Mxi1-0 regulates the growth of human umbilical vein endothelial cells through extracellular signal-regulated kinase 1/2 (ERK1/2) and interleukin-8 (IL-8)-dependent pathways.

Weiling Wu,Xi Zhan,Datong Zheng,Hao Gu,Zhenzhen Hu,Zhengdong Zhang,Feng Wang,Jinjin Xu,Xiuqin Jiang,Ramani Ramchandran

doi:10.1371/journal.pone.0178831

Abstract

Mxi1 plays an important role in the regulation of cell proliferation. Mxi1-0, a Mxi1 isoform, has a different N-terminal amino acid sequence, intracellular location and expression profile from Mxi1. However, the precise role of Mxi1-0 in cell proliferation and the molecular mechanism underlying its function remain poorly understood. Here, we showed that Mxi1-0 suppression decreased the proliferation of human umbilical vein endothelial cells (HUVECs) along with cell accumulation in the G2/M phase. Mxi1-0 suppression also significantly decreased the expression and secretion of interleukin (IL-8). Neutralizing IL-8 in conditioned medium (CM) from Mxi1-0-overexpressed HUVECs significantly eliminated CM-induced proliferation of HUVECs. In addition, Mxi1-0 suppression significantly decreased the activity of MAP kinase ERK1/2. Treatment of HUVECs with U0126, an ERK1/2 signaling inhibitor, attenuated autocrine production of IL-8 induced by Mxi1-0 overexpression. On the other hand, Mxi1-0 overexpression-induced IL-8 increased the level of phosphorylated ERK1/2 in HUVECs, and such increasing was diminished in cells incubated with CM, which neutralized with anti-IL-8 antibody. Taken together, our results suggest that Mxi1-0 regulates the growth of HUVECs via the IL-8 and ERK1/2 pathways, which apparently reciprocally activate each other.

Highlights

Mxi1-0 is a transcription factor containing a basic helix-loop-helix leucine zipper and belongs to the Myc-Max-Mad transcriptional network [1, 2]
Our results showed inhibition of proliferation in human umbilical vein endothelial cells (HUVECs) when cultured in CM1 and CM2 treated with neutralising antibody against IL-8 (Fig 3D)
We found that Mxi1-0 suppression induced significant G2/ M phase cell cycle arrest

Summary

Introduction

Mxi0 is a transcription factor containing a basic helix-loop-helix leucine zipper (bHLHzip) and belongs to the Myc-Max-Mad transcriptional network [1, 2]. In contrast to Mxi, Mxi0 is unable to inhibit c-Myc-dependent transcriptional events [4, 5], resides in distinct cellular compartments and has an expression profile different from Mxi1 [3]. Previous studies have suggested that secretion of IL-8 from cancer cells can aggravate the proliferation and survival of cancer cells, in part by autocrine signaling pathways [9, 10]. Secretion of IL-8 from cancer cells can activate endothelial cells to promote angiogenesis [7, 11]. IL-8 is secreted by endothelial cells, thereby enhancing endothelial cell survival, proliferation, and angiogenesis [7, 12]. The role for IL-8 in mediating endothelial cell survival, proliferation and angiogenesis has been strongly suggested, the upstream signaling events associated with IL-8 expression and secretion have not been well characterized

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