Pattern and Dynamics of FLT3 Duplications

FMS-like tyrosine kinase 3 (FLT3)
is mutated in ∼30% of
patients that suffer from acute myeloid leukemia (AML). In about 25%
of all AML patients, in-frame insertions are observed in the sequence.
Most of those insertions are internal tandem duplications (ITDs) of
a sequence from the protein. The characteristics of such mutations
in terms of length, sequence, and location were hitherto studied in
different populations, but not in a comprehensive mutation database.
Here, in-frame insertions into the FLT3 gene were extracted from the
Catalogue of Somatic Mutations in Cancer (COSMIC) database. These
were analyzed with respect to the length, location, and sequence of
the mutations. Furthermore, characteristic strings (sequences) of
different lengths were identified. Mutations were shown to occur most
often in the juxtamembrane zipper (JM-Z) domain of FLT3, followed
by the hinge domain and first tyrosine kinase domain (TKD1), upstream
of the phosphate-binding loop (P-loop). Interestingly, there are specific
hot spot residues where insertions are more likely to occur. The insertions
vary in length between one and 67 amino acids, with the largest insertions
spanning the phosphate binding loop. Insertions that occur downstream
of the P-loop are shorter. Our analysis further shows that acidic
and aromatic residues are enriched in the insertions. Finally, molecular
dynamics simulations were run for FLT3 with ITD insertions in the
hinge and tyrosine kinase domains. On the basis of the findings, a
mechanism is proposed for activation by ITDs, according to which there
is no direct coupling between the length of the insertion and the
activity of the mutated protein. The effect of insertions on the sensitivity
of FLT3 to kinase inhibitors is discussed based on our findings.