Autocrine Motility Factor Receptor Research Articles

A duplicated pair of Arabidopsis RING‐finger E3 ligases contribute to the RPM1‐ and RPS2‐mediated hypersensitive response

The Arabidopsis RPM1 protein confers resistance to disease caused by Pseudomonas syringae strains delivering either the AvrRpm1 or AvrB type III effector proteins into host cells. We characterized two closely related RPM1-interacting proteins, RIN2 and RIN3. RIN2 and RIN3 encode RING-finger type ubiquitin ligases with six apparent transmembrane domains and an ubiquitin-binding CUE domain. RIN2 and RIN3 are orthologs of the mammalian autocrine motility factor receptor, a cytokine receptor localized in both plasma membrane caveolae and the endoplasmic reticulum. RIN2 is predominantly localized to the plasma membrane, as are RPM1 and RPS2. The C-terminal regions of RIN2 and RIN3, including the CUE domain, interact strongly with an RPM1 N-terminal fragment and weakly with a similar domain from the Arabidopsis RPS2 protein. RIN2 and RIN3 can dimerize through their C-terminal regions. The RING-finger domains of RIN2 and RIN3 encode ubiquitin ligases. Inoculation with P. syringae DC3000(avrRpm1) or P. syringae DC3000(avrRpt2) induces differential decreases of RIN2 mobility in SDS-PAGE and disappearance of the majority of RIN2. A rin2 rin3 double mutant expresses diminished RPM1- and RPS2-dependent hypersensitive response (HR), but no alteration of pathogen growth. Thus, the RIN2/RIN3 RING E3 ligases apparently act on a substrate that regulates RPM1- and RPS2-dependent HR.

Autocrine Motility Factor Receptor Expression Implies an Unfavourable Prognosis in Resected Stage I Pulmonary Adenocarcinomas

Background : Pulmonary adenocarcinomas constitute a different histological subtype among the histological subtypes of non small cell lung carcinomas by showing comparably unfavourable rates of prognosis and different immunobiological features. Autonomous motility of tumour cells plays an important role in the regulation of local invasion and distant metastasis of tumour lesions which have great impact on overall survival. AMF (Autocrine motility factor) is a tumour secreted cytokine that stimulates motility during invasion and metastasis via its receptor, AMFR. We conducted an immunohistochemical study to investigate AMFR expression in pulmonary adenocarcinomas and its effect on survival.Material and methods : We assessed AMFR expression using a monoclonal antibody (3F3A) in a total of 32 surgical specimens with stage I pulmonary adenocarcinomas that underwent curative resection. We analyzed AMFR expression as a possible prognostic factor on survival and its correlations with clinicopathological features. Results : A total of 19 (59.3%) specimens showed AMFR expression. The 3-year survival rates of AMFR positive and AMFR negative patients were 47.3% and 84.6%, respectively, which was a significant difference (P = 0.0197). The univariate predictors of surgical outcome were AMFR expression (P = 0.032) and perineural invasion (P = 0.038). However, multivariate analysis revealed AMFR expression (P = 0.045) as the only independent prognostic factor. Conclusions : AMFR expression predicts an unfavourable surgical outcome in patients with stage I pulmonary adenocarcinomas.

Overexpression of autocrine motility factor in metastatic tumor cells: possible association with augmented expression of KIF3A and GDI-β

Autocrine motility factor (AMF), which is identical to phosphohexose isomerase (PHI)/glucose-6-phosphate isomerase (GPI) , a ubiquitous enzyme essential for glycolysis, neuroleukin (NLK), a neurotrophic growth factor, and maturation factor (MF) mediating the differentiation of human myeloid cells, enhances the motility and metastatic ability of tumor cells. AMF/PHI activity is elevated in the serum or urine in patients with malignant tumors. Here, we constructed an amf/phi/nlk/mf gene using adenovirus vector and transfected into two tumor cell lines. Overexpression of AMF/PHI/NLK/MF enhanced AMF secretion into the culture media in both tumor cell lines. However, upregulation of motility and metastatic ability was found only in metastatic fibrosarcoma cells expressing an AMF receptor, gp78, and was not found in gp78-undetectable osteosarcoma cells. Thus, not only serum AMF activity but also gp78-expression in tumor cells may be required for metastasis-related motility induction. With the use of microarray analyses, we detected two augmented genes, rho GDP dissociation inhibitor beta and kinesin motor 3A, as well as AMF itself. The RNA message and protein expression of these two molecules was confirmed to be upregulated, suggesting a possible association with AMF-induced signaling for cell motility and metastasis.

