Transcriptional regulation of HIF-2α in neuroblastoma

Abstract

Abstract

Expression of hypoxia-inducible factor (HIF)-2α correlates with an aggressive tumor phenotype and poor patient outcome in neuroblastoma. Despite the high sequence homology between HIF-1α and HIF-2α, these two transcription factors are differentially regulated and the mechanisms underlying HIF-2α regulation are not fully understood. To investigate the regulation of HIF2A transcription via the IGF-1R/insulin receptor - PI3K - mTORC2 signaling pathway, which is independent from the PI3K - Akt - mTORC1 pathway that regulates HIF-1α translation, we looked at the individual roles of mTORC1 and mTORC2 specific components Raptor and Rictor. However, we found siRNA transfections to be an ineffective tool to knock down Rictor in the SK-N-BE(2)c neuroblastoma cell line. It has been recently shown in our group that HIF-2α is affected at the transcriptional level through insulin-like growth factor (IGF)-II. In an attempt to further investigate the effect of IGF-I and IGF-II to induce HIF-2α transcription, we treated neuroblastoma cells with these growth factors for a prolonged period of time at normoxia (21% O2) and hypoxia (1% O2). However, we found no influence of these factors on HIF1A and HIF2A mRNA levels. We further inhibited insulin receptor function in the SK-N-BE(2)c neuroblastoma cell line at both normoxia and hypoxia and show here that HIF2A mRNA expression is significantly decreased at hypoxia. We conclude that the insulin receptor plays a distinct role in HIF-2α transcription in neuroblastoma cells.

Abstract

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Transcriptional regulation of HIF-2α in neuroblastoma

Neuroblastoma is the most common solid tumor in childhood. The presence of hypoxia -regions of low levels of oxygen- causes a more immature tumor phenotype that is related to a more aggressive form of this cancer. Hypoxia is mainly directed by Hypoxia Inducible Factors (HIF)-1α and HIF-2α. High levels of HIF-2α expression correlate with aggressive tumor growth and poor patient outcome in neuroblastoma. The mechanisms underlying HIF-2α regulation are not fully understood.

To investigate the individual roles of the two mTOR complexes, mTORC1 and mTORC2, on HIF2A expression we aimed to knock down the expression of Rictor and Raptor, specific components of the respective complexes. Unfortunately, we only succeeded to knock down Raptor expression and cannot draw any conclusions from this experiment. Insulin-like growth factor (IGF)-II has been shown to be co-expressed with, and further to regulate the transcription of HIF-2α in neuroblastoma. To test the possible effect of IGF-I and IGF-II on HIF-2α transcription, we treated neuroblastoma cells with these growth factors for a prolonged period of time at normoxia (21% O2) and hypoxia (1% O2). However, we found no influence of these factors on HIF1A and HIF2A mRNA levels. We further inhibited insulin receptor function in the SK-N-BE(2)c neuroblastoma cell line at both normoxia and hypoxia and demonstrated the significant decrease of only HIF2A mRNA expression at hypoxia. We concluded that the insulin receptor plays a distinct role in HIF-2α transcription in neuroblastoma cells. Finding a clear picture of all players and their mechanisms of effect in the pathway controlling HIF2A expression has a great therapeutic potential in neuroblastoma.


Supervisor: Sofie Mohlin
Cosupervisor: Sven Påhlman
Master´s Degree Project 30 credits in Cell and Molecular Biology, 2013
Department of Biology, Lund University

• author: Farah, Farahani
• supervisor: Sofie Mohlin
• organization: Degree Projects in Molecular Biology
• course: MOBM15 20132
• year: 2013
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 4225674
• date added to LUP: 2014-01-02 15:16:07
• date last changed: 2014-01-13 08:47:23