Characterization of Laminin Binding Integrin Internalization in Prostate Cancer Cells

Aptamer Targets Triple-Negative Breast Cancer through Specific Binding to Surface CD49c

Simple Summary

Targeted therapy directed against many biomarkers has not shown significant improvement in outcome in TNBC, and therefore it is urgent to discover more biomarker candidates. Here, we found a DNA aptamer that bound to TNBC cells and identified CD49c as a specific surface marker for TNBC cells using the aptamer-facilitated biomarker discovery technology. The findings suggest that this DNA aptamer can be a drug delivery vehicle and CD49c is a potential target of targeted therapy for TNBC.

Abstract

Although targeted cancer therapy can induce higher therapeutic efficacy and cause fewer side effects in patients, the lack of targetable biomarkers on triple-negative breast cancer (TNBC) cells limits the development of targeted therapies by antibody technology. Therefore, we investigated an alternative approach to target TNBC by using the PDGC21T aptamer, which selectively binds to poorly differentiated carcinoma cells and tumor tissues, although the cellular target is still unknown. We found that synthetic aptamer probes specifically bound cultured TNBC cells in vitro and selectively targeted TNBC xenografts in vivo. Subsequently, to identify the target molecule on TNBC cells, we performed aptamer-mediated immunoprecipitation in lysed cell membranes followed by liquid chromatography tandem mass spectrometry (LC-MS/MS). Sequencing analysis revealed a highly conserved peptide sequence consistent with the cell surface protein CD49c (integrin α3). For target validation, we stained cultured TNBC and non-TNBC cells with an aptamer probe or a CD49c antibody and found similar cell staining patterns. Finally, competition cell-binding assays using both aptamer and anti-CD49c antibody revealed that CD49c is the biomarker targeted by the PDGC21T aptamer on TNBC cells. Our findings provide a molecular foundation for the development of targeted TNBC therapy using the PDGC21T aptamer as a targeting ligand.

Insulin-like Growth Factor-1 Influences Prostate Cancer Cell Growth and Invasion through an Integrin α3, α5, αV, and β1 Dependent Mechanism

Simple Summary

Insulin-like growth factor-1 (IGF-1) is a growth hormone and is implicated in prostate cancer progression. Most prostate cancers begin in an androgen-dependent state so that androgen deprivation therapy results in improved clinical outcome. However, some cancerous cells may survive androgen deprivation, growing into therapy-resistant, androgen-independent prostate cancer. The present study investigated the influence of IGF-1 on tumor growth and migration properties using androgen-dependent LNCaP and VCaP and androgen-independent PC3 and DU145 prostate cancer cells. Stimulation with IGF-1 activated growth in all cell lines. There were changes in transmembrane receptors (integrins) that bind cells to each other and changes in focal adhesion kinase that controls cell motility. Intracellular Akt/mTOR signaling, regulating cell division, was also activated. Thus, it seems that prostate cancer progression is controlled by a fine-tuned network between IGF-1-driven integrin-FAK signaling and the Akt-mTOR pathway. Concerted targeting of both pathways may, therefore, help prevent cancer dissemination.

Abstract

Insulin-like growth factor-1 (IGF-1)-related signaling is associated with prostate cancer progression. Links were explored between IGF-1 and expression of integrin adhesion receptors to evaluate relevance for growth and migration. Androgen-resistant PC3 and DU145 and androgen-sensitive LNCaP and VCaP prostate cancer cells were stimulated with IGF-1 and tumor growth (all cell lines), adhesion and chemotaxis (PC3, DU145) were determined. Evaluation of Akt/mTOR-related proteins, focal adhesion kinase (FAK) and integrin α and β subtype expression followed. Akt knock-down was used to investigate its influence on integrin expression, while FAK blockade served to evaluate its influence on mTOR signaling. Integrin knock-down served to investigate its influence on tumor growth and chemotaxis. Stimulation with IGF-1 activated growth in PC3, DU145, and VCaP cells, and altered adhesion and chemotactic properties of DU145 and PC3 cells. This was associated with time-dependent alterations of the integrins α3, α5, αV, and β1, FAK phosphorylation and Akt/mTOR signaling. Integrin blockade or integrin knock-down in DU145 and PC3 cells altered tumor growth, adhesion, and chemotaxis. Akt knock-down (DU145 cells) cancelled the effect of IGF-1 on α3, α5, and αV integrins, whereas FAK blockade cancelled the effect of IGF-1 on mTOR signaling (DU145 cells). Prostate cancer growth and invasion are thus controlled by a fine-tuned network between IGF-1 driven integrin-FAK signaling and the Akt-mTOR pathway. Concerted targeting of integrin subtypes along with Akt-mTOR signaling could, therefore, open options to prevent progressive dissemination of prostate cancer.

