Genome-wide CRISPR screen for human factors involved in alternative polyadenylation based on differential localization of CD47

At least 70% of the human protein-coding genes contain multiple polyadenylation sites (PAS) and undergo alternative polyadenylation (APA), generating distinct transcripts from a single gene. While APA has been implicated in various physiological and pathological processes, its regulatory factors and cellular mechanisms remain incompletely understood. A previous study demonstrated that APA influences the localization of the cell surface marker CD47. Here, we present the results of a genome-wide CRISPR screen aimed at identifying APA regulators using CD47 as a reporter. Given that isoform-specific knockdown of CD47, as well as knockdown of core 3' end processing factors, alters CD47 localization, we developed an immunofluorescence-based method that simultaneously detects cell surface and intracellular CD47 protein, enabling the visualization of APA-dependent changes at the single-cell level. Leveraging this approach, we conducted a CRISPR screen and identified multiple genes affecting CD47 cell-surface expression. In addition to known membrane trafficking factors, we uncovered several nuclear factors, among which POLDIP2 emerged as a potential novel APA regulator with a global impact on APA. This study provides a foundation for further investigations into the molecular mechanisms governing APA.