Differential expression of cell adhesion molecules in variants of K1735 melanoma cells differing in metastatic capacity

Intrinsic disorder in integral membrane proteins

The well-defined roles and specific protein-protein interactions of many integral membrane proteins (IMPs), such as those functioning as receptors for extracellular matrix proteins and soluble growth factors, easily align with considering IMP structure as a classical "lock-and-key" concept. Nevertheless, continued advances in understanding protein conformation, such as those which established the widespread existence of intrinsically disordered proteins (IDPs) and especially intrinsically disordered regions (IDRs) in otherwise three-dimensionally organized proteins, call for ongoing reevaluation of transmembrane proteins. Here, we present basic traits of IDPs and IDRs, and, for some select single-span IMPs, consider the potential functional advantages intrinsic disorder might provide and the possible conformational impact of disease-associated mutations. For transmembrane proteins in general, we highlight several investigational approaches, such as biophysical and computational methods, stressing the importance of integrating them to produce a more-complete mechanistic model of disorder-containing IMPs. These procedures, when synergized with in-cell assessments, will likely be key in translating in silico and in vitro results to improved understanding of IMP conformational flexibility in normal cell physiology as well as disease, and will help to extend their potential as therapeutic targets.

L1-CAM knock-down radiosensitizes neuroblastoma IMR-32 cells by simultaneously decreasing MycN, but increasing PTEN protein expression

Childhood neuroblastoma is one of the most malignant types of cancers leading to a high mortality rate. These cancerous cells can be highly metastatic and malignant giving rise to disease recurrence and poor prognosis. The proto-oncogene myelocytomatosis neuroblastoma (MycN) is known to be amplified in this type of cancer, thus, promoting high malignancy and resistance. The L1 cell adhesion molecule (L1-CAM) cleavage has been found upregulated in many types of malignant cancers. In the present study, we explored the interplay between L1-CAM, MycN and PTEN as well as the role played by PDGFR and VEGFR on tumorigenicity in neuroblastoma cells. We investigated the effect of L1-CAM knock-down (KD) and PDGFR/VEGFR inhibition with sunitinib malate (Sutent®) treatment on subsequent tumorsphere formation and cellular proliferation and migration in the MycN-amplified IMR-32 neuroblastoma cells. We further examined the effect of combined L1-CAM KD with Sutent treatment or radiotherapy on these cellular functions in our cells. Tumorsphere formation is one of the indicators of aggressiveness in malignant cancers, which was significantly inhibited in IMR-32 cells after L1-CAM KD or Sutent treatment, however, no synergistic effect was observed with dual treatments, rather L1-CAM KD alone showed a greater inhibition on tumorsphere formation compared to Sutent treatment alone. In addition, cellular proliferation and migration were significantly inhibited after L1-CAM KD in the IMR-32 cells with no synergistic effect observed on the rate of cell proliferation when combined with Sutent treatment. Again, L1-CAM KD alone exhibited greater inhibitory effect than Sutent treatment on cell proliferation. L1-CAM KD led to the simultaneous downregulation of MycN, but the upregulation of PTEN protein expression. Notably, radiotherapy (2 Gy) of the IMR-32 cells led to significant upregulation of both L1-CAM and MycN, which was abrogated with L1-CAM KD in our cells. In addition, L1-CAM KD radiosensitized the cells as exhibited by the synergistic effect on the reduction in cell proliferation compared to radiotherapy alone. Taken together, our data show the importance of L1-CAM interplay with MycN and PTEN on the MycN amplified neuroblastoma cell radioresistance, proliferation and motility.

Association between tumorigenic potential and the fate of cancer cells in a syngeneic melanoma model

The self-renewal potential of a cancer cell can be estimated by using particular assays, which include xenotransplantation in immunocompromised animals or culturing in non-adherent serum-free stem-cells media (SCM). However, whether cells with self-renewal potential actually contribute to disease is unknown. Here we investigated the tumorigenic potential and fate of cancer cells in an in-vivo melanoma model. We examined cell lines which were derived from the same parental line: a non-metastatic cell line (K1735/16), a metastatic cell line (K1735/M4) and a cell line which was selected in non-adherent conditions (K1735/16S). All cell lines exhibited similar proliferation kinetics when grown on culture plates. K1735/16 cells grown in soft agar or in suspension non-adherent conditions failed to form colonies or spheroids, whereas the other cell lines showed prominent colonogenicity and spheroid formation capacity. By using sphere limiting dilution analysis (SLDA) in serum-free media, K1735/16S and K1735/M4 cells grown in suspension were capable of forming spheroids even in low frequencies of concentrations, as opposed to K1735/16 cells. The tumorigenic potential of the cell lines was determined in SCID mice using intra footpad injections. Palpable tumors were evident in all mice. In agreement with the in-vitro studies, the K1735/M4 cell line exhibited the highest growth kinetics, followed by the K1735/16S cell line, whereas the K1735/16 cell line had the lowest tumor growth potential (P<0.001). In contrast, when we repeated the experiments in syngeneic C3H/HeN mice, the K1735/16 cell line produced macroscopic tumors 30–100 days after injection, whereas K1735/M4 and K1735/16S derived tumors regressed spontaneously in 90–100% of mice. TUNEL analysis revealed significantly higher number of apoptotic cells in K1735/16S and K1735/M4 cell line-derived tumors compared to K1735/16 tumors (P<0.001). The models we have examined here raised the possibility, that cells with high-tumorigenic activity may be more immunogenic and hence are more susceptible to immune-regulation.

Water extract of ashwagandha leaves limits proliferation and migration, and induces differentiation in glioma cells

Root extracts of Withania somnifera (Ashwagandha) are commonly used as a remedy for a variety of ailments and a general tonic for overall health and longevity in the Indian traditional medicine system, Ayurveda. We undertook a study to investigate the anti-proliferative and differentiation-inducing activities in the water extract of Ashwagandha leaves (ASH-WEX) by examining in glioma cells. Preliminary detection for phytochemicals was performed by thin-layer chromatography. Cytotoxicity was determined using trypan blue and MTT assays. Expression level of an hsp70 family protein (mortalin), glial cell differentiation marker [glial fibrillary acidic protein (GFAP)] and neural cell adhesion molecule (NCAM) were analyzed by immunocytochemistry and immunoblotting. Anti-migratory assay was also done using wound-scratch assay. Expression levels of mortalin, GFAP and NCAM showed changes, subsequent to the treatment with ASH-WEX. The data support the existence of anti-proliferative, differentiation-inducing and anti-migratory/anti-metastasis activities in ASH-WEX that could be used as potentially safe and complimentary therapy for glioma.

L1-CAM in cancerous tissues

BACKGROUND

L1-cell adhesion molecule (L1-CAM) is a cell adhesion receptor of the immunoglobulin superfamily, known for its roles in nerve cell function. While originally believed to be present only in brain cells, in recent years L1-CAM has been detected in other tissues, and in a variety of cancer cells, including some common types of human cancer.

OBJECTIVE/METHODS

We review the prevalence of L1-CAM in human cancer, the possible mechanisms involved in L1-CAM-mediated tumorigenesis, and cancer therapies based upon L1-CAM antibody treatment.

RESULTS/CONCLUSIONS

In colon cancer cells, the L1-CAM gene was identified as a target of the Wnt/beta-catenin-TCF signaling pathway, and L1-CAM was exclusively detected at the invasive front of colon and ovarian cancer tissue. The expression of L1-CAM in normal and cancer cells enhanced tumorigenesis and conferred metastasis in colon cancer cells. Antibodies against the L1-CAM ectodomain severely inhibited the proliferation of a variety of cancer cells in culture and reduced tumor burden when injected into mice harboring cancer cells expressing L1-CAM. These results, in addition to the presence of L1-CAM on the cell surface and its restricted distribution in normal tissues, make it an ideal target for tumor therapy.

