Modeling the behavior of monoclonal antibodies on hydrophobic interaction chromatography resins.

Monoclonal antibodies (mAbs) require a high level of purity for regulatory approval and safe administration. High-molecular weight (HMW) species are a common impurity associated with mAb therapies. Hydrophobic interaction chromatography (HIC) resins are often used to remove these HMW impurities. Determination of a suitable HIC resin can be a time and resource-intensive process. In this study, we modeled the chromatographic behavior of seven mAbs across 13 HIC resins using measurements of surface hydrophobicity, surface charge, and thermal stability for mAbs, and hydrophobicity and zeta-potential for HIC resins with high fit quality (adjusted R2 > 0.80). We identified zeta-potential as a novel key modeling parameter. When using these models to select a HIC resin for HMW clearance of a test mAb, we were able to achieve 60% HMW clearance and 89% recovery. These models can be used to expedite the downstream process development for mAbs in an industry setting.

Benchmarking and optimization of a high-throughput sequencing based method for transgene sequence variant analysis in biotherapeutic cell line development.

In recent years, High-Throughput Sequencing (HTS) based methods to detect mutations in biotherapeutic transgene products have become a key quality step deployed during the development of manufacturing cell line clones. Previously we reported on a higher throughput, rapid mutation detection method based on amplicon sequencing (targeting transgene RNA) and detailed its implementation to facilitate cell line clone selection. By gaining experience with our assay in a diverse set of cell line development programs, we improved the computational analysis as well as experimental protocols. Here we report on these improvements as well as on a comprehensive benchmarking of our assay. We evaluated assay performance by mixing amplicon samples of a verified mutated antibody clone with a non-mutated antibody clone to generate spike-in mutations from ∼60% down to ∼0.3% frequencies. We subsequently tested the effect of 16 different sample and HTS library preparation protocols on the assay's ability to quantify mutations and on the occurrence of false-positive background error mutations (artifacts). Our evaluation confirmed assay robustness, established a high confidence limit of detection of ∼0.6%, and identified protocols that reduce error levels thereby significantly reducing a source of false positives that bottlenecked the identification of low-level true mutations.

CHOmics: A web-based tool for multi-omics data analysis and interactive visualization in CHO cell lines.

Chinese hamster ovary (CHO) cell lines are widely used in industry for biological drug production. During cell culture development, considerable effort is invested to understand the factors that greatly impact cell growth, specific productivity and product qualities of the biotherapeutics. While high-throughput omics approaches have been increasingly utilized to reveal cellular mechanisms associated with cell line phenotypes and guide process optimization, comprehensive omics data analysis and management have been a challenge. Here we developed CHOmics, a web-based tool for integrative analysis of CHO cell line omics data that provides an interactive visualization of omics analysis outputs and efficient data management. CHOmics has a built-in comprehensive pipeline for RNA sequencing data processing and multi-layer statistical modules to explore relevant genes or pathways. Moreover, advanced functionalities were provided to enable users to customize their analysis and visualize the output systematically and interactively. The tool was also designed with the flexibility to accommodate other types of omics data and thereby enabling multi-omics comparison and visualization at both gene and pathway levels. Collectively, CHOmics is an integrative platform for data analysis, visualization and management with expectations to promote the broader use of omics in CHO cell research.

Advancing Biologics Development Programs with Legacy Cell Lines: Advantages and Limitations of Genetic Testing for Addressing Clonality Concerns Prior to Availability of Late Stage Process and Product Consistency Data.

