Comprehensive characterization of the Hsp70 interactome reveals novel client proteins and interactions mediated by posttranslational modifications.

Hsp70 interactions are critical for cellular viability and the response to stress. Previous attempts to characterize Hsp70 interactions have been limited by their transient nature and the inability of current technologies to distinguish direct versus bridged interactions. We report the novel use of cross-linking mass spectrometry (XL-MS) to comprehensively characterize the Saccharomyces cerevisiae (budding yeast) Hsp70 protein interactome. Using this approach, we have gained fundamental new insights into Hsp70 function, including definitive evidence of Hsp70 self-association as well as multipoint interaction with its client proteins. In addition to identifying a novel set of direct Hsp70 interactors that can be used to probe chaperone function in cells, we have also identified a suite of posttranslational modification (PTM)-associated Hsp70 interactions. The majority of these PTMs have not been previously reported and appear to be critical in the regulation of client protein function. These data indicate that one of the mechanisms by which PTMs contribute to protein function is by facilitating interaction with chaperones. Taken together, we propose that XL-MS analysis of chaperone complexes may be used as a unique way to identify biologically important PTMs on client proteins.

Vps501, a novel vacuolar SNX-BAR protein cooperates with the SEA complex to regulate TORC1 signaling.

The sorting nexins (SNX), constitute a diverse family of molecules that play varied roles in membrane trafficking, cell signaling, membrane remodeling, organelle motility and autophagy. In particular, the SNX-BAR proteins, a SNX subfamily characterized by a C-terminal dimeric Bin/Amphiphysin/Rvs (BAR) lipid curvature domain and a conserved Phox-homology domain, are of great interest. In budding yeast, many SNX-BARs proteins have well-characterized endo-vacuolar trafficking roles. Phylogenetic analyses allowed us to identify an additional SNX-BAR protein, Vps501, with a novel endo-vacuolar role. We report that Vps501 uniquely localizes to the vacuolar membrane and has physical and genetic interactions with the SEA complex to regulate TORC1 inactivation. We found cells displayed a severe deficiency in starvation-induced/nonselective autophagy only when SEA complex subunits are ablated in combination with Vps501, indicating a cooperative role with the SEA complex during TORC1 signaling during autophagy induction. Additionally, we found the SEACIT complex becomes destabilized in vps501Δsea1Δ cells, which resulted in aberrant endosomal TORC1 activity and subsequent Atg13 hyperphosphorylation. We have also discovered that the vacuolar localization of Vps501 is dependent upon a direct interaction with Sea1 and a unique lipid binding specificity that is also required for its function. This article is protected by copyright. All rights reserved.

Creating a chimeric clathrin heavy chain that functions independently of yeast clathrin light chain.

Clathrin facilitates vesicle formation during endocytosis and sorting in the trans-Golgi network (TGN)/endosomal system. Unlike in mammals, yeast clathrin function requires both the clathrin heavy (CHC) and clathrin light (CLC) chain, since Chc1 does not form stable trimers without Clc1. To further delineate clathrin subunit functions, we constructed a chimeric CHC protein (Chc-YR) , which fused the N-terminus of yeast CHC (1-1312) to the rat CHC residues 1318-1675, including the CHC trimerization region. The novel CHC-YR allele encoded a stable protein that fractionated as a trimer. CHC-YR also complemented chc1Δ slow growth and clathrin TGN/endosomal sorting defects. In strains depleted for Clc1 (either clc1Δ or chc1Δ clc1Δ), CHC-YR, but not CHC1, suppressed TGN/endosomal sorting and growth phenotypes. Chc-YR-GFP (green fluorescent protein) localized to the TGN and cortical patches on the plasma membrane, like Chc1 and Clc1. However, Clc1-GFP was primarily cytoplasmic in chc1Δ cells harboring pCHC-YR, indicating that Chc-YR does not bind yeast CLC. Still, some partial phenotypes persisted in cells with Chc-YR, which are likely due either to loss of CLC recruitment or chimeric HC lattice instability. Ultimately, these studies have created a tool to examine non-trimerization roles for the clathrin LC.

Atg27 tyrosine sorting motif is important for its trafficking and Atg9 localization.