L1 cell adhesion molecule (L1CAM) in invasive tumors

The L1 cell adhesion molecule (L1CAM) belongs to the immunoglobulin superfamily and was originally identified in the nervous system. Recent studies demonstrated L1CAM expression in various types of cancer, predominantly at the invasive front of tumors and in metastases, suggesting its involvement in advanced stages of tumor progression. Overexpression of L1CAM in normal and cancer cells increased motility, enhanced growth rate and promoted cell transformation and tumorigenicity. Moreover, the expression of L1CAM in tumor cells conferred the capacity to form metastases. These properties of L1CAM, in addition to its cell surface localization, make it a potentially useful diagnostic marker for cancer progression and a candidate for anti-cancer therapy. We review the role of L1CAM in cancer progression with particular emphasis on colon cancer, and the potential of anti-L1CAM antibodies as a therapeutic tool for cancer.

Characterization of the neuron-specific L1-CAM cytoplasmic tail: naturally disordered in solution it exercises different binding modes for different adaptor proteins

L1, a highly conserved transmembrane glycoprotein member of the immunoglobulin superfamily of cell adhesion molecules, mediates many developmental processes in the nervous system. Here we present the biophysical characterization and the binding properties of the least structurally defined part of this receptor: its cytoplasmic tail (CT). We have shown by analytical ultracentrifugation and dynamic light scattering experiments that it is mostly monomeric and unstructured in aqueous solution. We have defined by nuclear magnetic resonance the molecular details of L1-CT binding to two major targets: a membrane-cytoskeletal linker (MCL), ezrin, and an endocytosis mediator, AP2. Surprisingly, in addition to the two previously identified ezrin binding motifs, the juxtamembrane and the (1176)YRSLE regions, we have discovered a third one, a part of which has been previously associated with binding to another MCL, ankyrin. For the L1 interaction with AP2 we have determined the precise interaction region surrounding the (1176)YRSLE binding site and that this overlaps with the second ezrin binding site. In addition, we have shown that the juxtamembrane region of L1-CT has some binding affinity to AP2-mu2, although the specificity of this interaction needs further investigation. These data indicate that L1-CT belongs to the class of intrinsically disordered proteins. Endogenous flexibility of L1-CT might play an important role in dynamic regulation of intracellular signaling: the ability of cytoplasmic tails to accommodate different targets has the potential to fine-tune signal transduction via cell surface receptors.

The role of adhesion molecules, alpha v beta 3, alpha v beta 5 and their ligands in the tumor cell and endothelial cell adhesion

Tumor metastasis is a complex process involving the interaction between tumor cells and endothelial cells in which some adhesion molecules play an important role. It was our aim to investigate the role of the adhesion molecules, alpha v beta 3 and alpha v beta 5 and their ligands, developmental endothelial locus-1 (Del-1) and L1, in tumor cell adhesion to endothelial cells in vitro. In this study, the expression and regulation of alpha v beta 3, alpha v beta 5 and intercellular adhesion molecule -1 on liver sinusoidal endothelial cells and liver cancer endothelial cells (T3A) were analyzed by real-time PCR and fluorescent-activated cell sorter. The expression and regulation of the integrin ligands, Del-1 and L1, in six tumor cell lines were analyzed by real-time PCR and western blot. We found the expressions of alpha v beta 3 and alpha v beta 5 were higher on T3A than that on liver sinusoidal endothelial cells, whereas expression of intercellular adhesion molecule-1 was lower on T3A than that on liver sinusoidal endothelial cells. After 24 h hypoxia, the expressions of alpha v beta 3 and alpha v beta 5 were upregulated on T3A and liver sinusoidal endothelial cells; the expression of intercellular adhesion molecule-1 was increased on liver sinusoidal endothelial cells, but remained unchanged on T3A. Del-1 and L1 expression levels were obviously diverse in various tumor cell lines and differentially modulated after 12 h hypoxia. The adhesion of tumor cells with Del-1 and L1 expression was higher in T3A than that in liver sinusoidal endothelial cells, and was significantly increased under hypoxic conditions. Interestingly, the tumor cell adherence could be inhibited by antibodies against alpha v beta 5 and alpha v beta 5, but not by an antibody against intercellular adhesion molecule-1. The adhesion of tumor cells without Del-1 and L1 expression was also higher on T3A than that on liver sinusoidal endothelial cells, but the adhesion could not be inhibited by antibodies against alpha v beta 5, alpha v beta 5 or intercellular adhesion molecule-1, suggesting that other receptors are involved. In conclusion, alpha v beta 5, alpha v beta 5 and their ligands Del-1 and L1 play an important role in the process of tumor cells moving from the original place.

L1 is associated with micrometastatic spread and poor outcome in colorectal cancer

L1 is a cell adhesion molecule expressed at the invasive front of colorectal tumors with an important role in metastasis. The aim of the present study was to determine L1 protein expression in a large cohort of colorectal cancer patients and its impact on early metastatic spread and survival. A total of 375 patients that underwent surgical treatment for colorectal cancer were chosen retrospectively. A tissue microarray was constructed of 576 tissue samples from these patients and analyzed by immunohistochemistry with a monoclonal antibody against human L1 (UJ127). Lymph node and bone marrow micrometastasis were assessed with monoclonal antibodies Ber-EP4 and pancytokeratin A45-B/B3, respectively. Associations between L1 expression and lymph node, bone marrow micrometastasis and survival were investigated with Fisher's, log-rank test and Cox multivariate analysis. All statistical tests were two-sided. L1 was detected in a subset of 48 (13%) of 375 patients examined. Analysis of L1 expression and survival revealed a significantly worse outcome for L1-positive patients by log-rank test (P<0.05). Multivariate Cox regression analysis showed the strongest independent prognostic impact of L1 expression (P<0.05). Fisher's test revealed a significant association of L1 expression and presence of disseminated tumor cells in lymph nodes and bone marrow (P<0.05). L1 is a powerful prognostic marker for patients that undergo complete surgical resection. It may have a role in early metastatic spread, as L1 is associated with micrometastases to both the lymph nodes and bone marrow. Thus, L1 should be explored further as a target for adjuvant therapy for micrometastatic disease.

L1 is associated with favorable outcome in neuroblastomas in contrast to adult tumors

BACKGROUND

Neuroblastoma is the most common solid tumor in childhood with unconventional clinical behavior. L1, a neuronal cell adhesion molecule, is associated with poor survival in malignant adult tumors. The aim of the current study was to determine expression of L1 in pediatric neuroblastoma.

METHODS

L1 expression was assessed on a tissue microarray with 66 surgically resected neuroblastoma samples by immunohistochemistry with a monoclonal antibody and peroxidase method. Additionally, mRNA expression was analyzed by reverse transcriptase-polymerase chain reaction with L1-specific primers. Data were correlated survival data by log rank test and Cox regression multivariate analysis.

RESULTS

L1 was detected in 57 (86%) of 66 neuroblastomas, whereas 9 (14%) were L1 negative. Median survival of all children was 72 months. Analysis with Kaplan-Meier method revealed a surprising and contrary finding to adult tumor entities: an association of L1 positivity with better event-free and overall survival (P < .001 and P < .01 by log rank test). Multivariate Cox regression analysis showed an independent prognostic impact of L1 negativity for event-free and overall survival of the children (P < .05).

CONCLUSIONS

In contrast to adult tumor entities, where L1 is associated with aggressive clinical behavior, our data show that L1 predicts good outcome in children with neuroblastoma. This novel finding suggests an inverse role of L1 in neuroblastoma. Future studies might focus on the molecular basis of the varying effect of L1 in different tumors.

