The TGF-β type II receptor in chronic myeloid leukemia: analysis of microsatellite regions and gene expression

Genomic instability is one mechanism proposed to play a role in the disease progression of chronic myeloid leukemia (CML). Microsatellite regions in the type II transforming growth factor-βreceptor (TGF-βRII) gene appear to be targets for mutation in some cancers displaying microsatellite instability (replication error phenotype, RER+). Furthermore, TGF-βRII mutations in RER+ tumors have been associated with decreased TGF-βRII mRNA levels. As TGF-βis a potent negative growth regulator of hematopoietic cells, investigations were undertaken to determine whether inactivation of the receptor by microsatellite alteration might be involved in the progression of CML. Analysis of TGF-βRII mRNA expression by RNase protection, with comparison of cells from the chronic, accelerated and blast phases of CML, showed no change in TGF-βRII transcript levels during disease progression. However, during each phase of the disease, low levels of TGF-βRII were detected when compared with the hematopoietic cells of normal donors. Furthermore, this decreased expression was also observed in the other myeloproliferative disorders, polycythemia rubra vera (PRV) and essential thrombocythemia (ET). The leukemia cell lines K562 and HL-60 had no detectable TGF-βRII mRNA. Two microsatellite regions found altered in RER+ colon cancers were analyzed to establish if these sequences were aberrant in CML. No alteration was detected in either of these regions in any phase of the disease. These results suggest that alterations of the microsatellite regions in the TGF-βRII gene are not involved in the progression of CML. Decreased expression of TGF-βRII in CML cells and leukemia cell lines raises the possibility that altered expression of the receptor may play a role in the initiation and/or maintenance of the disease state.