The bioprocessing industry uses recombinant mammalian cell lines to generate therapeutic biologic drugs. To ensure consistent product quality of the therapeutic proteins, it is imperative to have a controlled production process. Regulatory agencies and the biotechnology industry consider cell line "clonal origin" an important aspect of maintaining process control. Demonstration of clonal origin of the cell substrate, or production cell line, has received considerable attention in the past few years, and the industry has improved methods and devised standards to increase the probability and/or assurance of clonal derivation. However, older production cell lines developed before the implementation of these methods, herein referred to as "legacy cell lines," may not meet current regulatory expectations for demonstration of clonal derivation. In this article, the members of the IQ Consortium Working Group on Clonality present our position that the demonstration of process consistency and product comparability of critical quality attributes throughout the development life cycle should be sufficient to approve a license application without additional genetic analysis to support clonal origin, even for legacy cell lines that may not meet current day clonal derivation standards. With this commentary, we discuss advantages and limitations of genetic testing methods to support clonal derivation of legacy cell lines and wish to promote a mutual understanding with the regulatory authorities regarding their optional use during early drug development, subsequent to Investigational New Drug (IND) application and before demonstration of product and process consistency at Biologics License Applications (BLA) submission.

Challenging the workhorse: Comparative analysis of eukaryotic micro-organisms for expressing monoclonal antibodies.

For commercial protein therapeutics, Chinese hamster ovary (CHO) cells have an established history of safety, proven capability to express a wide range of therapeutic proteins and high volumetric productivities. Expanding global markets for therapeutic proteins and increasing concerns for broadened access of these medicines has catalyzed consideration of alternative approaches to this platform. Reaching these objectives likely will require an order of magnitude increase in volumetric productivity and a corresponding reduction in the costs of manufacture. For CHO-based manufacturing, achieving this combination of targeted improvements presents challenges. Based on a holistic analysis, the choice of host cells was identified as the single most influential factor for both increasing productivity and decreasing costs. Here we evaluated eight wild-type eukaryotic micro-organisms with prior histories of recombinant protein expression. The evaluation focused on assessing the potential of each host, and their corresponding phyla, with respect to key attributes relevant for manufacturing, namely (a) growth rates in industry-relevant media, (b) adaptability to modern techniques for genome editing, and (c) initial characterization of product quality. These characterizations showed that multiple organisms may be suitable for production with appropriate engineering and development and highlighted that yeast in general present advantages for rapid genome engineering and development cycles.

CHO genome mining for synthetic promoter design.

Synthetic promoters are an attractive alternative for use in mammalian hosts such as CHO cells as they can be designed de novo with user-defined functionalities. In this study, we describe and validate a method for bioprocess-directed design of synthetic promoters utilizing CHO genomic sequence information. We designed promoters with two objective features, (i) constitutive high-level recombinant gene transcription, and (ii) upregulated transcription under mild hypothermia or late-stage culture. CHO genes varying in transcriptional activity were selected based on a comparative analysis of RNA-Seq transcript levels in normal and biphasic cultures in combination with estimates of mRNA half-life from published genome scale datasets. Discrete transcription factor regulatory elements (TFREs) upstream of these genes were informatically identified and functionally screened in vitro to identify a subset of TFREs with the potential to support high activity recombinant gene transcription during biphasic cell culture processes. Two libraries of heterotypic synthetic promoters with varying TFRE combinations were then designed in silico that exhibited a maximal 2.5-fold increase in transcriptional strength over the CMV-IE promoter after transient transfection into host CHO-K1 cells. A subset of synthetic promoters was then used to create stable transfectant pools using CHO-K1 cells under glutamine synthetase selection. Whilst not achieving the maximal 2.5-fold increase in productivity over stable pools harboring the CMV promoter, all stably transfected cells utilizing synthetic promoters exhibited increased reporter production - up to 1.6-fold that of cells employing CMV, both in the presence or absence of intron A immediately downstream of the promoter. The increased productivity of stably transfected cells harboring synthetic promoters was maintained during fed-batch culture, with or without a transition to mild hypothermia at the onset of stationary phase. Our data exemplify that it is important to consider both host cell and intended bioprocess contexts as design criteria in the de novo construction of synthetic genetic parts for mammalian cell engineering.

Implementation of Plate Imaging for Demonstration of Monoclonality in Biologics Manufacturing Development.

