Ca 2+ is a ubiquitous and dynamic second messenger molecule that is induced by many factors including receptor activation, environmental factors, and voltage, leading to pleiotropic effects on cell function including changes in migration, metabolism and transcription. As such, it is not surprising that aberrant regulation of Ca 2+ signals can lead to pathological phenotypes, including cancer progression. However, given the highly context-specific nature of Ca 2+ -dependent changes in cell function, delineation of its role in cancer has been a challenge. Hence, the role of store-operated Ca 2+ entry (SOCE) in melanoma metastasis is still not fully elucidated. To address this, we examined UVdependent metastasis, revealing a critical role for SOCE suppression. As previous literature demonstrated a role for cholesterol (CHL) in melanoma progression, our investigations corroborate this revealing UV-induced CHL biosynthesis as a critical mediator for UV-induced SOCE suppression and subsequent metastasis. However, SOCE suppression alone was both necessary and sufficient for metastasis to occur. CHAPTER 1 INTRODUCTION Part 1: Calcium I. Ca 2+ signal generation: Ca 2+ signals are generated in response to a wide variety of autocrine, paracrine, hormonal, neurocrine and environmental factors. Here, we will briefly discuss some of the major underlying approaches that cells use to generate Ca 2+ responses. A. Receptor-mediated control of Ca 2+ signals G-Protein Coupled Receptor (GPCR) and Receptor Tyrosine Kinase (RTK) families are widely expressed and facilitate Ca 2+ responses in virtually all cell types through phospholipase C (PLC). Briefly, as shown in Figure 1-1, when Gαq-coupled GPCRs (driving PLCβ activation) or RTKs with PLCγ docking sites are activated, PLC hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) into Inositol Trisphosphate (InsP3) and diacylglycerol (DAG). InsP3 diffuses within the cell towards the ER where it encounters InsP3 Receptors (InsP3Rs), ER-localized Ca 2+ channels that mediate ER Ca 2+ release. The resultant ER Ca 2+ depletion leads to a highly conserved process known as store-operated Ca 2+ entry (SOCE) (4-7). SOCE is initiated by Stromal Interaction Molecule (STIM), a single pass membrane protein that acts as an Endoplasmic Reticulum (ER) Ca 2+ sensor, responding to ER Ca 2+ depletion by translocating within the ER towards the plasma membrane (PM) where it binds to and activates members of the Orai family of Ca 2+ -selective channels (6, 8). STIM1 and Orai1 serve as the predominant mediators of SOCE in most cell types (8), although the other members of the STIM and Orai families can function analogously, although with distinct characteristics. For example, a decrease

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