Hypoxic Regulation of Id-1 and Activation of the Unfolded Protein Response Are Aberrant in Neuroblastoma

S Maureen Nemetski,Lawrence B Gardner

doi:10.1074/jbc.m607275200

Abstract

The Id proteins play an important role in proliferation, differentiation and tumorigenesis. Many tumors are hypoxic, but it is unknown if expression of Id proteins is regulated in hypoxic cells. Here we show that Id-1 is down-regulated in multiple primary, immortalized, and neoplastic hypoxic cell lines, and the transcriptional repressor ATF-3 is both necessary and sufficient for this hypoxia-induced repression of Id-1. Hypoxic up-regulation of ATF-3 is due in part to activation of the unfolded protein response, a cellular stress response. Remarkably, we observe that the unfolded protein response is de-regulated in all neuroblastoma cell lines tested. Indeed, in the absence of ATF-3 the hypoxia-induced transcription factor HIF-1 up-regulates Id-1 in hypoxic neuroblastoma cells. Hypoxic neuroblastoma cells diminish expression of some neuronal differentiation markers, and forced expression of ATF-3 in hypoxic neuroblastoma cells represses Id-1 and prevents the loss of these markers. The divergent regulation of Id proteins in distinct hypoxic cells may explain some of the varied effects hypoxia has on cellular differentiation and proliferation.

Highlights

The existence of cell-specific factors may play a role in the marked phenotypic differences noted between different hypoxic cell lines and tumors
Mouse embryo fibroblasts (MEFs) stably expressing tagged Id-1 from a retroviral construct were treated with cycloheximide, and lysates were collected at regular intervals and subjected to immunoblot to assess stability of the Id-1 protein
ATF-3 Is Induced in Hypoxic Cells in Part by the Unfolded Protein Response—Since our data demonstrate that ATF-3 is necessary for the hypoxia-induced down-regulation of Id-1, we focused on the mechanism of the hypoxic up-regulation of ATF-3

Summary

Introduction

The existence of cell-specific factors may play a role in the marked phenotypic differences noted between different hypoxic cell lines and tumors. Id-1 Is Down-regulated in Hypoxic Cells via Transcriptional Repression Mediated by ATF-3—During the course of an unbiased screen to identify transcription factors with altered activity in hypoxic cells, we determined that Id-1 protein expression is diminished in a variety of hypoxic primary, immortalized, and transformed cell lines (Fig. 1A and data not shown).

Results

Conclusion