Loss of L3MBTL1, a Candidate 20q12 Tumor Suppressor Gene, Leads to DNA Damage.

Abstract 1974

Poster Board I-997

The L3MBTL1 gene is located on the long arm of chromosome 20 (q12), a region commonly lost in several myeloid malignancies, including myeloproliferative diseases (MPD), myeloprodysplastic disorders (MDS), and acute myeloid leukemias (AML). MDS and AML frequently have complex cytogenetic profiles, and are thought to arise due to accumulation of several cooperating mutations. We have previously reported that L3MBTL1 is highly expressed in human hematopoietic progenitor cells. L3MBTL1 is a homolog of Drosophila polycomb L3MBTL tumor suppressor protein. Thus, L3MBTL1 is a candidate gene in 20q12 myeloid disorders. We have depleted L3MBTL1 by RNAi in several human cell lines, and find that loss of L3MBTL1 leads to a decrease of cells in the S phase of the cell cycle and accumulation in G2/M phase. Cells with depleted L3MBTL1 have an increase of spontaneous DNA breaks, as evidenced by accumulation of γH2A.X foci and comet assay. The presence of DNA breaks leads to activation of DNA damage response, as the L3MBTL1 knockdown cells have increased levels of phosphoChk1 (Ser317 and Ser345), phosphoChk2 (Thr68), phosphoATM (Ser1981), p21 and p53. The DNA damage in the L3MBTL1-depleted cells activates DNA repair machinery, as shown by the increase in Rad51 levels. We propose that the spontaneous DNA damage caused by depletion of L3MBTL1 could contribute to the development of 20q12 myeloid malignancies.