Down regulation of Akirin-2 increases chemosensitivity in human glioblastomas more efficiently than Twist-1.

Sebastian Krossa,Jürgen Fritsch,Janka Held-Feindt,Axel J Scheidig,Anne Dorothée Schmitt,Hubertus Maximilian Mehdorn,Kirsten Hattermann

doi:10.18632/oncotarget.3763

Abstract

The Twist-1 transcription factor and its interacting protein Akirin-2 regulate apoptosis. We found that in glioblastomas, highly malignant brain tumors, Akirin-2 and Twist-1 were expressed in glial fibrillary acidic protein positive tumor regions as well as in tumor endothelial cells and infiltrating macrophages / microglia. Temozolomide (TMZ) induced the expression of both molecules, partly shifting their nuclear to cytosolic localization. The knock-down (kd) of Akirin-2 increased the activity of cleaved (c)Caspase-3/-7, the amounts of cCaspases-3, -7 and cPARP-1 and resulted in an increased number of apoptotic cells after TMZ exposure. Glioblastoma cells containing decreased amounts of Akirin-2 after kd contained increased amounts of cCaspase-3 as determined by the ImageStreamx Mark II technology. For Twist-1, similar results were obtained with the exception that the combination of TMZ treatment and Twist-1 kd failed to significantly reduce chemoresistance compared with controls. This could be attributed to a cell population containing only slightly increased cCaspase-3 together with decreased Twist-1 levels, which was clearly larger than the respective population observed under Akirin-2 kd. Our results showed that, compared with Twist-1, Akirin-2 is the more promising target for RNAi strategies antagonizing Twist-1/Akirin-2 facilitated glioblastoma cell survival.

Highlights

Akirins, initially discovered as genes involved in the innate immune system of Drosophila melanogaster [1], are a group of highly evolutionary conserved proteins among all metazoa
Akirin-2 and Twist-1 are expressed in human glioblastomas and are regulated through temozolomide treatment
The mean Akirin-2 mRNA level was higher than the mean Twist-1 mRNA level in GIMS, solid and cultured GBMs (Fig. 1a: Twist-1 / Akirin-2 mean ∆cycle threshold (CT) values were for solid GBM samples 9.3 / 5.2, for cultured GBM cells 9.0 / 5.8 and for glioma infiltrating macrophages/microglia (GIM) 9.1 / 4.7; matched samples are indicated by filled symbols) in contrast to approximately equal levels in GBM cell lines (Fig. 1b)

Summary

Introduction

Initially discovered as genes involved in the innate immune system of Drosophila melanogaster [1], are a group of highly evolutionary conserved proteins among all metazoa. FBI1/ Akirin-2 has been shown to be upregulated in several (rat) tumor cell lines and to promote anchorage-independent growth, tumorigenicity, and metastasis [3,4,5]. Twist itself is an evolutionary highly conserved class B helix-loop-helix protein which e.g. is required for cranial neural tube morphogenesis or for cell survival during limb morphogenesis [7, 8]. Twist-1 is well known to be involved in cancer progression – through activation of the epithelial-mesenchymal transition process which promotes tumor invasiveness and metastasis [for review: 9]

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Results

Conclusion