Similarly, the amounts of pJAK2 and pSTAT5 have been significantly re duced in K562 cells expressing SOCS 3 or SOCS three without affecting the complete protein ranges of JAK2 and STAT5. K562 cells expressing SOCS 3 exhibited a slightly decreased level of pJAK2 but unchanged degree of pSTAT5 compared with management cells. With each other, these experiments demon strated that Bcr Abl dependent tyrosine phosphorylation of SOCS one and SOCS 3 coincided together with the activation of JAK2 and STAT5 in K562 leukemic cells. Disrupting the Tyrosine Phosphorylation of SOCS 1 or SOCS three Sensitizes K562 Cells to Undergo Apoptosis Simply because activation of JAK2 and STAT5 was inhibited by disrupting the tyrosine phosphorylation of SOCS one or SOCS 3 and given that ac tivation of JAK2/STAT5 signaling contributes to elevated cell survival, we hypothesized that decreasing the levels of tyrosine phosphorylated SOCS one or SOCS three might sensitize K562 cells to undergo apoptosis in response to drug therapy.
As shown in Figure 6A, 77. 5% of K562 cells expressing GFP manage and 64. 4% of cells expressing SOCS one remained viable immediately after therapy with etoposide for 48 hours under our culture situation. Even so, only 33. 8% of K562 cells ex pressing SOCS one and 21. 7% of cells hop over to these guys expressing SOCS one were viable under the same culture disorders. As expected, 70. 4% of cells expressing SOCS three remained viable just after treatment with etoposide for 48 hours, which was comparable to that of management cells. Strikingly, only 28. 7% of K562 cells expressing SOCS three were viable, whereas 63. 4% of K562 cells expressing SOCS 3 were viable beneath the exact same condi tions. Collectively, these information indicate that disrupting the tyrosine phosphorylation of SOCS 1 or SOCS 3 sensitizes K562 cells to undergo apoptosis.
Former price MLN9708 studies have suggested that inefficient apoptotic signaling in Bcr Abl transformed cells could possibly be attributed towards the STAT5 dependent expression of antiapoptotic Bcl XL protein. As a result, we rea soned that increased apoptosis of K562 cells expressing SOCS mu tants presented above was possible as a consequence of impaired expression of Bcl XL. To test this likelihood, we examined the amounts of Bcl XL and Bcl 2 in K562 cell lines stably expressing GFP handle, SOCS 1, SOCS three, or their mutants. Indeed, we observed that the level of Bcl XL significantly decreased in K562 cells expressing SOCS one, SOCS 1, SOCS 3, or SOCS three com pared with these in cells expressing wild variety SOCS proteins or GFP alone. In contrast, no major

improvements in protein expression of Bcl 2 were observed in cells expressing these SOCS mutants. Selective Mutation of Tyrosine Phosphorylation Web-sites of SOCS one or SOCS 3 Thoroughly Blocks Tumor Formation Attributable to K562 Cells in Mouse Model A vital extension of our hypothesis was to set up no matter whether tyrosine phosphorylation of SOCS one or SOCS 3 is needed for Bcr Abl induced tumorigensis.