The cell surface glycoprotein CDCP1 in cancer--insights, opportunities, and challenges

Pre-diagnostic plasma inflammatory proteins and risk of hepatocellular carcinoma in three population-based cohort studies from the United States and the United Kingdom

Previous studies suggest a role for inflammation in hepatocarcinogenesis. However, no study has comprehensively evaluated associations between circulating inflammatory proteins and risk of hepatocellular carcinoma (HCC) among the general population. We conducted a nested case-control study in the Nurses' Health Study (NHS) and the Health Professionals Follow-up Study (HPFS) with 56 pairs of incident HCC cases and controls. External validation was performed in the UK Biobank (34 HCC cases and 48,471 non-HCC controls). Inflammatory protein levels were measured in pre-diagnostic plasma using the Olink® Inflammation Panel. We used conditional logistic regression to calculate multivariable odds ratios (ORs) with 95% confidence intervals (CIs) for associations between a 1-standard deviation (SD) increase in biomarker levels and HCC risk, considering a statistically significant threshold of false discovery rate (FDR)-adjusted p < .05. In the NHS/HPFS, among 70 analyzed proteins with call rates >80%, 15 proteins had significant associations with HCC risk (pFDR < .05). Two proteins (stem cell factor, OR per SD = 0.31, 95% CI = 0.16-0.58; tumor necrosis factor superfamily member 12, OR per SD = 0.51, 95% CI = 0.31-0.85) were inversely associated whereas 13 proteins were positively associated with risk of HCC; positive ORs per SD ranged from 1.73 for interleukin (IL)-10 to 2.35 for C-C motif chemokine-19. A total of 11 proteins were further replicated in the UK Biobank. Seven of the eight selected positively associated proteins also showed positive associations with HCC risk by enzyme-linked immunosorbent assay, with ORs ranging from 1.56 for IL-10 to 2.72 for hepatocyte growth factor. More studies are warranted to further investigate the roles of these observed inflammatory proteins in HCC etiology, early detection, risk stratification, and disease treatment.

From proteome to pathogenesis: investigating polycystic ovary syndrome with Mendelian randomization analysis

Background

Polycystic ovary syndrome (PCOS) is defined by oligo/anovulation, hyperandrogenism, and polycystic ovaries with uncertain pathogenesis. The proteome represents a substantial source of therapeutic targets, and their coding genes may elucidate the mechanisms underlying PCOS. However, reports on the profiles of the human plasma protein-coding genes and PCOS are limited. Here, we aimed to investigate novel biomarkers or drug targets for PCOS by integrating genetics and the human plasma proteome.

Methods

Our study acquired the protein quantitative trait loci from DECODE Genetics, offering 4,907 proteins in 35,559 individuals while obtaining PCOS summary statistics by accessing the FinnGen biobank (1,639 cases and 218,970 controls) and the genome-wide association study catalog (797 cases and 140,558 controls). Herein, we sequentially used two-sample Mendelian randomization (MR) analyses and colocalization to verify the causal link between candidate proteins, their coding genes, and PCOS. Further PCOS data download was conducted by accessing the Gene Expression Omnibus and Zenodo platforms. Gene expression level analysis, pathway enrichment analysis, immune cell infiltration, and transcription factor prediction were performed, aiming at detecting specific cell types with enriched expression and exploring potential optimized treatments for PCOS.

Results

MR analysis revealed 243 protein-coding genes with a causal relationship to PCOS risk, of which 12 were prioritized with the most significant evidence. Through colocalization analysis, three key genes, CUB domain-containing protein 1 (CDCP1), glutaredoxin 2 (GLRX2), and kirre-like nephrin family adhesion molecule 2 (KIRREL2), were identified. Subsequently, the three genes were strongly related to immune function and metabolism in terms of biological significance. In single-cell analysis, the expression levels of genes in ovarian theca cells were explored.

Conclusion

Overall, three protein-coding genes (CDCP1, GLRX2, and KIRREL2) may be related to a higher PCOS risk, suggesting that they may be entry points for exploration of PCOS pathogenesis and treatment, warranting further clinical investigations.

Regulation of Metabolic Plasticity in Cancer Stem Cells and Implications in Cancer Therapy

Cancer stem cells (CSCs), a subpopulation of tumor cells with self-renewal capacity, have been associated with tumor initiation, progression, and therapy resistance. While the bulk of tumor cells mainly use glycolysis for energy production, CSCs have gained attention for their ability to switch between glycolysis and oxidative phosphorylation, depending on their energy needs and stimuli from their microenvironment. This metabolic plasticity is mediated by signaling pathways that are also implicated in the regulation of CSC properties, such as the Wnt/β-catenin, Notch, and Hippo networks. Two other stemness-associated processes, autophagy and hypoxia, seem to play a role in the metabolic switching of CSCs as well. Importantly, accumulating evidence has linked the metabolic plasticity of CSCs to their increased resistance to treatment. In this review, we summarize the metabolic signatures of CSCs and the pathways that regulate them; we especially highlight research data that demonstrate the metabolic adaptability of these cells and their role in stemness and therapy resistance. As the development of drug resistance is a major challenge for successful cancer treatment, the potential of specific elimination of CSCs through targeting their metabolism is of great interest and it is particularly examined.

Targeting a proteolytic neoepitope on CUB domain containing protein 1 (CDCP1) for RAS-driven cancers

Extracellular proteolysis is frequently dysregulated in disease and can generate proteoforms with unique neoepitopes not found in healthy tissue. Here, we demonstrate that Abs that selectively recognize a proteolytic neoepitope on CUB domain containing protein 1 (CDCP1) could enable more effective and safer treatments for solid tumors. CDCP1 is highly overexpressed in RAS-driven cancers, and its ectodomain is cleaved by extracellular proteases. Biochemical, biophysical, and structural characterization revealed that the 2 cleaved fragments of CDCP1 remain tightly associated with minimal proteolysis-induced conformational change. Using differential phage display, we generated recombinant Abs that are exquisitely selective to cleaved CDCP1 with no detectable binding to the uncleaved form. These Abs potently targeted cleaved CDCP1-expressing cancer cells as an Ab-drug conjugate, an Ab-radionuclide conjugate, and a bispecific T cell engager. In a syngeneic pancreatic tumor model, these cleaved-specific Abs showed tumor-specific localization and antitumor activity with superior safety profiles compared with a pan-CDCP1 approach. Targeting proteolytic neoepitopes could provide an orthogonal "AND" gate for improving the therapeutic index.

Fast-tracking antibody maturation using a B cell-based display system

Affinity maturation, an essential component of antibody engineering, is crucial for developing therapeutic antibodies. Cell display system coupled with somatic hypermutation (SHM) initiated by activation-induced cytidine deaminase (AID) is a commonly used technique for affinity maturation. AID introduces targeted DNA lesions into hotspots of immunoglobulin (Ig) gene loci followed by erroneous DNA repair, leading to biased mutations in the complementary determining regions. However, systems that use an in vivo mimicking mechanism often require several rounds of selection to enrich clones possessing accumulated mutations. We previously described the human ADLib® system, which features autonomous, AID-mediated diversification in Ig gene loci of a chicken B cell line DT40 and streamlines human antibody generation and optimization in one integrated platform. In this study, we further engineered DT40 capable of receiving exogenous antibody genes and examined whether the antibody could be affinity matured. The Ig genes of three representative anti-hVEGF-A antibodies originating from the human ADLib® were introduced; the resulting human IgG1 antibodies had up to 76.4-fold improvement in binding affinities (sub-picomolar K_D) within just one round of optimization, owing to efficient accumulation of functional mutations. Moreover, we successfully improved the affinity of a mouse hybridoma-derived anti-hCDCP1 antibody using the engineered DT40, and the observed mutations remained effective in the post-humanized antibody as exhibited by an 8.2-fold increase of in vitro cytotoxicity without compromised physical stability. These results demonstrated the versatility of the novel B cell-based affinity maturation system as an easy-to-use antibody optimization tool regardless of the species of origin.Abbreviations: ADLib®: Autonomously diversifying library, ADLib® KI-AMP: ADLib® knock-in affinity maturation platform, AID: activation-induced cytidine deaminase, CDRs: complementary-determining regions, DIVAC: diversification activator, ECD: extracellular domain, FACS: fluorescence-activated cell sorting, FCM: flow cytometry, HC: heavy chainIg: immunoglobulin, LC: light chain, NGS: next-generation sequencing, PBD: pyrrolobenzodiazepine, SHM: somatic hypermutation, SPR: surface plasmon resonance.