Deciphering the Molecular Machinery-Influence of sE-Cadherin on Tumorigenic Traits of Prostate Cancer Cells

Simple Summary

Despite recent advances in the therapeutic management of metastasized prostate cancer, disease progression is still inevitable, with often fatal outcomes. Elucidating molecular mechanisms crucial to cancer development and progression is therefore necessary to find ways to interfere in metastatic processes and ultimately improve prognosis. Since soluble (s)E-cadherin is elevated in the serum of patients with prostate cancer, we investigated its influence on prostate cancer cell behavior in vitro. Exposure to sE-cadherin increased the systemic spread of the cells. Thus, targeting sE-cadherin might be a novel and innovative concept to treat advanced PCa.

Abstract

The serum level of soluble (s)E-cadherin is elevated in several malignancies, including prostate cancer (PCa). This study was designed to investigate the effects of sE-cadherin on the behavior of PCa cells in vitro, with the aim of identifying a potential therapeutic target. Growth as well as adhesive and motile behavior were evaluated in PC3, DU-145, and LNCaP cells. Flow cytometry was used to assess cell cycle phases and the surface expression of CD44 variants as well as α and β integrins. Confocal microscopy was utilized to visualize the distribution of CD44 variants within the cells. Western blot was applied to investigate expression of α3 and β1 integrins as well as cytoskeletal and adhesion proteins. Cell growth was significantly inhibited after exposure to 5 µg/mL sE-cadherin and was accompanied by a G0/G1-phase arrest. Adhesion of cells to collagen and fibronectin was mitigated, while motility was augmented. CD44v4, v5, and v7 expression was elevated while α3 and β1 integrins were attenuated. Blocking integrin α3 reduced cell growth and adhesion to collagen but increased motility. sE-cadherin therefore appears to foster invasive tumor cell behavior, and targeting it might serve as a novel and innovative concept to treat advanced PCa.

RGD-Binding Integrins Revisited: How Recently Discovered Functions and Novel Synthetic Ligands (Re-)Shape an Ever-Evolving Field

Integrins have been extensively investigated as therapeutic targets over the last decades, which has been inspired by their multiple functions in cancer progression, metastasis, and angiogenesis as well as a continuously expanding number of other diseases, e.g., sepsis, fibrosis, and viral infections, possibly also Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV-2). Although integrin-targeted (cancer) therapy trials did not meet the high expectations yet, integrins are still valid and promising targets due to their elevated expression and surface accessibility on diseased cells. Thus, for the future successful clinical translation of integrin-targeted compounds, revisited and innovative treatment strategies have to be explored based on accumulated knowledge of integrin biology. For this, refined approaches are demanded aiming at alternative and improved preclinical models, optimized selectivity and pharmacological properties of integrin ligands, as well as more sophisticated treatment protocols considering dose fine-tuning of compounds. Moreover, integrin ligands exert high accuracy in disease monitoring as diagnostic molecular imaging tools, enabling patient selection for individualized integrin-targeted therapy. The present review comprehensively analyzes the state-of-the-art knowledge on the roles of RGD-binding integrin subtypes in cancer and non-cancerous diseases and outlines the latest achievements in the design and development of synthetic ligands and their application in biomedical, translational, and molecular imaging approaches. Indeed, substantial progress has already been made, including advanced ligand designs, numerous elaborated pre-clinical and first-in-human studies, while the discovery of novel applications for integrin ligands remains to be explored.

