PML/RARα Mediates Resistance to Apoptosis and Down-Regulation of the NF-κB Pathway in Acute Promyelocytic Leukemia.

Acute promyelocytic leukemia (APL) is genetically characterized by the translocation t(15;17) that results in the fusion gene PML/RARα. The chimeric protein renders hematopoietic progenitor cells resistant to FAS-, TNF- and IFN-induced apoptosis and caspase-3 activation, supporting a role for apoptosis impairment in the pathogenesis of APL. To better investigate apoptosis deregulation in APL, we analyzed the expression profile of 53 newly diagnosed APL patients (27M/26F; median age: 41 yr. (range: 9–80); median WBC count x 10⁹/L: 2.67 (range: 0.5–128); median platelet count x 10⁹/L: 19 (range: 4.4–135); FAB subtype: 39 M3/14 M3v) using the OncoChip®, a cDNA microarray especially designed for analyzing genes involved in cancer which contains 6,386 genes. After array processing, a total of 371 and 249 known genes were found to be ≥2 fold down- or up-regulated, respectively. To verify the results of microarray analysis, six differentially expressed genes (JAG1, JUN, CDKN1C, FAS, TRAIL, TRAF6 and MMP9) were tested by real-time quantitative PCR analysis (Q-RT-PCR). As initially hypothesized, numerous genes involved in apoptotic pathways were deregulated. In particular, we found a significant down-regulation of genes involved in the activation of NF-κB and of genes related to TNF-mediated apoptosis (FAS, TRAIL, TNFSF13B), with 46 and 24 genes deregulated, respectively. Expression changes in other genes implicated in apoptosis were also identified, being of special interest those affecting to the BCL2 family. Thus, anti-apoptotic genes BCL2 and BCL11A were up-regulated while pro-apoptotic members of the family were down-regulated in the analyzed series. Genes involved in the regulation of p53-dependent apoptosis (such as APAF1, p53DINP1, ATM), as well as numerous genes involved in diverse mechanisms of DNA repair, were also inhibited. Finally, the protein kinase C-δ (PKCδ) and several interferon- and interleukin-related genes were also infraexpressed in APL. These findings suggest that inactivation of apoptotic pathways is a common event in the pathogenesis of APL and may have important implications in the design of therapeutic protocols. It was of particular interest the unexpected inhibition of the NF-κB pathway. It could be in accordance with the hypothesis that NF-κB is an inductor of apoptosis under some circumstances. The role of NF-κB in promoting or repressing cell death in APL should be further investigated.