Overexpression of the Tumor Autocrine Motility Factor Receptor Gp78, a Ubiquitin Protein Ligase, Results in Increased Ubiquitinylation and Decreased Secretion of Apolipoprotein B100 in HepG2 Cells

Apolipoprotein B100 (apoB) is a large (520-kDa) complex secretory protein; its secretion is regulated posttranscriptionally by several degradation pathways. The best described of these degradative processes is co-translational ubiquitinylation and proteasomal degradation of nascent apoB, involving the 70- and 90-kDa heat shock proteins and the multiple components of the proteasomal pathway. Ubiquitinylation involves several proteins, including ligases called E3s, that coordinate the covalent binding of ubiquitin to target proteins. The recent discovery that tumor autocrine motility factor receptor, also known as gp78, is an endoplasmic reticulum (ER)-associated E3, raised the possibility that this E3 might be involved in the ER-associated degradation of nascent apoB. In a series of experiments in HepG2 cells, we demonstrated that overexpression of gp78 was sufficient for increased ubiquitinylation and proteasomal degradation of apoB, with reduced secretion of apoB-lipoproteins. This action of gp78 was specific: overexpression of the protein did not affect secretion of either albumin or apolipoprotein AI. Furthermore, overexpression of a cytosolic E3, Itch, had no effect on apoB secretion. Finally, using an in vitro translation system, we demonstrated that gp78 led to increased ubiquitinylation and proteasomal degradation of apoB48. Together, these results indicate that an ER-associated protein, gp78, is a bona fide E3 ligase in the apoB ER-associated degradation pathway.

Overexpression of autocrine motility factor receptor (AMFR) in NIH3T3 fibroblasts induces cell transformation.

Autocrine motility factor receptor (AMFR) is a cell surface glycoprotein of 78000 molecular weight (gp78), regulating cell motility signaling in vitro and metastasis in vivo. To test whether AMFR could be a common mediator of transformation and oncogenic itself, we transfected NIH3T3 fibroblast cells with expression vectors carrying the full-length cDNA for mouse AMFR and evaluated the effects of increased AMFR on transforming potential. The cells stably expressing high levels of AMFR as a result of transfection displayed a complete morphological change and acquired the ability to grow even in low serum. Furthermore, they were anchorage-independent for growth in soft agar and more motile in phagokinetic track assay. Interestingly, the enhanced expression of AMFR produced tumors in nude mice. Our findings provide a direct evidence that overexpression of the AMFR is associated with the acquisition of a transformation phenotype.

RING finger ubiquitin protein ligases: implications for tumorigenesis, metastasis and for molecular targets in cancer

Covalent modification of proteins with ubiquitin regulates almost all aspects of eukaryotic cellular function. Ubiquitin protein ligases (E3s) play central regulatory roles in that they provide substrate specificity to this process and therefore, represent attractive molecular targets for disease therapy. We summarize recent advances in our understanding of RING finger and RING finger-related E3s with emphasis on BRCA1 and the tumor autocrine motility factor receptor (gp78), as well as discuss the potential for components of the ubiquitin pathway for proteasomal degradation as molecular targets.

Autocrine motility factor secreted by tumor cells upregulates vascular endothelial growth factor receptor (Flt-1) expression in endothelial cells.

The autocrine motility factor (AMF) is known as a cytokine regulating tumor cells motility via AMF receptor (AMFR) and promotes their metastasis. Recently, AMFRs have been found on the surface of host cells and it was showed that AMF possibly affects them. The signaling of AMF-AMFR in the host endothelial cells induces expression of a vascular endothelial growth factor receptor (VEGFR) Flt-1 and AMFR feedback that is regulated at the transcriptional level. AMF-exposure stimulated the Flt-1 expression on human umbilical vein endothelial cells (HUVECs) surface and this AMF-treated cells exhibited high-responsibility against VEGF. The protein kinase C (PKC) and phosphatidylinositol 3 kinase (PI3K) play an important role in this signal transduction. The findings of our study suggest the possibility of "tumor AMF-->host AMFR-->PKC, PI3K-->-->VEGFR or AMFR-->angiogenesis, metastasis" as a new signal cross talk between the tumor and the host.

