Sphingosine-1-Phosphate as a Regulator of Hypoxia-Induced Factor-1α in Thyroid Follicular Carcinoma Cells

Veronica Kalhori,Muhammad Yasir Asghar,Kid Törnquist,Nina Bergelin,Kati Kemppainen,Panu Jaakkola,Rajesh Mohanraj

doi:10.1371/journal.pone.0066189

Veronica Kalhori, Muhammad Yasir Asghar + Show 5 more

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https://doi.org/10.1371/journal.pone.0066189

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Abstract

Sphingosine-1-phosphate (S1P) is a bioactive lipid, which regulates several cancer-related processes including migration and angiogenesis. We have previously shown S1P to induce migration of follicular ML-1 thyroid cancer cells. Hypoxia-induced factor-1 (HIF-1) is an oxygen-sensitive transcription factor, which adapts cells to hypoxic conditions through increased survival, motility and angiogenesis. Due to these properties and its increased expression in response to intratumoral hypoxia, HIF-1 is considered a significant regulator of tumor biology. We found S1P to increase expression of the regulatory HIF-1α subunit in normoxic ML-1 cells. S1P also increased HIF-1 activity and expression of HIF-1 target genes. Importantly, inhibition or knockdown of HIF-1α attenuated the S1P-induced migration of ML-1 cells. S1P-induced HIF-1α expression was mediated by S1P receptor 3 (S1P3), Gi proteins and their downstream effectors MEK, PI3K, mTOR and PKCβI. Half-life measurements with cycloheximide indicated that S1P treatment stabilized the HIF-1α protein. On the other hand, S1P activated translational regulators eIF-4E and p70S6K, which are known to control HIF-1α synthesis. In conclusion, we have identified S1P as a non-hypoxic regulator of HIF-1 activity in thyroid cancer cells, studied the signaling involved in S1P-induced HIF-1α expression and shown S1P-induced migration to be mediated by HIF-1.

Highlights

The bioactive sphingolipid sphingosine-1-phosphate (S1P) has emerged as a potent signaling molecule
HIF-1a Small interfering RNA (siRNA) was from MWG (Ebersberg, Germany), HIF-1a, vascular endothelial growth factor (VEGF)-A, autocrine motility factor (AMF), transforming growth factor-a (TGFa), S1P1, S1P2, S1P receptor 3 (S1P3), PKCa, protein kinase C bI (PKCbI) and HPRT1 primers from TAG Copenhagen (Copenhagen, Denmark) and Universal Probe Library probes from Roche (Basel, Switzerland)
S1P is a Non-hypoxic Regulator of HIF-1a Expression Since S1P treatment of ML-1 thyroid cancer cells strongly increases their migration [16] and Hypoxiainduced factor-1 (HIF-1) is a known regulator of invasion and metastasis [7], [8], we investigated whether S1P could affect expression of the regulatory HIF-1a subunit in ML-1 cells

Summary

Introduction

The bioactive sphingolipid sphingosine-1-phosphate (S1P) has emerged as a potent signaling molecule. It regulates cellular survival, proliferation and motility as well as angiogenesis and inflammation, all processes relevant for tumorigenesis and cancer progression. S1P is normally present in blood at high levels and functions both intra- and extracellularly [1], [2]. Extracellular S1P activates five high affinity S1P receptors (S1P1–5) which couple to various G proteins and have both overlapping and opposing effects [3], [4]. The first intracellular targets of S1P were identified [5], [6]. SK1 is considered oncogenic and its expression is elevated in several types of cancers [2]

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