Targeted Drug Delivery via the Use of ECM-Mimetic Materials

The use of drug delivery vehicles to improve the efficacy of drugs and to target their action at effective concentrations over desired periods of time has been an active topic of research and clinical investigation for decades. Both synthetic and natural drug delivery materials have facilitated locally controlled as well as targeted drug delivery. Extracellular matrix (ECM) molecules have generated widespread interest as drug delivery materials owing to the various biological functions of ECM. Hydrogels created using ECM molecules can provide not only biochemical and structural support to cells, but also spatial and temporal control over the release of therapeutic agents, including small molecules, biomacromolecules, and cells. In addition, the modification of drug delivery carriers with ECM fragments used as cell-binding ligands has facilitated cell-targeted delivery and improved the therapeutic efficiency of drugs through interaction with highly expressed cellular receptors for ECM. The combination of ECM-derived hydrogels and ECM-derived ligand approaches shows synergistic effects, leading to a great promise for the delivery of intracellular drugs, which require specific endocytic pathways for maximal effectiveness. In this review, we provide an overview of cellular receptors that interact with ECM molecules and discuss examples of selected ECM components that have been applied for drug delivery in both local and systemic platforms. Finally, we highlight the potential impacts of utilizing the interaction between ECM components and cellular receptors for intracellular delivery, particularly in tissue regeneration applications.

Development and application of two novel monoclonal antibodies against overexpressed CD26 and integrin α3 in human pancreatic cancer

Monoclonal antibody (mAb) technology is an excellent tool for the discovery of overexpressed cell surface tumour antigens and the development of targeting agents. Here, we report the development of two novel mAbs against CFPAC-1 human pancreatic cancer cells. Using ELISA, flow cytometry, immunoprecipitation, mass spectrometry, Western blot and immunohistochemistry, we found that the target antigens recognised by the two novel mAbs KU44.22B and KU44.13A, are integrin α3 and CD26 respectively, with high levels of expression in human pancreatic and other cancer cell lines and human pancreatic cancer tissue microarrays. Treatment with naked anti-CD26 mAb KU44.13A did not have any effect on the growth and migration of cancer cells nor did it induce receptor downregulation. In contrast, treatment with anti-integrin α3 mAb KU44.22B inhibited growth in vitro of Capan-2 cells, increased migration of BxPC-3 and CFPAC-1 cells and induced antibody internalisation. Both novel mAbs are capable of detecting their target antigens by immunohistochemistry but not by Western blot. These antibodies are excellent tools for studying the role of integrin α3 and CD26 in the complex biology of pancreatic cancer, their prognostic and predictive values and the therapeutic potential of their humanised and/or conjugated versions in patients whose tumours overexpress integrin α3 or CD26.

ADAP1 promotes invasive squamous cell carcinoma progression and predicts patient survival

ADAP1, a GTPase-activating protein (GAP) for the small GTPase ARF6, is a strong predictor of poor survival in early-stage squamous cell carcinoma patients and a critical mediator of TGF-β-induced invasive cell migration by facilitating basement membrane breakdown.

Invasive squamous cell carcinoma (SCC) is aggressive cancer with a high risk of recurrence and metastasis, but the critical determinants of its progression remain elusive. Here, we identify ADAP1, a GTPase-activating protein (GAP) for ARF6 up-regulated in TGF-β-responding invasive tumor cells, as a strong predictor of poor survival in early-stage SCC patients. Using a mouse model of SCC, we show that ADAP1 overexpression promotes invasive tumor progression by facilitating cell migration and breakdown of the basement membrane. We found that ADAP1-rich, TGF-β-responding tumor cells exhibit cytoplasmic laminin localization, which correlated with the absence of laminin and type IV collagen from the pericellular basement membrane. Interestingly, although tumors overexpressing a GAP activity-deficient mutant of ADAP1 resulted in morphologically complex tumors, those tumor cells failed to breach the basement membrane. Moreover, Adap1 deletion in tumor cells ameliorated the basement membrane breakdown and had less invading cells in the stroma. Our study demonstrates that ADAP1 is a critical mediator of TGF-β-induced cancer invasion and might be exploited for the treatment of high-risk SCC.

