Pharmacological inhibition of RAS overcomes FLT3 inhibitor resistance in FLT3-ITD+ AML through AP-1 and RUNX1

\ua9 2024 The Author(s). AML is characterized by mutations in genes associated with growth regulation such as internal tandem duplications (ITD) in the receptor kinase FLT3. Inhibitors targeting FLT3 (FLT3i) are being used to treat patients with FLT3-ITD+ but most relapse and become resistant. To elucidate the resistance mechanism, we compared the gene regulatory networks (GRNs) of leukemic cells from patients before and after relapse, which revealed that the GRNs of drug-responsive patients were altered by rewiring their AP-1-RUNX1 axis. Moreover, FLT3i induces the upregulation of signaling genes, and we show that multiple cytokines, including interleukin-3 (IL-3), can overcome FLT3 inhibition and send cells back into cycle. FLT3i leads to loss of AP-1 and RUNX1 chromatin binding, which is counteracted by IL-3. However, cytokine-mediated drug resistance can be overcome by a pan-RAS inhibitor. We show that cytokines instruct AML growth via the transcriptional regulators AP-1 and RUNX1 and that pan-RAS drugs bypass this barrier

?-Tropomyosin with a D175N or E180G Mutation in Only One Chain Differs from Tropomyosin with Mutations in Both Chains

?-Tropomyosin (Tm) carrying hypertrophic cardiomyopathy mutation D175N or E180G was expressed in Escherichia coli. We have assembled dimers of two polypeptide chains in vitro that carry one (??*) or two (?*?*) copies of the mutation. We found that the presence of the mutation has little effect on dimer assembly, thereby predicting that individuals heterozygous for the Tm mutations are likely to express both ??* and ?*?* Tm. Depending on the expression level, the heterodimer may be the predominant form in individuals carrying the mutation. Thus, it is important to define differences in the properties of Tm molecules carrying one or two copies of the mutation. We examined the Tm homo- and heterodimer properties: actin affinity, thermal stability, calcium regulation of myosin subfragment 1 binding, and calcium regulation of myofibril force. We report that the properties of the heterodimer may be similar to those of the wild-type homodimer (actin affinity, thermal stability, D175N ??*), similar to those of the mutant homodimer (calcium sensitivity, D175N ??*), intermediate between the two (actin affinity, E180G ??*), or different from both (thermal stability, E180G ??*). Thus, the properties of the homodimer are not a completely reliable guide to the properties of the heterodimer