Isolation, expression, and characterization of three alternatively spliced variants of the RECK tumor suppressor gene in the human astrocytoma model

Author(s)

Marina Trombetta Lima

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ)
• Defense date: 2014-04-14

Examining board members

Mari Cleide Sogayar; Anamaria Aranha Camargo; Roger Chammas; Guido Lenz; Alexander Henning Ulrich

• Advisor: Mari Cleide Sogayar

Abstract

Glioblastoma multiforme (GBM) or grade IV astrocytoma is the most common and lethal tumor of the central nervous system. One of the most striking features of GBMs is their invasive potential of the normal surrounding brain tissue. It has been described that MMP-2 and MMP-9 expression levels increase during astrocytoma progression. Canonical RECK suppresses tumor invasion and metastasis by negatively regulating at least three matrix metalloproteinases, namely: MMP-9, MMP-2 and MT1-MMP. A positive correlation has been observed between the abundance of RECK express ion in tumor samples and a more favorable prognosis for patients with several types of tumors. In this study, splice variants of the RECK tumor suppressor gene were identified by Expressed Sequence Tag (EST) analysis, isolated by RT-PCR, sequenced and cloned. Three novel alternatively spliced variants of the RECK tumor suppressor gene were identified and characterized. The RECK transcripts expression profiles were investigated using quantitative RT-PCR assays in a normal tissue RNA panel and, also, during astrocytoma progression in macrodissected tumor samples of patients with astrocytoma grades I (n=15), II (n=15), III (n=15) and IV/GBM (n=30). The results show that higher canonical RECK expression, accompanied by a higher ratio of canonical to alternative transcript expression, positively correlated with higher overall survival rate after chemotherapeutic treatment of GBM patients. Our findings suggest that these RECK transcript variants may potentially be used as biomarkers for prognosis of GBM patients. U87 MG cells overexpressing each RECK alternative variant were generated and found to lack the supressive role of cellular invasion processes found upon overexpressing the canonical protein. Among the characterized isoforms, RECK-B stands out, since this isoform is potentially anchored to the cell membrane by a GPI anchor, exactly as the canonical RECK and, also, since cells overexpressing RECK-B display greater tumorigenic capacity. The results indicate that RECK variants and the balance between the expressions of these variants, play an important role in the behavior and aggressiviness of GBMs, therefore have a potential translational application. In addition, in order to investigate new perspectives for the analysis of these isoforms, the expression balance of RECK transcripts was assessed during osteogenesis and adipogenesis, by qRT - PCR. The results show that the expression of the canonical RECK variant is more abundant that that of its alternative isoforms in later stages of adipogenic differentiation. The opposite profile is found regarding RECK-B during osteogenesis, suggesting that the balance between the expressions of these transcripts may have a potential role during these processes. Taken together, the results show the existence of, at least, three alternatively spliced variants of the RECK tumor suppressor gene, which are involved in tumogigenesis and cellular differentiation, o pening new perspectives for studies and clinical application of the RECK gene. (AU)