C-KIT IS EXPRESSED IN SOFT-TISSUE SARCOMA OF NEUROECTODERMIC ORIGIN AND ITS LIGAND PREVENTS APOPTOSIS OF NEOPLASTIC-CELLS

During development, mice with mutations of stem cell factor (SCF) or i ts receptor c-kit exhibit defects in melanogenesis, as well as hematop oiesis and gonadogenesis. Consequently, accumulating evidence suggests that the c-kit/SCF system plays a crucial role in all of these proces ses and in tumors which derive from them. Especially in neuroblastoma (infant tumors of neuroectoderm crest derivation such as melanocytes) it would appear that an autocrine loop exists between c-kit and SCF, a nd that the functional block of the c-kit receptors with monoclonal an tibodies (MoAbs) results in a significant decrease in cellular prolife ration. We studied the expression and role of c-kit and SCF in cell li nes of soft tissue sarcoma of neuroectodermic origin, such as Ewing's sarcoma (ES) and peripheral neuro-ectodermal tumors (PNFT). Using flow cytometry with MoAb CD117 PE, c-kit expression was highlighted in all six of the cell lines examined. This receptor was specifically and fu nctionally activated by SCF as shown by the binding experiments and th e intracellular phosphotyrosine and immunoprecipitation studies that w ere performed. Using reverse transcriptase polymerase chain reaction a nalysis, five of the six cellular lines expressed the mRNA of SCF. In the medium measured by using an enzyme-linked immunosorbent assay, low concentrations of SCF were found: only the TC32 cellular line produce d significantly higher levers (32 pg) than control. In serum-free cult ure the addition of SCF reduced the percentage of apoptotic cells from 25% to 90% in five out of the six cellular lines. This observation wa s confirmed by (1) the functional block of c-kit with MoAb: after 7 da ys of culture more than 30% of the cells were apoptotic (range 31.5% t o 100%) in five out of six cell lines and there was also a decrease in the percentage of cells in phase S, and (2) c-kit antisense oligonucl eotides: in the cellular lines treated with oligonucleotides (in relat ion to the untreated lines) there was a notable reduction (P < .001) b oth in the absolute number of cells and the H-3-thymidine uptake. Thes e results indicate that ES and PNET express c-kit and its ligand SCF a nd that SCF is capable of protecting the tumor cells against apoptosis . Furthermore, the reverse transcriptase-polymerase chain reaction per formed on the biopsies revealed the presence of mRNA both of SCF and c -kit in practically all of the samples studied. Our in vitro data lead us to assume that SCF may also inhibit tumor cell apoptosis in vivo. (C) 1998 by The American Society of Hematology.