Role of SIRT7 in FLT3 ITD driven cell differentiation and transformation
Final Report Abstract
Blocked cellular differentiation is a central pathologic feature of myeloid malignancies, like AML. Oncogenic mutations in the receptor tyrosine kinase FLT3 are driver mutations for Acute Myeloid Leukemia (AML). About 25 % of AML patients carry so-called FLT3 ITD mutations, which result in constitutive kinase activation. The histone deacetylase SIRT7 was recently identified as a key factor regulating hematopoietic stem cell (HSC) quiescence and aging. Quiescent HSC with unbiased differentiation are characterized by high SIRT7 levels, whereas its down-regulation results in HSC aging, proliferation and myeloid-biased differentiation. Recent work of our laboratory demonstrated reduced SIRT7 levels in FLT3- ITD-positive AML cells. Gene expression data from AML patients carrying FLT3 ITD or BCR- ABL mutations showed decreased SIRT7 expression. Suppression of SIRT7 is controlled by the aberrant FLT3 ITD kinase activity. Inhibition of the oncogenic FLT3 ITD kinase activity restored the cellular SIRT7 level. Importantly, AML patients with low SIRT7 have poor prognosis, demonstrating the clinical relevance of this protein for patient survival. Insight into the molecular correlation of FLT3 ITD-mediated SIRT7 suppression as well as the effect of Sirt7 on FLT3 ITD activity will elucidate ways to affect the blockage of myeloid differentiation of FLT3 ITD in AML patients. In this project the role of SIRT7 activity on FLT3 ITD expressing cells was addressed. Effects of Sirt7 inactivation as well as re-expression or Resveratrol-mediated activation of SIRT7 was studied in a murine 32D FLT3 ITD cell system. The activation of SIRT7 resulted in a reduction of proliferative capacity, clonal growth, and activity of FLT3 ITD downstream signaling. By using the FLT3-ITD-positive human cell line MV4-11, we obtained genetic and pharmacological evidence that Sirt7 is involved in the differentiation of HSC. Resveratrolmediated activation of Sirt7 did contribute to overcome the FLT3-ITD-mediated differentiation block. To study the in vivo effect of activated SIRT7, FLT3 ITD Ptprc KO mice with a severe hematologic phenotype were used. Here a pronounced retardation of the hematologic aberrancies in response to Resveratrol-mediated Sirt7 activation could be observed. In particular, Resveratrol treatment restored B cell defect and amplification of myeloid undifferentiated cells. Taken together, our data currently indicate that SIRT7 plays an antagonistic role on FLT3 ITD-mediated cell transformation. In addition, the specific role of Sirt7 on HSC was addressed by analysing the haematological profile of a created B6 Vav- CRE Sirt7flox/flox mouse. Here we could demonstrate that Sirt7 affects the differentiation of the myeloid line and affects T cell development, in addition.
