Vav1 is one of the signalling proteins normally restricted to hematopoietic cells that results ectopically expressed in solid tumors, including breast cancer. By immunohistochemical analysis on TMAs containing invasive breast tumor from patients without lymph node involvement, we have found that Vav1 is expressed in almost all investigated cancers and shows a peculiar localization inside the nucleus of tumor cells. High amounts of nuclear Vav1 are positively correlated with low incidence of relapse, regardless phenotype and molecular subtype of breast neoplasia. In particular, Kaplan-Meier plots showed an elevated risk of distant metastasis in patients with low Vav1 expression compared with patients with high Vav1 expression in their tumors. Experiments performed with breast tumor-derived cells indicated that Vav1 negatively modulates their invasiveness in vitro and their metastatic efficiency in vivo, possibly by affecting the expression of genes involved in invasion and/or metastasis of breast tumors. Since the high heterogeneity of breast tumors makes difficult to predict the evolution of early breast neoplasias, the evaluation of nuclear Vav1 levels may help in the characterization and management of early breast cancer patients. In particular, Vav1 may serve as a prognostic biomarker and a target for new therapies aimed to prevent breast cancer progression.

Beyond its possible correlation with stemness of tumor cells, CD133/prominin1 is considered an important marker in breast cancer, since it correlates with tumor size, metastasis and clinical stage of triple-negative breast cancers (TNBC), to date the highest risk breast neoplasia.

It has been recently demonstrated that high pre-treatment levels of miR-29b positively correlated with the response of patients with acute myeloid leukaemia (AML) to hypomethylating agents. Upmodulation of miR-29b by restoring its transcriptional machinery appears indeed a tool to improve therapeutic response in AML. In cells from acute promyelocytic leukaemia (APL), miR-29b is regulated by PU.1, in turn upmodulated by agonists currently used to treat APL. We explored here the ability of PU.1 to also regulate miR-29b in non-APL cells, in order to identify agonists that, upmodulating PU.1 may be beneficial in hypomethylating agents-based therapies. We found that PU.1 may regulate miR-29b in the non-APL Kasumi-1 cells, showing the t(8;21) chromosomal rearrangement, which is prevalent in AML and correlated with a relatively low survival. We demonstrated that the PU.1-mediated contribution of the 2 miR-29b precursors is cell-related and almost completely dependent on adequate levels of Vav1. Nuclear PU.1/Vav1 association accompanies the transcription of miR-29b but, at variance with the APL-derived NB4 cells, in which the protein is required for the association of PU.1 with both miRNA promoters, Vav1 is part of molecular complexes to the PU.1 consensus site in Kasumi-1. Our results add new information on the transcriptional machinery that regulates miR-29b expression in AML-derived cells and may help in identifying drugs useful in upmodulation of this miRNA in pre-treatment of patients with non-APL leukaemia who can take advantage from hypomethylating agent-based therapies.