845 A nuclear cAMP microdomain functions as a tumor suppressor in melanoma

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Cyclic AMP (cAMP), a ubiquitous second messenger, has a broad impact on cellular processes such as proliferation, differentiation, apoptosis, migration, and gene expression. It has been widely linked to melanomagenesis; however, studies often report contradictory functions for cAMP (e.g., cancer promotion but also tumor suppression and therapy resistance). Thus, a huge conundrum exists in the field of cAMP signaling and melanoma – one that might be explained by examining cAMP at the level of microdomains. In mammalian cells, two classes of adenylyl cyclases synthesize cAMP: the transmembrane adenylyl cyclases (tmACs) and the soluble adenylyl cyclase (sAC). Unlike tmACs, which are tethered to the plasma membrane, sAC is expressed throughout the cell and within organelles (e.g., nucleus and mitochondria). Thus, sAC and tmACs generate cAMP in spatially separated cell regions. Since cAMP signaling cascades can be evoked and restricted to small compartments in mammalian cells, it is imperative that we interrogate all available cAMP microdomains to truly unravel their role in melanoma. To address this question, we created a panel of sAC KO melanoma cell lines containing doxycycline-inducible sAC cDNAs, targeted to specific cellular compartments, i.e. nucleus, cytoplasm or mitochondria. Utilizing these model cell lines, we showed that only the nuclear sAC-dependent cAMP microdomain inhibits melanoma growth in vitro or in mice. Neither the mitochondrial, nor cytoplasmic sAC cAMP microdomains affected tumor cell growth. Using ATACseq and RNAseq, we discovered that the nuclear cAMP microdomain leads to specific changes in chromatin landscape and a unique gene expression profile that is distinct from the canonical MC1R/cAMP-dependent gene expression profile and encompasses a range of genes with both established and potentially new roles in melanomagenesis. Thus, our findings support a novel tumor suppressor cAMP pathway contained within the mammalian cell nucleus.