The oncogene HER2/neu (ERBB2) requires the hypoxia-inducible factor HIF-1 for mammary tumor growth and anoikis resistance

Distinct roles of HIF1A in endothelial adaptations to physiological and ambient oxygen

Fetoplacental endothelial cells reside under physiological normoxic conditions (∼2-8% O2) in vivo. Under such conditions, cells are believed to sense O2 changes primarily via hypoxia inducible factor 1 α (HIF1A). However, little is known regarding the role of HIF1A in fetoplacental endothelial function under physiological normoxia. We recently reported that physiological chronic normoxia (PCN; 20-25 day, 3% O2) enhanced FGF2- and VEGFA-stimulated proliferation and migration of human umbilical vein endothelial cells (HUVECs) via the MEK/ERK1/2 and PI3K/AKT1 pathways compared to standard cell culture normoxia (SCN; ambient O2: ∼21% O2). Here, we investigated the action of HIF1A in regulating these cellular responses in HUVECs. HIF1A adenovirus infection in SCN-cells increased HIF1A protein expression, enhanced FGF2- and VEGFA-stimulated cell proliferation by 2.4 and 2.0-fold respectively, and promoted VEGFA-stimulated cell migration by 1.4-fold. HIF1A adenovirus infection in SCN-cells did not affect either basal or FGF2- and VEGFA-induced ERK1/2 activation, but it decreased basal AKT1 phosphorylation. Interestingly, HIF1A knockdown in PCN-cells via specific HIF1A siRNA transfection did not alter FGF2- and VEGFA-stimulated cell proliferation and migration, or ERK1/2 activation; however, it inhibited FGF2-induced AKT1 activation by ∼50%. These data indicate that HIF1A differentially regulates cell proliferation and migration, and ERK1/2 and AKT1 activation in PCN- and SCN-HUVECs. These data also suggest that HIF1A critically regulates cell proliferation and migration in SCN-, but not in PCN-HUVECs.

The role of HIF1α in renal cell carcinoma tumorigenesis

The transcription factor HIF1α is implicated in the development of clear cell renal cell carcinoma (ccRCC). Although HIF1α was initially believed to be essential for ccRCC development, recent studies hypothesize an oncogenic role for HIF2α in ccRCC, but a tumor suppressor role for HIF1α, leading to uncertainty as to the precise roles of the different HIF transcription factors in this disease. Using evidence available from studies with human ccRCC cell lines, mouse xenografts, murine models of ccRCC, and human ccRCC specimens, we evaluate the roles of HIF1α and HIF2α in the pathogenesis of ccRCC. We present a convergence of clinical and mechanistic data supporting an important role for HIF1α in promoting tumorigenesis in a clinically important and large subset of ccRCC. This indicates that current understanding of the exact roles of HIF1α and HIF2α is incomplete and that further research is required to determine the diverse roles of HIF1α and HIF2α in ccRCC.

KEY MESSAGES

The TRACK mouse ccRCC model with constitutively active HIF1α but not HIF2α expressed in proximal tubules develops RCC. HIF1α protein is expressed in the majority of human ccRCC specimens. Elevated HIF1α in ccRCC correlates with a worse prognosis. Many publications do not support a tumor suppressor role for HIF1α in ccRCC. HIF1α, but not HIF2α, is expressed in some types of cancer stem cells.

Prospective neoadjuvant analysis of PET imaging and mechanisms of resistance to Trastuzumab shows role of HIF1 and autophagy

Background:

Although Trastuzumab has improved survival of HER2+ breast cancer patients, resistance to the agent pre-exists or develops through the course of therapy. Here we show that a specific metabolism and autophagy-related cancer cell phenotype relates to resistance of HER2+ breast cancer to Trastuzumab and chemotherapy.

Methods:

Twenty-eight patients with locally advanced primary breast cancer were prospectively scheduled to received one cycle of Trastuzumab followed by a new biopsy on day 21, followed by taxol/Trastuzumab chemotherapy for four cycles before surgery. FDG PET/CT scan was used to monitor tumour response. Tissue samples were immunohistochemically analysed for metabolism and autophagy markers.

Results:

In pre-Trastuzumab biopsies, the LC3A+/HER2+ cell population was correlated with HIF1α expression (P=0.01), while GLUT1 and LC3B expression were correlated with Ki67 proliferation index (P=0.01 and P=0.01, respectively). FDG PET tumour dimensions before therapy were correlated with LC3B expression (P=0.005). Administration of Trastuzumab significantly reduced clinical and PET-detected tumour dimensions (P<0.01). An inverse association of tumour response with the percentage of cells expressing HIF1α at baseline was documented (P=0.01). Administration of Trastuzumab resulted in a decrease of the proliferation index (P=0.004), GLUT1 (P=0.04) and HER2 (P=0.01) expression. In contrast, the percentage of LC3A+/HER2+ cells was increased (P=0.01). High baseline HIF1α expression was the only parameter associated with poorer pathological response to preoperative chemotherapy (P=0.001).

Conclusions:

As the HER2+/LC3A+ phenotype, which often overexpresses HIF1α, is a major subpopulation increasing after therapy with Trastuzumab, LC3A- and HIF1α-targeting therapies should be investigated for the augmentation of anti-HER2 therapy efficacy.

Phosphoprotein secretome of tumor cells as a source of candidates for breast cancer biomarkers in plasma

Breast cancer is a heterogeneous disease whose molecular diversity is not well reflected in clinical and pathological markers used for prognosis and treatment selection. As tumor cells secrete proteins into the extracellular environment, some of these proteins reach circulation and could become suitable biomarkers for improving diagnosis or monitoring response to treatment. As many signaling pathways and interaction networks are altered in cancerous tissues by protein phosphorylation, changes in the secretory phosphoproteome of cancer tissues could reflect both disease progression and subtype. To test this hypothesis, we compared the phosphopeptide-enriched fractions obtained from proteins secreted into conditioned media (CM) derived from five luminal and five basal type breast cancer cell lines using label-free quantitative mass spectrometry. Altogether over 5000 phosphosites derived from 1756 phosphoproteins were identified, several of which have the potential to qualify as phosphopeptide plasma biomarker candidates for the more aggressive basal and also the luminal-type breast cancers. The analysis of phosphopeptides from breast cancer patient plasma and controls allowed us to construct a discovery list of phosphosites under rigorous collection conditions, and second to qualify discovery candidates generated from the CM studies. Indeed, a set of basal-specific phosphorylation CM site candidates derived from IBP3, CD44, OPN, FSTL3, LAMB1, and STC2, and luminal-specific candidates derived from CYTC and IBP5 were selected and, based on their presence in plasma, quantified across all cell line CM samples using Skyline MS1 intensity data. Together, this approach allowed us to assemble a set of novel cancer subtype specific phosphopeptide candidates for subsequent biomarker verification and clinical validation.

Cancer metabolism: cross talk between signaling and O-GlcNAcylation

Cancer cells exhibit a unique metabolic shift to aerobic glycolysis that has been exploited diagnostically and therapeutically in the clinic. Oncogenes and tumor suppressors alter signaling pathways that lead to alterations of glycolytic flux. Stemming from glycolysis, the hexosamine biosynthetic pathway leads to elevated posttranslational addition of O-linked-β-N-acetylglucosamine (O-GlcNAc) on a diverse population of nuclear and cytosolic proteins, many of which regulate signaling pathways. This unit outlines techniques used to detect metabolic alterations in cancer cells, regulation by signaling pathways, and cellular O-GlcNAcylation.