Investigation of the role of IRS1 in the β-catenin signaling pathway in acute lymphoblastic leukemia

Author(s)

Jaqueline Cristina Fernandes

• Document type: Master's Dissertation
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina de Ribeirão Preto (PCARP/BC)
• Defense date: 2016-10-11

Examining board members

Fabíola Traina; Carlos Alberto Scrideli; José Andrés Yunes

• Advisor: Fabíola Traina

Abstract

The acute lymphoblastic leukemia (ALL) is a heterogeneous group of malignancies characterized by abnormal proliferation and accumulation of immature cells in the bone marrow, which impairs the production of erythrocytes, leukocytes and platelets. Insulin-like growth factor 1 (IGF1) and its receptor (IGF1R) regulate normal cell growth and contribute to transformation and growth of malignant cells through activation of downstream signaling pathways. The IGF1 signaling pathway is initiated through activation of its receptor followed by activation of its substrates, including insulin receptor substrate 1 (IRS1). IRS1 is well known as a cytosolic protein involved in signal transduction, but also plays a role in malignant transformation, being highly expressed in many cancers. In mouse fibroblasts, Irs1, through Igf1 signaling, was found to be the key protein for nuclear translocation of ?-catenin and transcription activation of its target genes, such as Myc and cyclin D1. MYC and cyclin D1 may act as oncogenes, contributing to the development of cancers, including hematopoietic neoplasm. Thus, the aims of this study were to investigate the role of nuclear IRS1 in the ?-catenin pathway in LLA. We used in the study ALL cell lines (Jurkat, MOLT-4, Namalwa and Raji) and primary hematopoietic cells from healthy donors (n=13) and from adult patients with ALL (n=45) treated at our Institution. Studies of gene expression (qPCR), protein expression, association (Western blotting and immunoprecipitation) and cell location (subcellular fractionation and confocal microscopy) were used. Jurkat cells were submitted to IGF1 stimulation and/or IGF1R pharmacological inhibition (OSI-906). IRS1, ?-catenin and MYC relative gene expression were significantly elevated in ALL patients compared to normal controls (p<0.05), but there was no difference in gene expression of cyclin D1 and IGF1R between the two groups. A positive correlation between ?-catenin and MYC relative expression (p=0.0004; r=0.50) and between IRS1 and MYC expression (p=0.001; r=0.45) was found. Univariate analysis revealed that increasing age and elevated expression of MYC are factors that adversely affect the overall survival; age was an independent prognostic factor for survival. IRS1 and ?-catenin co-localized in the nucleus and cytoplasm of ALL cell lines (Jurkat, MOLT4, Raji e Namalwa). In primary cell of normal donor, IRS1 and ?-catenin were found predominantly in the cytoplasm. In Jurkat cells, a constitutive IRS1 and ?-catenin protein interaction was observed and IGF1 stimulation increased IRS1 tyrosine phosphorylation. OSI-906 treatment decreased IGF1R tyrosine phosphorylation, nuclear translocation of ?-catenin and MYC protein expression in Jurkat cells. In conclusion, our data support a link between the signaling pathway IGF1R/IRS1 and activation of ?-catenin in acute lymphoblastic leukemia, which may represent an important axis involved in the pathophysiology of the disease. (AU)

• FAPESP's process: 13/26213-0 - Investigation of the role of IRS1 in the beta-catenin signaling pathway in acute lymphoblastic leukemia
• Grantee: Jaqueline Cristina Fernandes
• Support Opportunities: Scholarships in Brazil - Master