During autophagy, the transmembrane protein Atg27 facilitates transport of the major autophagy membrane protein Atg9 to the preautophagosomal structure (PAS). To better understand the function of Atg27 and its relationship with Atg9, Atg27 trafficking and localization were examined. Atg27 localized to endosomes and the vacuolar membrane, in addition to previously described PAS, Golgi and Atg9-positive structures. Atg27 vacuolar membrane localization was dependent on the adaptor AP-3, which mediates direct transport from the trans-Golgi to the vacuole. The four C-terminal amino acids (YSAV) of Atg27 comprise a tyrosine sorting motif. Mutation of the YSAV abrogated Atg27 transport to the vacuolar membrane and affected its distribution in TGN/endosomal compartments, while PAS localization was normal. Also, in atg27(ΔYSAV) or AP-3 mutants, accumulation of Atg9 in the vacuolar lumen was observed upon autophagy induction. Nevertheless, PAS localization of Atg9 was normal in atg27(ΔYSAV) cells. The vacuole lumen localization of Atg9 was dependent on transport through the multivesicular body, as Atg9 accumulated in the class E compartment and vacuole membrane in atg27(ΔYSAV) vps4Δ but not in ATG27 vps4Δ cells. We suggest that Atg27 has an additional role to retain Atg9 in endosomal reservoirs that can be mobilized during autophagy.

Role of Scd5, a protein phosphatase-1 targeting protein, in phosphoregulation of Sla1 during endocytosis.

Phosphorylation regulates assembly and disassembly of proteins during endocytosis. In yeast, Prk1 and Ark1 phosphorylate factors after vesicle internalization leading to coat disassembly. Scd5, a protein phosphatase-1 (PP1)-targeting subunit, is proposed to regulate dephosphorylation of Prk1/Ark1 substrates to promote new rounds of endocytosis. In this study we analyzed scd5-PP1Δ2, a mutation causing impaired PP1 binding. scd5-PP1Δ2 caused hyperphosphorylation of several Prk1 endocytic targets. Live-cell imaging of 15 endocytic components in scd5-PP1Δ2 revealed that most factors arriving before the invagination/actin phase of endocytosis had delayed lifetimes. Severely affected were early factors and Sla2 (Hip1R homolog), whose lifetime was extended nearly fourfold. In contrast, the lifetime of Sla1, a Prk1 target, was extended less than twofold, but its cortical recruitment was significantly reduced. Delayed Sla2 dynamics caused by scd5-PP1Δ2 were suppressed by SLA1 overexpression. This was dependent on the LxxQxTG repeats (SR) of Sla1, which are phosphorylated by Prk1 and bind Pan1, another Prk1 target, in the dephosphorylated state. Without the SR, Sla1ΔSR was still recruited to the cell surface, but was less concentrated in cortical patches than Pan1. sla1ΔSR severely impaired endocytic progression, but this was partially suppressed by overexpression of LAS17, suggesting that without the SR region the SH3 region of Sla1 causes constitutive negative regulation of Las17 (WASp). These results demonstrate that Scd5/PP1 is important for recycling Prk1 targets to initiate new rounds of endocytosis and provide new mechanistic information on the role of the Sla1 SR domain in regulating progression to the invagination/actin phase of endocytosis.

Introducing Wound Healing Assays in the Undergraduate Biology Laboratory Using Ibidi Plates.

The wound healing assay is a simple and inexpensive method that allows researchers to experimentally mimic cell growth and migration leading to wound healing. In this assay, a wound is created on a monolayer of cultured mammalian cells and cell migration is monitored. Micrographs are captured at regular intervals during the duration of the experiment. These microscopy images are analyzed to compare cell migration and wound closure under different conditions. Introduction of different cytotoxic treatments into a wound healing assay can provide information as to whether a particular drug or compound of interest has the ability to affect cell migration. This type of analysis is important when assessing the ability of a particular cancer cell line to display invasive and metastatic behaviors. One of the challenges of this assay is to create the original wound in a way that is consistent across plates or treatments, facilitating comparisons across experimental groups. This is a particular challenge when using the wound healing assay in the context of an undergraduate biology class to expose students to a distinct form of mammalian cell culture and help them apply scientific knowledge and research skills. We found an easy way to overcome this obstacle by using ibidi plates. In this article, we provide a simple protocol to use ibidi plates and HeLa cells to set up wound healing assays. This laboratory exercise allows undergraduate students to utilize different skills developed through cell culture experience, such as growing, treating, and imaging mammalian cells.

Refining a DEI Assessment Tool for Use in Optimizing Professional STEM Societies for Gender Equity.