Dynamics of cell interactions and communications during melanoma development

Melanoma development not only involves genetic and epigenetic changes that take place within the cell, but also involves processes determined collectively by micro-environmental factors, including cell-cell interactions and communications. During the transition from normal cells to benign and malignant lesions, and subsequently to metastatic cancer, stepwise changes in intercellular communications provide tumor cells with the ability to overcome cell-cell adhesion and micro-environmental controls from the host and to invade surrounding tissues and disperse to distant locations. Cadherins are major cell-cell adhesion molecules involved in the development and maintenance of skin. E-cadherin expressed in normal melanocytes mediates growth and invasion control by keratinocytes. Progressive loss of E-cadherin and gain of N-cadherin during melanoma development not only free melanoma cells from control by keratinocytes, but also provide new adhesion properties, resulting in switched partnerships with fibroblasts and vascular endothelial cells. The cadherin subtype switching also dictates gap junctional specificity in melanocytic cells during tumor development. This selective intercellular communication may contribute to the regulation of cell growth, differentiation, apoptosis, and migration of melanocytic cells in both physiologic and pathologic conditions. Abnormal up-regulation of the immunoglobin repeat-containing cell adhesion molecules Mel-CAM and L1-CAM potentiates invasion and migration of melanoma. Thus, abnormal expression of intercellular adhesion receptors and dysregulated intercellular communication underlies melanoma development and progression.

L1 (CD171) is highly expressed in gastrointestinal stromal tumors

The treatment strategy for mesenchymal tumors of the gastrointestinal tract is based upon typing of the tumor. Especially differential diagnosis of gastrointestinal stromal tumors (GISTs) to leiomyomas is crucial for determining radicality of surgery. L1 cell adhesion molecule (CD171) plays an essential role in tumor progression. The aim of this study was to determine expression of L1 in GISTs, smooth muscle tumors, desmoid-type fibromatosis and peripheral nerve sheath tumors (PNSTs). We retrospectively analyzed a total of 129 surgically resected primary tumors or metastases of 72 GISTs, 29 smooth muscle tumors, seven PNSTs and 21 desmoid-type fibromatosis by immunohistochemistry for c-kit, CD34, smooth muscle actin, desmin, vimentin, S-100 and L1 expression. L1 expression was detected in 53 (74%) of 72 GISTs but in none of 29 smooth muscle tumors or 21 desmoid-type fibromatosis (P<0.01 by Fisher's test). In all, four (57%) of seven peripheral nerve sheath tumors were L1-positive. Survival analysis of 55 surgically completely resected GISTs presenting without metastasis at initial diagnosis revealed no tumor-specific death among L1-negative patients (P=0.13 by log-rank test; median follow-up time 41 months) and one recurrence was observed (P=0.12). Interestingly high levels of L1 were seen in tumor vascular endothelial cells of smooth muscle tumors and PNSTs, but not in GISTs. Our data show that L1 is highly expressed in GISTs but not in smooth muscle tumors and desmoid-type fibromatosis being important differential diagnoses. The trend towards a reduced survival of L1-positive patients in this study has to be further evaluated in future trials with higher patient numbers.

L1 is a potential marker for poorly-differentiated pancreatic neuroendocrine carcinoma

AIM: To determine the expression of L1 in pancreatic neuroendocrine tumor and to correlate it with WHO classification of this tumor.

METHODS: We retrospectively analyzed L1 expression in 63 cases of pancreatic neuroendocrine tumor by immunohistochemistry on paraffin sections of primary tumors or metastases. Staining was performed by peroxidase technique with monoclonal antibody UJ127.11 against human L1. All tumors were classified according to WHO classification as well-differentiated neuroendocrine tumors and carcinomas or poorly-differentiated neuroendocrine carcinomas.

RESULTS: L1 was detected in 5 (7.9%) of 63 pancreatic neuroendocrine tumors. Four (44.4%) of 9 poorly-differentiated carcinomas expressed L1. In contrast, only 1 (1.9%) of 54 well-differentiated tumors or carcinomas was positive for L1. No expression was found in Langerhans islet cells of normal pancreatic tissue. Cross table analysis showed a significant association between L1 expression and classification of neuroendocrine tumors of the pancreas (P<0.01).

CONCLUSION: L1 is specifically expressed in poorly-differentiated pancreatic neuroendocrine carcinomas that are known to have the worst prognosis. L1 might be a marker for risk prediction of patients diagnosed with pancreatic neuroendocrine carcinomas.

L1 augments cell migration and tumor growth but not beta3 integrin expression in ovarian carcinomas

L1 is a neural cell adhesion molecule involved in cell migration, axon growth and guidance. Recent data have shown that L1 is overexpressed in ovarian and endometrial tumors and is associated with bad prognosis. How L1 promotes tumor progression is presently unknown. Here we show that L1 expression is predominantly confined to the invasive front of ovarian carcinomas. Overexpression of L1 in carcinoma cell lines by adenovirus-mediated gene transfer enhanced the haptotactic cell migration on extracellular matrix proteins. Expression of L1 augmented tumor growth of carcinomas xenografted in nonobese diabetic/severe combined immunodeficient mice (NOD/SCID). A recent report has demonstrated L1-dependent upregulation of beta3 integrin involving activation of the extracellular signal-regulated kinase (erk) pathway. We find that L1 and beta3 integrin are not coexpressed in ovarian carcinoma tissues. Overexpression of L1 did not upregulate beta3 integrin in ovarian carcinoma cell lines but could do so in HEK293 cells. Our results suggest that L1 could drive progression by enhancing cell migration and tumor growth but that L1 dependent and erk-regulated gene expression requires cell-type specific elements.

Heterophilic interactions between cell adhesion molecule L1 and alphavbeta3-integrin induce HUVEC process extension in vitro and angiogenesis in vivo

Cell adhesion molecule L1 was implicated in angiogenic processes, tumor formation and metastasis. Here, we provide evidence that the sixth Ig-like domain of L1 (L1Ig6) interacts with alpha(v)beta3 to induce process extension of human umbilical vein endothelial cells (HUVECs) in vitro and angiogenesis in vivo. HUVECs formed network-like structures on full-length L1 or L1Ig6 substrates comparable to structures found on matrigel. In the presence of mab alpha(v)beta3 or cyclic RGD, apoptosis was induced. In fibrin matrices where L1Ig6 was covalently incorporated, HUVECs formed multicellular and hollow processes through interactions between cell-surface alpha(v)beta3 and RGD-sites of matrix-immobilized L1Ig6. No such processes were induced by L1Ig6 having non-functional RDG-sites, or in the presence of mab alpha(v)beta3 or cyclic RGD. In those matrices, increased apoptosis was found. Co-immunoprecipitation of L1 or L1Ig6 with alpha(v)beta3 suggests close interactions. Furthermore, L1Ig6 stimulated HUVECs showed increased tyrosine phosphorylation of alpha(v)beta3 and phosphorylation of MAP kinases (ERK1 and ERK2) but not AKT indicating specific activation of alpha(v) and alpha(v)beta3 followed by activation of downstream kinases. Application of L1Ig6-modified fibrin matrices on CAMs induced 50-60% increased alpha(v) and alpha(v)beta3 protein expression and in vivo angiogenesis indicated by approximately 50% increased mean vascular length density. The results demonstrate angiogenic potential of L1Ig6 involving ligation and activation of alpha(v)beta3.

Brain metastasis from colorectal cancer

PURPOSE

The mechanism of brain metastasis is not well understood, but the affinity between cancer cells and neural tissues may be involved in the process. The aim of our study is to elucidate the involvement of neural cell adhesion molecule (NCAM) and therapeutic parameters in patients with brain metastasis from colorectal cancer.