Monoclonality of mammalian cell lines used for production of biologics is a regulatory expectation and one of the attributes assessed as part of a larger process to ensure consistent quality of the biologic. Historically, monoclonality has been demonstrated through statistics generated from limiting dilution cloning or through verified flow cytometry methods. A variety of new technologies are now on the market with the potential to offer more efficient and robust approaches to generating and documenting a clonal cell line.Here we present an industry perspective on approaches for the application of imaging and integration of that information into a regulatory submission to support a monoclonality claim. These approaches represent the views of a consortium of companies within the BioPhorum Development Group and include case studies utilising imaging technology that apply scientifically sound approaches and efforts in demonstrating monoclonality. By highlighting both the utility of these alternative approaches and the advantages they bring over the traditional methods, as well as their adoption by industry leaders, we hope to encourage acceptance of their use within the biologics cell line development space and provide guidance for regulatory submission using these alternative approaches.LAY ABSTRACT: In the manufacture of biologics produced in mammalian cells, one recommendation by regulatory agencies to help ensure product consistency, safety, and efficacy is to produce the material from a monoclonal cell line derived from a single, progenitor cell. The process by which monoclonality is assured can be supplemented with single-well plate images of the progenitor cell. Here we highlight the utility of that imaging technology, describe approaches to verify the validity of those images, and discuss how to analyze that information to support a biologic filing application. This approach serves as an industry perspective to increased regulatory interest within the scope of monoclonality for mammalian cell culture-derived biologics.

Debottlenecking protein secretion and reducing protein aggregation in the cellular host.

Chinese hamster ovary (CHO) cells have been extensively used for industrial production of biotherapeutics. With advances in cell line development and process optimization, production levels of therapeutic proteins using the CHO expression system have increased to beyond 10g per liter scale. These high-titer processes could challenge the secretory capacity of CHO cells, which can result in degradation and aggregation of the protein of interest. This review discusses bottlenecks in the secretory pathway of CHO cells that lead to inefficient secretion and aggregation of proteins, and summarizes current strategies to tackle these bottlenecks. In addition, emerging technologies that facilitate better understanding of cellular mechanisms in protein production could provide new avenues to improve the secretion and quality of protein therapeutics.

Leveraging a CHO cell line toolkit to accelerate biotherapeutics into the clinic.

The Biogen upstream platform is capable of delivering equivalent quality material throughout the cell line generation process. This allows us to rapidly deliver high-quality biopharmaceuticals to patients with unmet medical needs. The drive to reduce time-to-market led the cell engineering group to develop an expression system that can enable this strategy. We have developed a clonal Chinese Hamster Ovary (CHO) host cell line that can routinely produce consistent antibody material at high titers throughout the cell line generation process. This host line enables faster delivery of early phase material through use of the highly productive stable pool or a mixture of high performance clones. Due to unique characteristics of this cell line, the product quality of material from early cell populations is very comparable to material from the final clones. This lends itself to a "fast-to-tox" strategy whereby toxicology studies can be performed with representative material from an earlier cell population, thus accelerating the clinical timelines. Our new clonal host offers robust and consistent performance that enables a highly productive, flexible process and faster preclinical timelines. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1468-1475, 2017.

Strategies and Considerations for Improving Expression of "Difficult to Express" Proteins in CHO Cells.

Despite substantial advances in the field of mammalian expression, there are still proteins that are characterized as difficult to express. Determining the expression bottleneck requires troubleshooting techniques specific for the given molecule and host. The complex array of intracellular processes involved in protein expression includes transcription, protein folding, post-translation processing, and secretion. Challenges in any of these steps could result in low protein expression, while the inherent properties of the molecule itself may limit its production via mechanisms such as cytotoxicity or inherent instability. Strategies to identify the rate-limiting step and subsequently improve expression and production are discussed here.

Assessing mNIS+7Ionis and international neurologists' proficiency in a familial amyloidotic polyneuropathy trial.

