Translational studies on acute myeloid leukemia focus on the receptor tyrosine kinase FLT3

Abstract: Among adults, acute myeloid leukemia (AML) is the second most frequent type of leukemia. In spite of recent improvements in the treatment of this disease, a majority of patients develop drug resistance, leading to poor overall survival. One of the factors behind this is mutations in the tyrosine kinase receptor (FLT3). It is one of the most commonly mutated genes and is present in almost 40% of the patients with AML. In order to deal with the resistance and improve current treatments, a better understanding of FLT3 signalling and functioning is required.In our first study, we focused on the tyrosine residue at the 842 position of FLT3. We demonstrated that Y842 is not involved in FLT3 activation or ubiquitination, but is important in regulating downstream signalling via RAS/ERKpathway, as well as controlling receptor stability. The following study’s purpose was to understand if it was the location or the nature of the FLT3 mutation thatplayed the larger role in leukemogenesis. Therefore, we looked at how ITD mutations in the juxtamembrane domain (JMD) compared with those in the tyrosine kinase domain (TKD), as well as with the point mutation in the tyrosinekinase domain, D835Y. The cells with TKD-ITD were able to activate the STAT5 pathway and had a higher cell proliferation and survival than cells expressing D835Y. Overall, TKD-ITD and JMD-ITD showed similar oncogenic potential, but still had a higher oncogenic potential than the D835Y point mutation.In the third and fourth paper we focused on the associating proteins, since tyrosine kinase receptors signal with the help of those in order to activate downstream signalling. First, with the help of an SH2 domain array, we identifiedABL2 as a potent interacting partner of FLT3. It turned out that ABL2 expression did not change the kinase activity of FLT3, its stability or ubiquitination. However, ABL2 acted as a negative regulator of downstream signalling of FLT3 via partial inhibition of AKT pathway. Another interacting partner of FLT3 was identified to be LCK, and its role was studied in paper four. In Ba/F3 cells the expression of LCK enhanced the FLT3-ITD STAT5 phosphorylation. We alsoobserved that those cells exhibited a higher capacity to form colonies. Furthermore, in vivo these cells developed tumours faster than the control. In conclusion, our data show that LCK works together with the oncogenic FLT3-ITD in cellular transformation.