Type I insulin-like growth factor receptor (IGF-IR) tyrosine kinase is a homodimeric protein that is composed of 2 extracellular α; and 2 transmembranous β; subunits connected by disulfide bonds. IGF-IR belongs to the insulin receptor family whose members exhibit a common structural characteristic in the form of an amino acid motif (YXXXYY) within the activation loop of their respective kinase domains. Ligand stimulation of IGF-IR causes its dimerization, phosphorylation, and the subsequent activation of downstream signaling systems. It has been shown that IGF-IR is aberrantly overexpressed in and contributes to the survival of a variety of human solid tumors and hematological neoplasms and, therefore, it may represent an important therapeutic target. Pathological activation of IGF-IR induces cellular transformation and protection from apoptosis-- prerequisites for the establishment and growth of malignant tumors. Of important note is that the mechanisms underlying increased expression of IGF-IR in cancer cells are not completely understood. For instance, only a few transcription factors are known to bind the IGF-IR gene promoter (15q26.3) and modulate its activity through stimulation or inhibition. These transcription factors include Sp1, WT1, E2F1, STAT1, and EGR-1.
Recently, we identified IGF-IR as a major survival molecule that interacts reciprocally with nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) in a subtype of T-cell anaplastic large-cell lymphoma. NPM-ALK+ T-cell lymphoma is an aggressive type of cancer that is frequently encountered in children and young adults. Compared with its expression in normal human T lymphocytes and reactive lymphoid tissues, the expression of IGF-IR mRNA and protein is remarkably upregulated in NPM-ALK+ T-cell lymphoma cell lines and primary human tumors. Similar to other types of cancer, the mechanisms leading to increased expression of IGF-IR in NPM-ALK+ T-cell lymphoma have not been identified.
In this study, we hypothesized that increased IGF-IR expression can be explained by transcriptional aberrancies that exist inherently in NPM-ALK+ T-cell lymphoma. To identify transcription factors that may potentially bind to the human IGF-IR gene promoter, 3 web-based transcription factor search algorithms were used: TFSearch (www.cbrc.jp/research/db/TFSEARCH.html), Genomatix (www.genomatix.de), and MATCH (www.gene-regulation.com/pub/programs.html). These algorithms identified the transcription factors Ikaros (Ik) and myeloid zinc finger 1 (MZF1) to potentially bind to IGF-IR gene promoter. Western blotting (WB) studies demonstrated lower levels of Ik-1 and MZF1 in 5 NPM-ALK+ T-cell lymphoma cell lines than in T lymphocytes. WB also showed that Ik-1 and MZF1 are decreased in 85% and 100%, respectively, of 15 ALK+ T-cell lymphoma patient specimens. A luciferase assay supported that Ik-1 and MZF1 regulate the IGF-IR gene promoter. Furthermore, ChIP assay showed that these transcription factors bind specific sites located within the IGF-IR gene promoter. Forced expression of Ik-1 and MZF1 in NPM-ALK+ T-cell lymphoma cells significantly decreased IGF-IR mRNA and protein expression levels. This decrease in IGF-IR was associated with downregulation of pIGF-IR and the phosphorylation of its interacting molecules, including IRS-1, AKT, and NPM-ALK. In addition, overexpression of Ik-1 and MZF1 decreased the viability, proliferation, migration, and anchorage-independent colony formation of NPM-ALK+ T-cell lymphoma cells.
Collectively, our findings provide novel evidence that aberrant decreases in the transcription factors Ik-1 and MZF1 play important roles in the pathogenesis of NPM-ALK+ T-cell lymphoma through upregulation of IGF-IR expression. These findings could be exploited to devise more effective strategies to treat this lymphoma.
Citation Format: Deeksha Vishwamitra, Choladda V. Curry, Serhan Alkan, Ping Shi, Hesham M. Amin. Decreased levels of the transcription factors Ik-1 and MZF1 contribute to upregulation of IGF-IR expression in NPM-ALK+ T-cell anaplastic large-cell lymphoma. [abstract]. In: Proceedings of the AACR Special Conference on Hematologic Malignancies: Translating Discoveries to Novel Therapies; Sep 20-23, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(17 Suppl):Abstract nr A36.