EXPRESSION OF TIE RECEPTOR TYROSINE KINASE IN LEUKEMIA-CELL LINES

The tie receptor tyrosine kinase mRNA was originally identified as an amplified product in reverse transcription-polymerase chain reaction a nalysis of human K562 leukemia cell RNA. In situ hybridization analysi s revealed that the corresponding mouse gene is expressed predominantl y in endothelial cells. We have explored tie mRNA and protein expressi on in tumor cell lines. The 4.4 kb tie mRNA was expressed at high leve ls in five of five human megakaryoblastic leukemia cell lines studied and in two IL-3-dependent mouse myeloid leukemia cell lines, but not i n 42 other leukemia cell lines representing various hematopoietic line ages. Increased expression of tie mRNA and protein was observed upon t reatment of the megakaryoblastic leukemia cells with the tumor promote r 12-0-tetradecanoyl-phorbol-13-acetate (TPA), known to enhance megaka ryoblastic markers. Among several cell lines from solid tumors, two fi brosarcomas, one rhabdomyosarcoma and one melanoma cell line were posi tive for tie mRNA. These results suggest that among hematopoietic line ages tie is predominantly expressed in cells with megakaryoblastic pro perties and that the tie tyrosine kinase is a receptor for a regulator y factor specific tor megakaryoblasts, endothelial cells, and occasion al tumor cell lines derived from mesenchymal tissues.