Historic science, technology, engineering and mathematics (STEM) disciplinary cultures were founded in a system that was predominately male, white, heterosexual, and able-bodied (i.e., "majority"). Some societal norms have changed, and so has demand for inclusive STEM engagement. However, legacy mental models, or deeply held beliefs and assumptions, linger and are embedded in the STEM system and disciplinary cultures. STEM reform is needed to maximize talent and create inclusive professions, but cannot be achieved without recognizing and addressing norms and practices that disproportionately serve majority vs. minoritized groups. As leading voices in disciplinary work and application, disciplinary and professional societies (Societies) are instrumental in shaping and sustaining STEM norms. We, leaders of the Amplifying the Alliance to Catalyze Change for Equity in STEM Success (ACCESS+) project, recognize the need to provide Society diversity, equity, and inclusion (DEI) change leaders with tools necessary to foster systemic change. In this Perspectives article, we present the Equity Environmental Scanning Tool (EEST) as an aid to help Society DEI change leaders elucidate legacy mental models, discern areas of strength, identify foci for advancement, and benchmark organizational change efforts. We share our rationale and work done to identify, and, ultimately, adapt a Society DEI self-assessment tool from the United Kingdom. We share background information on the UK tool, content and structural changes made to create the EEST, and an overview of the resulting EEST. Ultimately, we seek to increase awareness of a Society-specific DEI self-assessment tool designed to help Society DEI change leaders advance inclusive reform.

Scientific Societies Integrating Gender and Ethnoracial Diversity Efforts: A First Meeting Report from Amplifying the Alliance to Catalyze Change for Equity in STEM Success (ACCESS+).

Professional STEM societies have been identified as an important lever to address STEM diversity, equity, and inclusion. In this Perspectives article, we chronicle the highlights of the first Amplifying the Alliance to Catalyze Change for Equity in STEM Success (ACCESS+) convening held in September 2021. Here, we introduce the three-part ACCESS+ approach using a model that entails (i) completion of a DEI self-assessment known as the equity environmental scanning tool, (ii) guided action plan development and iteration, and (iii) sustained participation in a community of practice.

Atg27p co-fractionates with clathrin-coated vesicles in budding yeast.

Atg27p, a single-pass transmembrane protein that functions in autophagy, localizes to a variety of cellular compartments including the pre-autophagosomal structure, late Golgi, vacuolar membrane, as well as early and late endosomes. Its cytoplasmic C-terminus contains a tyrosine sorting motif that allows for its transport to the vacuolar membrane and an additional sequence that allows for its retrieval from the vacuolar membrane to the endosome. Since clathrin is well known to mediate vesicular transport in the endomembrane system, the trafficking of Atg27p and its tyrosine sorting motif suggested that it might be trafficked inside clathrin-coated vesicles (CCVs). In our previous studies, Atg27p was identified by mass spectrometry as a potential component in CCVs, as it was present in CCVs isolated from both WT and auxilin-depleted cells. We now confirm that Atg27p is a component of CCVs using immunoblotting and additional mass spectrometry data.

Atg27p localization is clathrin- and Ent3p/5p-dependent.

The autophagy-related protein Atg27p has been previously shown to localize to the autophagy-specific pre-autophagosomal structure (PAS) as well as to several organelles, including the late Golgi, the vacuolar membrane, and the endosome. Given that Atg27p localization to the vacuolar membrane in particular has been shown to be dependent on both its C-terminal tyrosine sorting motif and the AP-3 adaptor, and that Atg27p can be found in clathrin-coated vesicles, we set out to determine whether Atg27p localization inside cells is dependent on clathrin or on any of its cargo adaptors. We report that Atg27p localization is clathrin- and Ent3p/5p-dependent.

Taking ownership of your career: professional development through experiential learning.

Experiential learning can facilitate the development of transferrable skills necessary for success in attaining tenure and promotion in academia. In this article, we discuss the benefits of designing and implementing an individualized professional development experience or practicum. By doing this, we describe the experiential learning component of the Accomplishing Career Transitions (ACT) Program of the American Society for Cell Biology. The ACT program aims to assist postdoctoral trainees and junior faculty from backgrounds underrepresented in STEM as they strive to transition into tenure-track positions and ultimately attain tenure at research-intensive or teaching-intensive academic institutions.

Autophagy as an on-ramp to scientific discovery.

