Acid-base transporters and pH dynamics in human breast carcinomas predict proliferative activity, metastasis, and survival

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Abstract

Breast cancer heterogeneity in histology and molecular subtype influences metabolic and proliferative activity and hence the acid load on cancer cells. We hypothesized that acid-base transporters and intracellular pH (pH_i) dynamics contribute inter-individual variability in breast cancer aggressiveness and prognosis. We show that Na⁺,HCO₃^--cotransport and Na⁺/H⁺-exchange dominate cellular net acid extrusion in human breast carcinomas. Na⁺/H⁺-exchange elevates pH_i preferentially in estrogen receptor-negative breast carcinomas, whereas Na⁺,HCO₃^--cotransport raises pH_i more in invasive lobular than ductal breast carcinomas and in higher malignancy grade breast cancer. HER2-positive breast carcinomas have elevated protein expression of Na⁺/H⁺-exchanger NHE1/SLC9A1 and Na⁺,HCO₃^--cotransporter NBCn1/SLC4A7. Increased dependency on Na⁺,HCO₃^--cotransport associates with severe breast cancer: enlarged CO₂/HCO₃^--dependent rises in pH_i predict accelerated cell proliferation; whereas enhanced CO₂/HCO₃^--dependent net acid extrusion, elevated NBCn1 protein expression, and reduced NHE1 protein expression predict lymph node metastasis. Accordingly, we observe reduced survival for patients suffering from Luminal A or Basal-like/triple-negative breast cancer with high SLC4A7 and/or low SLC9A1 mRNA expression. We conclude that the molecular mechanisms of acid-base regulation depend on clinicopathological characteristics of breast cancer patients. NBCn1 expression and dependency on Na⁺,HCO₃^--cotransport for pH_i regulation, measured in biopsies of human primary breast carcinomas, independently predict proliferative activity, lymph node metastasis, and patient survival.

Data availability

- In order to comply with the ethical approval, we share the human data presented in Figure 1-8 and corresponding Figure Supplements (data on acid-base transport activity, intracellular pH, and protein expression of transporters linked to clinicopathological information) in de-identified form. Following consultation with the legal team at the Regional Committee on Health Research Ethics, we have generated dataset files where restricted information is grouped in intervals each consisting of no less than five individuals. To provide the reader with the best possible data insight, we also show Figure Supplements with more detailed and advanced plots of the data and include the corresponding de-identified dataset.- The meta analyses presented in Figure 9, 10, and corresponding figure supplements (data on RNA expression linked to patient survival) are based on data that have previously been published by other investigators (references 28-34), as detailed in the manuscript and the dataset list.

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Article and author information

Author details

Nicolai J Toft

Department of Biomedicine, Aarhus University, Aarhus C, Denmark

Competing interests
No competing interests declared.
Trine V Axelsen

Department of Biomedicine, Aarhus University, Aarhus C, Denmark

Competing interests
No competing interests declared.
Helene L Pedersen

Department of Pathology, Regionshospitalet Randers, Randers, Denmark

Competing interests
No competing interests declared.
Marco Mele

Department of Surgery, Regionshospitalet Randers, Randers, Denmark

Competing interests
No competing interests declared.

"This ORCID iD identifies the author of this article:" 0000-0002-8156-7804
Mark Burton

Department of Clinical Genetics, University of Southern Denmark, Odense, Denmark

Competing interests
No competing interests declared.
Eva Balling

Department of Surgery, Regionshospitalet Randers, Randers, Denmark

Competing interests
No competing interests declared.
Tonje Johansen

Department of Pathology, Regionshospitalet Randers, Randers, Denmark

Competing interests
No competing interests declared.
Mads Thomassen

Department of Clinical Genetics, University of Southern Denmark, Odense, Denmark

Competing interests
No competing interests declared.
Peer M Christiansen

Department of Surgery, Regionshospitalet Randers, Randers, Denmark

Competing interests
No competing interests declared.
Ebbe Boedtkjer

Department of Biomedicine, Aarhus University, Aarhus C, Denmark

For correspondence
eb@biomed.au.dk

Competing interests
Ebbe Boedtkjer, is an inventor on patents covering NBCn1 as target for cancer therapy (EP 3271402)..

"This ORCID iD identifies the author of this article:" 0000-0002-5078-9279

Funding

Sundhed og Sygdom, Det Frie Forskningsråd (7025-00050B)

Ebbe Boedtkjer

Novo Nordisk Fonden (NNF18OC0053037)

Ebbe Boedtkjer

Danish Cancer Society (R136-A8670)

Nicolai J Toft

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Ethics

Human subjects: All participants gave written informed consent. The Mid-Jutland regional division of the Danish Committee on Health Research Ethics (M-20100288) and the Danish Data Protection Agency (1-16-02-191-16) approved the procedures for tissue sampling and data handling, respectively.

Copyright

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.