HIF has Biff – Crosstalk between HIF1a and the family of bHLH/PAS proteins

https://doi.org/10.1016/j.yexcr.2017.03.055Get rights and content

Abstract

Two decades of research into functions of the ubiquitous transcription factor HIF have revealed pervasive roles in development, oxygen homeostasis, metabolism, cancer and responses to ischemia. Unsurprisingly, HIF activities impinge on many pathologies, for which underlying molecular mechanisms are actively sought. HIF is a member of the heterodimeric bHLH/PAS family of transcription factors, a set of proteins that commonly function in developmental pathways and adaptive responses to environmental or physiological stress. Similarities in the mechanisms that regulate gene targeting by these transcription factors create opportunities for extensive crosstalk between family members. Data supporting pathway interactions between HIF1a and other bHLH/PAS factors, both collaborative and antagonistic, is beginning to surface in the areas of cancer, circadian rhythm, and immune responses. This review summarises the status of HIF1a-bHLH/PAS protein crosstalk and is dedicated to the memory of Lorenz Poellinger, a pioneer investigator into the molecular mechanisms of HIF, AHR, and ARNT bHLH/PAS factors.

Introduction

The Hypoxia-Inducible Factor 1α (HIF1α) is an oxygen regulated member of the basic Helix-Loop-Helix/PER-ARNT-SIM (bHLH/PAS) family of transcription factors that plays key roles in embryonic and adult oxygen homeostasis. HIF1α is essential for development of embryonic vasculature and thereafter maintains roles in angiogenesis throughout life, particularly during times of oxygen deficiency, when HIF1α activity co-ordinately adjusts cellular metabolism and erythropoiesis to aid adaption and survival. To achieve these functions, HIF1α dimerises with a second bHLH/PAS protein, ARNT (also known as HIF1β), to regulate hundreds of genes across a range of tissues. HIF1α represents a Class I bHLH/PAS factor, proteins characterized by being either ubiquitously expressed and signal regulated, or alternatively, constitutively active and tissue specific. Class I factors bind DNA upon dimerision with a Class II partner factor, one of ARNT (Aryl Hydrocarbon Receptor Nuclear Translocator), ARNT2 or ARNT-Like (ARNTL, aka BMAL). Other well studied Class I factors include the Aryl hydrocarbon Receptor (AhR, aka Dioxin Receptor), which is critical for toxin metabolism and differentiation of distinct subsets of T and B immune cells [1]; Single Minded 1 (SIM1), essential for specification of neuroendocrine secreting cells of the hypothalamus and control of appetite [2], [3]; Neural PAS factors (NPAS 1, 3 & 4), which function in neuron development and synaptic plasticity [4]; and CLOCK and NPAS2, which control circadian rhythms. Members of this family all share a conserved domain organisation. The amino-terminal bHLH domain is involved in DNA binding and serves as a primary dimerization interface. This is followed by a PAS domain consisting of two PAS repeats, PAS A and PAS B, that are important for secondary dimerization and in some cases, binding small organic ligands. The carboxy-terminal halves contain either transactivation or transrepression domains for target gene regulation. Cognate DNA sequences bound by the heterodimers are variations of the canonical E-box sequence, all containing a core NNCGTG [5], [6].

Class I bHLH/PAS factors have structural similarities and commonly heterodimerise with ARNT to bind similar DNA response elements, features that invite direct crosstalk between the proteins. Additionally, an increasing number of studies are showing that there are intersections between the pathways bHLH/PAS factors control in biological functions such as immune cell regulation, the circadian rhythm and cancer progression. This review focuses on the various bHLH/PAS family members and how their functions and pathways are involved in crosstalk with the activities and functions of HIF.

Section snippets

HIF1α and SIM2 crosstalk in cancer

Single-Minded 2 (SIM2) is a Class I bHLH/PAS factor that has been identified as misregulated in a number of cancers, particularly prostate, where it has been suggested as a potential biomarker due to correlation of high levels with poor patient survival [7], [8], [9]. HIF1α can play multiple positive and negative roles in solid cancers. It primarily aids tumourigenesis and progression via adaption to hypoxia, but conversely, can also be anti-tumourigenic by activating pro-apoptotic genes. In

HIF1α crosstalk with the circadian clock

BMAL1 (Brain and Muscle ARNT-Like, or simply ARNTL) is a Class II bHLH/PAS transcription factor that, together with its Class I partner factor CLOCK, forms one of the essential core components of the circadian clock that controls central and peripheral circadian rhythms. Other core proteins include the circadian repressors, PAS domain-containing PERIOD homologues 1, 2 and 3 (PER1 PER2, PER3), and CRYPTOCHROME 1 and 2 (CRY1 and CRY2) [5]. It has long been known that HIF1α can heterodimerise with

