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MicroRNAs in HER2-Amplified Breast Cancer

Newie, Inga LU (2015) In Lund University, Faculty of Medicine Doctoral Dissertation Series 2015:87.
Abstract (Swedish)
Popular Abstract in English

Breast cancer is the most common cancer in women worldwide and the leading cause of cancer-related deaths. Although survival rates are low compared to other cancers, more than 500,000 women worldwide die of breast cancer every year. It is however not a single disease but rather a collection of different diseases with similar appearance but distinct molecular mechanisms. Thus, in order to have higher chances of therapy success, it is crucial that the tumor is not only detected as early as possible but that treatment is adjusted to the subtype of disease.

One of the main breast tumor classifications relies on the presence or absence of three main cellular indicators of biological state,... (More)
Popular Abstract in English

Breast cancer is the most common cancer in women worldwide and the leading cause of cancer-related deaths. Although survival rates are low compared to other cancers, more than 500,000 women worldwide die of breast cancer every year. It is however not a single disease but rather a collection of different diseases with similar appearance but distinct molecular mechanisms. Thus, in order to have higher chances of therapy success, it is crucial that the tumor is not only detected as early as possible but that treatment is adjusted to the subtype of disease.

One of the main breast tumor classifications relies on the presence or absence of three main cellular indicators of biological state, so called biomarkers: estrogen receptor alpha (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2). These subdivisions do not only have prognostic value, but also guide treatment choices. Targeted therapies against the hormone receptors (ER and PR) and HER2 have improved clinical outcomes considerably. However, resistance to targeted drugs is frequent and it has become apparent that further, more detailed classifications are required to identify patients that will respond to known therapies as well as to develop new drugs for those that do not.

The biomarker HER2 is an oncogene, i.e. it promotes tumor growth when produced at higher levels. Almost a fifth of breast tumors show an increase of the HER2 gene, which contains the hereditary information for the growth factor receptor. Elevated production of HER2 is usually accompanied by lower levels of ER and resistance against ER-related drugs.

Our group reported earlier that a rise in production of HER2 might also lead to the increase of a small non-coding RNA, whose gene is located within the HER2 gene. RNAs are transcribed short ‘copies’ of our hereditary information and have important roles in coding, regulation and synthesis of proteins. Non-coding RNAs, unlike coding RNAs, are not translated into proteins but rather exert their full functions on RNA level through sequence-specific or structural interactions with other cellular components. The small non-coding RNA within the HER2 gene is a so called microRNA (miRNA), an emerging class of molecules that regulate the expression of the majority of cellular proteins. The aim of this study was to investigate the levels and biological functions of this miRNA named mir-4728, and to explore its suitability as a biomarker in breast cancer.

The results from the first study show that mir-4728 directly regulates ER, which establishes a direct connection between HER2 and ER, two of the main breast cancer biomarkers. The miRNA thus contributes to the observed effect that ER is present at lower levels in HER2 positive breast cancer. This finding can aid in unravelling the complex cellular interactions in breast cancer and help to understand drug resistance mechanisms.

The second study focused on the potential threats of miRNA-based drugs. Some miRNAs have very important functions but are lost in diseases like cancer. One therapeutic approach is to replace the cell’s missing miRNAs to restore their function, and the first clinical studies are ongoing. We observed that if quality control is not performed properly by the manufacturers of these replacement miRNAs, there can be large differences between production batches, potentially leading to severe adverse effects with unexpected consequences. This observation is clinically relevant to prevent undesired side-effects in miRNA replacement therapy.

The third study investigated miRNA isoforms, variations of the same miRNA, which differ only minimally in sequence but can have very distinct cellular functions. A miRNA that is often elevated in breast and other cancers is miR-21. Our results show that this miRNA is regulated by a degradation pathway, which appears to be low or missing in many tumors.

The fourth study then continues to show that the HER2 miRNA mir-4728 actually represses this degradation pathway and thus leads to higher levels of tumor-promoting miR-21. Elevated miR-21 then downregulates the tumor suppressor programmed cell death 4 or PDCD4, which we show to be connected to worse prognoses in HER2 positive breast cancer. Together, these results open up new possibilities for therapeutic strategies and help understand molecular mechanisms in cancer.

The fifth study evaluated more global effects of mir-4728. We observed that blocking the function of this miRNA led to a strong decrease of metabolism-related genes in the cell. This indicates that the active miRNA is somehow involved in upregulation of tumor metabolism, thus contributing to cancer progression.

In summary, we have found that the microRNA mir-4728 can contribute to tumor development through several mechanisms. Since it is located in the gene of the important breast cancer biomarker HER2 and they are produced together, it might not contribute additional information as a biomarker. However, the molecular mechanisms this microRNA uses to contribute to cancer could be exploited for therapeutic use in the future. (Less)
Abstract
Background: Breast cancer is the most common female malignancy and the leading cause of cancer-related deaths worldwide. Targeted therapy against the main biomarkers estrogen receptor alpha (ER) and human epidermal growth factor receptor 2 (HER2/ERBB2) have greatly improved mortality rates, but ab initio or acquired therapy resistance is common. It is imperative to identify patients who will benefit from targeted therapy and develop new treatment modalities for resistant tumors. microRNAs (miRNAs) are small, non-coding RNAs that regulate expression of up to 60% of human protein-coding genes. Their frequent deregulation in cancer makes miRNAs attractive candidate biomarkers and clinical targets. We previously reported that the HER2 locus,... (More)
Background: Breast cancer is the most common female malignancy and the leading cause of cancer-related deaths worldwide. Targeted therapy against the main biomarkers estrogen receptor alpha (ER) and human epidermal growth factor receptor 2 (HER2/ERBB2) have greatly improved mortality rates, but ab initio or acquired therapy resistance is common. It is imperative to identify patients who will benefit from targeted therapy and develop new treatment modalities for resistant tumors. microRNAs (miRNAs) are small, non-coding RNAs that regulate expression of up to 60% of human protein-coding genes. Their frequent deregulation in cancer makes miRNAs attractive candidate biomarkers and clinical targets. We previously reported that the HER2 locus, which is amplified in 15-20% of breast cancers, also encodes an intronic miRNA, mir-4728.

