Biology subjects

Constam, D. B.

Publications and source records attributed to Constam, D. B..

5 recordsLinked to original sources

bioRxiv2021

Dual modulation of phase-transitioning licenses the Bicc1 network of ciliopathy proteins to bind specific target mRNAs

Perturbations in biomolecular condensates that form by phase-transitioning are linked to a growing number of degenerative diseases. For example, mutations in a multivalent interaction network of the Ankyrin (ANK) and sterile alpha motif (SAM) domain-containing ANKS3 and ANKS6 proteins with the RNA-binding protein Bicaudal-C1 (Bicc1) associate with laterality defects and chronic kidney diseases known as ciliopathies. However, insights into the mechanisms that control RNA condensation in ribonucleoprotein particles (RNPs) are scarce. Here, we asked whether heterooligomerization modulates Bicc1 binding to RNA. Reconstitution assays in vitro and live imaging in vivo show that a K homology (KH) repeat of Bicc1 self-interacts and synergizes with SAM domain self-polymerization independently of RNA to concentrate bound mRNAs in gel-like granules that can split or fuse with each other. Importantly, emulsification of Bicc1 by ANKS3 inhibited binding to target mRNAs, whereas condensation by ANKS6 co-recruitment increased it by liberating the KH domains from ANKS3. Our findings suggest that the perturbation of Bicc1-Anks3-Anks6 RNP dynamics is a likely cause of associated ciliopathies.

developmental biology↗

bioRxiv2021

Time-resolved scanning ion conductance microscopy for three-dimensional tracking of nanoscale cell surface dynamics

Nanocharacterization plays a vital role in understanding the complex nanoscale organization of cells and organelles. Understanding cellular function requires high-resolution information about how the cellular structures evolve over time. A number of techniques exist to resolve static nanoscale structure of cells in great detail (super-resolution optical microscopy1, EM2, AFM3). However, time-resolved imaging techniques tend to either have lower resolution, are limited to small areas, or cause damage to the cells thereby preventing long-term time-lapse studies. Scanning probe microscopy methods such as atomic force microscopy (AFM) combine high-resolution imaging with the ability to image living cells in physiological conditions. The mechanical contact between the tip and the sample, however, deforms the cell surface, disturbs the native state, and prohibits long-term time-lapse imaging. Here, we develop a scanning ion conductance microscope (SICM) for high-speed and long-term nanoscale imaging. By utilizing recent advances in nanopositioning4, nanopore fabrication5, microelectronics6, and controls engineering7 we developed a microscopy method that can resolve spatiotemporally diverse three-dimenional processes on the cell membrane at sub-5nm axial resolution. We tracked dynamic changes in live cell morphology with nanometer details and temporal ranges of sub-second to days, imagining diverse processes ranging from endocytosis, micropinocytosis, and mitosis, to bacterial infection and cell differentiation in cancer cells. This technique enables a detailed look at membrane events and may offer insights into cell-cell interactions for infection, immunology, and cancer research.

biophysics↗

bioRxiv2020

Fluid flow-induced left-right asymmetric decay of Dand5 mRNA in the mouse embryo requires Bicc1-Ccr4 RNA degradation complex

Molecular left-right (L-R) asymmetry is established at the node of the mouse embryo as a result of the sensing of a leftward fluid flow by immotile cilia of perinodal crown cells and the consequent degradation of Dand5 mRNA on the left side. We here examined how the fluid flow induces Dand5 mRNA decay. We found that the 3 untranslated region (3-UTR) of Dand5 mRNA is necessary and sufficient for the left-sided decay and is responsive to the flow direction, loss of the cation channel Pkd2, and Ca2+. The 200-nucleotide proximal-most portion of the 3-UTR, which is conserved among mammals, is essential for the asymmetric mRNA decay and binds Bicc1, an RNA binding protein specifically expressed at the node. Bicc1 preferentially recognizes GAC and GACR sequences in RNA, and these motifs are enriched in the 200-nucleotide region of the Dand5 3-UTR. The Cnot3 component of the Ccr4-Not deadenylase complex interacts with Bicc1 and is also required for Dand5 mRNA decay at the node. Our results thus suggest that leftward fluid flow induces binding of Bicc1 to the 3-UTR of Dand5 mRNA in crown cells on the left side of the node, and that consequent recruitment of Ccr4-Not mediates mRNA degradation.

developmental biology↗

bioRxiv2018

A novel cell-based sensor detecting the activity of individual basic proprotein convertases

The basic proprotein convertases (PCs) furin, PC1/3, PC2, PC5/6, PACE4, PC4, and PC7 are promising drug targets for human diseases. However, developing selective inhibitors remains challenging due to overlapping substrate recognition motifs and limited structural information. Classical drug screening approaches for basic PC inhibitors involve homogeneous biochemical assays using soluble recombinant enzymes combined with fluorogenic substrate peptides and do not accurately recapitulate the complex cellular context of the basic PC-substrate interaction. We report here PCific, a novel cell-based molecular sensor that allows rapid screening of candidate inhibitors and their selectivity toward individual basic PCs within mammalian cells. PCific consists of Gaussia luciferase linked to a sortilin-1 membrane anchor via a cleavage motif that allows efficient release of luciferase specifically if individual basic PCs are provided in cis. Screening of selected candidate peptidomimetic inhibitors revealed that PCific can readily distinguish between general and selective PC inhibitors in a high-throughput screening format.

biochemistry↗

bioRxiv2017

Paracrine Activin-A Signaling Promotes Melanoma Growth And Metastasis Through Immune Evasion

The secreted growth factor Activin-A of the TGF{beta} family and its receptors can promote or inhibit several cancer hallmarks including tumor cell proliferation and differentiation, vascularization, lymphangiogenesis and inflammation. However, a role in immune evasion and its relationship with tumor-induced muscle wasting and tumor vascularization, and the relative contributions of autocrine versus paracrine Activin signaling remain to be evaluated. To address this, we compared the effects of truncated soluble Activin receptor II B as a ligand trap, or constitutively active mutant type IB receptor versus secreted Activin-A or the related ligand Nodal in mouse and human melanoma cell lines and tumor grafts. We found that while cell-autonomous receptor activation arrested tumor cell proliferation, Activin-A secretion stimulated melanoma cell dedifferentiation and tumor vascularization by functional blood vessels, and it increased primary and metastatic tumor burden and muscle wasting. Importantly, in mice with impaired adaptive immunity, the tumor-promoting effect of Activin-A was lost despite sustained vascularization and cachexia, suggesting that Activin-A promotes melanoma progression by inhibiting anti-tumor immunity. Paracrine Activin-A signaling emerges as a potential target for personalized therapies, both to reduce cachexia and to enhance the efficacy of immunotherapies.

cancer biology↗