Biology subjects

Smith, C. N.

Publications and source records attributed to Smith, C. N..

4 recordsLinked to original sources

bioRxiv2025

Lipid Metabolism and Contact Site Homologs Are Enriched at the Chloroplast Envelope-Thylakoid Interface

Biogenesis and maintenance of the photosynthetic thylakoid membrane requires transport of lipids from their site of synthesis in the chloroplast envelopes to their destination in the thylakoid. While vesicle trafficking is likely involved, we hypothesized a complementary mechanism involving direct membrane interactions. Using domain homology and proteomic profiling of chloroplast membrane fractions, we identified candidate lipid transport proteins enriched in a distinct, intermediate-density membrane population. This fraction was enriched in lipid metabolic enzymes and proteins homologous to known membrane organization factors. Several candidates, including TVP38 FAMILY PROTEIN (TVPFP), PLASMA MEMBRANE FUSION PROTEIN (PMFP), and LETM1-LIKE, localized to discrete subdomains within chloroplasts. Loss- of-function tvpfp or pmfp mutants exhibited altered chloroplast ultrastructure, including changes in thylakoid-envelope proximity, supporting their roles in maintaining membrane architecture. These findings identify a specialized chloroplast membrane region enriched in lipid-related functions and offer a foundation for elucidating the molecular architecture of these regions.

biochemistry↗

bioRxiv2025

Phosphatase activity is dispensable for PRL-3-mediated oncogenesis and tumor progression

Phosphatase of Regenerating Liver 3 (PRL-3) is frequently upregulated in cancer and associated with poor prognosis, yet its oncogenic mechanism remains unresolved. Although traditionally studied for its phosphatase activity, PRL-3 also engages in protein-protein interactions via its catalytic site, notably binding the CNNM magnesium transporters, rendering these functions mutually exclusive. The commonly used C104S mutant disrupts both activities, confounding interpretations of prior studies. To dissect PRL-3s distinct functions, we employed mutants selectively deficient in phosphatase activity (C104D) or CNNM binding (R138E). In zebrafish models of acute lymphoblastic leukemia (ALL) and rhabdomyosarcoma (RMS), as well as in human cancer cell lines, both wild-type PRL-3 and C104D enhanced tumor initiation, growth, and dissemination, while R138E had no effect. These findings indicate that PRL-3 promotes cancer via non-catalytic mechanisms. To support therapeutic development, we established an in vitro FRET-based assay to screen for inhibitors of the PRL-3:CNNM interaction and validated a cyclic peptide as a positive control. By demonstrating that PRL-3 enhances cancer progression independently of its catalytic activity, this study shifts focus toward targeting its binding functions as a therapeutic strategy. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=158 SRC="FIGDIR/small/654016v1_ufig1.gif" ALT="Figure 1"> View larger version (57K): org.highwire.dtl.DTLVardef@41de8dorg.highwire.dtl.DTLVardef@7a3bbdorg.highwire.dtl.DTLVardef@e800d2org.highwire.dtl.DTLVardef@18df51a_HPS_FORMAT_FIGEXP M_FIG C_FIG Statement of significanceThis study demonstrates that PRL-3 drives cancer initiation and progression through a phosphatase-independent mechanism across diverse models, highlighting the need to therapeutically target its non-catalytic protein interactions in future cancer treatment strategies.

cancer biology↗

bioRxiv2020

Development and validation of nanobodies specific to the oncogenic phosphatase Protein Tyrosine Phosphatase 4A3 (PTP4A3 or PRL-3)

Phosphatase of Regenerating Liver-3 (PRL-3) is associated with cancer progression and metastasis in various solid tumors and leukemias. The mechanisms that drive PRL-3s oncogenic functions are not well understood, in part due to a lack of research tools available to study this protein. In particular, small molecules do not exhibit binding specificity for PRL-3 over highly homologous family members PRL-1 and PRL-2, and antibodies directed against PRL-3 are limited by assay type. We have begun to address these issues by developing alpaca-derived single domain antibodies, or nanobodies, targeting PRL-3 with a KD of 30-300 nM and no activity towards PRL-1 and PRL-2. Hydrogen deuterium exchange mass spectrometry (HDX-MS) and co-immunoprecipitation with a known PRL-3 substrate showed the nanobodies bind PRL-3 outside of the active site, meaning they can be used to study PRL-3 interaction with binding partners. The nanobodies were also specific to PRL-3 over other PRLs in immunoprecipitation and immunofluorescence experiments in human cancer cells that overexpressed the PRL family. We found that N-terminal tags on PRL-3, such as GFP and FLAG, changed PRL-3 localization compared to untagged protein, indicating that the nanobodies may provide new insights into PRL-3 trafficking and function. The anti-PRL-3 nanobodies represent an important expansion of the research tools available to study PRL-3 function and can be used to define the role of PRL-3 in cancer progression.

biochemistry↗

bioRxiv2020

A screen of FDA-approved drugs identifies inhibitors of Protein Tyrosine Phosphatase 4A3 (PTP4A3 or PRL-3)

Protein tyrosine phosphatase 4A3 (PTP4A3 or PRL-3) is highly expressed in a variety of cancers, where it promotes tumor cell migration and metastasis leading to poor prognosis. Despite its clinical significance, there are currently no viable options to target PRL-3 in vivo. Here, we screened 1,443 FDA-approved drugs for their ability to inhibit the activity of the PRL phosphatase family. We identified five specific inhibitors for PRL-3 as well as one selective inhibitor of PRL-2. Additionally, we found nine drugs that broadly and significantly suppressed PRL activity. Two of these broad PRL inhibitors, Salirasib and Candesartan blocked PRL-3-induced migration in human embryonic kidney (HEK) cells with no negative impact on cell viability. Both drugs prevented migration of PRL-3 expressing human colorectal cancer cells to a similar degree as the research-grade PRL inhibitor, Thienopyridone, and are selective towards PRLs over other phosphatases. In silico modeling revealed that Salirasib binds a putative allosteric site near the WPD loop of PRL-3, while Candesartan binds a potentially novel targetable site adjacent to the CX5R motif. Inhibitor binding at either of these sites is predicted to trap PRL-3 in a closed conformation, preventing substrate binding and inhibiting function.

cancer biology↗