Elevated CSF inflammatory markers in patients with idiopathic normal pressure hydrocephalus do not promote NKCC1 hyperactivity in rat choroid plexus

BACKGROUND

Idiopathic normal pressure hydrocephalus (iNPH) is a potentially reversible neurological condition of unresolved etiology characterized by a clinical triad of symptoms; gait disturbances, urinary incontinence, and cognitive deterioration. In the present study, we aimed to elucidate the molecular coupling between inflammatory markers and development of iNPH and determine whether inflammation-induced hyperactivity of the choroidal Na⁺/K⁺/2Cl^- cotransporter (NKCC1) that is involved in cerebrospinal fluid (CSF) secretion could contribute to the iNPH pathogenesis.

METHODS

Lumbar CSF samples from 20 iNPH patients (10 with clinical improvement upon CSF shunting, 10 without clinical improvement) and 20 elderly control subjects were analyzed with the novel proximity extension assay technique for presence of 92 different inflammatory markers. RNA-sequencing was employed to delineate choroidal abundance of the receptors for the inflammatory markers found elevated in the CSF from iNPH patients. The ability of the elevated inflammatory markers to modulate choroidal NKCC1 activity was determined by addition of combinations of rat version of these in ex vivo experiments on rat choroid plexus.

RESULTS

11 inflammatory markers were significantly elevated in the CSF from iNPH patients compared to elderly control subjects: CCL28, CCL23, CCL3, OPG, CXCL1, IL-18, IL-8, OSM, 4E-BP1, CXCL6, and Flt3L. One inflammatory marker, CDCP1, was significantly decreased in iNPH patients compared to control subjects. None of the inflammatory markers differed significantly when comparing iNPH patients with and without clinical improvement upon CSF shunting. All receptors for the elevated inflammatory markers were expressed in the rat and human choroid plexus, except CCR4 and CXCR1, which were absent from the rat choroid plexus. None of the elevated inflammatory markers found in the CSF from iNPH patients modulated the choroidal NKCC1 activity in ex vivo experiments on rat choroid plexus.

CONCLUSION

The CSF from iNPH patients contains elevated levels of a subset of inflammatory markers. Although the corresponding inflammatory receptors are, in general, expressed in the choroid plexus of rats and humans, their activation did not modulate the NKCC1-mediated fraction of choroidal CSF secretion ex vivo. The molecular mechanisms underlying ventriculomegaly in iNPH, and the possible connection to inflammation, therefore remains to be elucidated.

Preclinical Molecular PET-CT Imaging Targeting CDCP1 in Colorectal Cancer

Colorectal cancer (CRC) is the third most common malignancy in the world, with 22% of patients presenting with metastatic disease and a further 50% destined to develop metastasis. Molecular imaging uses antigen-specific ligands conjugated to radionuclides to detect and characterise primary cancer and metastases. Expression of the cell surface protein CDCP1 is increased in CRC, and here we sought to assess whether it is a suitable molecular imaging target for the detection of this cancer. CDCP1 expression was assessed in CRC cell lines and a patient-derived xenograft to identify models suitable for evaluation of radio-labelled 10D7, a CDCP1-targeted, high-affinity monoclonal antibody, for preclinical molecular imaging. Positron emission tomography-computed tomography was used to compare zirconium-89 (⁸⁹Zr)-10D7 avidity to a nonspecific, isotype control ⁸⁹Zr-labelled IgGκ1 antibody. The specificity of CDCP1-avidity was further confirmed using CDCP1 silencing and blocking models. Our data indicate high avidity and specificity for of ⁸⁹Zr-10D7 in CDCP1 expressing tumors at. Significantly higher levels than normal organs and blood, with greatest tumor avidity observed at late imaging time points. Furthermore, relatively high avidity is detected in high CDCP1 expressing tumors, with reduced avidity where CDCP1 expression was knocked down or blocked. The study supports CDCP1 as a molecular imaging target for CRC in preclinical PET-CT models using the radioligand ⁸⁹Zr-10D7.

CDCP1 on Dendritic Cells Contributes to the Development of a Model of Kawasaki Disease

The etiology and pathology of Kawasaki disease (KD) remain elusive. Cub domain-containing protein 1 (CDCP1), a cell-surface protein that confers poor prognosis of patients with certain solid tumors, was recently identified as one of the most significantly upregulated genes in SARS-CoV-2-infected children who developed systemic vasculitis, a hallmark of KD. However, a potential role of CDCP1 in KD has not previously been explored. In this study, we found that CDCP1 knockout (KO) mice exhibited attenuated coronary and aortic vasculitis and decreased serum Candida albicans water-soluble fraction (CAWS)-specific IgM/IgG2a and IL-6 concentrations compared with wild-type mice in an established model of KD induced by CAWS administration. CDCP1 expression was not detectable in cardiomyocytes, cardio fibroblasts, or coronary endothelium, but constitutive expression of CDCP1 was observed on dendritic cells (DCs) and was upregulated by CAWS stimulation. CAWS-induced IL-6 production was significantly reduced in CDCP1 KO DCs, in association with impaired Syk-MAPK signaling pathway activation. These novel findings suggest that CDCP1 might regulate KD development by modulating IL-6 production from DCs via the Syk-MAPK signaling pathway.

Identification of CD318, TSPAN8 and CD66c as target candidates for CAR T cell based immunotherapy of pancreatic adenocarcinoma

A major roadblock prohibiting effective cellular immunotherapy of pancreatic ductal adenocarcinoma (PDAC) is the lack of suitable tumor-specific antigens. To address this challenge, here we combine flow cytometry screenings, bioinformatic expression analyses and a cyclic immunofluorescence platform. We identify CLA, CD66c, CD318 and TSPAN8 as target candidates among 371 antigens and generate 32 CARs specific for these molecules. CAR T cell activity is evaluated in vitro based on target cell lysis, T cell activation and cytokine release. Promising constructs are evaluated in vivo. CAR T cells specific for CD66c, CD318 and TSPAN8 demonstrate efficacies ranging from stabilized disease to complete tumor eradication with CD318 followed by TSPAN8 being the most promising candidates for clinical translation based on functionality and predicted safety profiles. This study reveals potential target candidates for CAR T cell based immunotherapy of PDAC together with a functional set of CAR constructs specific for these molecules.

CDCP1 promotes compensatory renal growth by integrating Src and Met signaling

CDCP1 promotes HGF-induced compensatory renal growth by focally and temporally integrating Src and Met-STAT3 signaling in lipid rafts.

Compensatory growth of organs after loss of their mass and/or function is controlled by hepatocyte growth factor (HGF), but the underlying regulatory mechanisms remain elusive. Here, we show that CUB domain-containing protein 1 (CDCP1) promotes HGF-induced compensatory renal growth. Using canine kidney cells as a model of renal tubules, we found that HGF-induced temporal up-regulation of Src activity and its scaffold protein, CDCP1, and that the ablation of CDCP1 robustly abrogated HGF-induced phenotypic changes, such as morphological changes and cell growth/proliferation. Mechanistic analyses revealed that up-regulated CDCP1 recruits Src into lipid rafts to activate STAT3 associated with the HGF receptor Met, and activated STAT3 induces the expression of matrix metalloproteinases and mitogenic factors. After unilateral nephrectomy in mice, the Met-STAT3 signaling is transiently up-regulated in the renal tubules of the remaining kidney, whereas CDCP1 ablation attenuates regenerative signaling and significantly suppresses compensatory growth. These findings demonstrate that CDCP1 plays a crucial role in controlling compensatory renal growth by focally and temporally integrating Src and Met signaling.

The CDCP1 Signaling Hub: A Target for Cancer Detection and Therapeutic Intervention

CUB-domain containing protein 1 (CDCP1) is a type I transmembrane glycoprotein that is upregulated in malignancies of the breast, lung, colorectum, ovary, kidney, liver, pancreas, and hematopoietic system. Here, we discuss CDCP1 as an important hub for oncogenic signaling and its key roles in malignant transformation and summarize approaches focused on exploiting it for cancer diagnosis and therapy. Elevated levels of CDCP1 are associated with progressive disease and markedly poorer survival. Predominantly located on the cell surface, CDCP1 lies at the nexus of key tumorigenic and metastatic signaling cascades, including the SRC/PKCδ, PI3K/AKT, WNT, and RAS/ERK axes, the oxidative pentose phosphate pathway, and fatty acid oxidation, making important functional contributions to cancer cell survival and growth, metastasis, and treatment resistance. These findings have stimulated the development of agents that target CDCP1 for detection and treatment of a range of cancers, and results from preclinical models suggest that these approaches could be efficacious and have manageable toxicity profiles.

