Plasmalemmal and Secretory Pathway Calcium ATPases in the Mammary Gland

Helen Faddy (2007). Plasmalemmal and Secretory Pathway Calcium ATPases in the Mammary Gland PhD Thesis, School of Pharmacy, The University of Queensland.

       
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Author Helen Faddy
Thesis Title Plasmalemmal and Secretory Pathway Calcium ATPases in the Mammary Gland
School, Centre or Institute School of Pharmacy
Institution The University of Queensland
Publication date 2007-11
Thesis type PhD Thesis
Supervisor Monteith, Gregory R.
Roberts-Thomson, Sarah J.
Subjects 11 Medical and Health Sciences
Abstract/Summary Calcium (Ca2+) is an indispensable intracellular second messenger, essential for cellular life and death. Given the duality of the Ca2+ signal, intracellular Ca2+ levels must be tightly regulated to ensure Ca2+ homeostasis is maintained. Indeed, dysregulation of Ca2+ handling and homeostasis has been associated with a number of different disease states. The cellular arsenal for controlling intracellular Ca2+ includes a multitude of Ca2+ transport proteins, including the plasmalemmal and secretory pathway Ca2+ ATPases (the PMCAs, and SPCAs, respectively). Multiple isoforms of each exist, many of which have different tissue distributions and regulate diverse physiological functions. Secretory pathway Ca2+ ATPase 2 (SPCA2) was first characterised in 2005, and, as such, is the most recently identified Ca2+ ATPase. To date, only a small number of functional studies have been reported on SPCA2, however, a physiological role in secretory cells has been proposed for this novel enzyme. The mammary gland is a unique secretory organ in many ways, but when it comes to Ca2+ regulation and homeostasis it is especially so; during lactation the mammary epithelial cell must transport large quantities of Ca2+ in a unidirectional fashion, concurrent to maintaining a low intracellular Ca2+ concentration. Specific isoforms of plasmalemmal and secretory pathway Ca2+ ATPases are associated with lactation, and indeed with the supply of Ca2+ ions for the enrichment of milk. The recently identified SPCA2 has a number of characteristics suggestive of a role in lactation. This thesis reports the results of an investigation of the hypotheses that SPCAs, in particular the recently identified and less widely expressed SPCA2, are important in mammary gland development, and that different isoforms of plasmalemmal and secretory pathway Ca2+ ATPases have different Plasmalemmal and Secretory Pathway Ca2+ ATPases in the Mammary Gland vii localisations during lactation. The expression of both SPCA1 and SPCA2 in mammary glands isolated from virgin, pregnant, lactating and involuting mice was assessed; a more pronounced increase in SPCA2 mRNA was observed during lactation compared to SPCA1, suggesting that SPCA2 is the predominant SPCA isoform associated with the lactating phenotype. Immunolocalisation studies indicate that different plasmalemmal (PMCA1, PMCA2) and secretory pathway (SPCA1, SPCA2) Ca2+ ATPases have different localisations in the lactating mammary gland in vivo, and in a three-dimensional mammary gland culture model, suggesting different functional roles for these different Ca2+ ATPases during lactation. It is not uncommon for ion transporters, which are up-regulated in lactation to be similarly over-expressed in breast cancer. In addition, there is accumulating evidence to suggest that alterations in cellular Ca2+ signalling and homeostasis are associated with cancer. Indeed certain Ca2+ transport proteins are associated with tumorigenicity and have been identified as possible targets for anti¬cancer therapies. This thesis also reports the results of an investigation of the hypothesis that SPCAs, particularly SPCA2, are important in breast cancer. SPCA1 and SPCA2 mRNA levels were assessed in a bank of breast cancer derived and normal human breast epithelial cell lines and human clinical breast cancer samples. A pronounced increase in SPCA2 mRNA was observed in the breast cancer derived cell lines compared to the normal cell lines, and also in the clinical tumour samples compared to surrounding normal tissue, suggesting that up-regulated SPCA2 is associated with breast cancer. Given that SPCA2 was only identified in 2005, there is a paucity of published studies investigating SPCA2 function. Indeed, there have only been four published reports to date specifically characterising this novel Ca2+ ATPase, coming from only three research laboratories. This thesis reports the results of an investigation, which has attempted to further characterise SPCA2 function viii Plasmalemmal and Secretory Pathway Ca2+ ATPases in the Mammary Gland through gene over-expression and knock-down studies. Collectively, the results presented in this thesis suggest that SPCA2 is not involved in global Ca2+ regulation and proposes that SPCA2 may have a highly specialised role within the cell, which may be associated with Golgi function. In summary, the results presented in this thesis are the first to implicate SPCA2 in a physiological process, and in a disease state, and highlight the importance of this novel enzyme in the mammary gland. They also demonstrate that different isoforms of plasmalemmal and secretory pathway Ca2+ ATPases have different cellular localisations during lactation in the mammary gland, which may suggest different functional roles for these Ca2+ ATPases during this physiological process. In addition, the work presented in this thesis has attempted to characterise the recently identified Ca2+ ATPase, SPCA2, and collectively suggests that SPCA2 is not involved in global Ca2+ regulation, but rather, propose a highly specific physiological role for this novel enzyme within the cell.

 
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Created: Mon, 28 Mar 2011, 14:26:56 EST by Noela Stallard on behalf of Library - Information Access Service