Calcium signaling in development and disease

The calcium ion (Ca) is a highly versatile signaling messenger involved in a diverse range of physiological processes such as gene transcription/expression, proliferation, differentiation and cell death. Intracellular Ca signals are generated through a 10 000 – 20 000 fold gradient across the cell membrane and via release from the external milieu and/or internal Ca stores. Cells have a unique signaling toolkit to control Ca homeostasis including a selection of ion channels, pumps, exchangers and Ca binding proteins. We have reported that ouabain, an endogenous steroid hormone and ligand to the Na,K-ATPase, can trigger dendritic growth in cortical neurons through signal transduction. This involves a Ca-dependent transcriptional program regulated by CREB and CRE-mediated gene activation, primarily regulated through Ca/calmodulin-dependent protein kinases. The process also includes Ca oscillations and phosphorylation of mitogen-activated protein kinases (ERK 1/2). These data suggest a novel role for Na,K-ATPase and Ca in dendritic growth during development. Previous work has shown that treatment with protein kinase C (PKC) inhibitors results in a prolonged Ca increase leading to calpain activation and release of apoptosis-inducing factor (AIF). We have demonstrated that hyperpolarizationactivated cyclic nucleotide-gated (HCN) channel 2 is responsible for the Ca influx. The influx is regulated via dephosphorylation of a residue in the intracellular Cterminal. This data shows a novel role for HCN channel 2 in cell death and a new possible drug target. Bladder cancer is overall one of the ten most common cancers. We have shown that treatment with Bacillus Calmette-Guerin (BCG), currently the most effective intravesical agent against bladder cancer, induces an intracellular Ca increase and reduces cell proliferation in urinary bladder cancer (T24) cells. Store depletion by SERCA inhibition blocked the BCG-triggered signal, thereby suggesting a role of the endoplasmic reticulum as a Ca source. This signaling event was dependent on phospholipas C since pharmacological inhibition or small interference RNA-mediated gene silencing abolished the response. Finally EdU incorporation revealed that BCGcontrolled cell proliferation was mediated via a Caand PLC-dependent signaling cascade. In summary this thesis presents three studies highlighting three different roles for Ca signaling. They show that Ca signaling is involved in processes critical for cell differentiation, cell proliferation, and cell death, three aspects highly coordinated with development and disease. List of Publications I. Desfrere L, Karlsson M, Hiyoshi H, Malmersjö S, Nanou E, Estrada M, Miyakawa A, Lagercrantz H, El Manira A, Lal M, Uhlén P (2009). Na,KATPase signal transduction triggers CREB activation and dendritic growth. Proc Natl Acad Sci U S A;106(7), 2212-7 II. Norberg E, Karlsson M, Korenovska O, Szydlowski S, Silberberg G, Uhlén P, Orrenius S, Zhivotovsky B (2010). Critical role for hyperpolarizationactivated cyclic nucleotide-gated channel 2 in the AIF-mediated apoptosis. EMBO J.;29(22), 3869-78 III. Karlsson M, Ibarra C, Kjällquist U, Zajac P, Lundgren K, Kaba R, BavandChobot N, Linnarsson S, Wiklund P, Miyakawa A, and Uhlén P. Bacillus Calmette-Guerin (BCG) Triggers PLC-Dependent Ca Signaling in Bladder Cancer Cells. Manuscript