CDCP1 overexpression drives prostate cancer progression and can be targeted in vivo

The mechanisms by which prostate cancer shifts from an indolent castration-sensitive phenotype to lethal castration-resistant prostate cancer (CRPC) are poorly understood. Identification of clinically relevant genetic alterations leading to CRPC may reveal potential vulnerabilities for cancer therapy. Here we find that CUB domain-containing protein 1 (CDCP1), a transmembrane protein that acts as a substrate for SRC family kinases (SFKs), is overexpressed in a subset of CRPC. Notably, CDCP1 cooperates with the loss of the tumor suppressor gene PTEN to promote the emergence of metastatic prostate cancer. Mechanistically, we find that androgens suppress CDCP1 expression and that androgen deprivation in combination with loss of PTEN promotes the upregulation of CDCP1 and the subsequent activation of the SRC/MAPK pathway. Moreover, we demonstrate that anti-CDCP1 immunoliposomes (anti-CDCP1 ILs) loaded with chemotherapy suppress prostate cancer growth when administered in combination with enzalutamide. Thus, our study identifies CDCP1 as a powerful driver of prostate cancer progression and uncovers different potential therapeutic strategies for the treatment of metastatic prostate tumors.

CDCP1-targeted nanoparticles encapsulating phase-shift perfluorohexan for molecular US imaging in vitro

BACKGROUND

Molecular targeted contrast-enhanced ultrasound (CEUS) imaging is a potential imaging strategy to improve the diagnostic accuracy of conventional ultrasound (US) imaging. US contrast agents are usually micrometer-sized and non-target gas bubbles while nano-sized and targeted agents containing phase-shift materials absorb more attractions for their size and the liquid core and excellent molecular imaging effect.

METHODS

PLGA12k-mPEG2k-NH2, DSPE-mPEG2k and perfluorohexan (PFH) were used to construct a new targeted ultrasound contrast agent with CUB domain-containing protein 1 (CDCP1) receptor for the detection and diagnosis of prostate cancer. The potential of tumor-targeted nanoparticles (CDCP1-targeted perfluorohexan-loaded phase-transitional nanoparticles, anti-CDCP1 NPs) as contrast agents for ultrasound (US) imaging was assessed in vitro. Moreover, studies on the cytotoxicity and the targeting ability of anti-CDCP1 NPs assisted by US were carried out.

RESULTS

The results showed that anti-CDCP1 NPs had low cytotoxicity, and with the increasing of polymer concentration in anti-CDCP1 NPs, the CEUS imaging of agent gradually enhanced, and enhanced imaging associated with the length of observing time. Furthermore, it was testified that anti-CDCP1 assisted the agent to target cells expressing CDCP1, which demonstrated the active targeting of anti-CDCP1 NPs in vitro.

CONCLUSION

All in all, the feasibility of using targeted anti-CDCP1 NPs to enhance ultrasound imaging has been demonstrated in vitro, which laid a solid foundation for molecular US imaging in vivo, and anti-CDCP1 NPs might have a great clinical application prospect.

Increased Plasma Levels of the Co-stimulatory Proteins CDCP1 and SLAMF1 in Patients With Autoimmune Endocrine Diseases

Despite that autoimmune diseases share similar immunogenetic mechanisms, studies comparing the protein composition in peripheral blood from patients with autoimmune endocrine diseases are limited. In this study, we applied proximity extension assay to measure proteins related to signaling and interactions within the immune system in peripheral blood from patients with new-onset (N-T1D) and long-standing (L-T1D) type 1 diabetes, Hashimoto's thyroiditis (HT), Graves' disease (GD), and autoimmune Addison's disease in addition to healthy controls (HC). Proteins in plasma and supernatants from cultured PBMC were measured by using a 92-plex Olink® INFLAMMATION panel. Soluble CDCP1 was more abundant in plasma from patients with N-T1D, L-T1D, HT, and GD than in HC. The L-T1D and HT groups had elevated plasma levels of SLAMF1 compared with HC. Patients and HC could not be distinguished by their protein composition in PBMC supernatants. The high-throughput multiplex technology enabled us to detect two low-abundant proteins that have been gradually connected to autoimmune diseases. Our study provides novel associations between CDCP1, SLAMF1, and autoimmune endocrine diseases, which might reflect a higher degree of inflammation and lymphocyte activation.

CUB Domain-Containing Protein-1 Promotes Proliferation, Migration and Invasion in Cervical Cancer Cells

Purpose

Emerging evidence have revealed significant contributions of CUB domain-containing protein-1 (CDCP1) in tumorigenesis, including colon, renal, ovarian, pancreatic, prostate and breast cancers. However, the roles of CDCP1 in cervical cancer (CC) still remain elusive.

Materials and Methods

Quantitative reverse transcription polymerase chain reaction, immunohistochemistry and Western blotting were used to confirm the expression of CDCP1 in CC tissues compared with matched non-tumor tissues. In vitro, gain-of-function and loss-of-function studies were used to investigate the biological function and underlying mechanism of CDCP1 in cervical carcinogenesis. Furthermore, tumor growth was evaluated using a xenogenous subcutaneously implant model of CC cells in vivo.

Results

Here, we confirmed that CDCP1 was significantly increased in human CC both in mRNA and in protein levels compared to normal cervical tissues. Furthermore, we demonstrated that increased CDCP1 expression promotes proliferation, migration, invasion and mediates the epithelial-to-mesenchymal transition phenotype in HeLa and C33A cells. Also, CDCP1 knockdown reverses all the effects of enhanced CDCP1 on cell behavior in SiHa and Caski cells. Importantly, the suppressive expression of CDCP1 repressed tumor growth in a mouse xenograft model of CC.

Conclusion

In summary, our current study results provide novel insights into the role of CDCP1 in CC progression. Potentially, CDCP1 might serve as a diagnostic biomarker and a novel therapeutic target for CC.

An oncogenic viral interferon regulatory factor upregulates CUB domain-containing protein 1 to promote angiogenesis by hijacking transcription factor lymphoid enhancer-binding factor 1 and metastasis suppressor CD82

Kaposi's sarcoma (KS), a highly angiogenic and invasive vascular tumor, is the most common AIDS-associated cancer caused by KS-associated herpesvirus (KSHV) infection. We have recently shown that KSHV-encoded viral interferon regulatory factor 1 (vIRF1) contributes to KSHV-induced cell motility (PLoS Pathog. 15:e1007578, 2019). However, the role of vIRF1 in KSHV-induced angiogenesis remains unknown. Here, using two in vivo angiogenesis models including the chick chorioallantoic membrane assay (CAM) and the matrigel plug angiogenesis assay in mice, we show that vIRF1 promotes angiogenesis by upregulating CUB domain (for complement C1r/C1s, Uegf, Bmp1) containing protein 1 (CDCP1). Mechanistically, vIRF1 enhances the expression of transcription factor lymphoid enhancer-binding factor 1 (Lef1) and binds to Lef1 to promote CDCP1 transcription. Meanwhile, vIRF1 degrades metastasis suppressor CD82 through an ubiquitin-proteasome pathway by recruiting E3 ubiquitin ligase AMFR to CD82, which protects CDCP1 from CD82-mediated, palmitoylation-dependent degradation. CDCP1 activates AKT signaling, which is required for vIRF1-induced cell motility but not angiogenesis. Our results illustrate that, by hijacking Lef1 and CD82, vIRF1 upregulates CDCP1 to promote angiogenesis and cell invasion. These novel findings demonstrate the vIRF1 targets multiple cellular proteins and pathways to promote the pathogenesis of KS, which could be attractive therapeutic targets for KSHV-induced malignancies.

Theranostic Targeting of CUB Domain Containing Protein 1 (CDCP1) in Pancreatic Cancer

PURPOSE

The recent emergence of radioligand therapies for cancer treatment has increased enthusiasm for developing new theranostic strategies coupling both imaging and cytotoxicity in the same entity. In this study, we evaluated whether CUB domain containing protein 1 (CDCP1), a single-pass transmembrane protein highly overexpressed in diverse human cancers, might be a target for cancer theranostics.

EXPERIMENTAL DESIGN

The ectodomain of CDCP1 was targeted using radiolabeled forms of 4A06, a potent and specific recombinant human antibody that we developed. Imaging and antitumor assessment studies were performed in animal models of pancreatic cancer, including two patient-derived xenograft models we developed for this study. For antitumor assessment studies, the endpoints were death due to tumor volume >3,000 mm³ or ≥20% loss in body weight. Specific tracer binding or antitumor effects were assessed with an unpaired, two-tailed Student t test and survival advantages were assessed with a log rank (Mantel-Cox) test. Differences at the 95% confidence level were interpreted to be significant.

