The STK/RON receptor tyrosine kinase is expressed on erythroid progenitor cells. In these cells, two RNA transcripts encoding STK are expressed; one encoding the fulllength receptor, and a second mRNA encoding a short form of STK/RON (SF-STK) which lacks the extracellular ligand binding domain of the full length STK/RON. Recently, we have shown that Fv2, the Friend virus susceptibility 2 locus, encodes SF-STK. The ability of SF-STK to drive Erythropoietin (Epo)-independent expansion of BFU-E in Friend induced erythroleukemia suggests that full-length STK may also play a role in normal erythropoiesis. Previous work has suggested that MSP, the ligand for STK/RON, inhibits erythroid differentiation. We show, however, that this effect is concentration dependent. Consistent with published data, we observed a decrease in BFU-E colony formation in the presence of 100 ng/ml MSP. However, at 10 ng/ml MSP, a two-fold increase in BFU-E formation was observed. To evaluate the role of the MSP/STK signaling pathway on the proliferation of primary erythroid progenitor cells, we have adapted a method for the expansion of human primary erythroid progenitors (Panzenbock et al, Blood 22:3658-3668, 1999) for use with murine bone marrow mononuclear cells. This culture system resulted in an increase in BFU-E and CFU-E which peaked between days 2-4, associated with a decrease in GDI Ib (MacI) and Ly-6G (Gr-1) positive cells, and an increase in Ly-76 (ter 119) and CD117 (c-kit) levels at day 4. RT-PCR analysis demonstrated enhanced STK expression in the expanded cells, compared to the non-expanded bone marrow, suggesting that we are expanding a population of STK positive cells. Using these cells, we observed a synergistic activation of CFU-E in response to low doses of Epo (0.1 U/ml) and MSP (10 ng/ml). Initial studies to determine whether MSP affected proliferation of erythroid progenitors in response to Epo suggest that high doses of MSP inhibit proliferation of erythroid progenitors in response to Epo, whereas low doses of MSP do not significantly affect the proliferation. Furthermore, we observed that the activation of MAP Kinase in response to Epo is enhanced by two-fold at 10 ng/ml MSP, but not at 100 ng/ml MSP. Future studies will determine the effects of MSP on the differentiation and survival of these cells in response to Epo.
|Original language||English (US)|
|Issue number||11 PART II|
|State||Published - 2000|
All Science Journal Classification (ASJC) codes
- Cell Biology