Young, Ryan M.

TAF7, a core subunit of the general transcription factor TFIID, regulates transcription and additionally functions as an RNA chaperone that directs nascent nuclear RNAs to cytoplasmic polysomes, thereby influencing protein synthesis. Here, we identify a set of novel cytoplasmic interactors and a previously unappreciated cytoplasmic role for TAF7 in oncogenesis. BioID-mediated proximity labeling identified STAT3 and the CCT and WASH complexes as prominent cytoplasmic interactors of TAF7. These interactions were validated by co-immunoprecipitation and proximity ligation assays. We further showed that cytoplasmic TAF7 levels increased during oncogenesis in proportion to cancer cell pathogenicity. Notably, TAF7 engagement with STAT3, CCT and WASH complexes is markedly enhanced during cellular transformation, consistent with their functions in cancer progression. Together, these findings reveal a cytoplasmic TAF7 interactome and implicate elevated cytoplasmic TAF7 as associated with oncogenesis.

Abstract Transcription factors and their cofactors are major and selective nononcogene dependencies in multiple myeloma cells. By performing a gain-of-function perturbation screen in human multiple myeloma cell lines, we identified the inhibitor of DNA binding (ID) genes as putative suppressors of multiple myeloma cell fitness. Among them, ID2 was found to be downregulated in multiple myeloma patient cells and acted as a tumor suppressor by directly binding and repressing the basic helix-loop-helix factor TCF3, also known as E2A. Lower ID2 expression in multiple myeloma cells conferred a proliferative advantage by increasing TCF3 activity, leading to a dependency on this transcription factor. In contrast, ID2 overexpression reduced TCF3 binding to DNA, which resulted in cell-cycle arrest and a halt in multiple myeloma cell proliferation. The myeloma bone marrow milieu supported this process by further decreasing the expression of ID2 and enhancing TCF3 activity, partly via IL6, revealing a mechanism by which the tumor microenvironment affects multiple myeloma cell behavior. Significance: Multiple myeloma cells exploit the oncogenic and proliferative potential of TCF3 by downregulating the transcriptional regulator ID2, a process facilitated by the bone marrow microenvironment.