RESULTS

⁸⁹Zr-4A06 detected a broad dynamic range of full length or cleaved CDCP1 expression on seven human pancreatic cancer tumors (n = 4/tumor). Treating mice with single or fractionated doses of ¹⁷⁷Lu-4A06 significantly reduced pancreatic cancer tumor volume compared with mice receiving vehicle or unlabeled 4A06 (n = 8; P < 0.01). A single dose of ²²⁵Ac-4A06 also inhibited tumor growth, although the effect was less profound compared with ¹⁷⁷Lu-4A06 (n = 8; P < 0.01). A significant survival advantage was imparted by ²²⁵Ac-4A06 (HR = 2.56; P < 0.05).

CONCLUSIONS

These data establish that CDCP1 can be exploited for theranostics, a finding with widespread implications given its breadth of overexpression in cancer.

Radiation-induced small extracellular vesicles as "carriages" promote tumor antigen release and trigger antitumor immunity

Rationale: Accumulating evidence supports the importance of radiation therapy in the induction of antitumor immunity. Small extracellular vesicles (sEVs) play essential roles in tumor antigen loading and delivery. However, the role of sEVs in radiation-induced antitumor immunity remains unclear. It is therefore important to determine the role and regulatory mechanisms of sEVs in radiation-induced immunity.

Methods: Tumor cells were irradiated (8 Gy), and sEVs were purified via ultracentrifugation. Primary tumor and experimental lung metastasis models were established in mice to evaluate antitumor immunity triggered by immunization with sEVs. Proteomic and bioinformatic analyses were performed to identify altered cargos in sEVs induced by radiation. Peptides derived from up-regulated proteins in sEVs were designed and synthesized as vaccines according to major histocompatibility complex (MHC) I binding and immunogenicity.

Results: Here, we demonstrated that sEVs derived from irradiated tumor cells could trigger antitumor immunity against primary tumor and experimental lung metastasis by enhancing CD8⁺ and CD4⁺ T cell infiltration. Radiation may also enrich sEVs with tumor antigens and heat-shock proteins. Furthermore, CUB domain-containing protein 1 (CDCP1) derived from radiation-induced sEVs was identified as a novel tumor-associated antigen and developed as a peptide vaccine that may generate antitumor immune responses.

Conclusions: Our results demonstrate that the use of sEVs secreted by irradiated tumor cells constitutes an efficient approach for tumor antigen delivery and presentation and highlight the role of sEVs in radiation-triggered antitumor immunity.

Anti-CDCP1 immuno-conjugates for detection and inhibition of ovarian cancer

CUB-domain containing protein 1 (CDCP1) is a cancer associated cell surface protein that amplifies pro-tumorigenic signalling by other receptors including EGFR and HER2. Its potential as a cancer target is supported by studies showing that anti-CDCP1 antibodies inhibit cell migration and survival in vitro, and tumor growth and metastasis in vivo. Here we characterize two anti-CDCP1 antibodies, focusing on immuno-conjugates of one of these as a tool to detect and inhibit ovarian cancer. Methods: A panel of ovarian cancer cell lines was examined for cell surface expression of CDCP1 and loss of expression induced by anti-CDCP1 antibodies 10D7 and 41-2 using flow cytometry and Western blot analysis. Surface plasmon resonance analysis and examination of truncation mutants was used to analyse the binding properties of the antibodies for CDCP1. Live-cell spinning-disk confocal microscopy of GFP-tagged CDCP1 was used to track internalization and intracellular trafficking of CDCP1/antibody complexes. In vivo, zirconium 89-labelled 10D7 was detected by positron-emission tomography imaging, of an ovarian cancer patient-derived xenograft grown intraperitoneally in mice. The efficacy of cytotoxin-conjugated 10D7 was examined against ovarian cancer cells in vitro and in vivo. Results: Our data indicate that each antibody binds with high affinity to the extracellular domain of CDCP1 causing rapid internalization of the receptor/antibody complex and degradation of CDCP1 via processes mediated by the kinase Src. Highlighting the potential clinical utility of CDCP1, positron-emission tomography imaging, using zirconium 89-labelled 10D7, was able to detect subcutaneous and intraperitoneal xenograft ovarian cancers in mice, including small (diameter <3 mm) tumor deposits of an ovarian cancer patient-derived xenograft grown intraperitoneally in mice. Furthermore, cytotoxin-conjugated 10D7 was effective at inhibiting growth of CDCP1-expressing ovarian cancer cells in vitro and in vivo. Conclusions: These data demonstrate that CDCP1 internalizing antibodies have potential for killing and detection of CDCP1 expressing ovarian cancer cells.

Association between Biomarkers of Low-grade Inflammation and Sex Hormones in Women with Polycystic Ovary Syndrome

Objective Women with polycystic ovary syndrome (PCOS) have higher circulating levels of C-reactive protein, but the relationship between inflammation and endocrine function in PCOS remains poorly understood. Thus, this study aimed to investigate the association between low-grade inflammation and sex hormones in women with PCOS.

Design and Patients A comprehensive panel of biomarkers of inflammation was measured in serum of 63 women with PCOS using proximity extension assay technology. Associations of 65 biomarkers with sex hormones were assessed without and with adjustment for age and body mass index (BMI).

Results In the unadjusted analysis, 20 biomarkers were positively correlated with 17-OH-progesterone (17-OH-P), 14 with prolactin and 6 with free testosterone, whereas inverse associations were found for 16 biomarkers with sex hormone-binding globulin (SHBG), 6 with luteinizing hormone (LH) and 6 with estrogen (all p<0.05). Among the positive associations, correlations were mainly found for five chemokines (CXCL11, CCL4, MCP-4/CCL13, CXCL5, CXCL6) and for VEGF-A, LAP-TGFβ1, TNFSF14 and MMP-1. Inverse associations with sex hormones were mainly present for two chemokines (CXCL1, MCP-2/CCL8), CDCP1, CST5 and CSF-1. Adjustment for age and BMI reduced the number of biomarker associations for SHBG and estrogen, but had hardly any impact on associations with 17-OH-P, prolactin, free testosterone and LH.

Conclusion Women with PCOS feature BMI-independent associations between biomarkers of inflammation and certain sex steroid and hypophyseal hormones. Most of these inflammation-related biomarkers were chemokines, which may be relevant as potential mediators of the increased cardiometabolic risk of women with PCOS.

Targeting oxidative pentose phosphate pathway prevents recurrence in mutant Kras colorectal carcinomas

Recurrent tumors originate from cancer stem cells (CSCs) that survive conventional treatments. CSCs consist of heterogeneous subpopulations that display distinct sensitivity to anticancer drugs. Such a heterogeneity presents a significant challenge in preventing tumor recurrence. In the current study, we observed that quiescent CUB-domain–containing protein 1 (CDCP1)+ CSCs are enriched after chemotherapy in mutant Kirsten rat sarcoma viral oncogene homolog (Kras) colorectal carcinomas (CRCs) and serve as a reservoir for recurrence. Mechanistically, glucose catabolism in CDCP1+ CSCs is routed to the oxidative pentose phosphate pathway (PPP); multiple cycling of carbon backbones in the oxidative PPP potentially maximizes NADPH reduction to counteract chemotherapy-induced reactive oxygen species (ROS) formation, thereby allowing CDCP1+ CSCs to survive chemotherapeutic attack. This is dependent on silent mating type information regulation 2 homolog 5 (Sirt5)-mediated inhibition of the glycolytic enzyme triosephosphate isomerase (TPI) through demalonylation of Lys56. Blocking demalonylation of TPI at Lys56 increases chemosensitivity of CDCP1+ CSCSs and delays recurrence of mutant Kras CRCs in vivo. These findings pinpoint a new therapeutic approach for combating mutant Kras CRCs.

This study shows that CDCP1-positive cancer stem cells represent a critical driving force behind tumor relapse in colorectal tumors that have mutant Kras and reveals a unique role for the oxidative pentose phosphate pathway in this process.