Inhibition Mechanism of Cytokine Activity of Human Autocrine Motility Factor Examined by Crystal Structure Analyses and Site-directed Mutagenesis Studies

Autocrine motility factor (AMF), a tumor-secreted cytokine, stimulates cell migration in vitro and metastasis in vivo. AMF is genetically identical with the extracellular cytokines neuroleukin (NLK) and maturation factor (MF) and, interestingly, the intracellular enzyme phosphohexose isomerase (PHI). The crystal structures of the inhibitor-free open form and the inhibitor (erythrose 4-phosphate, E4P, a strong inhibitor of AMF's cytokine activity)-bound closed form of human AMF have been determined at 1.9 Å and 2.4 Å resolution, respectively. Upon E4P binding, local conformation changes (open to closed) occur around the inhibitor-binding site. The E4P-bound structure shows that the location of the inhibitor (of cytokine activity) binding site of human AMF is very similar to those of the inhibitor (of enzymatic activity) binding sites of PHIs. The present study shows clearly that there is structural overlap of the regions responsible for the enzymatic and cytokine functions of AMF and PHI and suggests two scenarios for the inhibition mechanism of cytokine activity of AMF by the carbohydrate phosphate group. One likely scenario is that the compound could compete for AMF binding with the carbohydrate moiety of the AMF receptor (AMFR), which is a glycosylated seven-transmembrane helix protein. The other scenario is that the local conformation changes upon inhibitor binding may affect the AMF–AMFR interactions. To examine roles of the residues in the inhibitor-binding site, two mutant AMFs were prepared. Replacements of His389, which is hydrogen-bonded to the hydroxyl group of E4P by Phe, and Thr215, which is hydrogen-bonded to the phosphate group of E4P by Asp, result in mutant AMFs that are impaired in cytokine activity. These results suggest a role for these amino acids in recognition of a carbohydrate moiety of the AMFR. Since the E4P is one of the smallest compounds having AMF inhibitor activity, knowledge of the present crystal structure would provide an insight into the lead compound design of more effective AMF inhibitors.

Caveolin-1 Is a Negative Regulator of Caveolae-mediated Endocytosis to the Endoplasmic Reticulum

Caveolae are flask-shaped invaginations at the plasma membrane that constitute a subclass of detergent-resistant membrane domains enriched in cholesterol and sphingolipids and that express caveolin, a caveolar coat protein. Autocrine motility factor receptor (AMF-R) is stably localized to caveolae, and the cholesterol extracting reagent, methyl-beta-cyclodextrin, inhibits its internalization to the endoplasmic reticulum implicating caveolae in this distinct receptor-mediated endocytic pathway. Curiously, the rate of methyl-beta-cyclodextrin-sensitive endocytosis of AMF-R to the endoplasmic reticulum is increased in ras- and abl-transformed NIH-3T3 cells that express significantly reduced levels of caveolin and few caveolae. Overexpression of the dynamin K44A dominant negative mutant via an adenovirus expression system induces caveolar invaginations sensitive to methyl-beta-cyclodextrin extraction in the transformed cells without increasing caveolin expression. Dynamin K44A expression further inhibits AMF-R-mediated endocytosis to the endoplasmic reticulum in untransformed and transformed NIH-3T3 cells. Adenoviral expression of caveolin-1 also induces caveolae in the transformed NIH-3T3 cells and reduces AMF-R-mediated endocytosis to the endoplasmic reticulum to levels observed in untransformed NIH-3T3 cells. Cholesterol-rich detergent-resistant membrane domains or glycolipid rafts therefore invaginate independently of caveolin-1 expression to form endocytosis-competent caveolar vesicles via rapid dynamin-dependent detachment from the plasma membrane. Caveolin-1 stabilizes the plasma membrane association of caveolae and thereby acts as a negative regulator of the caveolae-mediated endocytosis of AMF-R to the endoplasmic reticulum.