A Method to Reuse Archived H&E Stained Histology Slides for a Multiplex Protein Biomarker Analysis

Archived Hematoxylin and Eosin (H&E) stained pathology slides are routinely stored to index formalin-fixed paraffin-embedded (FFPE) sample tissue blocks. FFPE blocks are clinically annotated human tumor specimens that can be valuable in studies decades after the tissue is collected. If stored properly, they have the potential to yield a valuable number of serial sectioned slides for diagnostic or research purposes. However, some retrospective studies are limited in scope because the tissue samples have been depleted or not enough material is available in stored blocks for serial sections. The goal of these studies was to determine if archived H&E-stained slides can be directly reutilized by optimizing methods to de-stain and then re-stain the H&E stained slides to allow the detection of several biomarkers of interest using a conjugated antibody with chromogen multiplex immunohistochemistry procedure. This simple but innovative procedure, combined with image analysis techniques, demonstrates the ability to perform precise detection of relevant markers correlated to disease progression in initially identified tumor regions in tissue. This may add clinical value in retaining H&E slides for further use.

Integrin α5/ITGA5 Promotes The Proliferation, Migration, Invasion And Progression Of Oral Squamous Carcinoma By Epithelial-Mesenchymal Transition

Background

Integrin signalling is involved in cell migration, invasion, proliferation and motility. Integrin α5/ITGA5 is a subunit of Integrin and contributes to the activation of Integrin signalling. The potential role of Integrin α5/ITGA5 in oral squamous cancer remains unknown. The aim of this study was to uncover the effect and mechanism of Integrin α5/ITGA5 in the progression of oral squamous carcinoma.

Method

TCGA database scanning, qRT-PCR, immunohistochemistry and Western blotting assays were used to detect the expression of Integrin α5/ITGA5 in tissues and cell lines. We established stable Integrin α5/ITGA5 overexpressing and Integrin α5/ITGA5 knockdown cell lines. We investigated the biological function and the underlying mechanism of Integrin α5/ITGA5 through a series of experiments.

Results

Integrin α5/ITGA5 was upregulated in cancer tissue, and its levels negatively correlated with the overall survival (OS) of patients. Integrin α5/ITGA5 promoted proliferation, migration and invasion in an oral squamous carcinoma cell line by EMT (epithelial-mesenchymal transition).

Conclusion

Integrin α5/ITGA5 promotes the proliferation, migration and invasion of oral squamous carcinoma.

Integrin α-3 ß-1's central role in breast cancer, melanoma and glioblastoma cell aggregation revealed by antibodies with blocking activity

Breast cancer, melanoma and glioblastoma cells undergo cell-mediated aggregation and aggregate coalescence in a transparent 3D Matrigel environment. Cells from normal tissue and non-tumorigenic cell lines do not exhibit these behaviors. Here, 266 monoclonal antibodies (mAbs) demonstrated to interact with a wide variety of membrane, secreted and matrix proteins, have been screened for their capacity to block these tumorigenic cell-specific behaviors in a 3D environment. Remarkably, only six of the 266 tested mAbs exhibited blocking activity, four targeting integrin ß-1, one targeting integrin α-3 and one targeting CD44. Colocalization of integrins ß-1 and α-3 in fixed cells and in live aggregates suggests that the integrin α-3 ß-1 dimer plays a central role in cancer cell aggregation in the 3D environment provided by Matrigel. Our results suggest that blocking by anti-integrin and anti-CD44 mAbs involves interference in cell-cell interactions.

Integrin α6β4E variant is associated with actin and CD9 structures and modifies the biophysical properties of cell-cell and cell-extracellular matrix interactions

