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chronic hypoxia

acute hypoxia

Environmental stress as a result of low oxygen and proper nutrient deprivation, such as glucose deprivation, are capable of inducing VEGF mRNA stabilization resulting in increased levels of the secreted ligand and angiogenic growth

HIFalpha subunits accumulate in the cytoplasm where they bind HIFbeta to form a heterodimer that subsequently translocates to the nucleus to activate transcription of target genes, including genes important for various processes such as metabolism (glucose transporter (GLUT)-1, hexokinase (HK)-1), cell growth (cyclin (CCN)-D1 [23]) and also angiogenesis, such as erythropoietin, VEGF and PDGF [24] (summarized in Fig. 1)

When oxygen levels are low (hypoxia; red arrow) PHDs cannot hydroxylate HIFalphas thereby allowing them to escape pVHL-mediated degradation. HIFalpha subunits accumulate and bind to their heterodimeric partner, HIFbeta, translocate into the nucleus and activate a cascade of hypoxic signaling first by the transcription of various target genes including microRNAs that are important for tumor promoting pathways

c-Src is also capable of activating HIFs by indirectly inhibiting PHD activity via the NADPH oxidase/Rac pathway.

mTOR can also promote stabilization and HIF transcriptional activity

hypoxia inducible factors (HIFs), heterodimeric transcription factors composed from alpha and beta subunits, which can be rapidly stabilized to fluidly adapt to and overcome the effects of a hypoxic environment

Curcumin inhibits the expression of epidermal growth factor receptor (EGFR), VEGFR-1, VEGFR-2 and VEGFR-3, and the kinase activity of Src and FAK, which are responsible for the induction of angiogenic genes as well as endothelial cell polarity and migration

Curcumin also reduces the MMP-2 and MMP-9 expression, along with the suppression of growth and invasion potential of tumor cells in culture and xenograft experiments

The expression of angiogenic biomarkers COX-2 and serum levels of VEGF were significantly reduced in the curcumin-treated group

Resveratrol inhibits capillary endothelial cell growth and new blood vessel growth in animals

interrupting cell proliferation, inducing apoptosis

[155] and impeding angiogenesis by suppressing VEGF expression through down-regulation of HIF-1alpha

resveratrol was reported to inhibit cell proliferation of human ovarian cancer cells and human osteosarcoma cells by attenuating HIF-1alpha

prevents cytokine-induced vascular leakage and tumor metastasis

The underlying molecular mechanisms include: blocking VEGF- and FGF-receptor-mediated MAPK activation, inhibiting Akt- and MAPK-driven HIF-1alpha basal expression and its induction by IGF-1, stimulating the proteasomal degradation of HIF-1alpha, inhibiting phosphatidyl inositol (PI)-3K/Akt and Ras/mitogen/extracellular signal-regulated kinase (MEK)/ERK pathways, and activation of forkhead box (FOX)O transcription factors

some steroid hormone-induced nuclear events can occur in minutes

the genomic effects of steroid hormones take longer, with changes in gene expression occurring on the timescale of hours

Classical steroid hormone signaling occurs when hormone binds nuclear receptors (NR) in the cytoplasm, setting off a chain of genomic events that results in, among other changes, dimerization and translocation to the nucleus where the ligand-bound receptor forms a complex with coregulators to modulate gene transcription through direct interactions with a hormone response element (HRE)

NRs have been found at the plasma membrane of cells, where they can propagate signal transduction often through kinase pathways

Membrane-localized ER, PR and AR have been reported to modulate the activity of MAPK/ERK, phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt), nitric oxide (NO), PKC, calcium flux and increase inositol triphosphate (IP3) levels to promote cell processes including autophagy, proliferation, apoptosis, survival, differentiation, and vasodilation

ERα36, a 36kDa truncated form of ERα that lacks the transcriptional activation domains of the full-length protein. Membrane-localized ERα36 can activate pathways including protein kinase C (PKC) and/or mitogen activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) to promote the progression of various cancers

G protein-coupled receptor 30 (GPR30), also referred to as G protein-coupled estrogen receptor (GPER), is a membrane-localized receptor that has been observed to respond to estrogen to activate rapid signaling

hormone-responsive G protein coupled receptor is Zip9, which androgens can activate

GPRC6A is another G protein-coupled membrane receptor that is responsive to androgen

androgen-mediated non-genomic signaling through this GPCR can modulate male fertility, hormone secretion and prostate cancer progression

non-NR proteins located at the cell surface can bind to steroid hormones and respond by eliciting rapid signaling events

Estrogens have been shown to induce rapid (i.e. seconds) calcium flux via membrane-localized ER (mER)

ER-calcium dynamics lead to activation of kinase pathways such as MAPK/ERK which can result in cellular effects like migration and proliferation

17β-estradiol (E2) has been reported to promote angiogenesis through the activation of GPER

Membrane NRs may also mediate rapid signaling through crosstalk with growth factor receptors (GFR)

A similar crosstalk occurs between the receptor tyrosine kinase insulin-related growth factor-1 receptor (IGF-IR) and ERα. Not only does IGF-IR activate ERα, but inhibition of IGF-IR downregulates estrogen-mediated ERα activity, suggesting that IGF-IR is essential for maximal ERα signaling

Further, ER activates IGF-IR pathways including MAPK

GPER is involved in the transactivation of the EGFR independent of classical ER

tight interconnection between genomic and non-genomic effects of NRs.

non-genomic pathways can also lead to genomic effects

androgen-bound AR associates with the kinase Src at the plasma membrane, activating Src which then leads to a signaling cascade through MAPK/ERK

However, Src can also increase the expression of AR target genes by the ligand-independent transactivation of AR

extranuclear steroid hormone actions can potentially reprogram nuclear NR events

estrogen modulated the expression of several genes including endothelial nitric oxide synthase (eNOS) via rapid signaling pathways

epigenetic changes can then mediate genomic events in uterine tissue and breast cancer cells