METHODS

We retrospectively identified 17 patients with brain metastasis from colorectal cancer. Data were collected with regard to patients' characteristics, location, and stage of primary tumor, and extent and location of metastatic disease. NCAM histochemical staining was undertaken using a paraffin block, and compared with 56 Dukes C patients and 13 Dukes D patients.

RESULTS

Neural cell adhesion molecule expression was significantly higher in the primary tumors of the brain metastasis patients than in the lesions of the Dukes C and Dukes D control groups (p = 0.0004). Patients whose tumor was managed by radiosurgery survived longer than patients who had had whole brain radiation or those who had been left untreated.

CONCLUSION

The fact that NCAM expression was high in the primary tumors of brain metastasis patients suggests that the affinity of cancer cells to a particular organ is important for circulation-mediated metastasis. Controlling local tumors using radiosurgery is certainly going to play an important role in extending survival and improving the patient's quality of life (QOL).

N-glycoproteins bearing beta1-6 branched oligosaccharides from the A375 human melanoma cell line analysed by tandem mass spectrometry

Tumour-associated alterations of cell surface glycosylation play a crucial role in the adhesion and metastasis of cancer cells. It is well known that the metastatic potential is associated with increased GlcNAc beta1-6 branching in N-glycans of tumour cells specifically recognized by a lectin from Phaseolus vulgaris leukoagglutinin (PHA-L). We identified proteins bearing GlcNAc beta1-6 branched N-glycans in the A375 human melanoma cell line by affinity chromatography separation on a PHA-L agarose column, followed by immunoidentification and tandem mass spectrometry (MS/MS) analysis. Amongst the proteins identified were integrin subunits alpha2, alpha3, alpha5 and beta1, as well as N-cadherin and lysosome-associated membrane proteins (LAMP-1 and LAMP-2). In addition, L1, Mac-2 binding protein (Mac-2-BP), activated leukocyte cell adhesion molecule/CD166 (ALCAM) and melanotransferrin were shown to react with PHA-L. Some of these proteins are connected mainly with nervous tissues or the immune system and play a crucial role in cell adhesion processes. The presence of GlcNAc beta1-6 branched oligosaccharides in these proteins may influence their adhesion properties, reducing adhesion of the cells to the extracellular matrix (ECM) and thus facilitating tumour cell invasion.

Extracellular signal-regulated kinase (ERK)-dependent gene expression contributes to L1 cell adhesion molecule-dependent motility and invasion

The cell adhesion molecule L1 has been implicated in a variety of motile processes, including neurite extension, cerebellar cell migration, extravasation, and metastasis. Homophilic or heterophilic L1 binding and concomitant signaling have been shown to promote cell motility in the short term. In this report, L1 is also shown to induce and maintain a motile and invasive phenotype by promoting gene transcription. In the presence of serum or platelet-derived growth factor, L1 promotes heightened and sustained activation of the extracellular signal-regulated kinase pathway. Activation of this pathway then induces the expression of motility- and invasion-associated gene products, including the beta(3)-integrin subunit, small GTPases, and the cysteine proteases cathepsin-L and -B. Induction of integrin alpha(v)beta(3) and rac-1 is shown to contribute directly to L1-dependent haptotaxis, whereas induction of cathepsins-L and -B promotes matrix invasion. This study provides a novel translational mechanism to account for the association between L1 expression and motile processes involved in metastasis and development.

Modulation of prostate cancer growth in bone microenvironments

Bone remains one of the major sites, and most lethal host organs, for prostate cancer metastasis. Prostate cell spread and establishment in bone depends on multiple reciprocal modifications of bone stromal and epithelial cancer cell behaviors. This review focuses on recent advances in the characterization of cell-cell and cell-matrix interplay, effects on cell growth, adhesion and invasion, and several therapeutic possibilities for co-targeting prostate cancer cells and bone stroma. We address the topic from three main perspectives: (1) the normal and aging bone stromal environment, (2) the "reactive" bone stromal environment, and (3) the cancerous prostate epithelial cells themselves. First, normal, and especially aging, bones provide uniquely rich and "fertile soil" for roaming cancer cells. The interactions between prostate cancer cells and insoluble extracellular matrices, soluble growth factors, and/or sex steroid hormones trigger bone remodeling, through increased osteoclastogenesis and furthur matrix metalloproteinase activity. Second, after cancer cell arrival and establishment in the bone, host stromal cells respond, becoming "reactive" in a process again involving extracellular matrix remodeling, together with growth factor and steroid receptor signaling this process ultimately enhances cancer cell migration, stromal transdifferentiation, and invasion of the cancer tissues by stromal, inflammatory, and immune-responsive cells. Third, prostate cancer cells also respond to supportive bone microenvironments, where soluble and matrix-associated molecules affect cancer cell growth and gene expression, especially altering cancer cell surface receptor and integrin-mediated cell signaling. We discuss both integrin cell-matrix and gap junctional cell-cell communication between cancer cells and their microenvironments during prostate cancer progression.

L1 adhesion molecule (CD 171) in development and progression of human malignant melanoma

The L1 adhesion molecule (CD171) plays an important role in axon guidance and cell migration in the nervous system. In the human, L1 is expressed on tumors derived from neurocrest and on certain carcinomas. We have analyzed immunohistochemically L1 expression on paraffin embedded specimens of acquired melanocytic nevi, primary cutaneous melanomas, and cutaneous and lymph node metastases of malignant melanomas. We found an increase in L1 immunoreactivity in malignant melanomas and metastases of malignant melanomas as compared to acquired melanocytic nevi that was statistically significant (P<0.05). Additionally, a correlation of L1 immunoreactivity with histological data of prognostic value such as Clark level and the expression of alphav-integrins was found. We detected soluble L1 in the conditioned medium of cultivated melanoma cells but only in 1/40 serum samples from a panel of melanoma patients representing various stages of disease. Our findings suggest that the presence of L1 might contribute to tumor progression by promoting cell adhesion and migration.

Overexpression of the cell adhesion molecule L1 is associated with metastasis in cutaneous malignant melanoma

Modulation of cell adhesion molecule expression plays a key role in melanoma metastasis. In particular, the expression of the cell adhesion molecule L1 has been associated with the metastatic phenotype in a murine model of malignant melanoma. However, no such association between L1 expression and metastasis has been investigated in a clinical study. Therefore, L1 expression was determined immunohistochemically in 100 cases of malignant melanoma and correlated with metastasis in a 10-year retrospective study. Furthermore, nine distant metastases and five sentinel lymph node metastases were analysed for their L1 expression. Additionally, the expression of alpha2,3 sialic acid residues, which are recognised by the siglec domain of L1, was determined by Maackia amurensis agglutinin (MAA) lectin histochemistry. The log-rank test between Kaplan-Meier curves revealed a positive association between L1 expression and metastasis (P<0.0001) and multivariate Cox regression analysis adjusted for tumour thickness, ulceration and mitotic rate confirmed the prognostic power of L1 in malignant melanoma. As alpha2,3 sialic acid residues were absent in melanoma cells, homotypic adhesion between melanoma cells via their siglec domain can be excluded, suggesting a different adhesive function of L1 during melanoma metastasis. The functional role of L1 was further stressed by the fact that its expression was preserved in metastatic lesions.