INTRODUCTION: Polyneuropathy signs (Neuropathy Impairment Score, NIS), neurophysiologic tests (m+7Ionis ), disability, and health scores were assessed in baseline evaluations of 100 patients entered into an oligonucleotide familial amyloidotic polyneuropathy (FAP) trial. METHODS: We assessed: (1) Proficiency of grading neurologic signs and correlation with neurophysiologic tests, and (2) clinometric performance of modified NIS+7 neurophysiologic tests (mNIS+7Ionis ) and its subscores and correlation with disability and health scores. RESULTS: The mNIS+7Ionis sensitively detected, characterized, and broadly scaled diverse polyneuropathy impairments. Polyneuropathy signs (NIS and subscores) correlated with neurophysiology tests, disability, and health scores. Smart Somatotopic Quantitative Sensation Testing of heat as pain 5 provided a needed measure of small fiber involvement not adequately assessed by other tests. CONCLUSIONS: Specially trained neurologists accurately assessed neuropathy signs as compared to referenced neurophysiologic tests. The score, mNIS+7Ionis , broadly detected, characterized, and scaled polyneuropathy abnormality in FAP, which correlated with disability and health scores. Muscle Nerve 56: 901-911, 2017.

Integrated cell and process engineering for improved transient production of a "difficult-to-express" fusion protein by CHO cells.

Based on an optimized electroporation protocol, we designed a rapid, milliliter-scale diagnostic transient production assay to identify limitations in the ability of Chinese hamster ovary (CHO) cells to produce a model "difficult-to-express" homodimeric Fc-fusion protein, Sp35Fc, that exhibited very low volumetric titer and intracellular formation of disulfide-bonded oligomeric aggregates post-transfection. As expression of Sp35Fc induced an unfolded protein response in transfected host cells, we utilized the transient assay to compare, in parallel, multiple functionally diverse strategies to engineer intracellular processing of Sp35Fc in order to increase production and reduce aggregation as two discrete design objectives. Specifically, we compared the effect of (i) co-expression of ER-resident molecular chaperones (BiP, PDI, CypB) or active forms of UPR transactivators (ATF6c, XBP1s) at varying recombinant gene load, (ii) addition of small molecules known to act as chemical chaperones (PBA, DMSO, glycerol, betaine, TMAO) or modulate UPR signaling (PERK inhibitor GSK2606414) at varying concentration, (iii) a reduction in culture temperature to 32°C. Using this information, we designed a biphasic, Sp35Fc-specific transient manufacturing process mediated by lipofection that utilized CypB co-expression at an optimal Sp35Fc:CypB gene ratio of 5:1 to initially maximize transfected cell proliferation, followed by addition of a combination of PBA (0.5 mM) and glycerol (1% v/v) at the onset of stationary phase to maximize cell specific production and eliminate Sp35Fc aggregation. Using this optimal, engineered process transient Sp35Fc production was significantly increased sixfold over a 12 day production process with no evidence of disulfide-bonded aggregates. Finally, transient production in clonally derived sub-populations (derived from parental CHO host) screened for a heritably improved capability to produce Sp35Fc was also significantly improved by the optimized process, showing that protein-specific cell/process engineering can provide a solution that exceeds the limits of genetic/functional diversity within heterogeneous host cell populations. .

Integration of cell line and process development to overcome the challenge of a difficult to express protein.

This case study addresses the difficulty in achieving high level expression and production of a small, very positively charged recombinant protein. The novel challenges with this protein include the protein's adherence to the cell surface and its inhibitory effects on Chinese hamster ovary (CHO) cell growth. To overcome these challenges, we utilized a multi-prong approach. We identified dextran sulfate as a way to simultaneously extract the protein from the cell surface and boost cellular productivity. In addition, host cells were adapted to grow in the presence of this protein to improve growth and production characteristics. To achieve an increase in productivity, new cell lines from three different CHO host lines were created and evaluated in parallel with new process development workflows. Instead of a traditional screen of only four to six cell lines in bioreactors, over 130 cell lines were screened by utilization of 15 mL automated bioreactors (AMBR) in an optimal production process specifically developed for this protein. Using the automation, far less manual intervention is required than in traditional bench-top bioreactors, and much more control is achieved than typical plate or shake flask based screens. By utilizing an integrated cell line and process development incorporating medium optimized for this protein, we were able to increase titer more than 10-fold while obtaining desirable product quality. Finally, Monte Carlo simulations were performed to predict the optimal number of cell lines to screen in future cell line development work with the goal of systematically increasing titer through enhanced cell line screening.