HIF and the NPAS transcription factors

Hypoxia plays multiple roles in nervous system development and function, via both HIF-dependent and independent pathways. Through HIF, hypoxia acts as a morphogen to organize normal developmental programs [23]. This is illustrated by conditional deletion of HIF1α in the CNS leading to hydrocephalus, failure of neuronal differential and increased neural apoptosis [24]. Not surprisingly, aberrant hypoxia can lead to disrupted development and pathological processes [23], [25]. For example, genetic

HIF and AHR function in immunomodulation

The Aryl Hydrocarbon Receptor (AHR) is a ligand dependent Class I bHLH/PAS factor important for regulating development and function of immune cells. In the absence of a ligand, latent AHR is located in the cytoplasm, bound to chaperone proteins. Upon binding of aromatic hydrocarbons, typified by xenobiotics such as dioxins and PCBs (polychlorinated biphenyls), dietary indoles or tryptophan metabolites, the AHR translocates to the nucleus where it dimerises with the Class II partner factor ARNT

Conclusions and future directions

While the exploration of interplay between HIF1α and the signalling pathways of other bHLH/PAS transcription factors is in its infancy, some startling examples illustrate the potential for discoveries in this area to expand our understanding of how environmental and physiological perturbations are sensed and integrated at the molecular level. It will be interesting to see whether there are more instances of either direct competition or synergistic collaboration between HIF and other bHLH/PAS

Acknowledgements

The authors’ work has been supported by grants from the Australian Research Council, National Health and Medical Research Council, and Cancer Council SA.

References (54)

  • G. Macintyre

    Association of NPAS3 exonic variation with schizophrenia

    Schizophr. Res.

    (2010)
  • L. Zhou

    AHR function in lymphocytes: emerging concepts

    Trends Immunol.

    (2016)
  • W.K. Chan

    Cross-talk between the aryl hydrocarbon receptor and hypoxia inducible factor signaling pathways. Demonstration of competition and compensation

    J. Biol. Chem.

    (1999)
  • M. Nie et al.

    Interactions between aryl hydrocarbon receptor (AhR) and hypoxia signaling pathways

    Environ. Toxicol. Pharmacol.

    (2001)
  • A. Palazon

    HIF transcription factors, inflammation, and immunity

    Immunity

    (2014)
  • E.V. Dang

    Control of TH17/Treg balance by hypoxia-inducible factor 1

    Cell

    (2011)
  • J.A. Goettel

    AHR activation is protective against colitis driven by T cells in humanized mice

    Cell Rep.

    (2016)
  • J.L. Michaud

    Development of neuroendocrine lineages requires the bHLH-PAS transcription factor SIM1

    Genes Dev.

    (1998)
  • J.L. Michaud

    Sim1 haploinsufficiency causes hyperphagia, obesity and reduction of the paraventricular nucleus of the hypothalamus

    Hum. Mol. Genet.

    (2001)
  • K. Ramamoorthi

    Npas4 regulates a transcriptional program in CA3 required for contextual memory formation

    Science

    (2011)
  • D.C. Bersten

    bHLH-PAS proteins in cancer

    Nat. Rev. Cancer

    (2013)
  • M.S. Arredouani

    Identification of the transcription factor single-minded homologue 2 as a potential biomarker and immunotherapy target in prostate cancer

    Clin. Cancer Res.

    (2009)
  • O.J. Halvorsen

    Increased expression of SIM2-s protein is a novel marker of aggressive prostate cancer

    Clin. Cancer Res.

    (2007)
  • M. Ema

    Two new members of the murine Sim gene family are transcriptional repressors and show different expression patterns during mouse embryogenesis

    Mol. Cell Biol.

    (1996)
  • P. Moffett et al.

    The murine Sim-2 gene product inhibits transcription by active repression and functional interference

    Mol. Cell. Biol.

    (1997)
  • A.L. Farrall et al.

    The HIF1 alpha-inducible pro-cell death gene BNIP3 is a novel target of SIM2s repression through cross-talk on the hypoxia response element

    Oncogene

    (2009)
  • A.E. Sullivan

    Characterization of human variants in obesity-related SIM1 protein identifies a hot-spot for dimerization with the partner protein ARNT2

    Biochem. J.

    (2014)
  • Cited by (0)

    View full text