The neural cell adhesion molecule L1 potentiates integrin-dependent cell migration to extracellular matrix proteins

The L1 adhesion molecule regulates axon growth and is mutated in the X-linked mental retardation syndrome CRASH (acronym for corpus callosum agenesis, retardation, aphasia, spastic paraplegia, hydrocephalus). A novel role for L1 as a potentiator of neuronal cell migration to extracellular matrix proteins through beta1 integrins and intracellular signaling to mitogen-activated protein (MAP) kinase was identified. L1 potentiated haptotactic migration of B35 neuroblastoma cells toward fibronectin, vitronectin, and laminin through the signaling intermediates c-Src, phosphatidylinositol-3 kinase, and MAP kinase. L1 potentiated migration toward fibronectin through alpha5beta1 integrin in human embryonic kidney 293 cells and depended on determinants of L1 endocytosis: dynamin I, c-Src, and the AP2/clathrin binding site (Arg-Ser-Leu-Glu) in the neuronal splice form of L1. L1 clustering on the cell surface enhanced the internalization of activated beta1 integrins and L1 into distinct endocytic vesicles. L1-potentiated migration, enhancement of beta1 integrin endocytosis, and activation of MAP kinase were coordinately inhibited by mutation of an RGD sequence in the sixth immunoglobulin-like domain of L1. Moreover, three CRASH mutations in the L1 cytoplasmic domain (1194L, S1224L, Y1229H), two of which interfere with ankyrin association, inhibited L1-potentiated migration and MAP kinase activation. Function-blocking antibodies to L1 and beta1 integrin retarded the migration of 5-bromo-2'-deoxyuridine-labeled mouse cerebellar granule cells in slice cultures, underscoring the potential physiological relevance of these findings. These studies suggest that L1 functionally interacts with beta1 integrins to potentiate neuronal migration toward extracellular matrix proteins through endocytosis and MAP kinase signaling, and that impairment of this function by L1 cytoplasmic domain mutations may contribute to neurological deficits in CRASH.

Ectodomain shedding of L1 adhesion molecule promotes cell migration by autocrine binding to integrins

The L1 adhesion molecule plays an important role in axon guidance and cell migration in the nervous system. L1 is also expressed by many human carcinomas. In addition to cell surface expression, the L1 ectodomain can be released by a metalloproteinase, but the biological function of this process is unknown. Here we demonstrate that membrane-proximal cleavage of L1 can be detected in tumors and in the developing mouse brain. The shedding of L1 involved a disintegrin and metalloproteinase (ADAM)10, as transfection with dominant-negative ADAM10 completely abolishes L1 release. L1-transfected CHO cells (L1-CHO) showed enhanced haptotactic migration on fibronectin and laminin, which was blocked by antibodies to alpha v beta 5 and L1. Migration of L1-CHO cells, but not the basal migration of CHO cells, was blocked by a metalloproteinase inhibitor, indicating a role for L1 shedding in the migration process. CHO and metalloproteinase-inhibited L1-CHO cells were stimulated to migrate by soluble L1-Fc protein. The induction of migration was blocked by alpha v beta 5-specific antibodies and required Arg-Gly-Asp sites in L1. A 150-kD L1 fragment released by plasmin could also stimulate CHO cell migration. We propose that ectodomain-released L1 promotes migration by autocrine/paracrine stimulation via alpha v beta 5. This regulatory loop could be relevant for migratory processes under physiological and pathophysiological conditions.

Involvement of integrin alpha(v)beta(3) and cell adhesion molecule L1 in transendothelial migration of melanoma cells

Tumor metastasis involves many stage-specific adhesive interactions. The expression of several cell adhesion molecules, notably the integrin alpha(v)beta(3), has been associated with the metastatic potential of tumor cells. In this study, we used a novel in vitro assay to examine the role of alpha(v)beta(3) in the transmigration of melanoma cells through a monolayer of human lung microvascular endothelial cells. Confocal microscopy revealed the presence of the integrin alpha(v)beta(3) on melanoma membrane protrusions and pseudopods penetrating the endothelial junction. alpha(v)beta(3) was also enriched in heterotypic contacts between endothelial cells and melanoma cells. Transendothelial migration of melanoma cells was inhibited by either a cyclic Arg-Gly-Asp peptide or the anti-alpha(v)beta(3) monoclonal antibody LM609. Although both platelet endothelial cell adhesion molecule-1 and L1 are known to bind integrin alpha(v)beta(3), only L1 serves as a potential ligand for alpha(v)beta(3) during melanoma transendothelial migration. Also, polyclonal antibodies against L1 partially inhibited the transendothelial migration of melanoma cells. However, addition of both L1 and alpha(v)beta(3) antibodies did not show additive effects, suggesting that they are components of the same adhesion system. Together, the data suggest that interactions between the integrin alpha(v)beta(3) on melanoma cells and L1 on endothelial cells play an important role in the transendothelial migration of melanoma cells.

Expression of neural cell adhesion molecules (polysialylated form of neural cell adhesion molecule and L1-cell adhesion molecule) on resected small cell lung cancer specimens: in relation to proliferation state

BACKGROUND AND OBJECTIVES

Alteration of homotypic cell-cell adhesion has been suggested to play an important role in tumor progression. The present study examined the relationship between neural cell adhesion molecules and state of proliferation of small cell lung cancer (SCLC) cells.

METHODS

Seventeen surgically resected specimens of SCLC were immunohistochemically examined, by using monoclonal antibodies against neural cell adhesion molecule (NCAM) and its polysialic acid side chains, and L1 cell adhesion molecule (L1-CAM). Ki-67 labeling indices were also determined immunohistochemically.

RESULTS

All patients were positive for L1-CAM. Fifteen patients (88.2%) were positive for NCAM. Among the fifteen patients, nine (60.0%) were positive for NCAM PSA side chain. The probability of survival of the NCAM without PSA side chain group was significantly higher than that of the NCAM with PSA side chain group (log-rank test; P = 0.500).

CONCLUSIONS

The expression of NCAM with PSA side chains might be a prognostic factor and NCAM a marker for SCLC. L1-CAM may be synthesized independent of state of proliferation of individual tumor cell and may affect clinical feature of SCLC.

Plasmin-sensitive dibasic sequences in the third fibronectin-like domain of L1-cell adhesion molecule (CAM) facilitate homomultimerization and concomitant integrin recruitment

L1 is a multidomain transmembrane neural recognition molecule essential for neurohistogenesis. While moieties in the immunoglobulin-like domains of L1 have been implicated in both heterophilic and homophilic binding, the function of the fibronectin (FN)-like repeats remains largely unresolved. Here, we demonstrate that the third FN-like repeat of L1 (FN3) spontaneously homomultimerizes to form trimeric and higher order complexes. Remarkably, these complexes support direct RGD-independent interactions with several integrins, including alpha(v)beta(3) and alpha(5)beta(1). A pep- tide derived from the putative C-C' loop of FN3 (GSQRKHSKRHIHKDHV(852)) also forms trimeric complexes and supports alpha(v)beta(3) and alpha(5)beta(1) binding. Substitution of the dibasic RK(841) and KR(845) sequences within this peptide or the FN3 domain limited multimerization and abrogated integrin binding. Evidence is presented that the multimerization of, and integrin binding to, the FN3 domain is regulated both by conformational constraints imposed by other domains and by plasmin- mediated cleavage within the sequence RK( downward arrow)HSK( downward arrow)RH(846). The integrin alpha(9)beta(1), which also recognizes the FN3 domain, colocalizes with L1 in a manner restricted to sites of cell-cell contact. We propose that distal receptor ligation events at the cell-cell interface may induce a conformational change within the L1 ectodomain that culminates in receptor multimerization and integrin recruitment via interaction with the FN3 domain.