Autocrine motility factor receptor gene expression and cell motility in lung cancer cell lines

The cell motility of tumor cells is an integral component of tumor invasion and metastasis. Autocrine motility factor (AMF) stimulates cell motility via a receptor (R)-mediated signal pathway. We studied the correlation between level of AMF-R gene expression by reverse transcription-polymerase chain reaction and cell motility by phagokinetic track assay with or without AMF in lung cancer cell lines. Lung cancer cell lines with higher AMF-R gene expression tended to have greater cell motility than those with lower AMF-R gene expression with or without AMF. Most of lung cancer cell lines showed significantly increased motility with the stimulation of AMF. We conclude that the presence of higher AMF-R gene expression and tumor cell motility via receptor in response to the stimulation of AMF could be an important aspect in the invasion and metastasis of lung cancer cell lines.

Regulation of cell motility via high and low affinity autocrine motility factor (AMF) receptor in human oral squamous carcinoma cells.

A tumour-secreted cytokine autocrine motility factor (AMF) induces in vivo invasion and metastasis, and in vitro tumour cell motility by a signal transduction through interaction with its cell surface receptor gp78. In this report, we investigated the characterization of a high-metastatic human oral squamous cell carcinoma (SCC) cell line LMF4 and low-metastatic HSC-3 in comparison with non-metastatic HSC-2 and HSC-4. Morphological and motility analyses revealed LMF4 cells to have the highest motile activity among those cells. However, LMF4 cells shared the similar features with HSC-3: high level secretion of AMF, enhancement of gp78 expression, co-expression of vimentin and cytokeratin, although LMF4 cells showed twice as high motile reactivity as HSC-3. The only difference was that LMF4 had twice as high amount of low-affinity receptor(s) as HSC-3, shown by Scatchard analysis.

The tumor autocrine motility factor receptor, gp78, is a ubiquitin protein ligase implicated in degradation from the endoplasmic reticulum

gp78, also known as the tumor autocrine motility factor receptor, is a transmembrane protein whose expression is correlated with tumor metastasis. We establish that gp78 is a RING finger-dependent ubiquitin protein ligase (E3) of the endoplasmic reticulum (ER). Consistent with this, gp78 specifically recruits MmUBC7, a ubiquitin-conjugating enzyme (E2) implicated in ER-associated degradation (ERAD), through a region distinct from the RING finger. gp78 can target itself for proteasomal degradation in a RING finger- and MmUBC7-dependent manner. Importantly, gp78 can also mediate degradation of CD3-delta, a well-characterized ERAD substrate. In contrast, gp78 lacking an intact RING finger or its multiple membrane-spanning domains stabilizes CD3-delta. gp78 has thus been found to be an example of a mammalian cellular E3 intrinsic to the ER, suggesting a potential link between ubiquitylation, ERAD, and metastasis.

Tumor Autocrine Motility Factor Is an Angiogenic Factor That Stimulates Endothelial Cell Motility

Autocrine motility factor (AMF) is a type of tumor-secreted cytokine which primarily stimulates tumor cell motility via receptor-mediated signaling pathways, and is thought to be connected to tumor progression and metastasis. Using in vivo models, we showed that critical neovascularization responded to a biological amount of AMF. This angiogenic activity was fixed by specific inhibitors against AMF. AMF stimulated in vitro motility of human umbilical vein endothelial cells (HUVECs), inducing the expression of cell surface AMF receptor localizing a single predominant perinuclear pattern closely correlated with its motile ability. AMF also elicited the formation of tube-like structures mimicking angiogenesis when HUVECs were grown in three-dimensional type I collagen gels. We further immunohistochemically detected AMF receptors on the surrounding sites of newborn microvessels. These findings suggest that AMF is a possible tumor progressive angiogenic factor which may act in a paracrine manner for the endothelial cells in the clinical neoplasm, and it will be a new target for antiangiogenic treatment.

Tumor Autocrine Motility Factor Is an Angiogenic Factor That Stimulates Endothelial Cell Motility

Autocrine motility factor (AMF) is a type of tumor-secreted cytokine that primarily stimulates tumor cell motility via receptor-mediated signaling pathways and is thought to be connected to tumor progression and metastasis. Using in vivo models, we showed that critical neovascularization responded to a biological amount of AMF. This angiogenic activity was fixed by specific inhibitors against AMF. AMF stimulated in vitro motility of human umbilical vein endothelial cells (HUVECs), inducing the expression of cell surface AMF receptor localizing a single predominant perinuclear pattern closely correlated with its motile ability. AMF also elicited the formation of tube-like structures mimicking angiogenesis when HUVECs were grown in three-dimensional type I collagen gels. We further immunohistochemically detected AMF receptors on the surrounding sites of newborn microvessels. These findings suggest that AMF is a possible tumor progressive angiogenic factor which may act in a paracrine manner for the endothelial cells in the clinical neoplasm, and it will be a new target for anti-angiogenic treatment.