Dynamic m6A mRNA methylation reveals the role of METTL3-m6A-CDCP1 signaling axis in chemical carcinogenesis

N6-methyladenosine (m⁶A) is the most abundant internal modification in mammalian mRNAs. Despite its functional importance in various physiological events, the role of m⁶A in chemical carcinogenesis remains largely unknown. Here we profiled the dynamic m⁶A mRNA modification during cellular transformation induced by chemical carcinogens and identified a subset of cell transformation-related, concordantly modulated m⁶A sites. Notably, the increased m⁶A in 3'-UTR mRNA of oncogene CDCP1 was found in malignant transformed cells. Mechanistically, the m⁶A methyltransferase METTL3 and demethylases ALKBH5 mediate the m⁶A modification in 3'-UTR of CDCP1 mRNA. METTL3 and m⁶A reader YTHDF1 preferentially recognize m⁶A residues on CPCP1 3'-UTR and promote CDCP1 translation. We further showed that METTL3 and CDCP1 are upregulated in the bladder cancer patient samples and the expression of METTL3 and CDCP1 is correlated with the progression status of the bladder cancers. Inhibition of the METTL3-m⁶A-CDCP1 axis resulted in decreased growth and progression of chemical-transformed cells and bladder cancer cells. Most importantly, METTL3-m⁶A-CDCP1 axis has synergistic effect with chemical carcinogens in promoting malignant transformation of uroepithelial cells and bladder cancer tumorigenesis in vitro and in vivo. Taken together, our results identify dynamic m⁶A modification in chemical-induced malignant transformation and provide insight into critical roles of the METTL3-m⁶A-CDCP1 axis in chemical carcinogenesis.

FBXL14 abolishes breast cancer progression by targeting CDCP1 for proteasomal degradation

Understanding the molecular mechanisms that underlie the aggressive behavior and relapse of breast cancer may help in the development of novel therapeutic interventions. CUB-domain-containing protein 1 (CDCP1), a transmembrane adaptor protein, is highly maintained and required in the context of cellular metastatic potential in triple-negative breast cancer (TNBC). For this reason, gene expression levels of CDCP1 have been considered as a prognostic marker in TNBC. However, not rarely, transcript levels of genes do not reflect always the levels of proteins, due to the post-transcriptional regulation. Here we show that miR-17/20a control the FBXL14 E3 ligase, establishing FBXL14 as an upstream regulator of the CDCP1 pathway. FBXL14 acts as an novel interaction partner of CDCP1, and facilitates its ubiquitination and proteasomal degradation with an enhanced capacity to suppress CDCP1 protein stability that eventually prevents CDCP1 target genes involved in breast cancer metastasis. Our findings first time uncovers the regulatory mechanism of CDCP-1 protein stabilization, more predictable criteria than gene expression levels for prognosis of breast cancer patients.

An insight into metastasis: Random or evolving paradigms?

Mechanical or fostered molecular events define metastatic cascade. Three distinct sets of molecular events characterize metastasis, viz invasion of extracellular matrix; angiogenesis, vascular dissemination and anoikis resistance; tumor homing and relocation of tumor cells to selective organ. Invasion of extracellular matrix requires epithelial to mesenchymal transition through disrupted lamellopodia formation and contraction of actin cytoskeleton; aberration of Focal adhesion complex formation involving integrins and the extracellular matrix; degradation of extracellular matrix by matrix metalloproteases; faulty immune surveillance in tumor microenvironment and an upregulated proton efflux pump NHE1 in tumors. Vascular dissemination and anoikis resistance depend upon upregulation of integrins, phosphorylation of CDCP1, attenuated apoptotic pathways and upregulation of angiogenesis. Tumor homing depends on recruitment of mesenchymal stem cells, expression on chemokines and growth factors, upregulated stem cell renewal pathways. Despite of many potential challenges in curbing metastasis, future targeted therapies involving immunotherapy, stem cell engineered and oncolytic virus based therapy, pharmacological activation of circadian clock are held promising. To sum up, metastasis is a complex cascade of events and warrants detailed molecular understanding for development of therapeutic strategies.

Regulation of inside-out β1-integrin activation by CDCP1

Tumor metastasis depends on the dynamic regulation of cell adhesion through β1-integrin. The Cub-Domain Containing Protein-1, CDCP1, is a transmembrane glycoprotein which regulates cell adhesion. Overexpression and loss of CDCP1 have been observed in the same cancer types to promote metastatic progression. Here, we demonstrate reduced CDCP1 expression in high-grade, primary prostate cancers, circulating tumor cells and tumor metastases of patients with castrate-resistant prostate cancer. CDCP1 is expressed in epithelial and not mesenchymal cells, and its cell surface and mRNA expression declines upon stimulation with TGFβ1 and epithelial-to-mesenchymal transition. Silencing of CDCP1 in DU145 and PC3 cells resulted in 3.4-fold higher proliferation of non-adherent cells and 4.4-fold greater anchorage independent growth. CDCP1-silenced tumors grew in 100% of mice, compared to 30% growth of CDCP1-expressing tumors. After CDCP1 silencing, cell adhesion and migration diminished 2.1-fold, caused by loss of inside-out activation of β1-integrin. We determined that the loss of CDCP1 reduces CDK5 kinase activity due to the phosphorylation of its regulatory subunit, CDK5R1/p35, by c-SRC on Y234. This generates a binding site for the C2 domain of PKCδ, which in turn phosphorylates CDK5 on T77. The resulting dissociation of the CDK5R1/CDK5 complex abolishes the activity of CDK5. Mutations of CDK5-T77 and CDK5R1-Y234 phosphorylation sites re-establish the CDK5/CDKR1 complex and the inside-out activity of β1-integrin. Altogether, we discovered a new mechanism of regulation of CDK5 through loss of CDCP1, which dynamically regulates β1-integrin in non-adherent cells and which may promote vascular dissemination in patients with advanced prostate cancer.

Hepatic stem cells with self-renewal and liver repopulation potential are harbored in CDCP1-positive subpopulations of human fetal liver cells

Background

Mature human hepatocytes are critical in preclinical research and therapy for liver disease, but are difficult to manipulate and expand in vitro. Hepatic stem cells (HpSCs) may be an alternative source of functional hepatocytes for cell therapy and disease modeling. Since these cells play an import role in regenerative medicine, the precise characterization that determines specific markers used to isolate these cells as well as whether they contribute to liver regeneration still remain to be shown.

Method

In this study, human HpSCs were isolated from human primary fetal liver cells (FLCs) by flow cytometry using CDCP1, CD90, and CD66 antibodies. The isolated CDCP1⁺CD90⁺CD66^– HpSCs were cultured on dishes coated with type IV collagen in DMEM nutrient mixture F-12 Ham supplemented with FBS, human γ-insulin, nicotinamide, dexamethasone, and l-glutamine for at least 2 weeks, and were characterized by transcriptomic profiling, quantitative real-time PCR, immunocytochemistry, and in-vivo transplantation.

Results

The purified CDCP1⁺CD90⁺CD66^– subpopulation exhibited clonal expansion and self-renewal capability, and bipotential capacity was further identified in single cell-derived colonies containing distinct hepatocytes and cholangiocytes. Moreover, in-vivo liver repopulation assays demonstrated that human CDCP1⁺CD90⁺CD66^– HpSCs repopulated over 90% of the mouse liver and differentiated into functional hepatocytes with drug metabolism activity.

Conclusions

We identified a human hepatic stem/progenitor population in the CDCP1⁺CD90⁺CD66^– subpopulation in human FLCs, indicating CDCP1 marker could potentially be utilized to identify and isolate HpSCs for further cytotherapy of liver disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0747-3) contains supplementary material, which is available to authorized users.

Cell-Surface Protein Profiling Identifies Distinctive Markers of Progenitor Cells in Human Skeletal Muscle

Skeletal muscle contains two distinct stem/progenitor populations. One is the satellite cell, which acts as a muscle stem cell, and the other is the mesenchymal progenitor, which contributes to muscle pathogeneses such as fat infiltration and fibrosis. Detailed and accurate characterization of these progenitors in humans remains elusive. Here, we performed comprehensive cell-surface protein profiling of the two progenitor populations residing in human skeletal muscle and identified three previously unrecognized markers: CD82 and CD318 for satellite cells and CD201 for mesenchymal progenitors. These markers distinguish myogenic and mesenchymal progenitors, and enable efficient isolation of the two types of progenitors. Functional study revealed that CD82 ensures expansion and preservation of myogenic progenitors by suppressing excessive differentiation, and CD201 signaling favors adipogenesis of mesenchymal progenitors. Thus, cell-surface proteins identified here are not only useful markers but also functionally important molecules, and provide valuable insight into human muscle biology and diseases.

