Expression and localization of the CDC34 ubiquitin-conjugating enzyme in pediatric acute lymphoblastic leukemia

Ubiquitin-dependent protein degradation impacts many cellular processes.However, the regulation of ubiquitin-conjugating enzymes (UBCs) in cancer is unknown. We find that the human CDC34 UBC protein is expressed at a 3-4 fold higher level (P < 0.001) in pediatric T cell than in pre-B-cell acute lymphoblastic leukemia (ALL) before treatment in two independent patient sets. The level of CDC34 mRNA was similar in both types of leukemia. CDC34 expression levels in normal resting T cells, B cells and activated T lymphocytes was comparable with pre-B-cell ALL. CDC34 protein (but not mRNA) was also increased in T-cell ALL compared with pre-B-cell ALL cell lines. The difference in expression was not attributable to mutation or associated with altered CDC34 stability. Immunohistochemistry and cellular fractionation reveals a heterogeneous CDC34 expression pattern including cells containing primarily cytoplasmic or nuclear protein. Thus, a feature of pediatric T-cell ALL is posttranscriptional up-regulation and heterogeneous localization of the human CDC34 UBC.