Abi-1 loss in the bone marrow results in instability of WAVE2 complex, and is accompanied by increased phosphorylation of STAT3, SFKs, and NF-κB. Western blot evaluation of the activity status of (A) NF-κB and its inhibitor IκB, (B) JAK2, STAT5, STAT3, Erk1/2, Akt, and (C) SFKs using phospho-site-specific antibodies, and (D) stability of WAVE2 complex components (WAVE2, Nap1, Abi-1, and Sra-1) in Abi-1-deficient bone marrow. Bone marrow from 3 different Abi-1^WT and Abi-1^KO sex-matched 20-week-old animals was used. (E) Volcano plot of fold change (log 2) vs q-value (−log10) of peak-area for 12 103 peptides identified in Abi-1^KO (n = 3) respective to Abi-1^WT (n = 3) bone marrow isolated from sex-matched 20-week-old animals. Green represents number of peptides with 2-fold decrease in abundancies, peptides with 2-fold increase in abundancies are presented in red. (F) Heat map showing significantly changed peptides derived from target proteins known to be associated with MPNs identified in liquid chromatography-tandem mass spectrometry analysis performed on Abi-1^WT or Abi-1^KO bone marrow samples. (G) Immunoblotting assessment of the levels of Abi-1 and activity status of SFKs, STAT3, and NF-κB in CD34⁺ cells isolated from the bone marrow of patients with PMF and compared with sex- and age-matched healthy control patients (sample details are presented in supplemental Table 1). Whole-cell lysates were used for immunoblotting analyses. (H) A hypothetical schematic depicting the effect of Abi-1 on SFKs, STAT3, and NF-κB signaling. Abi-1 acts as a negative regulator of SFKs activity. Its absence leads to overactive SFKs signaling to STAT3, which becomes activated and cross-activates NF-κB. Overactivity of STAT3 and NF-κB results in cells acquiring inflammatory molecular signature, positively affecting proliferation, survival and ultimately leading to transformation.