Tumor tissue samples for IHC were fixed in 4% PFA. For immunohistochemistry, sections were deparaffinized and rehydrated. myeloma (MM) and present an Anticalin-based CD98hc radiopharmaceutical for MM radio-theranostics. These data set up the CRBN-AHA1-HSP90 axis in the biogenesis of transmembrane proteins, link IMiD activity to tumor rate of metabolism, and nominate CD98hc and LAT1 as attractive diagnostic and restorative focuses on in MM. as a new vulnerability in MM, which becomes destabilized and inactivated upon IMiD treatment. We thus link IMiD activity to tumor rate of metabolism and characterize CD98hc as target for radio-theranostic methods. Results Cell surface proteomics reveal a broad effect of IMiDs on TP large quantity and specify CD98hc/LAT1 as novel CRBN clients To start investigating the effect of IMiDs on TPs, we performed quantitative unbiased proteomic screens of the MM cell surface proteome using cell surface biotinylation, streptavidin affinity purification, and mass spectrometry (Numbers 1A, S1A, and S1B). Strikingly, we observed broad alterations of Trimebutine maleate cell surface protein large quantity in response to lenalidomide treatment (Number?1A). We cross-validated these results with our earlier CRBN interactome dataset (Eichner et?al., 2016) in order to distinguish direct CRBN clients. This approach yielded CD98hc (CD98 heavy chain) as the most significant hit that becomes destabilized upon IMiD treatment and binds to CRBN (Number?1A; Number?S1C). Open in a separate window Number?1 Cell surface proteomics reveal a broad Rabbit Polyclonal to BTK (phospho-Tyr223) effect of IMiDs about transmembrane protein abundance and specify CD98hc/LAT1 as novel CRBN clients (A) Quantitative cell surface proteome of MM1s cells treated with lenalidomide versus solvent. MM1S cells were cultured in SILAC and control medium and subjected to treatment with 10? M lenalidomide or DMSO for 48 h, followed by cell surface biotinylation, streptavidin affinity purification, and mass spectrometry (MS) analysis. Plasma membrane proteins (relating to Gene Ontology cellular component [GOCC]) are depicted by blue circles. Solute carrier protein family members are marked by a yellow dot. Potential interactors of CRBN recognized by tandem-affinity purification and MS are circled in reddish. (B) Representative immunoblot analysis of MM1S cells that were treated with DMSO, 10?M lenalidomide (Len), 1?M pomalidomide (Pom), or 100?M thalidomide (Thal) for 72 h. (C) Representative immunoblot analysis of MM1SWT or MM1S with CRISPR-Cas9-mediated homozygous deletion of CRBN (clones T11 and T21). (D) Representative immunofluorescence images of HeLa cells that were transfected with constructs encoding both HA-CD98hc and FLAG-LAT1 and expressing the indicated short hairpin RNAs (shRNAs). Cells were stained with antibodies to HA (green) and FLAG (reddish), and DNA was stained with DAPI (blue). Level bars, 10?m. Quantification and confirmation of knockdown are offered in Number?S1E. (E) Immunoprecipitation (IP) of FLAG-tagged LAT1 from HEK293T cells. Immunocomplexes and respective whole-cell components (WCE) were Trimebutine maleate probed with antibodies to the indicated proteins. (F) IP of FLAG-CD98hc from HEK293T cells. Immunoblot analysis of whole-cell components and immunocomplexes was performed as indicated. (G) IP of FLAG-CRBNWT or CRBNYW/AA from CRBN?/? HEK293T co-expressing LAT1. Cells were pretreated with lenalidomide (50?M) or DMSO for 24?h prior to harvest and immunoblot analysis. CD98hc forms a heterodimeric amino acid transporter complex with LAT1, which preferentially transports neutral branched or aromatic amino acids (Yan et?al., 2019). LAT1 manifestation levels increase with progression of plasma cell disorders and have been associated with high proliferation and poor prognosis in MM individuals (Bolzoni et?al., 2016; Isoda et?al., 2014). To validate the display, we treated MM cells with thalidomide, lenalidomide, and pomalidomide and observed a substantial destabilization of CD98hc and LAT1 (Number?1B). We consequently went on to investigate CD98hc/LAT1 as potential novel CRBN-dependent IMiD target proteins. CRISPR-Cas9-mediated depletion of CRBN led to reduced protein large quantity of CD98hc Trimebutine maleate and LAT1 (Number?1C). Unchanged or elevated and mRNA levels upon lenalidomide treatment confirmed a post-transcriptional mechanism independent of the CRL4CRBN neo-substrate transcription factors IKZF1/3 (Number?S1D). In addition, depletion of CRBN led to subcellular mis-localization of the CD98hc/LAT1 complex and cytoplasmic build up in the ER/Golgi, indicative of protein misfolding (Numbers 1D, S1E, S6F, and S6G). We further found specific and direct connection of CRBN with CD98hc/LAT1 (Numbers 1E, 1F, and S1F) and mapped the binding site to the N-terminal intracellular regions of CD98hc and LAT1 (Number?S1F). The Trimebutine maleate IMiD binding-defective mutant CRBNYW/AA (mutation of Tyr384 and Trp386 to Ala) (Ito et?al., 2010) failed to interact with CD98hc and LAT1, and IMiD treatment abrogated the connection of CRBN with CD98hc and LAT1, suggesting that IMiDs compete with these TPs for binding to CRBNs TBD (Numbers 1G and S1G). Collectively,.