INTERLEUKIN-4 DOWN-REGULATES EXPRESSION OF C-KIT AND AUTOCRINE STEM-CELL FACTOR IN HUMAN COLORECTAL-CARCINOMA CELLS

Stem cell factor (SCF) is a cytokirie which plays an important role in the development of precursor cells. We have investigated the expressi on of SCF and its receptor, the c-kit proto-oncogene, in human colorec tal carcinoma cell lines. Using reverse transcription-PCR, we confirme d the expression of c-kif in two lines (LS174T and LS1034) and of SCF in 9 of 11 cell lines tested. In a Northern blot, a single transcript of 6.6 kb was detected for SCF mRNA. In addition, two lines (LS174T an d HT29) synthesized SCF protein, as detected by Western blot analysis. SCF stimulated proliferation and colony formation of LS174T in a dose -dependent manner up to 160%. A half-maximal effect was obtained with about 5.5 ng/ml of SCF under both growth conditions. LS174T cells expr essed the M(r) 145,000 c-kit protein on the cell surface and a neutral izing anti-c-kit mAb inhibited colony formation of LS174T by 40%. Inte rleukin 4 (IL-4) completely inhibited SCF-induced proliferation of LS1 74T cells. Interestingly, IL-4 induced an almost complete down-regulat ion of both c-kif and SCF expression in LS174T. Our findings suggest t hat in LS174T cells, an SCF-mediated autocrine loop is functional and that IL-4 down-regulates the expression of both the receptor and the l igand of this circuit.