FOXM1 and the NPM-ALK/STAT3 Axis Form a Novel Positive Feedback Loop in Promoting the Oncogenesis of ALK-Positive Anaplastic Large Cell Lymphoma

Peng Wang¹, Moinul Haque², Jing Li^2,3, Yung-Hsing Huang², Meaad Almowaled², Carter Bargar⁴, Adam Karpf⁴, Will Chen², Suzanne Turner⁵ and Raymond Lai^2,6

¹Division of Hematology, Dept of Medicine, University of Alberta, Edmonton, ² Department of Laboratory Medicine and Pathology, University of Alberta, Edmonton Alberta, Canada; ³Electron Microscopy Center, Basic Medical Science College, Harbin Medical University, Harbin, Heilongjiang, China; ⁴Eppley Institute and Fred & Pamela Buffett Cancer Center, University of Nebraska Medical Center, Omaha, USA; ⁵Division of Cellular and Molecular Pathology, Department of Pathology, University of Cambridge, Cambridge, UK;⁶Department of Oncology, University of Alberta, Edmonton, Alberta, Canada

1. Backgrounds and Aims

Forkhead Box M1 (FOXM1) is a transcription factor implicated in the pathogenesis of solid tumors, and it has been shown to promote cell-cycle progression, stem cell renewal and chemotherapeutic resistance in cancer cells. Nonetheless, the biological significance of FOXM1 in hematologic malignancies has not been extensively studied. Here, we studied the expression and role of FOXM1 in ALK-positive anaplastic large cell lymphoma (ALK+ALCL).

2 Methods and Results

In contrast with normal lymphocytes, FOXM1 was highly expressed in all ALK+ALCL cell lines (5/5), tumors from patients (6/6) and tumors arising from NPM-ALK transgenic mice. Experiments using nuclear/cytoplasmic fractionation, immunocytochemistry and reporter assays had provided evidence that FOXM1 is transcriptionally active in ALK+ALCL. Down-regulation of FOXM1 expression using shRNA and a pharmacologic agent (thiostrepton) resulted in a significant reduction in cell growth, colony formation in soft agar and cell-cycle arrest in ALK+ALCL cells. Further studies revealed that the oncogenic potential of FOXM1 is linked to substantial increases in the phosphorylation/activation status of NPM-ALK and STAT3, and the upregulations of a host of cytokines that have been previously shown to activate the NPM-ALK/STAT3 axis, including IGF-1, IL9 and IL21. Using co-immunoprecipitation, we found that NPM-ALK binds to FOXM1 in the nucleus of ALK+ALCL cells. Importantly, the binding of NPM-ALK to FOXM1 promotes the DNA binding ability and transcriptional activity of FOXM1, and functional inhibition of NPM-ALK using crizotinib or depletion of NPM-ALK using siRNA in ALK+ALCL cells significantly decreased the transcriptional activity of FOXM1.

1. Conclusions:

In conclusion, we have identified a novel oncogenic feedback loop involving FOXM1 and the NPM-ALK/STAT3 axis in ALK+ALCL. This study has revealed the first clear example in which NPM-ALK exerts important oncogenic functions in the nuclei of ALK+ALCL cells, by means of its binding to an oncogenic transcription factor so as to promote its DNA binding and transcription activity.