CD318 is a ligand for CD6

It has been proposed that CD6, an important regulator of T cells, functions by interacting with its currently identified ligand, CD166, but studies performed during the treatment of autoimmune conditions suggest that the CD6-CD166 interaction might not account for important functions of CD6 in autoimmune diseases. The antigen recognized by mAb 3A11 has been proposed as a new CD6 ligand distinct from CD166, yet the identity of it is hitherto unknown. We have identified this CD6 ligand as CD318, a cell surface protein previously found to be present on various epithelial cells and many tumor cells. We found that, like CD6 knockout (KO) mice, CD318 KO mice are also protected in experimental autoimmune encephalomyelitis. In humans, we found that CD318 is highly expressed in synovial tissues and participates in CD6-dependent adhesion of T cells to synovial fibroblasts. In addition, soluble CD318 is chemoattractive to T cells and levels of soluble CD318 are selectively and significantly elevated in the synovial fluid from patients with rheumatoid arthritis and juvenile inflammatory arthritis. These results establish CD318 as a ligand of CD6 and a potential target for the diagnosis and treatment of autoimmune diseases such as multiple sclerosis and inflammatory arthritis.

Cellular Prion Protein PrPC and Ecto-5'-Nucleotidase Are Markers of the Cellular Stress Response to Aneuploidy

Aneuploidy is a hallmark of most human tumors, but the molecular physiology of aneuploid cells is not well characterized. In this study, we screened cell surface biomarkers of approximately 300 proteins by multiparameter flow cytometry using multiple aneuploid model systems such as cell lines, patient samples, and mouse models. Several new biomarkers were identified with altered expression in aneuploid cells, including overexpression of the cellular prion protein CD230/PrP^C and the immunosuppressive cell surface enzyme ecto-5'-nucleotidase CD73. Functional analyses associated these alterations with increased cellular stress. An increased number of CD73⁺ cells was observed in confluent cultures in aneuploid cells relative to their diploid counterparts. An elevated expression in CD230/PrP^C was observed in serum-deprived cells in association with increased generation of reactive oxygen species. Overall, our work identified biomarkers of aneuploid karyotypes, which suggest insights into the underlying molecular physiology of aneuploid cells. Cancer Res; 77(11); 2914-26. ©2017 AACR.

Dysregulated expression of cell surface glycoprotein CDCP1 in prostate cancer

CUB-domain-containing protein 1 (CDCP1) is a trans-membrane protein regulator of cell adhesion with a potent pro-migratory function in tumors. Given that proteolytic cleavage of the ectodomain correlates with outside-in oncogenic signaling, we characterized glycosylation in the context of cellular processing and expression of CDCP1 in prostate cancer. We detected 135 kDa full-length and proteolytic processed 70 kDa species in a panel of PCa cell models. The relative expression of full-length CDCP1 correlated with the metastatic potential of syngeneic cell models and an increase in surface membrane expression of CDCP1 was observed in tumor compared to adjacent normal prostate tissues. We demonstrated that glycosylation of CDCP1 is a prerequisite for protein stability and plasma membrane localization, and that the expression level and extent of N-glycosylation of CDCP1 correlated with metastatic status. Interestingly, complex N-linked glycans with sialic acid chains were restricted to the N-terminal half of the ectodomain and absent in the truncated species. Characterization of the extracellular expression of CDCP1 identified novel circulating forms and revealed that extracellular vesicles provide additional processing pathways. Employing immunoaffinity mass spectrometry, we detected elevated levels of circulating CDCP1 in patient urine with high-risk disease. Our results establish that differential glycosylation, cell surface presentation and extracellular expression of CDCP1 are hallmarks of PCa progression.

Cell line and patient-derived xenograft models reveal elevated CDCP1 as a target in high-grade serous ovarian cancer

BACKGROUND

Development of targeted therapies for high-grade serous ovarian cancer (HGSC) remains challenging, as contributing molecular pathways are poorly defined or expressed heterogeneously. CUB-domain containing protein 1 (CDCP1) is a cell-surface protein elevated in lung, colorectal, pancreas, renal and clear cell ovarian cancer.

METHODS

CUB-domain containing protein 1 was examined by immunohistochemistry in HGSC and fallopian tube. The impact of targeting CDCP1 on cell growth and migration in vitro, and intraperitoneal xenograft growth in mice was examined. Three patient-derived xenograft (PDX) mouse models were developed and characterised for CDCP1 expression. The effect of a monoclonal anti-CDCP1 antibody on PDX growth was examined. Src activation was assessed by western blot analysis.

RESULTS

Elevated CDCP1 was observed in 77% of HGSC cases. Silencing of CDCP1 reduced migration and non-adherent cell growth in vitro and tumour burden in vivo. Expression of CDCP1 in patient samples was maintained in PDX models. Antibody blockade of CDCP1 significantly reduced growth of an HGSC PDX. The CDCP1-mediated activation of Src was observed in cultured cells and mouse xenografts.

CONCLUSIONS

CUB-domain containing protein 1 is over-expressed by the majority of HGSCs. In vitro and mouse model data indicate that CDCP1 has a role in HGSC and that it can be targeted to inhibit progression of this cancer.

New crossroads for potential therapeutic intervention in cancer - intersections between CDCP1, EGFR family members and downstream signaling pathways

Signaling pathways regulated by the receptor CDCP1 play central roles in promoting cancer and in mediating resistance to chemo- and targeted-therapies. In this perspective we briefly summarize these findings as well as data demonstrating poorer outcomes for several malignancies that exhibit elevated CDCP1 expression. Promising data from preclinical studies suggest that CDCP1 targeted agents, including therapeutic antibodies, could be useful in the treatment of cancer patients selected on the basis of activation of CDCP1 and its signaling partners including EGFR, HER2, Met and Src.

Androgen receptor non-nuclear regulation of prostate cancer cell invasion mediated by Src and matriptase

Castration-resistant prostate cancers still depend on nuclear androgen receptor (AR) function despite their lack of dependence on exogenous androgen. Second generation anti-androgen therapies are more efficient at blocking nuclear AR; however resistant tumors still develop. Recent studies indicate Src is highly active in these resistant tumors. By manipulating AR activity in several different prostate cancer cell lines through RNAi, drug treatment, and the use of a nuclear-deficient AR mutant, we demonstrate that androgen acting on cytoplasmic AR rapidly stimulates Src tyrosine kinase via a non-genomic mechanism. Cytoplasmic AR, acting through Src enhances laminin integrin-dependent invasion. Active Matriptase, which cleaves laminin, is elevated within minutes after androgen stimulation, and is subsequently shed into the medium. Matriptase activation and shedding induced by cytoplasmic AR is dependent on Src. Concomitantly, CDCP1/gp140, a Matriptase and Src substrate that controls integrin-based migration, is activated. However, only inhibition of Matriptase, but not CDCP1, suppresses the AR/Src-dependent increase in invasion. Matriptase, present in conditioned medium from AR-stimulated cells, is sufficient to enhance invasion in the absence of androgen. Thus, invasion is stimulated by a rapid but sustained increase in Src activity, mediated non-genomically by cytoplasmic AR, leading to rapid activation and shedding of the laminin protease Matriptase.

ADAM9 enhances CDCP1 protein expression by suppressing miR-218 for lung tumor metastasis

Metastasis is the leading cause of death in cancer patients due to the difficulty of controlling this complex process. MicroRNAs (miRNA), endogenous noncoding short RNAs with important biological and pathological functions, may play a regulatory role during cancer metastasis, but this role has yet to be fully defined. We previously demonstrated that ADAM9 enhanced the expression of the pro-migratory protein CDCP1 to promote lung metastasis; however, the regulatory process remains unknown. Here we demonstrate that endogenous miR-218, which is abundant in normal lung tissue but suppressed in lung tumors, is regulated during the process of ADAM9-mediated CDCP1 expression. Suppression of miR-218 was associated with high migration ability in lung cancer cells. Direct interaction between miR-218 and the 3'-UTR of CDCP1 mRNAs was detected in luciferase-based transcription reporter assays. CDCP1 protein levels decreased as expression levels of miR-218 increased, and increased in cells treated with miR-218 antagomirs. Induction of miR-218 inhibited tumor cell mobility, anchorage-free survival, and tumor-initiating cell formation in vitro and delayed tumor metastases in mice. Our findings revealed an integrative tumor suppressor function of miR-218 in lung carcinogenesis and metastasis.

