EXPRESSION AND SECRETION OF NEUROLEUKIN PHOSPHOHEXOSE ISOMERASE MATURATION FACTOR AS AUTOCRINE MOTILITY FACTOR BY TUMOR-CELLS

The results obtained from fragmented protein microsequencing have sugg ested that autocrine motility factor (AMF), a tumor-secreted M-r 55,00 0 cytokine that regulates cell motility in vitro as well as invasion a nd metastasis in vivo, is the neuroleukin (NLK)/phosphohexose isomeras e (PHI)/maturation factor (MF) polypeptide. Here, we cloned, sequenced , and studied the expression, secretion, and distribution of AMF/NLK/P HI/MF in neoplastic and their normal counterpart cells. Although both normal and neoplastic cells express the gene product, overexpression a ssociated with selective secretion of the protein was observed only in tumor cells. The cDNA sequences of AMF/NLK/PHI/MF found in both human cancer and normal cells were found to be identical, suggesting that i ts secretion by neoplastic cells is independent of mutation or alterna tive splicing. Immunohistochemical visualization has depicted AMF/NLK/ PHI/MF to be localized into tubular-like vesicles, diffusely distribut ed throughout the cytoplasm and not colocalized with any particular cy toskeletal network. Confocal microscopic imaging had shown a partial c olocalization between AMF and its receptor (M-r 78,000 glycoprotein), especially on the malignant cell surface periphery. The results sugges t that extracellular AMF activity may be a result of the product of in tracellular cleavage of a precursor polypeptide, which is overexpresse d and selectively secreted through a nonclassical secretory mechanism by neoplastic cells.