PDGF suppresses the sulfation of CD44v and potentiates CD44v-mediated binding of colon carcinoma cells to fibrin under flow.

Fibrin(ogen) mediates sustained tumor cell adhesion and survival in the pulmonary vasculature, thereby facilitating the metastatic dissemination of tumor cells. CD44 is the major functional fibrin receptor on colon carcinoma cells. Growth factors, such as platelet-derived growth factor (PDGF), induce post-translational protein modifications, which modulate ligand binding activity. In view of the roles of PDGF, fibrin(ogen) and CD44 in cancer metastasis, we aimed to delineate the effect of PDGF on CD44-fibrin recognition. By immunoprecipitating CD44 from PDGF-treated and untreated LS174T colon carcinoma cells, which express primarily CD44v, we demonstrate that PDGF enhances the adhesion of CD44v-coated beads to immobilized fibrin. Enzymatic inhibition studies coupled with flow-based adhesion assays and autoradiography reveal that PDGF augments the binding of CD44v to fibrin by significantly attenuating the extent of CD44 sulfation primarily on chondroitin and dermatan sulfate chains. Surface plasmon resonance assays confirm that PDGF enhances the affinity of CD44v-fibrin binding by markedly reducing its dissociation rate while modestly increasing the association rate. PDGF mildly reduces the affinity of CD44v-hyaluronan binding without affecting selectin-CD44v recognition. The latter is attributed to the fact that CD44v binds to selectins via sialofucosylated O-linked residues independent of heparan, dermatan and chondroitin sulfates. Interestingly, PDGF moderately reduces the sulfation of CD44s and CD44s-fibrin recognition. Collectively, these data offer a novel perspective into the mechanism by which PGDF regulates CD44-dependent binding of metastatic colon carcinoma cells to fibrin(ogen).

Distinct kinetic and molecular requirements govern CD44 binding to hyaluronan versus fibrin(ogen).

CD44 is a multifunctional glycoprotein that binds to hyaluronan and fibrin(ogen). Alternative splicing is responsible for the generation of numerous different isoforms, the smallest of which is CD44s. Insertion of variant exons into the extracellular membrane proximal region generates the variant isoforms (CD44v). Here, we used force spectroscopy to delineate the biophysical and molecular requirements of CD44-HA and CD44-fibrin(ogen) interactions at the single-molecule level. CD44v-HA and CD44s-HA single bonds exhibit similar kinetic and micromechanical properties because the HA-binding motif on CD44 is common to all of the isoforms. Although this is the primary binding site, O- and N-linked glycans and sulfation also contribute to the tensile strength of the CD44-HA bond. The CD44s-fibrin pair has a lower unstressed dissociation rate and a higher tensile strength than CD44s-fibrinogen but is weaker than the CD44-HA bond. In contrast to CD44-HA binding, the molecular interaction between CD44 and fibrin(ogen) is predominantly mediated by the chondroitin sulfate and dermatan sulfate on CD44. Blocking sulfation on CD44s modestly decreases the tensile strength of CD44s-fibrin(ogen) binding, which is in stark contrast to CD44v-fibrin interaction. Collectively, the results obtained by force spectroscopy in conjunction with biochemical interventions enable us to delineate the biophysical parameters and molecular constituents of CD44 binding to hyaluronan and fibrin(ogen).

Single-molecule binding of CD44 to fibrin versus P-selectin predicts their distinct shear-dependent interactions in cancer.