Integrin α6β4 is an essential, dynamic adhesion receptor for laminin 332 found on epithelial cells, required for formation of strong cell–extracellular matrix (ECM) adhesion and induced migration, and coordinated by regions of the β4C cytoplasmic domain. β4E, a unique splice variant of β4 expressed in normal tissue, contains a cytoplasmic domain of 231 amino acids with a unique sequence of 114 amino acids instead of β4C’s canonical 1089 amino acids. We determined the distribution of α6β4E within normal human glandular epithelium and its regulation and effect on cellular biophysical properties. Canonical α6β4C expressed in all basal cells, as expected, while α6β4E expressed within a subset of luminal cells. α6β4E expression was induced by three-dimensional culture conditions, activated Src, was reversible, and was stabilized by bortezomib, a proteasome inhibitor. α6β4C expressed in all cells during induced migration, whereas α6β4E was restricted to a subset of cells with increased kinetics of cell–cell and cell–ECM resistance properties. Interestingly, α6β4E presented in “ringlike” patterns measuring ∼1.75 × 0.72 microns and containing actin and CD9 at cell–ECM locations. In contrast, α6β4C expressed only within hemidesmosome-like structures containing BP180. Integrin α6β4E is an inducible adhesion isoform in normal epithelial cells that can alter biophysical properties of cell–cell and cell–ECM interactions.

Integrin trafficking in cells and tissues

Cell adhesion to the extracellular matrix is fundamental to metazoan multicellularity and is accomplished primarily through the integrin family of cell-surface receptors. Integrins are internalized and enter the endocytic-exocytic pathway before being recycled back to the plasma membrane. The trafficking of this extensive protein family is regulated in multiple context-dependent ways to modulate integrin function in the cell. Here, we discuss recent advances in understanding the mechanisms and cellular roles of integrin endocytic trafficking.

Photoactive platinum(iv) complex conjugated to a cancer-cell-targeting cyclic peptide

Conjugate of a cancer-cell targeting cyclic peptide with a photoactive platinum(iv) complex exhibits enhanced photocytotoxicity and cell accumulation.

HDAC Inhibition Counteracts Metastatic Re-Activation of Prostate Cancer Cells Induced by Chronic mTOR Suppression

This study was designed to investigate whether epigenetic modulation by histone deacetylase (HDAC) inhibition might circumvent resistance towards the mechanistic target of rapamycin (mTOR) inhibitor temsirolimus in a prostate cancer cell model. Parental (par) and temsirolimus-resistant (res) PC3 prostate cancer cells were exposed to the HDAC inhibitor valproic acid (VPA), and tumor cell adhesion, chemotaxis, migration, and invasion were evaluated. Temsirolimus resistance was characterized by reduced binding of PC3^res cells to endothelium, immobilized collagen, and fibronectin, but increased adhesion to laminin, as compared to the parental cells. Chemotaxis, migration, and invasion of PC3^res cells were enhanced following temsirolimus re-treatment. Integrin α and β receptors were significantly altered in PC3^res compared to PC3^par cells. VPA significantly counteracted temsirolimus resistance by down-regulating tumor cell–matrix interaction, chemotaxis, and migration. Evaluation of integrin expression in the presence of VPA revealed a significant down-regulation of integrin α5 in PC3^res cells. Blocking studies demonstrated a close association between α5 expression on PC3^res and chemotaxis. In this in vitro model, temsirolimus resistance drove prostate cancer cells to become highly motile, while HDAC inhibition reversed the metastatic activity. The VPA-induced inhibition of metastatic activity was accompanied by a lowered integrin α5 surface level on the tumor cells.

Novel Regulation of Integrin Trafficking by Rab11-FIP5 in Aggressive Prostate Cancer

The laminin-binding integrins, α3β1 and α6β1, are needed for tumor metastasis and their surface expression is regulated by endocytic recycling. β1 integrins share the Rab11 recycling machinery, but the trafficking of α3β1 and α6β1 are distinct by an unknown mechanism. Using a mouse PDX tumor model containing human metastatic prostate cancer, Rab11 family interacting protein 5 (Rab11-FIP5) was identified as a lead candidate for α6β1 trafficking. Rab11-FIP5 and its membrane-binding domain were required for α6β1 recycling, without affecting the other laminin-binding integrin (i.e., α3β1) or unrelated membrane receptors like CD44, transferrin receptor, or E-cadherin. Depletion of Rab11-FIP5 resulted in the intracellular accumulation of α6β1 in the Rab11 recycling compartment, loss of cell migration on laminin, and an unexpected loss of α6β1 recycling in cell-cell locations. Taken together, these data demonstrate that α6β1 is distinct from α3β1 via Rab11-FIP5 recycling and recycles in an unexpected cell-cell location.Implications: Rab11-FIP5-dependent α6β1 integrin recycling may be selectively targeted to limit migration of prostate cancer cells into laminin-rich tissues. Mol Cancer Res; 16(8); 1319-31. ©2018 AACR.