Elevated CDCP1 predicts poor patient outcome and mediates ovarian clear cell carcinoma by promoting tumor spheroid formation, cell migration and chemoresistance

Hematogenous metastases are rarely present at diagnosis of ovarian clear cell carcinoma (OCC). Instead dissemination of these tumors is characteristically via direct extension of the primary tumor into nearby organs and the spread of exfoliated tumor cells throughout the peritoneum, initially via the peritoneal fluid, and later via ascites that accumulates as a result of disruption of the lymphatic system. The molecular mechanisms orchestrating these processes are uncertain. In particular, the signaling pathways used by malignant cells to survive the stresses of anchorage-free growth in peritoneal fluid and ascites, and to colonize remote sites, are poorly defined. We demonstrate that the transmembrane glycoprotein CUB-domain-containing protein 1 (CDCP1) has important and inhibitable roles in these processes. In vitro assays indicate that CDCP1 mediates formation and survival of OCC spheroids, as well as cell migration and chemoresistance. Disruption of CDCP1 via silencing and antibody-mediated inhibition markedly reduce the ability of TOV21G OCC cells to form intraperitoneal tumors and induce accumulation of ascites in mice. Mechanistically our data suggest that CDCP1 effects are mediated via a novel mechanism of protein kinase B (Akt) activation. Immunohistochemical analysis also suggested that CDCP1 is functionally important in OCC, with its expression elevated in 90% of 198 OCC tumors and increased CDCP1 expression correlating with poor patient disease-free and overall survival. This analysis also showed that CDCP1 is largely restricted to the surface of malignant cells where it is accessible to therapeutic antibodies. Importantly, antibody-mediated blockade of CDCP1 in vivo significantly increased the anti-tumor efficacy of carboplatin, the chemotherapy most commonly used to treat OCC. In summary, our data indicate that CDCP1 is important in the progression of OCC and that targeting pathways mediated by this protein may be useful for the management of OCC, potentially in combination with chemotherapies and agents targeting the Akt pathway.

Interaction of CDCP1 with HER2 enhances HER2-driven tumorigenesis and promotes trastuzumab resistance in breast cancer

Understanding the molecular pathways that contribute to the aggressive behavior of HER2-positive breast cancers may aid in the development of novel therapeutic interventions. Here, we show that CDCP1 and HER2 are frequently co-overexpressed in metastatic breast tumors and associated with poor patient prognosis. HER2 and CDCP1 co-overexpression leads to increased transformation ability, cell migration, and tumor formation in vivo, and enhanced HER2 activation and downstream signaling in different breast cancer cell lines. Mechanistically, we demonstrate that CDCP1 binds to HER2 through its intracellular domain, thereby increasing HER2 interaction with the non-receptor tyrosine kinase c-SRC (SRC), leading to trastuzumab resistance. Taken together, our findings establish that CDCP1 is a modulator of HER2 signaling and a biomarker for the stratification of breast cancer patients with poor prognosis. Our results also provide a rationale for therapeutic targeting of CDCP1 in HER2-positive breast cancer patients.

The tyrosine phosphatase SHP2 associates with CUB domain-containing protein-1 (CDCP1), regulating its expression at the cell surface in a phosphorylation-dependent manner

CUB domain-containing protein-1 (CDCP1) is a transmembrane glycoprotein that is phosphorylated by SRC family kinases (SFK) before recruiting and activating PKCδ. CDCP1 is overproduced in many cancers. It promotes metastasis and resistance to anoïkis. The robust production of CDCP1 would be associated with stemness and has been proposed as a novel prognosis marker. The natural transmembrane location of CDCP1 makes it an ideal therapeutic target and treatments based on the use of appropriate antibodies are currently being evaluated. However, we still know very little about the molecular fate of CDCP1 and its downstream signaling events. Improvements in our understanding of the molecular events occurring downstream of CDCP1 are required to make use of changes of CDCP1 production or functions for therapeutic purposes. By the mean of co-immunoprecipitation and affinity precipitation we show here, for the first time, that CDCP1 interacts directly, with the cytosolic tyrosine phosphatase SHP2. Point mutants of CDCP1 show that residues Y734 and Y743 are responsible for its interaction with SHP2. It may therefore compete with SFK. We also demonstrate that a shRNA-mediated down regulation of SHP2 is associated with a stronger CDCP1 phosphorylation and an impairment of antibody-mediated CDCP1 internalization.

Prognostic Significance of CDCP1 Expression in Colorectal Cancer and Effect of Its Inhibition on Invasion and Migration

BACKGROUND

To assess the correlations and functions of complement C1r/C1s, Uegf, Bmp1 domain-containing protein-1 (CDCP1) in identifying colorectal cancer (CRC) patients who are at high risk for metastasis.

METHODS

Tumor specimens from 101 patients were analyzed by real-time polymerase chain reaction to detect CDCP1 expression. CDCP1 expression plasmids and shRNA were used to knock down CDCP1 expression in this study to investigate migratory and invasive abilities by Boyden chambers. The mRNA expression profiles in shCDCP1 transfectants were compared to those in control cells by conducting microarray analysis. Its downstream effectors were also invested in this study.

RESULTS

CRC patients with a high CDCP1 expression had a statistically significant lower overall survival and disease-free survival compared to those exhibiting low CDCP1 expression. In vitro, knock-down CDCP1 expression significantly decreased migratory and invasive abilities in HCT116. Aberrant expression of CDCP1 increased cancer cell migration and invasion. By using integrated genomics, we identified ROCK1 (rho-associated, coiled-coil-containing protein kinase 1 pseudogene 1) as a downstream effector in CDCP1-mediated migration and as an invasion mediator. Clinically, ROCK1 and CDCP1 mRNA expression exhibited a strong positive correlation in CRC patient samples.

CONCLUSIONS

Our results implicated CDCP1 as a key regulator of CRC migration and invasion, and suggest that it is a useful prognostic factor for patients with CRC. Improved identification of a high-risk subset of early metastatic patients may guide indications of individualized treatment in clinical practice.

CUB-domain-containing protein 1 overexpression in solid cancers promotes cancer cell growth by activating Src family kinases

The transmembrane glycoprotein, CUB (complement C1r/C1s, Uegf, Bmp1) domain-containing protein 1 (CDCP1) is overexpressed in several cancer types and is a predictor of poor prognosis for patients on standard of care therapies. Phosphorylation of CDCP1 tyrosine sites is induced upon loss of cell adhesion and is thought to be linked to metastatic potential of tumor cells. Using a tyrosine-phosphoproteomics screening approach, we characterized the phosphorylation state of CDCP1 across a panel of breast cancer cell lines. We focused on two phospho-tyrosine pTyr peptides of CDCP1, containing Tyr707 and Tyr806, which were identified in all six lines, with the human epidermal growth factor 2-positive HCC1954 cells showing a particularly high phosphorylation level. Pharmacological modulation of tyrosine phosphorylation indicated that, the Src family kinases (SFKs) were found to phosphorylate CDCP1 at Tyr707 and Tyr806 and play a critical role in CDCP1 activity. We demonstrated that CDCP1 overexpression in HEK293 cells increases global phosphotyrosine content, promotes anchorage-independent cell growth and activates several SFK members. Conversely, CDCP1 downregulation in multiple solid cancer cell lines decreased both cell growth and SFK activation. Analysis of primary human tumor samples demonstrated a correlation between CDCP1 expression, SFK and protein kinase C (PKC) activity. Taken together, our results suggest that CDCP1 overexpression could be an interesting therapeutic target in multiple solid cancers and a good biomarker to stratify patients who could benefit from an anti-SFK-targeted therapy. Our data also show that multiple tyrosine phosphorylation sites of CDCP1 are important for the functional regulation of SFKs in several tumor types.

EGF inhibits constitutive internalization and palmitoylation-dependent degradation of membrane-spanning procancer CDCP1 promoting its availability on the cell surface

Many cancers are dependent on inappropriate activation of epidermal growth factor receptor (EGFR), and drugs targeting this receptor can improve patient survival, although benefits are generally short-lived. We reveal a novel mechanism linking EGFR and the membrane-spanning, cancer-promoting protein CDCP1 (CUB domain-containing protein 1). Under basal conditions, cell surface CDCP1 constitutively internalizes and undergoes palmitoylation-dependent degradation by a mechanism in which it is palmitoylated in at least one of its four cytoplasmic cysteines. This mechanism is functional in vivo as CDCP1 is elevated and palmitoylated in high-grade serous ovarian tumors. Interestingly, activation of the EGFR system with EGF inhibits proteasome-mediated, palmitoylation-dependent degradation of CDCP1, promoting recycling of CDCP1 to the cell surface where it is available to mediate its procancer effects. We also show that mechanisms inducing relocalization of CDCP1 to the cell surface, including disruption of its palmitoylation and EGF treatment, promote cell migration. Our data provide the first evidence that the EGFR system can function to increase the lifespan of a protein and also promote its recycling to the cell surface. This information may be useful for understanding mechanisms of resistance to EGFR therapies and assist in the design of treatments for EGFR-dependent cancers.