Biological characteristics of carcinomatosa pleuritis in orthotopic model systems using immune-defficient rats

We assessed the association of vascular endothelial growth factor (VEGF) on the formation of carcinomatosa pleuritis in orthotopic model systems. Immune-deficient rats were inoculated with PC-14 cells into i) a subpleural space of the parietal pleura after pneumonectomy or ii) into the thoracic cavity directly. The rats bearing tumor cells were randomly separated into two groups: non-treatment and treatment with anti-VEGF neutralizing antibody groups. At the time of the autopsy, all rats developed gross pleural dissemination with/without malignant effusions. In the first model, despite no significant difference in the mean volume of the subpleural tumors between the groups, the degree of dissemination was suppressed in the treatment group with less tumor vasculature and with reduced expression of autocrine motility factor receptor (AMFR) in tumor cells. In the second model, although the inhibitory effect on dissemination was not clear, the formation of pleural effusion was inhibited in the treatment group. In addition to the ability of vascular permeability, the results demonstrated here showed the possible association of VEGF with the development of pleural dissemination/metastasis in the context of blood/lymphatic routes and cancer cell motility affected by AMFR.

Autocrine motility factor receptor expression in patients with stage I non–small cell lung cancer

Background. Expression of autocrine motility factor receptor (AMFR) associates with increased cell migration and poor survival in certain types of human cancers. We assessed the possible correlation between AMFR, clinicopathologic features, and survival in stage I non–small cell lung cancer (NSCLC). Methods. AMFR expression was analyzed immunohistochemically, using a monoclonal antibody (3F3A) in tumor specimens from 97 patients with curative resection. Vascular endothelial growth factor (VEGF) expression was also examined after accounting for AMFR expression. Results. Out of 97 tumors, 38 (39.2%) were positively stained with AMFR. The AMFR expression was significantly associated with histologic type of tumor, mainly in adenocarcinoma. Overall survival of patients with AMFR-positive tumors was significantly worse than that of AMFR-negative tumors ( p = 0.0050). The AMFR expression appears to be associated with VEGF expression. Patients who were AMFR positive and had high VEGF expression had a worse prognosis compared with the AMFR-negative and low VEGF-expression group ( p < 0.0001). Multivariate analysis revealed an independent prognostic impact of AMFR on survival ( p = 0.0039). Conclusions. These results indicate that evaluation of AMFR expression may provide useful guidance in follow-up of patients with NSCLC.

Significance of autocrine motility factor receptor gene expression as a prognostic factor in non-small-cell lung cancer.

Autocrine motility factor receptor (AMF-R) has been shown to play an important role in tumor cell migration, invasion and metastasis. We have detected AMF-R expression in tissue specimens from patients with non-small-cell lung cancer (NSCLC) and have assessed their clinical characteristics. Using RT-PCR and immunohistochemistry, we quantified the expression of AMF-R in 47 patients with NSCLC who underwent curative tumor resection, to investigate the relationship between AMF-R expression and clinicopathologic factors and prognosis. RT-PCR results agreed well with the immunohistochemic results (p < 0.0001). In 47 NSCLC patients, 34 (72.3%) samples were evaluated as having high AMF-R gene expression. AMF-R gene expression was significantly associated with lymph node metastasis and stage (p = 0.0295 for lymph node metastasis, p = 0.0152 for stage). The overall survival rate for patients with high AMF-R gene-expressing tumors was significantly worse than for those whose tumors had low AMF-R expression (p = 0.0029). Multivariate analysis also showed that AMF-R gene expression was significantly related to survival (p = 0.0165). These data indicate that AMF-R may contribute to tumor progression and that AMF-R gene expression can serve as a useful prognostic marker in NSCLC.

