Expression of two types of kit ligand mRNAs in human tumor cells

The primary structure of human kit ligand (KL) growth factor mRNA was analyzed by polymerase chain reaction (PCR) and nucleotide sequencing. Two bands from the total RNAs of a variety of human tumor cell lines were amplified by RT-PCR. Nucleotide sequences of these cloned cDNAs revealed that an 84-nucleotide stretch, corresponding to a spacer chain which contains the site for proteolytic release of the cytokine domain, was missing in the shorter clone, resulting in a transmembrane-bound form of KL. The relative intensity of the two bands in human bone marrow and tumor cells was then determined. In the bone marrow cells, THP1 and HuH7, the band for the membrane-bound type of KL was relatively more intense, whereas the reverse was the case in Daudi, K562 and HT1080 cells, suggesting that there are variations in the expression level of these two human KL mRNAs.