A potential role for the plasmin(ogen) system in the posttranslational cleavage of the neural cell adhesion molecule L1

L1 is a neural recognition molecule that promotes neural developmental and regenerative processes. Posttranslational cleavage of L1 is believed to be important for regulating its function in vivo, but little is known of the proteolytic systems responsible. In this study we present evidence that plasmin can regulate both L1 expression and function. The addition of plasmin to cell lines results in a dose-dependent loss of surface L1 expression, with the simultaneous appearance of soluble L1 species. The addition of plasminogen to primary neurons and melanoma cells also resulted in the generation of plasmin and the concomitant release of L1. One product of plasmin-mediated cleavage is an amino-terminal fragment of approximately 140 kDa that has been previously described as a natural posttranslational cleavage product in vivo. This fragment was confirmed to result from cleavage at two sites in the middle of the third fibronectin-like domain of L1. Cleavage at a further site, proximal to the transmembrane domain of L1, was also observed at higher plasmin concentrations. Plasmin was further confirmed to abrogate homophilic L1 interactions required for cellular aggregation. Based on these findings we propose that plasmin is likely to be an important regulator of L1-mediated processes including those documented in the nervous system.

Lymphovascular and neural invasion in low-lying rectal carcinoma

We have previously demonstrated that lymphovascular infiltration was correlated with an increased risk for developing lymph node metastasis in rectal adenocarcinomas confined within the submucosal layer. In another study, lymphovascular infiltration was also correlated with poor prognosis for patients with advanced rectal cancers. Considerations that low rectal tumors have an increased risk to develop recurrence and neural invasion have been recently implicated with a more localized pattern of tumor spread. We therefore assessed the lymphovascular and neural invasion in 65 specimens from patients with low rectal cancers who underwent curative operation to determine its implications in the treatment and prognosis. Lymphovascular invasion was noted in 60%, and neural invasion was found in 27% of the cases. Five-year survival rates (Kaplan-Meier method) were significantly decreased in patients with lymphovascular invasion (31 vs. 67%; p < 0.01) or neural invasion (30 vs. 58%; p < 0.01). Neither lymphovascular nor neural invasion was noted in Dukes' stage A tumors. There was no recurrence or distant metastasis in these patients. However, lymphovascular and neural invasion increased with tumor stage. Local recurrence and distant metastasis occurred respectively in three and four, and five and five patients with Dukes' B and C tumors, respectively. Both Dukes' B and C cases with local recurrence had a higher incidence of neural invasion as compared with the disease-free group. These results suggest that postoperative assessment of venous and neural invasion may provide valuable information to better determine which patients with low rectal cancers would benefit from adjuvant treatment.

Expression of highly polysialylated neural cell adhesion molecule in pancreatic cancer neural invasive lesion

Neurotropism of pancreatic cancer is one of the hypotheses explaining neural invasion, which is one of the characteristics of pancreatic cancer. In these studies, we immunohistochemically examined neural cell adhesion molecules (NCAM), homophilic adhesion molecules expressed on the nerve cells, as a factor of neurotropism, in 15 pancreatic cancer operatively obtained, especially in neural invasive lesions. We also investigated the role of polysialic acid (PSA), which is attached to NCAM and related to the malignant potential of cancers. NCAM was detected in 66.7% of pancreatic cancers, and in all 9 cases with massive perineural invasion. In neural invasive lesions, however, there were perineurium and endoneurium, which do not express NCAM, between the cancer and nerve cells. PSA was also detected in the pancreatic cancers expressing NCAM. Moreover, PSA expression was stronger in the perineural invasive lesions than in the main tumor and was related to the cancer cell proliferation investigated by Ki-67 staining. It is unlikely therefore, that NCAM plays an important role in neurotropism. However, the NCAM expressed on the pancreatic cancer was attached to PSA, which itself plays an important role in the malignant potential of this disease.

Cell-cell interactions during transendothelial migration of tumor cells

A key event in cancer metastasis is the transendothelial migration of tumor cells. This process involves multiple adhesive interactions between tumor cells and the endothelium. After adhering to the surface of endothelial cells, tumor cells must penetrate the endothelial junction, which contains high concentrations of the cell adhesion molecules VE-cadherin and PECAM-1. Studies using an in vitro model system, consisting of melanoma cells which are seeded onto a monolayer of endothelial cells cultured on Matrigel, have revealed reorganization of the cytoskeleton and dynamic changes in the cell shape of both tumor and endothelial cells. The initial stages of transmigration are characterized by numerous membrane blebs protruding from the basolateral surfaces of the melanoma cells. Contact regions also show an abundance of microfilaments arising from the underlying endothelial cells. These adhesive interactions lead to the redistribution of both VE-cadherin and PECAM-1 and, consequently, a localized dissolution of the endothelial junction. The penetration of the endothelial junction is initiated by melanoma pseudopods. Despite the disappearance of VE-cadherin from the retracting endothelial junction, heterotypic contacts between the tumor cell and its surrounding endothelial cells show a high concentration of pan-cadherin staining, suggesting that transmigration of melanoma cells might yet be facilitated by interactions with another member of the cadherin family. Upon adhesion to the Matrigel, melanoma cells begin to spread and invade the matrix material, while the endothelial cells extend processes over the melanoma cells to reform the monolayer. Interestingly, the leading margins of these endothelial processes contain a high concentration ofN-cadherin. VE-cadherin and PECAM-1 reappear only when the advancing endothelial processes meet to reform the endothelial junction. Together, these observations suggest that endothelial cells actively participate in the transmigration of tumor cells and specific cadherins are involved in different steps of this complex process.

A single immunoglobulin-like domain of the human neural cell adhesion molecule L1 supports adhesion by multiple vascular and platelet integrins

The neural cell adhesion molecule L1 has been shown to function as a homophilic ligand in a variety of dynamic neurological processes. Here we demonstrate that the sixth immunoglobulin-like domain of human L1 (L1-Ig6) can function as a heterophilic ligand for multiple members of the integrin superfamily including alphavbeta3, alphavbeta1, alpha5beta1, and alphaIIbbeta3. The interaction between L1-Ig6 and alphaIIbbeta3 was found to support the rapid attachment of activated human platelets, whereas a corresponding interaction with alphavbeta3 and alphavbeta1 supported the adhesion of umbilical vein endothelial cells. Mutation of the single Arg-Gly-Asp (RGD) motif in human L1-Ig6 effectively abrogated binding by the aforementioned integrins. A L1 peptide containing this RGD motif and corresponding flanking amino acids (PSITWRGDGRDLQEL) effectively blocked L1 integrin interactions and, as an immobilized ligand, supported adhesion via alphavbeta3, alphavbeta1, alpha5beta1, and alphaIIbbeta3. Whereas beta3 integrin binding to L1-Ig6 was evident in the presence of either Ca2+, Mg2+, or Mn2+, a corresponding interaction with the beta1 integrins was only observed in the presence of Mn2+. Furthermore, such Mn2+-dependent binding by alpha5beta1 and alphavbeta1 was significantly inhibited by exogenous Ca2+. Our findings suggest that physiological levels of calcium will impose a hierarchy of integrin binding to L1 such that alphavbeta3 or active alphaIIbbeta3 > alphavbeta1 > alpha5beta1. Given that L1 can interact with multiple vascular or platelet integrins it is significant that we also present evidence for de novo L1 expression on blood vessels associated with certain neoplastic or inflammatory diseases. Together these findings suggest an expanded and novel role for L1 in vascular and thrombogenic processes.