Aims: The aim of this thesis was to study the function of the main mature miRNA product of mir-4728, miR-4728-3p, and to investigate if this miRNA could serve as an independent diagnostic or treatment predictive biomarker in breast cancer.

Results: Expression of miR-4728-3p correlated with HER2, and ER was identified as a direct target of the miRNA, connecting these two important breast cancer biomarkers. Regulation of ER occurred in a non-canonical manner, expanding our understanding of miRNA-mediated target gene regulation. During functional studies in vitro, we sometimes detected strong, batch-dependent off-target effects of commercially available miRNA mimics, stressing the need to maintain high quality standards in clinical studies using miRNA replacement therapy. Furthermore, inhibition of miR-4728-3p led to upregulation of the predicted target PAPD5, a non-canonical poly(A) polymerase, that destabilized the oncogenic microRNA miR-21. HER2 signaling is known to activate mir-21 transcription through the MAPK/ERK pathway, suggesting that the HER2 locus has a dual role in increasing levels of miR-21 through both miR-4728-3p and HER2. Blocking miR-4728-3p also strongly inhibited cellular metabolism, indicating a role for the miRNA in improved nutrient processing. Taken together, these results establish the importance of miR-4728-3p as a breast cancer oncogene. (Less)
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author
supervisor
opponent
  • MD, PhD Kuchenbauer, Florian, University Hospital Ulm, Germany
organization
publishing date
type
Thesis
publication status
published
subject
keywords
miR-21, PAPD5, Breast Cancer, miR-4728, microRNA, ERBB2 / HER2
in
Lund University, Faculty of Medicine Doctoral Dissertation Series
volume
2015:87
pages
87 pages
publisher
Department of Clinical Sciences, Lund University
defense location
Segerfalksalen, BMC A10, Sölvegatan 17, Lund
defense date
2015-09-11 13:00
ISSN
1652-8220
ISBN
978-91-7619-166-8
language
English
LU publication?
yes
id
f61f4570-3fdc-43a0-871f-43925c107b6b (old id 7764295)
date added to LUP
2015-08-25 16:03:48
date last changed
2016-09-19 08:44:48
@phdthesis{f61f4570-3fdc-43a0-871f-43925c107b6b,
  abstract     = {Background: Breast cancer is the most common female malignancy and the leading cause of cancer-related deaths worldwide. Targeted therapy against the main biomarkers estrogen receptor alpha (ER) and human epidermal growth factor receptor 2 (HER2/ERBB2) have greatly improved mortality rates, but ab initio or acquired therapy resistance is common. It is imperative to identify patients who will benefit from targeted therapy and develop new treatment modalities for resistant tumors. microRNAs (miRNAs) are small, non-coding RNAs that regulate expression of up to 60% of human protein-coding genes. Their frequent deregulation in cancer makes miRNAs attractive candidate biomarkers and clinical targets. We previously reported that the HER2 locus, which is amplified in 15-20% of breast cancers, also encodes an intronic miRNA, mir-4728.<br/><br>
Aims: The aim of this thesis was to study the function of the main mature miRNA product of mir-4728, miR-4728-3p, and to investigate if this miRNA could serve as an independent diagnostic or treatment predictive biomarker in breast cancer.<br/><br>
Results: Expression of miR-4728-3p correlated with HER2, and ER was identified as a direct target of the miRNA, connecting these two important breast cancer biomarkers. Regulation of ER occurred in a non-canonical manner, expanding our understanding of miRNA-mediated target gene regulation. During functional studies in vitro, we sometimes detected strong, batch-dependent off-target effects of commercially available miRNA mimics, stressing the need to maintain high quality standards in clinical studies using miRNA replacement therapy. Furthermore, inhibition of miR-4728-3p led to upregulation of the predicted target PAPD5, a non-canonical poly(A) polymerase, that destabilized the oncogenic microRNA miR-21. HER2 signaling is known to activate mir-21 transcription through the MAPK/ERK pathway, suggesting that the HER2 locus has a dual role in increasing levels of miR-21 through both miR-4728-3p and HER2. Blocking miR-4728-3p also strongly inhibited cellular metabolism, indicating a role for the miRNA in improved nutrient processing. Taken together, these results establish the importance of miR-4728-3p as a breast cancer oncogene.},
  author       = {Newie, Inga},
  isbn         = {978-91-7619-166-8},
  issn         = {1652-8220},
  keyword      = {miR-21,PAPD5,Breast Cancer,miR-4728,microRNA,ERBB2 / HER2},
  language     = {eng},
  pages        = {87},
  publisher    = {Department of Clinical Sciences, Lund University},
  school       = {Lund University},
  series       = {Lund University, Faculty of Medicine Doctoral Dissertation Series},
  title        = {MicroRNAs in HER2-Amplified Breast Cancer},
  volume       = {2015:87},
  year         = {2015},
}