Migratory properties of neoplastic cells have long been suggested to play a central role in invasion and metastasis. We have previously demonstrated that cell adhesion, rearrangement of extracellular matrix, assembly of cytoskeleton networks, cell geometry and locomotion are all closely interrelated properties affecting tumor cell dissemination. The nature of tumor cell surface molecules that are involved in mediating such processes is unknown. 'Motility' and 'chemotactic-factors' which regulate cell movement and positioning have recently been discovered although their complimentary receptors remain to be identified. In response to cell geometry modulation, B16-F1 melanoma cells express augmented glycosylation of a 78,000 KDa (gp78) cell surface glycoprotein which is correlated with increased metastatic ability in vivo and motility in vitro. Affinity purified gp78 binds a purified 55,000 KDa B16-F1 autocrine motility factor (AMF), and inhibits migratory stimulation by AMF. Cell motility stimulation by AMF is associated with gp78 phosphorylation. We have cloned the human homologue of the murine AMF receptor and found it to share significant sequence homology with the suppressor/oncogene p53 protein.
The aim of this project is to determine directly the role of AMF receptor in vitro (motility) and in vivo (hematogenous spread). In particular, we intend to: 1) identify the presence of gp78, its cell surface expression density and distribution in relation to the motility and the metastatic phenotypes of various tumor cell systems. 2) study the signal transduction pathway of motility stimulation. 3) clone AMF from mouse and human cDNA libraries. 4) identify and clone the murine gene(s) coding for gp78. 5) chromosomally map the human gp78 and cloned its wild-type (normal) homologue. 6) transfect specific gp78 coding sequences into tumor cells that express high and low metastatic ability and compare the expression of the newly synthesized AMF receptor with the malignant cell phenotype in relation to motility, growth and metastasis. It is expected that these studies will allow the characterization and establishment of the role of cell surface receptor for autocrine motility factor in cell kinesis and its relevance to invasion and metastatic spread.
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