Loss of PI3 kinase association improves the sensitivity of secondary mutation of KIT to Imatinib

Background: KIT mutations are the predominant driver mutations in gastrointestinal stromal tumors (GISTs), and targeted therapy against KIT has improved treatment outcome dramatically. However, gaining secondary mutation of KIT confers drug resistance of GISTs leading to treatment failure. Results: In this study, we found that secondary mutation of KIT dramatically increases the ligand-independent activation of the receptor and their resistance to the often used KIT inhibitor Imatinib in the treatment of GISTs. PI3 kinase plays essential roles in the cell transformation mediated by the primary mutation of KIT. We found that loss of PI3 kinase association, but not the inhibition of the lipid kinase activity of PI3 kinase, inhibits the ligand-independent activation of secondary mutations of KIT, and increases their sensitivity to Imatinib, and loss of PI3 kinase association inhibits secondary mutations of KIT mediated cell survival and proliferation in vitro. The in vivo assay further showed that the growth of tumors carrying secondary mutations of KIT is more sensitive to Imatinib when PI3 kinase association is blocked while inhibition of the lipid kinase activity of PI3 kinase cannot inhibit tumor growth, indicating that PI3 kinase is important for the drug resistance of secondary mutation of KIT independent of the lipid kinase activity of PI3 kinase. Conclusions: Our results suggested that PI3 kinase is necessary for the ligand-independent activation of secondary mutations of KIT, and loss of PI3 kinase association improves the sensitivity of secondary mutations to the targeted therapy independent of the lipid kinase activity of PI3 kinase

Rassf2 overexpression mediated by AAV promotes the supporting cell-to-hair cell transformation in the cochlea

Sensory hair cells are responsible for detecting and transmitting sound in the inner ear, and damage to HCs leads to hearing loss. HCs do not regenerate spontaneously in adult mammals, which makes the hearing loss permanent. However, hair cells and supporting cells have the same precursors in the inner ear, and in newborn mice, the adjacent SCs can be activated by gene manipulation to differentiate into newly regenerated hair cells. Here, we demonstrate the role of the Ras association domain family member 2 (Rassf2) in supporting cell to hair cell trans-differentiation in the inner ear. Using the AAV vector (AAV-ie) to upregulate Rassf2 expression promoted supporting cell division and hair cell production in cultured cochlear organoids. Also, AAV-Rassf2 enhanced the regenerative ability of Lgr5+ SCs in the postnatal cochlea without impairing hearing, and this might due to the modulation of the Wnt, Hedgehog and Notch signaling pathways. Furthermore, AAV-Rassf2 enhances cochlear supporting cell division and hair cell production in the neomycin injury model. In summary, our results suggest that Rassf2 is a key component in HC regenerative repair, and gene modulation mediated by adeno-associated virus may be a promising gene therapy for hearing repair