Phosphotyrosine recognition domains: the typical, the atypical and the versatile

SH2 domains are long known prominent players in the field of phosphotyrosine recognition within signaling protein networks. However, over the years they have been joined by an increasing number of other protein domain families that can, at least with some of their members, also recognise pTyr residues in a sequence-specific context. This superfamily of pTyr recognition modules, which includes substantial fractions of the PTB domains, as well as much smaller, or even single member fractions like the HYB domain, the PKCδ and PKCθ C2 domains and RKIP, represents a fascinating, medically relevant and hence intensely studied part of the cellular signaling architecture of metazoans. Protein tyrosine phosphorylation clearly serves a plethora of functions and pTyr recognition domains are used in a similarly wide range of interaction modes, which encompass, for example, partner protein switching, tandem recognition functionalities and the interaction with catalytically active protein domains. If looked upon closely enough, virtually no pTyr recognition and regulation event is an exact mirror image of another one in the same cell. Thus, the more we learn about the biology and ultrastructural details of pTyr recognition domains, the more does it become apparent that nature cleverly combines and varies a few basic principles to generate a sheer endless number of sophisticated and highly effective recognition/regulation events that are, under normal conditions, elegantly orchestrated in time and space. This knowledge is also valuable when exploring pTyr reader domains as diagnostic tools, drug targets or therapeutic reagents to combat human diseases.

Cell surface remodeling by plasmin: a new function for an old enzyme

Plasmin, one of the most potent and reactive serine proteases, is involved in various physiological processes, including embryo development, thrombolysis, wound healing and cancer progression. The proteolytic activity of plasmin is tightly regulated through activation of its precursor, plasminogen, only at specific times and in defined locales as well as through inhibition of active plasmin by its abundant natural inhibitors. By exploiting the plasminogen activating system and overexpressing distinct components of the plasminogen activation cascade, such as pro-uPA, uPAR and plasminogen receptors, malignant cells can enhance the generation of plasmin which in turn, modifies the tumor microenvironment to sustain cancer progression. While plasmin-mediated degradation and modification of extracellular matrix proteins, release of growth factors and cytokines from the stroma as well as activation of several matrix metalloproteinase zymogens, all have been a focus of cancer research studies for decades, the ability of plasmin to cleave transmembrane molecules and thereby to generate functionally important cleaved products which induce outside-in signal transduction, has just begun to receive sufficient attention. Herein, we highlight this relatively understudied, but important function of the plasmin enzyme as it is generated de novo at the interface between cross-talking cancer and host cells.

Evaluation of antibodies directed against human protease-activated receptor-2

Protease-activated receptor 2 (PAR2) is a G protein-coupled receptor activated by intramolecular docking of a tethered ligand that is released by the actions of proteases, mainly of the serine protease family. Here, we evaluate four commercially available anti-PAR2 antibodies, SAM11, C17, N19 and H99, demonstrating marked differences in the ability of these reagents to detect the target receptor in Western blot, immunocytochemical and flow cytometry applications. In Western blot analysis, we evaluated antibody reactivity against both ectopic and endogenous receptors. Against material from transfected cells, we show that SAM11 and N19, and to a lesser extent C17, but not H99, are able to detect ectopic PAR2. Interestingly, these Western blot analyses indicate that N19 and C17 detect conformations of ectopic PAR2 distinct to those recognised by SAM11. Significantly, our data also indicate that Western blot signal detected by SAM11 and C17, and much of the signal detected by N19, against cells endogenously expressing PAR2 is non-specific. Despite confounding non-specific signals, we were able to discern N19 reactivity against endogenous PAR2 as a broad smear that we also observed in ectopically expressing human and mouse cells and that is sensitive to loss of N-glycosylation. In immunocytochemistry analysis, each antibody is able to detect ectopic PAR2 although it appears that H99 detects only a subset of the ectopically expressed receptor. In addition, SAM11 and N19 are able to detect both ectopic and endogenous cell surface PAR2 by flow cytometry. In summary: (1) each antibody can detect ectopic PAR2 by immunocytochemical analysis with SAM11 and N19 suitable for cell surface detection of both ectopic and endogenous receptor by flow cytometry; (2) in Western blot analysis, N19, SAM11 and C17 can detect ectopically expressed PAR2, with only N19 able to detect the endogenous receptor by this technique and (3) in each of these approaches, appropriate controls are essential to ensure that non-specific reactivity is identified.

Proteomic analysis of microvesicles released by the human prostate cancer cell line PC-3

Cancer biomarkers are invaluable tools for cancer detection, prognosis, and treatment. Recently, microvesicles have appeared as a novel source for cancer biomarkers. We present here the results from a proteomic analysis of microvesicles released to the extracellular environment by the metastatic prostate cancer cell line PC-3. Using nanocapillary liquid chromatography-tandem mass spectrometry 266 proteins were identified with two or more peptide sequences. Further analysis showed that 16% of the proteins were classified as extracellular and that intracellular proteins were annotated in a variety of locations. Concerning biological processes, the proteins found in PC-3 cell-released microvesicles are mainly involved in transport, cell organization and biogenesis, metabolic process, response to stimulus, and regulation of biological processes. Several of the proteins identified (tetraspanins, annexins, Rab proteins, integrins, heat shock proteins, cytoskeletal proteins, 14-3-3 proteins) have previously been found in microvesicles isolated from other sources. However, some of the proteins seem to be more specific to the vesicular population released by the metastatic prostate cancer PC-3 cell line. Among these proteins are the tetraspanin protein CD151 and the glycoprotein CUB domain-containing protein 1. Interestingly, our results show these proteins are promising biomarkers for prostate cancer and therefore candidates for clinical validation studies in biological fluids.

Cell-surface proteomics identifies lineage-specific markers of embryo-derived stem cells

The advent of reprogramming and its impact on stem cell biology has renewed interest in lineage restriction in mammalian embryos, the source of embryonic (ES), epiblast (EpiSC), trophoblast (TS), and extraembryonic endoderm (XEN) stem cell lineages. Isolation of specific cell types during stem cell differentiation and reprogramming, and also directly from embryos, is a major technical challenge because few cell-surface proteins are known that can distinguish each cell type. We provide a large-scale proteomic resource of cell-surface proteins for the four embryo-derived stem cell lines. We validated 27 antibodies against lineage-specific cell-surface markers, which enabled investigation of specific cell populations during ES-EpiSC reprogramming and ES-to-XEN differentiation. Identified markers also allowed prospective isolation and characterization of viable lineage progenitors from blastocysts by flow cytometry. These results provide a comprehensive stem cell proteomic resource and enable new approaches to interrogate the mechanisms that regulate cell fate specification.

KAI1 suppresses HIF-1α and VEGF expression by blocking CDCP1-enhanced Src activation in prostate cancer

Background

KAI1 was initially identified as a metastasis-suppressor gene in prostate cancer. It is a member of the tetraspan transmembrane superfamily (TM4SF) of membrane glycoproteins. As part of a tetraspanin-enriched microdomain (TEM), KAI1 inhibits tumor metastasis by negative regulation of Src. However, the underlying regulatory mechanism has not yet been fully elucidated. CUB-domain-containing protein 1 (CDCP1), which was previously known as tetraspanin-interacting protein in TEM, promoted metastasis via enhancement of Src activity. To better understand how KAI1 is involved in the negative regulation of Src, we here examined the function of KAI1 in CDCP1-mediated Src kinase activation and the consequences of this process, focusing on HIF-1 α and VEGF expression.

Methods

We used the human prostate cancer cell line PC3 which was devoid of KAI1 expression. Vector-transfected cells (PC3-GFP clone #8) and KAI1-expressing PC3 clones (PC3-KAI1 clone #5 and #6) were picked after stable transfection with KAI1 cDNA and selection in 800 μg/ml G418. Protein levels were assessed by immunoblotting and VEGF reporter gene activity was measured by assaying luciferase activitiy. We followed tumor growth in vivo and immunohistochemistry was performed for detection of HIF-1, CDCP1, and VHL protein level.

Results

We demonstrated that Hypoxia-inducible factor 1α (HIF-1α) and VEGF expression were significantly inhibited by restoration of KAI1 in PC3 cells. In response to KAI1 expression, CDCP1-enhanced Src activation was down-regulated and the level of von Hippel-Lindau (VHL) protein was significantly increased. In an in vivo xenograft model, KAI1 inhibited the expression of CDCP1 and HIF-1α.

Conclusions

These novel observations may indicate that KAI1 exerts profound metastasis-suppressor activity in the tumor malignancy process via inhibition of CDCP1-mediated Src activation, followed by VHL-induced HIF-1α degradation and, ultimately, decreased VEGF expression.