Proteins of the endoplasmic-reticulum-associated degradation pathway: domain detection and function prediction

Sequence database searches, using iterative-profile and Hidden-Markov-model approaches, were used to detect hitherto-undetected homologues of proteins that regulate the endoplasmic reticulum (ER)-associated degradation pathway. The translocon-associated subunit Sec63p (Sec=secretory) was shown to contain a domain of unknown function found twice in several Brr2p-like RNA helicases (Brr2=bad response to refrigeration 2). Additionally, Cue1p (Cue=coupling of ubiquitin conjugation to ER degradation), a yeast protein that recruits the ubiquitin-conjugating (UBC) enzyme Ubc7p to an ER-associated complex, was found to be one of a large family of putative scaffolding-domain-containing proteins that include the autocrine motility factor receptor and fungal Vps9p (Vps=vacuolar protein sorting). Two other yeast translocon-associated molecules, Sec72p and Hrd3p (Hrd=3-hydroxy-3-methylglutaryl-CoA reductase degradation), were shown to contain multiple tetratricopeptide-repeat-like sequences. From this observation it is suggested that Sec72p associates with a heat-shock protein, Hsp70, in a manner analogous to that known for Hop (Hsp70/Hsp90 organizing protein). Finally, the luminal portion of Ire1p (Ire=high inositol-requiring), thought to convey the sensing function of this transmembrane kinase and endoribonuclease, was shown to contain repeats similar to those in beta-propeller proteins. This finding hints at the mechanism by which Ire1p may sense extended unfolded proteins at the expense of compact folded molecules.

Calcium regulates the association between mitochondria and a smooth subdomain of the endoplasmic reticulum.

Association between the ER and mitochondria has long been observed, and the formation of close contacts between ER and mitochondria is necessary for the ER-mediated sequestration of cytosolic calcium by mitochondria. Autocrine motility factor receptor (AMF-R) is a marker for a smooth subdomain of the ER, shown here by confocal microscopy to be distinct from, yet closely associated with the calnexin- or calreticulin-labeled ER. By EM, smooth ER AMF-R tubules exhibit direct interactions with mitochondria, identifying them as a mitochondria-associated smooth ER subdomain. In digitonin-permeabilized MDCK cells, the addition of rat liver cytosol stimulates the dissociation of smooth ER and mitochondria under conditions of low calcium. Using BAPTA chelators of various affinities and CaEGTA buffers of defined free Ca(2+) concentrations and quantitative confocal microscopy, we show that free calcium concentrations <100 nM favor dissociation, whereas those >1 microM favor close association between these two organelles. Therefore, we describe a cellular mechanism that facilitates the close association of this smooth ER subdomain and mitochondria when cytosolic free calcium rises above physiological levels.

Clathrin-mediated endocytosis and recycling of autocrine motility factor receptor to fibronectin fibrils is a limiting factor for NIH-3T3 cell motility.

Autocrine motility factor receptor (AMF-R) is internalized via a clathrin-independent pathway to smooth endoplasmic reticulum tubules. This endocytic pathway is shown here to be inhibited by methyl-(beta)-cyclodextrin (m(beta)CD) implicating caveolae or caveolae-like structures in AMF internalization to smooth ER. AMF-R is also internalized via a clathrin-dependent pathway to a transferrin receptor-negative, LAMP-1/lgpA-negative endocytic compartment identified by electron microscopy as a multivesicular body (MVB). Endocytosed AMF recycles to cell surface fibrillar structures which colocalize with fibronectin; AMF-R recycling is inhibited at 20 degrees C, which blocks endocytosis past the early endosome, but not by m(beta)CD demonstrating that AMF-R recycling to fibronectin fibrils is mediated by clathrin-dependent endocytosis to MVBs. Microtubule disruption with nocodazole did not affect delivery of bAMF to cell surface fibrils indicating that recycling bAMF traverses the MVB but not a later endocytic compartment. Plating NIH-3T3 cells on an AMF coated substrate did not specifically affect cell adhesion but prevented bAMF delivery to cell surface fibronectin fibrils and reduced cell motility. AMF-R internalization and recycling via the clathrin-mediated pathway are therefore rate-limiting for cell motility. This recycling pathway to the site of deposition of fibronectin may be implicated in the de novo formation of cellular attachments or the remodeling of the extracellular matrix during cell movement.