P-selectin and fibrin(ogen) have pivotal roles in the hematogenous dissemination of tumor cells. CD44 variant isoforms, CD44v, have been identified as the major functional P-selectin ligands and fibrin receptors on metastatic colon carcinoma cells. The molecular recognition of CD44v by fibrin mediates firm adhesion at low shear, whereas CD44v-P-selectin binding supports transient rolling interactions at elevated shear stresses and low site densities of P-selectin. We used single-molecule force spectroscopy to provide a molecular interpretation for these two distinct adhesion events. The CD44v-P-selectin bond has a longer unstressed equilibrium lifetime, a lower reactive compliance and a higher tensile strength relative to the CD44v-fibrin bond. These intrinsic differences confer the ability to the CD44v-P-selectin pair to mediate binding at higher shear stresses. Increasing the duration of receptor-ligand contact (2-200 milliseconds) did not affect the micromechanical properties of the CD44v-P-selectin bond, but it increased the tensile strength and the depth of the free energy barrier of the CD44v-fibrin bond and decreased its reactive compliance. This bond strengthening at longer interaction times might explain why CD44v binding to immobilized fibrin occurs at low shear. Single-molecule characterization of receptor-ligand binding can predict the shear-dependent adhesive interactions between cells and substrates observed both in vitro and in vivo.

Biomolecular characterization of CD44-fibrin(ogen) binding: distinct molecular requirements mediate binding of standard and variant isoforms of CD44 to immobilized fibrin(ogen).

CD44 and fibrin(ogen) play critical roles in the hematogenous dissemination of tumor cells, including colon carcinomas. We recently reported that CD44 is the primary fibrin, but not fibrinogen, receptor on LS174T colon carcinomas. However, the biochemical nature of this interaction and the roles of CD44 standard (CD44s) versus CD44 variant (CD44v) isoforms in fibrin(ogen) recognition have yet to be delineated. Microspheres, coated with CD44 immunopurified from LS174T or T84 colon carcinoma cells, which express primarily CD44v, effectively bind to immobilized fibrin, but not fibrinogen, in shear flow. In contrast, CD44s from HL-60 cells binds to both immobilized fibrin and fibrinogen under flow. Use of highly specific enzymes and metabolic inhibitors reveals that LS174T CD44 binding to fibrin is dependent on O-glycosylation of CD44, whereas CD44s-fibrin(ogen) interaction has an absolute requirement for N-, but not O-, linked glycans. The presence of chondroitin and dermatan sulfate on CD44 standard and variant isoforms facilitates fibrin recognition. Use of the anti-CD44 function-blocking monoclonal antibody Hermes-1 nearly abolishes binding of LS174T CD44 to fibrin, although it has no effect on CD44s-fibrin(ogen) interaction. The CD44-binding site is localized within the N-terminal portion of the fibrin beta chains, including amino acid residues (beta15-66). Surface plasmon resonance experiments revealed high affinity binding of immobilized CD44 with solubilized fibrin but not fibrinogen. Collectively, these data suggest that immobilization of fibrinogen exposes a cryptic site that mediates binding to CD44s but not CD44v. Our findings may provide a rational basis for designing novel therapeutic strategies to combat metastasis.

Multifunctional surfaces with discrete functionalized regions for biological applications.

In this paper we describe a method for creating multifunctional glass surfaces presenting discrete patches of different proteins on an inert PEG-functionalized background. Microcontact printing is used to stamp the substrate with octadecyltrichlorosilane to define the active regions. The substrate is then back-filled with PEG-silane {[[2-methoxypoly(ethyleneoxy)]propyl]trimethoxysilane} to define passive regions. A microfluidics device is subsequently affixed to the substrate to deliver proteins to the active regions, with as many channels as there are proteins to be patterned. Examples of trifunctional surfaces are given which present three terminating functional groups, i.e., protein 1, protein 2, and PEG. These surfaces should be broadly useful in biological studies, as patch size is well established to influence cell viability, growth, and differentiation. Three examples of cellular interactions with the surfaces are demonstrated, including the capture of cells from a single cell suspension, the selective sorting of cells from a mixed suspension, and the adhesion of cells to ligand micropatches at critical shear stresses. Within these examples, we demonstrate that the patterned immobilized proteins are active, as they retain their ability to interact with either antibodies in solution or receptors presented by cells. When appropriate (e.g., for E-selectin), proteins are patterned in their physiological orientations using a sandwich immobilization technique, which is readily accommodated within our method. The protein surface densities are highly reproducible in the patches, as supported by fluorescence intensity measurements. Potential applications include biosensors based on the interaction of cells or of marker proteins with protein patches, fundamental studies of cell adhesion as a function of patch size and shear stress, and studies of cell differentiation as a function of surface cues.

