The role of the AHNAK protein in breast cancer : implications for tumour metastasis and chemoresistance

Davis, Tanja Andrea (2016-12)

Thesis (PhD)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: Introduction – Cancer continues to have a significant impact on society. While there has been much success in characterising tumours and identifying targetable markers, two major problems are still faced today, namely therapeutic failure and advanced progression of the disease. The human AHNAK protein is a giant scaffold protein involved in multiple cellular processes and has now also been suggested to be associated with cancer, particularly with regards to tumour metastasis and chemoresponse. However, limited information and several contradicting findings have contributed to a poor understanding of the role of AHNAK in cancer. Thus, we aimed to characterise the AHNAK protein in cancer by determining the role of the protein in the chemotherapeutic response of breast cancer to doxorubicin (DXR) and also in cellular migration. Methods – For the in vitro model the non-metastatic DXR-sensitive epithelial-like MCF-7 and metastatic DXR-resistant mesenchymal-like MDA-MB-231 cell lines were used. We performed DXR treatments and assessed AHNAK’s protein expression and intracellular localisation. We also assessed these properties in a tumour-bearing mouse model. AHNAK knockdown and overexpression was achieved by means of transient plasmid transfections in both cell lines and following DXR treatments we assessed apoptotic marker expression, cell cycle modulation, epithelial-mesenchymal transition (EMT) marker expression and cellular migration. Results – DXR induced dose-independent and dose-dependent changes in AHNAK protein expression in MCF-7 and MDA-MB-231 cells, respectively, but it did not affect its intracellular localisation in these cells. In the tumour-bearing mouse model DXR also induced dose-dependent changes in AHNAK expression without affecting its localisation, similar to the MDA-MB-231 cells. In the MDA-MB-231 cells, DXR promoted apoptosis inhibition by decreasing cPARP and cCasp7 expression. Knockdown of AHNAK prevented this inhibition while overexpression induced a similar inhibitory effect. With cell cycle analyses we observed that DXR also resulted in S phase arrest in these cells. AHNAK knockdown completely prevented the DXR-induced cell cycle arrest while overexpression was sufficient to cause such an arrest on its own. No significant effects were observed with these experiments in the MCF-7 cells. DXR induced EMT in the MCF-7 cells but AHNAK knockdown or overexpression did not affect this. In MDA-MB-231 cells DXR treatment showed a trend of decreased EMT and while AHNAK knockdown had no effect on this, its overexpression showed clearer evidence of EMT reduction. AHNAK knockdown also had no major effects on cell migration in both cell lines, although its overexpression generally decreased cellular migration. Conclusions – We show that AHNAK plays a novel role in the DXR-response of breast cancer cells and this involved AHNAK’s expression, apoptosis inhibition and cell cycle modulation. Possible molecular mechanisms are proposed but require further investigation. Our results regarding the role of AHNAK in tumour cell migration is less clear and contradicting when compared to other studies. These results may have potential therapeutic implications with regards to the modulation of DXR response to improve treatment efficacy.

AFRIKAANS OPSOMMING: Inleiding - Kanker het steeds 'n beduidende impak op die samelewing. Terwyl daar groot sukses in die karakterisering van gewasse en die identifisering van teikenbare merkers gemaak is, word twee groot probleme steeds vandag ervaar, naamlik terapeutiese mislukking en gevorderde progressie van die siekte. Die menslike AHNAK proteïen is 'n reuse steier proteïen betrokke by verskeie sellulêre prosesse en dit word ook voorgestel dat die proteïen verband hou met kanker, veral ten opsigte van kanker metastase en chemo-reaksie. Beperkte inligting en verskeie weersprekende bevindinge het egter bygedra tot 'n swak begrip van die rol van AHNAK in kanker. ‘n Oogmerk van hierdie studie is dus om AHNAK in kanker beter te karakteriseer deur die rol van die proteïen in chemoterapeutiese reaksie van borskanker teenoor doxorubicin (DXR) en ook in sellulêre migrasie te bepaal. Metodes - Vir die in vitro model is die nie-metastatiese DXR-sensitiewe epiteel-agtige MCF-7 en metastatiese DXR-weerstandige mesenkiemale MDA-MB-231 sellyne gebruik. Ons het DXR behandelings uitgevoer en AHNAK proteïen uitdrukking en intrasellulêre lokalisering bepaal. Ons het hierdie eienskappe ook in 'n kanker muis model bepaal. AHNAK uitklopping en ooruitdrukking is bereik deur middel van tydelike plasmied transfeksies in beide sellyne. DXR behandelinge is uitgevoer en daarna is apoptotiese merker uitdrukking, selsiklus modulasie, epiteel-mesenkiemale oorgang (EMO) merker uitdrukking en sellulêre migrasie bepaal. Resultate - DXR het dosis-onafhanklike en dosis-afhanklike veranderinge in AHNAK proteïen uitdrukking in MCF-7 en MDA-MB-231 selle, onderskeidelik, veroorsaak maar het geen invloed op intrasellulêre lokalisering gehad nie. Met die kanker muis model het DXR ook dosis-afhanklike veranderinge in AHNAK uitdrukking veroorsaak sonder ‘n verandering in lokalisering, soortgelyk aan dié in MDA-MB-231 selle. In die MDA-MB-231 selle het DXR apoptose inhibering bevorder deur cPARP en cCasp7 uitdrukking te verminder. AHNAK uitklopping het hierdie inhibisie verhinder terwyl ooruitdrukking tot ‘n soortgelyke inhiberende effek gelei het. Selsiklus analise het getoon dat DXR ook tot S-fase blokkering gelei het in hierdie selle. AHNAK uitklopping het die selsiklus blokkering heeltemal verhoed terwyl ooruitdrukking voldoende was om ‘n soortgelyke blokkering op sy eie teweeg te bring. Geen beduidende effekte was waargeneem met hierdie eksperimente in die MCF-7 selle nie. DXR het EMO bevorder in die MCF-7 selle maar AHNAK uitklopping of ooruitdrukking het geen invloed op dit gehad nie. In MDA-MB-231 selle het DXR behandeling 'n tendens van verminderde EMO getoon en terwyl AHNAK uitklopping geen effek op hierdie gehad het nie, het ooruitdrukking duideliker bewyse van EMO vermindering getoon. AHNAK uitklopping het ook nie 'n groot uitwerking op sel migrasie in beide sellyne gehad nie, alhoewel ooruitdruking sellulêre migrasie oor die algemeen verminder het. Gevolgtrekkings - Ons bewys dat AHNAK 'n nuwe rol speel in die DXR-reaksie van borskanker en dit betrek AHNAK uitdrukking, apoptose inhibering en selsiklus modulasie. Moontlike molekulêre meganismes word voorgestel, maar verdere ondersoek word vereis. Die resultate met betrekking tot die rol van AHNAK in kankersel migrasie is minder duidelik en weerspreek sekere studies. Hierdie resultate het moontlike potensiële terapeutiese implikasies met betrekking tot die modulasie van DXR-reaksie om behandeling doeltreffendheid te verbeter.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/100238
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