The common view of art and science as polar opposites along the educational spectrum can sometimes mask the degree to which they inform one another. In fact, art can also serve as a way to foster interest in querying the natural world, ultimately allowing us to recruit highly creative individuals to join the scientific community. We have experienced firsthand how cellular processes, such as autophagy, which are not usually highlighted or described in detail in foundational cell biology textbooks, have served as an on-ramp for artists at the undergraduate and high school levels in the context of scientific research and science outreach, respectively. We discuss our experiences in this article and highlight the ways in which art's many dimensions are well-suited, not only for forging connections between scientists and their communities but also for encouraging creativity in the way scientists engage with visually and conceptually complex phenomena, such as autophagy.Abbreviations: AP-3: adaptor protein complex 3; Atg27: autophagy related protein 27; STEAM: science, technology, engineering, arts, and mathematics; STEM: science, technology, engineering and math.

Accomplishing Career Transitions 2019: facilitating success towards the professoriate.

The Minorities Affairs Committee of the American Society for Cell Biology through its Accomplishing Career Transitions (ACT) program aims to ease critical transitions for postdocs and junior faculty from underrepresented backgrounds in STEM or from minority-serving institutions as they work towards promotion and tenure at a wide range of academic institutions. The ACT program is a 2-year cohort-based professional and skills development program that kicks off with a summer workshop and continues with additional online training sessions on selected topics, forging the creation of a permanent mentoring community for the participants. In this BMC Proceedings Supplement, we highlight selected content from the first ACT summer workshop held in 2019 at the Rizzo Center in Chapel Hill, NC. The goal of this BMC Proceedings Supplement is to amplify impact of ACT programming in a way that transcends the ACT Fellow community to benefit an increased number of scientists.

YML018C protein localizes to the vacuolar membrane independently of Atg27p.

The function of the budding yeast YML018C protein remains to be determined. High-throughput studies have reported that the YML018C protein localizes to the vacuolar membrane and physically interacts with the autophagy-related protein Atg27p. While this evidence suggests a potential role for this uncharacterized protein in the process of autophagy, the function of this putative interaction remains uncharacterized. In this micropublication, we report our finding that the localization of the YML018C protein to the vacuolar membrane does not require Atg27p.

The Inclusive Professional Framework for Societies: Changing Mental Models to Promote Diverse, Equitable, and Inclusive STEM Systems Change.

Science, technology, engineering, and mathematics (STEM) professional societies (ProSs) are uniquely positioned to foster national-level diversity, equity, and inclusion (DEI) reform. ProSs serve broad memberships, define disciplinary norms and culture, and inform accrediting bodies and thus provide critical levers for systems change. STEM ProSs could be instrumental in achieving the DEI system reform necessary to optimize engagement of all STEM talent, leveraging disciplinary excellence resulting from diverse teams. Inclusive STEM system reform requires that underlying "mental models" be examined. The Inclusive Professional Framework for Societies (IPF: Societies) is an interrelated set of strategies that can help ProSs change leaders (i.e., "boundary spanners") and organizations identify and address mental models hindering DEI reform. The IPF: Societies uses four "I's"-Identity awareness and Intercultural mindfulness (i.e., equity mindset) upon which inclusive relationships and Influential DEI actions are scaffolded. We discuss how the IPF: Societies complements existing DEI tools (e.g., Women in Engineering ProActive Network's Framework for Promoting Gender Equity within Organization; Amplifying the Alliance to Catalyze Change for Equity in STEM Success' Equity Environmental Scan Tool). We explain how the IPF: Societies can be applied to existing ProS policy and practice associated with common ProS functions (e.g., leadership, membership, conferences, awards, and professional development). The next steps are to pilot the IPF: Societies with a cohort of STEM ProSs. Ultimately, the IPF: Societies has potential to promote more efficient, effective, and lasting DEI organizational transformation and contribute to inclusive STEM disciplinary excellence.

ATG8 is conserved between Saccharomyces cerevisiae and psychrophilic, polar-collected fungi.

