PRODUCTION OF STEM-CELL FACTOR AND EXPRESSION OF C-KIT IN HUMAN RHABDOMYOSARCOMA CELLS - LACK OF AUTOCRINE GROWTH MODULATION

Human rhabdomyosarcoma cells produce autocrine and paracrine growth fa ctors that can sustain their growth and malignancy. Here we report con stitutive production of stem cell factor (SCF) by 5 of 5 human rhabdom yosarcoma cell lines both of alveolar and embryonal histotype. SCF pro duction, ranging from 30 to 162 pg/ml, was independent from the degree of myogenic differentiation and was not modulated by exogenous additi on of retinoic acid (RA) or tumor necrosis factor-alpha (TNF-alpha). F our of 5 rhabdomyosarcoma cell lines expressed the mRNA for SCF recept or c-kit, while the 5th cell line became weakly positive for c-kit mRN A only after stimulation with retinoic acid. On the cell surface, c-ki t protein was detectable at very low levels in only 1 of 5 rhabdomyosa rcoma cell lines and was not up-regulated by RA or TNF-alpha. Addition of anti-c-kit and anti-SCF blocking antibodies, or of exogenous SCF d id not alter the in vitro growth ability of rhabdomyosarcoma cells. In conclusion, our data show that rhabdomyosarcoma cells produce consist ent amounts of SCF but did not demonstrate autocrine growth modulation . SCF secretion may thus have a paracrine, rather than an autocrine ac tivity in this tumor. (C) 1998 Wiley-Liss, Inc.