Effect of NCAM-transfection on growth and invasion of a human cancer cell line

A cDNA encoding the human transmembrane 140 kDa isoform of the neural cell adhesion molecule (NCAM) was transfected into the highly invasive MDA-MB-231 human breast cancer cell line. Transfectants with a homogeneous expression of NCAM showed a restricted capacity for penetration of an artificial basement membrane. However, when injected into nude mice, both control and NCAM-expressing cell lines produced equally invasive tumors. Tumors generated from NCAM-transfected cells were heterogeneous, containing NCAM-positive as well as NCAM-negative areas, indicating the existence of host factors capable of modulating NCAM expression in vivo. In nude mice, NCAM-transfected cells developed tumors with longer latency periods and slower growth rates than tumors induced by NCAM-negative control cells, implying that NCAM may be involved not only in adhesive and motile behavior of tumor cells but also in their growth regulation. There was no indication of differences in cell proliferative characteristics between the different NCAM-transfected and the control transfected cells as determined by flow cytometric DNA analysis, suggesting an increased cell loss as the reason for decreased in vivo growth rate of the NCAM-transfected cells. The fact that NCAM expression influences growth regulation attributes a pivotal role to this cell adhesion molecule during ontogenesis and tumor development.

L1 adhesion molecule on human lymphocytes and monocytes: expression and involvement in binding to alpha v beta 3 integrin

The L1 adhesion molecule is a member of the immunoglobulin (Ig) superfamily initially identified in the nervous system which contains six Ig-like domains. Besides the known L1-L1 homotypic interaction, L1 was recently shown to bind to very late antigen (VLA)-5 in the mouse and alpha v beta 3 in the human. The sixth Ig domain is critical for this function. We now demonstrate that human CD4+ peripheral blood T lymphocytes, monocytes and B lymphocytes, but not CD8+ T lymphocytes, express L1. When compared to the expression of CD31, another ligand for alpha v beta 3 on T lymphocytes, only a small proportion of cells were CD31+L1+ double positive. L1 was also detected on the surface of human monocytic and lymphoid tumor lines and was shown to have a molecular mass of approximately 220 kDa, similar to the molecule present on neuroblastoma cells. The function of the sixth Ig domain of human L1 as an integrin ligand was also investigated. Using an RGD-containing peptide derived from the sixth Ig domain as well as a fusion protein of the sixth Ig domain of L1 and the Fc portion of human IgG1 (6.L1-Fc), we demonstrated the binding of human MED-B1 (alpha v beta 3hi, alpha 5 beta 1lo) tumor cells and this binding was blocked by alpha v-specific mAb. In contrast, human Nalm-6 cells (alpha v beta 3lo, alpha 5 beta 1hi) did not bind to the 6.L1-Fc fusion protein. MED-B1 cells could also be stained with the 6.L1-Fc fusion protein. Our results suggest that human L1 binds predominantly to alpha v beta 3 and that its presence on leukocytes could be important for adhesion and migration.

Human neural cell adhesion molecule L1 and rat homologue NILE are ligands for integrin alpha v beta 3

Integrin alpha v beta 3 is distinct in its capacity to recognize the sequence Arg-Gly-Asp (RGD) in many extra-cellular matrix (ECM) components. Here, we demonstrate that in addition to the recognition of ECM components, alpha v beta 3 can interact with the neural cell adhesion molecule L1-CAM; a member of the immunoglobulin superfamily (IgSF). M21 melanoma cells displayed significant Ca(++)-dependent adhesion and spreading on immunopurified rat L1 (NILE). This adhesion was found to be dependent on the expression of the alpha v-integrin subunit and could be significantly inhibited by an antibody to the alpha v beta 3 heterodimer. M21 cells also displayed some alpha v beta 3-dependent adhesion and spreading on immunopurified human L1. Ligation between this ligand and alpha v beta 3 was also observed to promote significant haptotactic cell migration. To map the site of alpha v beta 3 ligation we used recombinant L1 fragments comprising the entire extracellular domain of human L1. Significant alpha v beta 3-dependent adhesion and spreading was evident on a L1 fragment containing Ig-like domains 4, 5, and 6. Importantly, mutation of an RGD sequence present in the sixth Ig-like domain of L1 abrogated M21 cell adhesion. We conclude that alpha v beta 3-dependent recognition of human L1 is dependent on ligation of this RGD site. Despite high levels of L1 expression the M21 melanoma cells did not display significant adhesion via a homophilic L1-L1 interaction. These data suggest that M21 melanoma cells recognize and adhere to L1 through a mechanism that is primarily heterophilic and integrin dependent. Finally, we present evidence that melanoma cells can shed and deposit L1 in occluding ECM. In this regard, alpha v beta 3 may recognize L1 in a cell-cell or cell-substrate interaction.

Frequent loss of heterozygosity at the deleted in colorectal carcinoma gene locus and its association with histologic phenotypes in breast carcinoma

Loss of heterozygosity (LOH) at the deleted in colorectal carcinoma gene (DCC), a tumour suppressor gene that encodes a protein with high homology to the neural cell adhesion molecule, was investigated in 42 surgical specimens of primary breast carcinoma. LOH was analysed in breast carcinoma by amplifying the DNA, spanning a variable number of tandem repeats site and a restriction fragment length polymorphism site within DCC, using the polymerase chain reaction (PCR). Cell sorting was used to enrich carcinoma cells. The expression of the DCC gene was also investigated using a reverse transcription-PCR method followed by Southern blot hybridization. LOH at the DCC locus was detected in 15 (51.7%) of 29 informative cases and 10 of 13 cases having DCC-LOH showed distinct reduction or loss of DCC expression. The DCC-LOH was closely associated with certain histological phenotypes: DCC-LOH was more frequent in scirrhous carcinomas than in solid-tubular ones (P < 0.05), and was also more frequent in carcinomas with infiltration into fat tissue over the mammary gland than in those without infiltration (P < 0.05). DCC-LOH was detected in invasive lobular carcinomas (2/2), but in none of the noninvasive ductal carcinomas (0/2). These observations suggest that malignant histological phenotypes are associated with DCC-LOH.

Increasing N-CAM-mediated cell-cell adhesion does not reduce invasion of RSV-transformed WC5 rat cerebellar cells

The WC5 rat cerebellar cell line, infected with a Rous sarcoma virus (RSV) that is temperature-sensitive for pp60v-src transformation, expresses high levels of the neural cell adhesion molecule, N-CAM, when grown at the non-permissive temperature for pp60v-src activity. At the permissive temperature, N-CAM expression is 4- to 10-fold reduced and the cells aggregate poorly. To evaluate the effects of variations in N-CAM expression, we compared the invasive ability of transformed WC5 cells that express low levels of N-CAM with transformed cells in which N-CAM-mediated adhesion was restored. WC5 cells were transfected with expression vectors containing cDNAs encoding the 120 or 180 kDa forms of chicken N-CAM linked to constitutive promoters. Several permanently transfected lines that expressed chicken N-CAM at the cell surface were isolated. These cell lines showed enhanced aggregation at the permissive temperature relative to untransfected WC5 cells or cells transfected with control constructs. By comparing the ability of control and transfected WC5 cells to invade reconstituted extracellular matrix, we tested the effect of variations in N-CAM-mediated adhesion on invasion. Clones that expressed high levels of N-CAM showed invasion rates that were similar to control cells, indicating that increasing N-CAM-mediated adhesion does not inhibit the invasiveness of RSV-transformed WC5 cells.

