Abstract Advanced prostate cancer (PC) is the leading cause of death in the US because there is no effective treatment due to the poorly understood disease mechanism. Sex comb on midleg-like-2 (SCML2) is a member of Polycomb repressive complex 1 and regulates homeotic gene expression during development. Using proteomic approaches, we have identified SCML2 as a binding partner of the YAP1 protein complexes isolated from PC cell lines. Both SCML2 and YAP1 regulate basic cellular biology, including stem cell maintenance and carcinogenesis; however, whether SCML2 and YAP1 cooperate to contribute to the aggressive PC in humans remains unknown. We showed that AR-positive cell lines express high levels of SCML2 with a significant increase in castration-resistant PC cells compared to its castration-sensitive cell counter, suggesting a possible role of SCML2 in PC progression. We also showed that androgens regulated the protein-protein interaction between SCML2 and YAP1, as evaluated by proximity ligation assay. In addition, the GST-pulldown assay revealed that SCML2 interacted with the WW/SH3 domain of YAP1, where AR also binds. Besides, our RNAi-aided gene silencing experiment demonstrated that YAP1 and SCML2 might be functionally antagonistic. Moreover, gene silencing and growth assays showed that SCML2 might act as a growth suppressor in castration-sensitive PC cells while acting as a growth mediator or survival factor in castration-resistant PC cells. Furthermore, our analysis of the cancer genome atlas PC data set has indicated that amplification of SCML2 is associated with reduced progression-free survival. These observations suggest that SCML2 and YAP1 interaction is biologically functional, and the degree of their interaction may play a critical role in PC progression downstream of dysregulated androgen/AR signaling. Citation Format: Ava M. Boston, Abdulrahman M. Dwead, Marwah M. Al-Mathkour, Kezhan Khazaw, Bekir Cinar. Upregulation of the polycomb group protein SCML2 contributes to aggressive prostate cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5303.