Molecular pathogenesis of secondary myeloid leukemia: Resistance to inhibitory cytokines and autocrine vegf-dependence of the UOC-M1 cell line

Monosomy 7 (−7) is common in alkylating agent induced- or Fanconi anemia-related myelodysplastic syndrome and acute myeloid leukemia. Interested in using genetic complementation to discover tumor suppressor genes on chromosome 7 that may play a role in leukemogenesis, we are characterizing the phenotype of a factor-independent, megakaryoblastoid, CD34+ cell line (UoC-M1) with complex cytogenetics including (−7). UoC-M1 cells were resistant to 100ng/ml IFNγ and 5ng/ml TGFβ in colony forming unit assays. In contrast, TNFα inhibited growth and resulted in caspase 3 activation. UoC-M1 cells produced highly vascularized, solid tumors in NOD/SCID mice. The tumor cell karyotype was identical to UoC-M1. Supernatants from unstimulated UoC-M1 cells in vitro demonstrated VEGF production (240pg/ml/72 hours from 1×105 cells by ELISA) but no GM-CSF, FLT-3, SCF, IL-6, TPO, TNFα, or IL-1β. Normal human CD34+ cells yielded 4pg/ml VEGF/106 and 57pg/ml/106 when stimulated with 200U/ml rhGM-CSF for 3 days. UoC-M1 also expresses both VEGFR1 (FLT-1) and VEGFR2 (KDR). Because VEGF normally varies inversely with von Hippel-Lindau protein (VHL), we analyzed UoC-M1 mRNA for VHL and the VHL-interacting factors CUL2, HIF1α/β, elongin B/C, and SP1. All were constitutively expressed. We conclude that TGF and IFNγ resistance, VHL resistant-VEGF production, autocrine growth, and in vivo tumorigenesis will be of potential value in genetic complementation studies for the identification of tumor suppressor genes on chromosome 7.