Migration of human melanoma cells on hyaluronate is related to CD44 expression

Phenotypic and functional aspects of melanoma-hyaluronate interactions were investigated by studying the expression of CD44, cell migration, and transmembrane penetration of human melanoma cell lines on hyaluronate-coated substrates. Expression of CD44 was tested by flow cytometry on seven human melanoma cell lines. Strong reactivity with anti-CD44 monoclonal antibody was observed in four of seven of the cell lines. Migration studies of CD44(+) cell lines on hyaluronic acid- and chondroitin-6-sulfate-coated substrates, using time-lapse video-microscopy, showed a dramatic dose-dependent increase in migration rate on hyaluronate but not on chondroitin-6-sulfate. Moreover, CD44(-) cell lines showed no modification in migration rate on either substrate. Addition of soluble hyaluronate produced a dose-dependent inhibition of acceleration of CD44(+)cells on hyaluronate-coated substrates, whereas addition of chondroitin-6-sulfate had no effect. Migration inhibition experiments with soluble CD44 (CD44 receptor globulin) also showed specific blocking of the migration of CD44(+) cells on hyaluronate. Haptotactic invasion was increased in CD44(+) cell lines through hyaluronate-coated polycarbonate membranes, whereas no change was detected on chondroitin-6-sulfate-coated membranes. CD44(-) cell lines showed no response to either type of coating. In the melanoma cell lines tested, the expression of CD44 correlated with in vitro migration and invasiveness on hyaluronate substrates. Taken together, our data are consistent with the suggestion that CD44 may play a role in stimulating in vivo aggressiveness of tumors through hyaluronate-rich stroma.

Neural cell adhesion molecule distribution in soft tissue tumors

The distribution of the neural cell adhesion molecule (N-CAM; CD56) was studied immunohistochemically in acetone-fixed frozen sections of 83 soft tissue tumors and selected normal mesenchymal tissue using Leu-19 monoclonal antibody and avidin-biotin peroxidase immunostaining. Positive N-CAM immunostaining was found in gastrointestinal and uterine cells but not in vascular smooth muscle cells. Normal skeletal muscle was negative, but atrophic muscle fibers within tumors were positive. Strong and consistent immunoreactivity was seen in nerves, pheochromocytoma, malignant schwannoma, and spindle cells, but not in epithelial-like cells of synovial sarcoma, hemangiopericytoma, benign leiomyoma, and rhabdomyosarcoma. Variable staining was seen in benign schwannoma and malignant fibrous histiocytoma. Limited, usually focal N-CAM immunoreactivity was seen in desmoid tumor, dermatofibrosarcoma, and leiomyosarcoma. Although the N-CAM is consistently seen in neural tumors, it is not cell lineage specific. Changes on malignant transformation (comparing corresponding benign and malignant lesions) do not show any consistent pattern. Rather, there is neoexpression of the N-CAM in rhabdomyosarcoma, whereas there is loss of the N-CAM in leiomyosarcoma. Immunohistochemistry of the N-CAM can be a useful adjunct for characterization of soft tissue tumors, and its possible correlation with tumor behavior has to be examined in further studies.

Platelet endothelial cell adhesion molecule, PECAM-1, modulates cell migration

Cell migration is an important process in such phenomena as growth, development, and wound healing. The control of cell migration is orchestrated in part by cell surface adhesion molecules. These molecules fall into two major categories: those that bind to extracellular matrix and those that bind to adjacent cells. Here, we report on the role of a cell-cell adhesion molecule, platelet-endothelial cell adhesion molecule-1, (PECAM-1), a member of the lg superfamily, in the modulation of cell migration and cell-cell adhesion. PECAM-1 is a 120-130 kDa integral membrane protein that resides on endothelial cells and localizes at sites of cell-cell contact. Since endothelial cells express PECAM-1 constitutively, we studied the effects of PECAM-1 on cell-cell adhesion and migration in a null-cell population. Specifically, we transfected NIH/3T3 cells with the full length PECAM-1 molecule (two independent clones). Transfected cells containing only the neomycin resistance gene, cells expressing a construct coding for the extracellular domain of the molecule, and cells expressing the neu oncogene were used as controls. The PECAM-1 transfectants appeared smaller and more polygonal and tended to grow in clusters. Indirect immunofluorescence of PECAM-1 transfectants showed peripheral staining at sites of cell-cell contact, while the extracellular domain transfectants and the control cells did not. In two quantitative migration assays, the full-length PECAM-1 transfectants migrated more slowly than control cells. Thus, PECAM-1 transfected into a null cell appears to localize to sites of cell-cell contact, promote cell-cell adhesion, and diminish the rate of migration. These findings suggest a role for this cell-cell adhesion molecule in the process of endothelial cell migration.

Alternative splicing of neural-cell-adhesion molecule mRNA in human small-cell lung-cancer cell line H69

The neural-cell-adhesion molecule (NCAM) is expressed in all small-cell lung cancers (SCLC) and in approximately 20% of non-small-cell lung tumors (non-SCLC). These NCAM-positive lung tumors have a poor prognosis compared with NCAM-negative tumors. Multiple NCAM protein isoforms are expressed from a single-copy gene as a result of alternative splicing and/or post-translational modifications. Therefore, we studied the NCAM isoforms expressed in a human small-cell lung-cancer cell line, H69. NCAM mRNA transcripts of 7.2, 6.7, 4.3 and 4.0 were detected in these cells on Northern blots. Since the various NCAM isoforms may have different biological properties, we performed a more precise examination of NCAM mRNAs, using polymerase chain reactions (PCR) with primers flanking the various NCAM exon boundaries. The shortest alternatively spliced sequence that we found was the trinucleotide AAG located between exon 12 and 13 in the so-called hinge region of the NCAM protein. This AAG trinucleotide was present in the majority of the NCAM mRNAs. A second alternatively spliced 30 nt-exon VASE (immunoglobulin-variable domain-like alternatively spliced exon) was present in all NCAM transcript isoforms at the exon 7/exon 8 junction. VASE resulted in the insertion of 10 amino acids into the 4th immunoglobulin-like loop of the NCAM protein. Within the limits of the PCR methodology, no evidence for the presence of mRNA containing exon 15, encoding the glycosyl-phosphatidylinositol-linked (GPI-linked) NCAM isoform in H69 cells was obtained. Considering that H69 cells express 2 major NCAM protein classes (NCAM-180 and NCAM-140), and that the VASE and AAG alternative mRNA splice variants result in minor differences in protein sizes, at least 8 polypeptide isoforms of NCAM might be expressed in H69 cells that contribute to the binding interactions of NCAM.

Expression and function of the neural cell adhesion molecule L1 in mouse leukocytes

The neural cell adhesion molecule L1 is a cell surface glycoprotein of the immunoglobulin superfamily which mediates adhesion between neural cells. The possibility that similar cell-cell recognition mechanisms may be shared by the nervous and immune systems prompted us to study the expression and function of L1 in cells of the hematopoietic system. Immunofluorescence analysis using monoclonal L1 antibody revealed that the molecule is expressed in the bone marrow, spleen, and thymus of the mouse. This observation was confirmed by amplifying cDNA derived from these organs by the polymerase chain reaction with L1-specific oligonucleotide primers. Two-color fluorescence analysis indicated that bone marrow lymphoid and granulocyte precursor cells express low and high levels of L1, respectively. In the thymus L1 is primarily expressed by mature cells that have a strong expression of CD3 and in the spleen both B cells and T cells express L1. The possible function of L1 in lymphoid cells was studied using subcloned ESb-MP lymphoma cells having high or low densities of L1 on the cell surface as well as activated splenic B lymphoblasts. Parental and subcloned ESb-MP cells that strongly expressed L1 could form homotypic aggregates in the presence of low Ca2+ levels, whereas subcloned ESb-MP cells with a weak expression of L1 did not aggregate, suggesting that L1 mediates the Ca(2+)-independent aggregation of the parental ESb-MP cells. Furthermore, the aggregation of activated B lymphoblasts under physiological concentrations of Ca2+ and Mg2+ was inhibited by 30% in the presence of Fab fragments of polyclonal L1 antibodies, implying that L1 also mediates adhesion among normal lymphoid cells. A possible role of L1 on lymphocytes in stimulating the innervation of lymphoid organs is discussed.