Autophagy is a conserved catabolic process by which eukaryotic cells respond to stress by targeting damaged or unneeded molecules or organelles for sequestration into specialized vesicles known as autophagosomes. Autophagosomes ultimately facilitate the digestion and recycling of their contents by fusing with the degradative organelle of the cell. Studies of the budding yeast Saccharomyces cerevisiae have revealed various types of stress that can regulate autophagy, including starvation and extreme temperatures. While autophagy has not yet been directly shown to confer the ability to survive extreme cold or freeze-thaw stress in yeast, upregulation of autophagy has been directly implicated in the ability of arctic insects to survive cold temperatures. We are interested in investigating the potential role of autophagy in polar habitat survival by cold-loving (psychrophilic) yeast like Mrakia blollopsis. To begin to examine the conservation of Atg machinery in polar-collected yeast, we focused on Atg8, a small, ubiquitin-like protein that plays an important role in autophagy. We report that Atg8 is conserved between S. cerevisiae and polar-collected yeast, using Atg8 from Mrakia blollopsis (strain TGK1-2) as an example. This study represents the first direct examination of autophagy machinery conservation across mesophilic and psychrophilic species of yeast.

Establishing Partnerships for Science Outreach Inside and Outside the Undergraduate Classroom.

STEM outreach experiences provide aspiring scientists and healthcare professionals with opportunities to grow into new roles, integrate knowledge, and acquire soft skills. While STEM outreach publications often describe the outreach performed, few focus on how to establish strong partnerships, which are essential for outreach endeavors to succeed. Information on this is more important than ever before-grant agencies commonly require education and outreach plans that will reach a broader audience. Consequently, principal investigators who are not trained in education or outreach need tools to set up strong partnerships. To help fill this gap, here we outline the recommended steps for developing robust interdisciplinary STEM outreach programs that leverage institutional resources and community partnerships. This process yields strategic and sustainable opportunities for undergraduate students to learn as they engage with the STEM outreach team (students, faculty, university staff, and community partners) and the lay public. The outlined ideas broadly apply to creating outreach programs for trainees at any stage, not just undergraduates.

New Perspectives on SNARE Function in the Yeast Minimal Endomembrane System.

Saccharomyces cerevisiae is one of the best model organisms for the study of endocytic membrane trafficking. While studies in mammalian cells have characterized the temporal and morphological features of the endocytic pathway, studies in budding yeast have led the way in the analysis of the endosomal trafficking machinery components and their functions. Eukaryotic endomembrane systems were thought to be highly conserved from yeast to mammals, with the fusion of plasma membrane-derived vesicles to the early or recycling endosome being a common feature. Upon endosome maturation, cargos are then sorted for reuse or degraded via the endo-lysosomal (endo-vacuolar in yeast) pathway. However, recent studies have shown that budding yeast has a minimal endomembrane system that is fundamentally different from that of mammalian cells, with plasma membrane-derived vesicles fusing directly to a trans-Golgi compartment which acts as an early endosome. Thus, the Golgi, rather than the endosome, acts as the primary acceptor of endocytic vesicles, sorting cargo to pre-vacuolar endosomes for degradation. The field must now integrate these new findings into a broader understanding of the endomembrane system across eukaryotes. This article synthesizes what we know about the machinery mediating endocytic membrane fusion with this new model for yeast endomembrane function.

Cryopreservation and the Freeze-Thaw Stress Response in Yeast.

The ability of yeast to survive freezing and thawing is most frequently considered in the context of cryopreservation, a practical step in both industrial and research applications of these organisms. However, it also relates to an evolved ability to withstand freeze-thaw stress that is integrated with a larger network of survival responses. These responses vary between different strains and species of yeast according to the environments to which they are adapted, and the basis of this adaptation appears to be both conditioned and genetic in origin. This review article briefly touches upon common yeast cryopreservation methods and describes in detail what is known about the biochemical and genetic determinants of cell viability following freeze-thaw stress. While we focus on the budding yeast Saccharomyces cerevisiae, in which the freeze-thaw stress response is best understood, we also highlight the emerging diversity of yeast freeze-thaw responses as a manifestation of biodiversity among these organisms.

Using The Cancer Genome Atlas as an Inquiry Tool in the Undergraduate Classroom.

Undergraduate students in the biomedical sciences are often interested in future health-focused careers. This presents opportunities for instructors in genetics, molecular biology, and cancer biology to capture their attention using lab experiences built around clinically relevant data. As biomedical science in general becomes increasingly dependent on high-throughput data, well-established scientific databases such as The Cancer Genome Atlas (TCGA) have become publicly available tools for medically relevant inquiry. The best feature of this database is that it bridges the molecular features of cancer to human clinical outcomes-allowing students to see a direct connection between the molecular sciences and their future professions. We have developed and tested a learning module that leverages the power of TCGA datasets to engage students to use the data to generate and test hypotheses and to apply statistical tests to evaluate significance.