alpha4 beta1-Integrin regulates directionally persistent cell migration in response to shear flow stimulation.

alpha(4)beta(1)-Integrin plays a pivotal role in cell migration in vivo. This integrin has been shown to regulate the front-back polarity of migrating cells via localized inhibition of alpha(4)-integrin/paxillin binding by phosphorylation at the alpha(4)-integrin cytoplasmic tail. Here, we demonstrate that alpha(4)beta(1)-integrin regulates directionally persistent cell migration via a more complex mechanism in which alpha(4)-integrin phosphorylation and paxillin binding act via both cooperative and independent pathways. We show that, in response to shear flow, alpha(4)beta(1)-integrin binding to the CS-1 region of fibronectin was necessary and sufficient to promote directionally persistent cell migration when this integrin was ectopically expressed in CHO cells. Under shear flow, the alpha(4)beta(1)-integrin-expressing cells formed a fan shape with broad lamellipodia at the front and retracted trailing edges at the back. This "fanning" activity was enhanced by disrupting paxillin binding alone and inhibited by disrupting phosphorylation alone or together with disrupting paxillin binding. Notably, the phosphorylation-disrupting mutation and the double mutation resulted in the formation of long trailing tails, suggesting that alpha(4)-integrin phosphorylation is required for trailing edge retraction/detachment independent of paxillin binding. Furthermore, the stable polarity and directional persistence of shear flow-stimulated cells were perturbed by the double mutation but not the single mutations alone, indicating that paxillin binding and alpha(4)-integrin phosphorylation can facilitate directionally persistent cell migration in an independent and compensatory manner. These findings provide a new insight into the mechanism by which integrins regulate directionally persistent cell migration.

Carcinoembryonic antigen and CD44 variant isoforms cooperate to mediate colon carcinoma cell adhesion to E- and L-selectin in shear flow.

Selectin-mediated adhesion of tumor cells to platelets, leukocytes, and endothelial cells may regulate their hematogenous dissemination in the microvasculature. We recently identified CD44 variant isoforms (CD44v) as functional P-, but not E- or L-, selectin ligands on colon carcinoma cells. Moreover, an approximately 180-kDa sialofucosylated glycoprotein(s) mediated selectin binding in CD44-knockdown cells. Using immunoaffinity chromatography and tandem mass spectrometry, we identify this glycoprotein as the carcinoembryonic antigen (CEA). Blot rolling assays and flow-based adhesion assays using microbeads coated with CEA immunopurified from LS174T colon carcinoma cells and selectins as substrate reveal that CEA possesses E- and L-, but not P-, selectin ligand activity. CEA on CD44-knockdown LS174T cells exhibits higher HECA-452 immunoreactivity than CEA on wild-type cells, suggesting that CEA functions as an alternative acceptor for selectin-binding glycans. The enhanced expression of HECA-452 reactive epitopes on CEA from CD44-knockdown cells correlates with the increased CEA avidity for E- but not L-selectin. Through the generation of stable knockdown cell lines, we demonstrate that CEA serves as an auxiliary L-selectin ligand, which stabilizes L-selectin-dependent cell rolling against fluid shear. Moreover, CEA and CD44v cooperate to mediate colon carcinoma cell adhesion to E- and L-selectin at elevated shear stresses. The novel finding that CEA is an E- and L-selectin ligand may explain the enhanced metastatic potential associated with tumor cell CEA overexpression and the supportive role of selectins in metastasis.