Elucidating the role of intracellular cell-signaling pathways controlling FOXA1 functions in Breast Cancer

Østrogenreseptor (ER) formidler responsen på østrogener og er ansvarlig for å drive spredning hos ca. 70% av pasientene med brystkreft. Targeting ER er en vellykket terapeutisk tilnærming ved klinisk praksis for pasienter som uttrykker ER. Imidlertid reagerer et betydelig antall pasienter dårlig på anti-ER-behandlinger. En nøkkelbestemmende faktor for funksjonene til ER er transkripsjonsfaktoren FOXA1. Ved å identifisere regulatorene av FOXA1 hos brystkreftpasienter med motstand mot anti-ER-terapier, kan vi derfor åpne nye strategier for behandling av disse pasientene. Resultatene så langt har vist at FOXA1 er positivt regulert i resistente brystkreftceller av kinaser og proteindeacetylaser. Blant alle kandidatene har vi identifisert og videre karakterisert at cellesykluskinasene CDK2 / 4 og histondeacetylaser HDAC2 / 4 er viktige positive regulatorer av FOXA1 i hormonresistente kreftformer. Videre har vi i denne forskningen identifisert fosforylering eller acetylering av FOXA1. Spesielt har mutasjon av stedene som er fosforylert av CDK4 en effekt i binding av FOXA1 til kromatin. Når mutert, binder FOXA1 seg til gener involvert i kreftveier (Her2 og PTEN) og for unndragelse av apoptose. Det er viktig at hemming av alle identifiserte kinaser og proteindeacetylaser hadde en negativ innvirkning på spredning av cellene som var resistente mot anti-ER-terapier. Fremtidige eksperimenter i dyremodeller vil validere om inhiberingen av disse FOXA1-regulatorene kan hemme vekst og FOXA1-funksjon i resistente svulster.

We have identified cyclin dependent kinases (CDKs) as regulators of the activity of the transcription factor FOXA1. We have characterised the specific CDK complexes that impinge on its function (CDK4 and CDK2) and we have also identified the sites that have an impact on FOXA1 function. We have generated mutant versions of FOXA1 that cannot be phosphorylated and we have interrogated their genomic location. Importantly, they reprogram the binding of FOXA1 to chromatin, so that it interacts with genes involved in cancer pathways (e.g. Her2 and PTEN) and apoptosis evasion (e.g. Bcl2). Our results show that CDK negatively regulates FOXA1 on specific genomic locations involved in proliferation. This is particularly relevant since CDK inhibitors are currently used for advanced breast cancer treatment but resistance is starting to emerge. Here we show that a potential mechanism involves the reprogramming of FOXA1 binding to chromatin.

The present application is compatible with the Research Council of Norway?s call and priorities as set out in the FRIMEDBIO Program for Young Research Talents. Breast cancer is a heterogeneous disease. Tumors are generally classified into ER positive, HER2 positive and the triple negative (TN) subtype, which lacks hormone receptors and HER2. Considering the expression of these two markers, 70-75% of the tumors are ER positive; 20% fall in the group of HER2 positive and the remaining are the TN. Out of this 20%, half of them are also ER positive. Patients can be treated with therapies targeting these factors, which are known to induce proliferation. Unfortunately, a very significant number of patients become resistant to these therapies. One of the principal challenges in the field is the identification of alternative targets in the resistant tumors. The FOXA1 transcription factor is expressed in ER and HER2 tumors and its expression is associated with proliferation, metastasis and differentiation. Recently, my team has identified a new role for FOXA1 in breast cancers as a mediator of HER2 signal and as a potential therapeutic target for the treatment of resistant tumors to anti-ER therapies (abstract attached). Breast cancer cell proliferation results from many different factors that activate multiple intracellular signaling pathways. This work besides on the hypothesis that FOXA1 integrates input signals originating from multiple cell-signaling pathways to generate output responses that culminate in proliferation, differentiation or metastasis in HER2 as well as in ER breast cancer subtypes. By means of chemical biology, functional genomics and proteomic methods in combination with in vivo and in vitro models, this research aims to elucidate which cell-signaling pathways are required to control FOXA1 functions and how they execute its control. Identification of the key regulatory elements responsible for FOXA1 functions might be used as future therapeutic target.