ENHANCEMENT OF J6-1 HUMAN LEUKEMIC-CELL PROLIFERATION BY MEMBRANE-BOUND M-CSF THROUGH A CELL-CELL CONTACT MECHANISM II - ROLE OF AN M-CSF RECEPTOR-LIKE MEMBRANE-PROTEIN

We have isolated an M-CSF-like membrane-associated growth factor from human leukemic J6-1 cells that can enhance the growth and colony forma tion of J6-1 cells in vitro. Indirect evidence suggests that this memb rane-associated M-CSF-like growth factor may do so by stimulating a co rresponding receptor co-expressed on the adjacent J6-1 cells. The obje ctive of this study is to isolate the putative receptor in J6-1 cells by virtue of its ability to bind and thus ''block'' the growth of J6-1 cells. Based on this approach, we have isolated from the J6-1 cell me mbrane an inhibitory activity that can inhibit the clonal growth of J6 -1 cells. The activity of this inhibitor can be readily neutralized by either anti-M-CSFR MAb or anti-M-CSFR antiserum, suggesting that it i s related to M-CSFR, a product of c-fms proto-oncogene. Judging from S ephadex G-200 gel filtration, the molecular weight (MW) of this putati ve M-CSFR-like inhibitor was estimated to be approx. 150-180 kDa, comp arable with that of M-CSFR. The specificity of M-CSFR-like protein to recognize and block membrane-bound M-CSF also was implicated by its ab ility to upregulate the steady-state levels of c-fms mRNA in J6-1 cell s. Besides its antiproliferative activity in vitro, treatment of J6-1 cells with the putative receptor protein before inoculation effectivel y blocked the growth and tumor formation in vivo by J6-1 cells in a nu de mouse model. These findings suggest that the growth and tumor devel opment by J6-1 leukemic cells may involve a contact-mediated ''juxtacr ine mechanism''. (C) 1998 Elsevier Science Ltd. All rights reserved.