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.

Precision engineering of targeted nanocarriers

Since their introduction in 1980, the number of advanced targeted nanocarrier systems has grown considerably. Nanocarriers capable of targeting single receptors, multiple receptors, or multiple epitopes have all been used to enhance delivery efficiency and selectivity. Despite tremendous progress, preclinical studies and clinically translatable nanotechnology remain disconnected. The disconnect in targeting efficacy may stem from poorly-understood factors such as receptor clustering, spatial control of targeting ligands, ligand mobility, and ligand architecture. Further, the relationship between receptor distribution and ligand architecture remains elusive. Traditionally, targeted nanocarriers were engineered assuming a "static" target. However, it is becoming increasingly clear that receptor expression patterns change in response to external stimuli and disease progression. Here, we discuss how cutting-edge technologies will enable a better characterization of the spatiotemporal distribution of membrane receptors and their clustering. We further describe how this will enable the design of new nanocarriers that selectively target the site of disease. Ultimately, we explore how the precision engineering of targeted nanocarriers that adapt to receptor dynamics will have the potential to drive nanotechnology to the forefront of therapy and make targeted nanomedicine a clinical reality. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Biology-Inspired Nanomaterials > Lipid-Based Structures Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

Integrin Inhibitors in Prostate Cancer

Prostate cancer (PCa) is the most frequently diagnosed cancer and the third highest cause of cancer-related deaths in men in the U.S. The development of chemotherapeutic agents that can bind PCa tumor cells with high specificity is critical in order to increase treatment effectiveness. Integrin receptors and their corresponding ligands have different expression patterns in PCa cells. They have been identified as promising targets to inhibit pathways involved in PCa progression. Currently, several compounds have proven to target specific integrins and their subunits in PCa cells. In this article, we review the role of integrins inhibitors in PCa and their potential as therapeutic targets for PCa treatments. We have discussed the following: natural compounds, monoclonal antibodies, statins, campothecins analog, aptamers, d-aminoacid, and snake venom. Recent studies have shown that their mechanisms of action result in decrease cell migration, cell invasion, cell proliferation, and metastasis of PCa cells.

Laminin-1 induces endocytosis of 67KDa laminin receptor and protects Neuroscreen-1 cells against death induced by serum withdrawal

Although the function of laminin in the basement membrane is known, the function of soluble "neuronal" laminin is unknown. Since laminin is neuroprotective, we determined whether the soluble laminin-1 induces signaling for neuroprotection via its 67KDa laminin-1 receptor (67LR). Treatment of Neuroscreen-1 (NS-1) cells with laminin-1 or YIGSR peptide, which corresponds to a sequence in laminin-1 β1 chain that binds to 67LR, induced a decrease in the cell-surface expression of 67LR and caused its internalization. Furthermore, intracellular cAMP-elevating agents, dibutyryl-cAMP, forskolin, and rolipram, also induced this internalization. Both soluble laminin-1 and YIGSR induced a sustained elevation of intracellular cAMP under defined conditions, suggesting a causal role of cAMP in the endocytosis of 67LR. This endocytosis was not observed in cells deficient in protein kinase A (PKA) nor in cells treated with either SQ 22536, an inhibitor for adenylyl cyclase, or ESI-09, an inhibitor for the exchange protein directly activated by cAMP (Epac). In addition, when internalization occurred in NS-1 cells, 67LR and adenylyl cyclase were localized in early endosomes. Under conditions in which endocytosis had occurred, both laminin-1 and YIGSR protected NS-1 cells from cell death induced by serum withdrawal. However, under conditions in which endocytosis did not occur, neither laminin-1 nor YIGSR protected these cells. Conceivably, the binding of laminin-1 to 67LR causes initial signaling through PKA and Epac, which causes the internalization of 67LR, along with signaling enzymes, such as adenylyl cyclase, into early endosomes. This causes sustained signaling for protection against cell death induced by serum withdrawal.