Cutaneous melanoma is a highly aggressive tumor type with rising incidence. Despite remarkable therapeutic advances in recent years, metastatic melanoma remains a lethal disease for thousands of patients each year, thus new treatments are still needed. Overcoming this challenge requires deep knowledge of the underlying biology driving and sustaining melanoma metastasis. We are studying a novel type of RNA species, circular RNA (circRNA), which are covalently ligated RNA loops arising from cis back-splicing. We have observed that expression of the circRNA CDR1as is lost in melanoma cell lines and patient tissues. In primary melanoma patient tissues, loss of CDR1as strongly associates with poor patient outcomes, suggesting its loss may be a driver of melanoma progression. Modeling CDR1as silencing, shRNA-mediated depletion of CDR1as enhanced invasion and metastasis of melanoma cells in xenograft models. The precise mechanism(s) by which CDR1as silencing effects a pro-tumorigenic phenotype of melanoma cells remains undetermined. Initial publications suggested CDR1as functions as an endogenous inhibitor of the microRNA miR-7 in neurons. Surprisingly, in melanoma, we did not observe clear regulation of miR-7 expression or function after depletion of CDR1as, suggesting it has additional functions. We have preliminary data supporting a role for novel CDR1as interacting proteins, including members of the IGF2BP family, which are known to be pro-tumorigenic in a variety of cancer contexts. Our goals with this proposal are the following: Taking a candidate approach, we plan to dissect the contribution(s) of the IGF2BP proteins to the functional consequences of CDR1as silencing in melanoma cells. In addition, we plan to perform a set of unbiased analyses, such as RNA-seq, RIBO-seq, RNA pull downs and proteomic profiling, to comprehensively examine possible mechanism(s) regulated by CDR1as silencing, downstream or independent of IGF2BPs. We will use in vitro, xenograft models and genetically engineered mouse models (GEMMs) to elucidate the biological processes, pathways and molecules controlled by CDR1as during melanoma progression. Our studies might uncover novel therapeutic targets or strategies to exploit for melanoma patient treatment.