV-1) is its rapid rate of evolution within and among its various subtypes. Two complementary hypotheses are suggested to explain the sequence variability among HIV-1 subtypes. The first suggests that the functional constraints at each site remain the same across all subtypes, and the differences among subtypes are a direct reflection of random substitutions, which have occurred during the time elapsed since their divergence. The alternative hypothesis suggests that the functional constraints themselves have evolved, and thus sequence differences among subtypes in some sites reflect shifts in function. To determine the contribution of each of these two alternatives to HIV-1 subtype evolution, we have developed a novel Bayesian method for testing and detecting site-specific rate shifts. The RAte Shift EstimatoR (RASER) method determines whether or not site-specific functional shifts characterize the evolution of a protein and, if so, points to the specific sites and lineages in which these shifts have most likely occurred. Applying RASER to a dataset composed of large samples of HIV-1 sequences from different group M subtypes, we reveal rampant evolutionary shifts throughout the HIV-1 proteome. Most of these rate shifts have occurred during the divergence of the major subtypes, establishing that subtype divergence occurred together with functional diversification. We report further evidence for the emergence of a new sub-subtype, characterized by abundant rate-shifting sites. When focusing on the rate-shifting sites detected, we find that many are associated with known function relating to viral life cycle and drug resistance. Finally, we discuss mechanisms of covariation of rate-shifting sites

Estrogen Receptor Alpha Promotes Protein Synthesis by Fine-Tuning the Expression of the Eukaryotic Translation Initiation Factor 3 Subunit F (eIF3f)

Approximately two thirds of all breast cancer cases are estrogen receptor (ER)-positive. The treatment of this breast cancer subtype with endocrine therapies is effective in the adjuvant and recurrent settings. However, their effectiveness is compromised by the emergence of intrinsic or acquired resistance. Thus, identification of new molecular targets can significantly contribute to the development of novel therapeutic strategies. In recent years, many studies have implicated aberrant levels of translation initiation factors in cancer etiology and provided evidence that identifies these factors as promising therapeutic targets. Accordingly, we observed reduced levels of the eIF3 subunit eIF3f in ER-positive breast cancer cells compared with ER-negative cells, and determined that low eIF3f levels are required for proper proliferation and survival of ER-positive MCF7 cells. The expression of eIF3f is tightly controlled by ERalpha at the transcriptional (genomic pathway) and translational (nongenomic pathway) level. Specifically, estrogen-bound ERalpha represses transcription of the EIF3F gene, while promoting eIF3f mRNA translation. To regulate translation, estrogen activates the mTORC1 pathway, which enhances the binding of eIF3 to the eIF4F complex and, consequently, the assembly of the 48S preinitiation complexes and protein synthesis. We observed preferential translation of mRNAs with highly structured 5\u27-UTRs that usually encode factors involved in cell proliferation and survival (e.g. cyclin D1 and survivin). Our results underscore the importance of estrogen-ERalpha-mediated control of eIF3f expression for the proliferation and survival of ER-positive breast cancer cells. These findings may provide rationale for the development of new therapies to treat ER-positive breast cancer

Raptor localization predicts prognosis and tamoxifen response in estrogen receptor-positive breast cancer

Deregulated PI3K/mTOR signals can promote the growth of breast cancer and contribute to endocrine treatment resistance. This report aims to investigate raptor and its intracellular localization to further understand its role in ER-positive breast cancer. Raptor protein expression was evaluated by immunohistochemistry in 756 primary breast tumors from postmenopausal patients randomized to tamoxifen or no tamoxifen. In vitro, the MCF7 breast cancer cell line and tamoxifen-resistant MCF7 cells were studied to track the raptor signaling changes upon resistance, and raptor localization in ER alpha-positive cell lines was compared with that in ER alpha-negative cell lines. Raptor protein expression in the nucleus was high in ER/PgR-positive and HER2-negative tumors with low grade, features associated with the luminal A subtype. Presence of raptor in the nucleus was connected with ER alpha signaling, here shown by a coupled increase of ER alpha phosphorylation at S167 and S305 with accumulation of nuclear raptor. In addition, the expression of ER alpha-activated gene products correlated with nuclear raptor. Similarly, in vitro we observed raptor in the nucleus of ER alpha-positive, but not of ER-negative cells. Interestingly, raptor localized to the nucleus could still be seen in tamoxifen-resistant MCF7 cells. The clinical benefit from tamoxifen was inversely associated with an increase of nuclear raptor. High cytoplasmic raptor expression indicated worse prognosis on long-term follow-up. We present a connection between raptor localization to the nucleus and ER alpha-positive breast cancer, suggesting raptor as a player in stimulating the growth of the luminal A subtype and a possible target along with endocrine treatment.Funding Agencies|Swedish Cancer Society; Region of Ostergotland; Cancer Society in Stockholm; King Gustav V Jubilee Clinical Research Foundation; National Cancer Institute (NCI); American Cancer Society; Atol Charitable Trust</p

A nucleotide binding–independent role for γ-tubulin in microtubule capping and cell division

The γ-tubulin ring complex (γ-TuRC) has essential roles in centrosomal and non-centrosomal microtubule organization during vertebrate mitosis. While there have been important advances in understanding γ-TuRC-dependent microtubule nucleation, γ-TuRC capping of microtubule minus-ends remains poorly characterized. Here, we utilized biochemical reconstitutions and cellular assays to characterize the human γ-TuRC’s capping activity. Single filament assays showed that the γ-TuRC remained associated with a nucleated microtubule for tens of minutes. In contrast, caps at dynamic microtubule minus-ends displayed lifetimes of ∼1 min. Reconstituted γ-TuRCs with nucleotide-binding deficient γ-tubulin (γ-tubulinΔGTP) formed ring-shaped complexes that did not nucleate microtubules but capped microtubule minus-ends with lifetimes similar to those measured for wild-type complexes. In dividing cells, microtubule regrowth assays revealed that while knockdown of γ-tubulin suppressed non-centrosomal microtubule formation, add-back of γ-tubulinΔGTP could substantially restore this process. Our results suggest that γ-TuRC capping is a nucleotide-binding-independent activity that plays a role in non-centrosomal microtubule organization during cell division.ISSN:0021-9525ISSN:1540-814

Ethics of Social Media Research: State of the Debate and Future Challenges

Since the late 1990s, researchers have been investigating into the ethical issues of Internet research. Among the first works, AoIR Research Ethics Recommendations of 2002 can be mentioned. Internet research ethics issues are still compelling, especially about social media, that are consolidated fields of research but with ethical open questions that will be more and more complex in the future. The chapter will go through these questions, focusing on selected keywords and summarizing for each one the debate, holes, and challenges for the future. The chapter will begin with a definition of the key terms, such as Internet research ethics, social media, and social network sites, as an important step for assessing the ethical issues around social media research. The chapter will then address traditional issues about ethics, like privacy, informed consent, anonymization, Institutional Review Board, and traceability, and then it will focus on new topics, like Big Data, data storage and retrieval, and crowdsourcing work. Besides the specific issues, also broader approaches to privacy will be presented, such as the ones of distributed morality and distributed responsibility, as framework under which build a dialogue between the many actors involved (researchers, companies, users, data, algorithms, programmers)