Biology subjects

Little, S. R.

Publications and source records attributed to Little, S. R..

4 recordsLinked to original sources

bioRxiv2024

Cargo adaptor identity controls the mechanism and kinetics of dynein activation

Cytoplasmic dynein-1 (dynein), the primary retrograde motor in most eukaryotes, supports the movement of hundreds of distinct cargos, each with specific trafficking requirements. To achieve this functional diversity, dynein must bind to the multi-subunit complex dynactin and one of a family of cargo adaptors to be converted into an active, processive motor complex. Very little is known about the dynamic processes that promote the formation of this complex. To delineate the kinetic steps that lead to dynein activation, we developed a single-molecule fluorescence assay to visualize the real-time formation of dynein-dynactin-adaptor complexes in vitro. We found that dynactin and adaptors bind dynein independently rather than cooperatively. We also found that different dynein adaptors promote dynein-dynactin-adaptor assembly with dramatically different kinetics, which results in complex formation occurring via different assembly pathways. Despite differences in association rates or mechanism of assembly, all adaptors tested can generate a population of tripartite complexes that are very stable. Our work provides a model for how modulating the kinetics of dynein-dynactin-adaptor binding can be harnessed to promote differential dynein activation and reveals a new facet of the functional diversity of the dynein motor.

biophysics↗

bioRxiv2024

Modulatory Effects of M3 Muscarinic Acetylcholine Receptor on Inflammatory Profiles of Human Memory T Helper Cells

Memory T helper (Th) cells, generated after immunogenic challenge, are crucial in directing the adaptive immune response. Muscarinic ACh receptor (mAChR) subtypes expressed by immune cells can be stimulated with acetylcholine or muscarinic-selective drug oxotremorine-M. Cholinergic signaling can influence immune cells, but it is not known how cholinergic stimuli regulate memory Th cells. This study focused on the role of mAChRs, specifically the M3 muscarinic ACh receptor (M3R), in the cytokine profile and NF-{kappa}B p65 activity of primary human memory Th cells. Memory Th cells (CD3+CD4+CD45RA-CD45RO+) were isolated from healthy participants peripheral blood. Cell culture was performed with anti-CD3/anti-CD28/anti-CD2 reagent, oxotremorine-M (M1R-M5R agonist), atropine (M1R-M5R antagonist), and J104129 (M3R-selective antagonist). MR1-MR5 genes CHRM1-CHRM5 were measured with RT-qPCR. Protein expression of M3R and phosphorylated NF-{kappa}B p65 were quantified by Western blot. The secretion of IFN-{gamma}, IL-17A, and IL-4 was assessed by ELISA and intracellular cytokine staining flow cytometry. CHRM3, encoding M3R, was knocked out using CRISPR-Cas9 gene targeting. Memory Th cells expressed all five mAChR subtypes. Oxotremorine-M increased IFN-{gamma} and IL-17A while reducing IL-4 in an atropine-sensitive manner. Stimulation of mAChRs in cells with CHRM3-knockout or M3R blockade prevented increases in IFN-{gamma} and IL-17A but continued to inhibit IL-4. mAChR stimulation enhanced NF-{kappa}B p65 activity without affecting cell proliferation, viability, or M3R expression. This investigation demonstrates that muscarinic signaling increases the pro-inflammatory profile of memory Th cells, including NF-{kappa}B p65, IFN-{gamma}, and IL-17A, with a reduction in IL-4. Focusing on M3R blockers could modulate adaptive immune responses and alleviate immune-related conditions.

immunology↗

bioRxiv2024

A Digital Microfluidic Platform for the Microscale Production of Functional Immune Cell Therapies

Genetically engineering human immune cells has been shown to be an effective approach for developing novel cellular therapies to treat a wide range of diseases. To expand the scope of these cellular therapies while solving persistent challenges, extensive research and development is still required. Electroporation has recently emerged as one of the most popular techniques for inserting biological payloads into human immune cells to perform genetic engineering. However, several recent studies have reported that electroporation can negatively impact cell functionality. Additionally, the requirement to use large amounts of cells and expensive payloads to achieve efficient delivery can drive up the costs of development efforts. Here we use a digital microfluidic enabled electroporation system (referred to as triDrop) and compare them against two state-of-the-art commercially available systems for the engineering of human T cells. We describe the ability to use triDrop for highly viable, highly efficient transfection while using substantially fewer cells and payload. Subsequently, we perform transcriptomic analysis on cells engineered with each of the three systems and show that electroporation with triDrop lead to less dysregulation of several functionally relevant pathways. Finally, in a direct comparison of immunotherapeutic functionality, we show that T cells engineered with triDrop have an improved ability to mount an immune response when presented with tumor cells. These results show that the triDrop platform is uniquely suited to produce functionally engineered immune cells while also reducing the costs of cell engineering compared to other commercially available systems.

bioengineering↗

bioRxiv2023

Ndel1 modulates dynein activation in two distinct ways

Dynein is the primary minus-end-directed microtubule motor [1]. To achieve activation, dynein binds to the dynactin complex and an adaptor to form the "activated dynein complex" [2, 3]. The protein Lis1 aids activation by binding to dynein and promoting its association with dynactin and adaptor [4, 5]. Ndel1 and its orthologue Nde1 are dynein and Lis1 binding proteins that help control where dynein localizes within the cell [6]. Cell-based assays suggest that Ndel1/Nde1 also work with Lis1 to promote dynein activation, although the underlying mechanism is unclear [6]. Using purified proteins and quantitative binding assays, we found that Ndel1s C-terminal region contributes to binding to dynein and negatively regulates binding to Lis1. Using single-molecule imaging and protein biochemistry, we observed that Ndel1 inhibits dynein activation in two distinct ways. First, Ndel1 disfavors the formation of the activated dynein complex. We found that phosphomimetic mutations in Ndel1s C-terminal domain increase its ability to inhibit dynein-dynactin-adaptor complex formation. Second, we observed that Ndel1 interacts with dynein and Lis1 simultaneously and sequesters Lis1 away from its dynein binding site. In doing this, Ndel1 prevents Lis1-mediated dynein activation. Our work suggests that in vitro, Ndel1 is a negative regulator of dynein activation, which contrasts with cellular studies where Ndel1 promotes dynein activity. To reconcile our findings with previous work, we posit that Ndel1 functions to scaffold dynein and Lis1 together while keeping dynein in an inhibited state. We speculate that Ndel1 release can be triggered in cellular settings to allow for timed dynein activation.

biochemistry↗