Bif-1 interacts with Beclin 1 through UVRAG and regulates autophagy and tumorigenesis. Bif-1, also known as Endophilin B1, forms a complex with Beclin 1 via UVRAG and acts as a positive mediator of the class III PI3-kinase (PI3KC3). It is involved in autophagosome formation and regulates autophagy, which is essential for cellular homeostasis, development, and survival. Bif-1 loss suppresses autophagosome formation and enhances tumor development in mice. Bif-1 is required for the activation of PI3KC3 and autophagosome formation, and its absence leads to increased cell survival under nutrient starvation. Bif-1 is also a tumor suppressor, as its knockout significantly enhances the development of spontaneous tumors in mice. Bif-1 interacts with Beclin 1 through UVRAG, and its SH3 domain is sufficient for binding to UVRAG. The BAR domain of Bif-1 is required for autophagosome formation. Bif-1 localizes to autophagosomal membranes and is involved in the early stages of autophagosome formation. Bif-1 regulates PI3KC3 activity, which is essential for autophagy. Bif-1 knockout mice develop normally and have a higher incidence of spontaneous tumors, indicating that Bif-1 is a tumor suppressor. The study highlights the role of Bif-1 in autophagy and tumorigenesis, and its potential as a therapeutic target for cancer treatment.Bif-1 interacts with Beclin 1 through UVRAG and regulates autophagy and tumorigenesis. Bif-1, also known as Endophilin B1, forms a complex with Beclin 1 via UVRAG and acts as a positive mediator of the class III PI3-kinase (PI3KC3). It is involved in autophagosome formation and regulates autophagy, which is essential for cellular homeostasis, development, and survival. Bif-1 loss suppresses autophagosome formation and enhances tumor development in mice. Bif-1 is required for the activation of PI3KC3 and autophagosome formation, and its absence leads to increased cell survival under nutrient starvation. Bif-1 is also a tumor suppressor, as its knockout significantly enhances the development of spontaneous tumors in mice. Bif-1 interacts with Beclin 1 through UVRAG, and its SH3 domain is sufficient for binding to UVRAG. The BAR domain of Bif-1 is required for autophagosome formation. Bif-1 localizes to autophagosomal membranes and is involved in the early stages of autophagosome formation. Bif-1 regulates PI3KC3 activity, which is essential for autophagy. Bif-1 knockout mice develop normally and have a higher incidence of spontaneous tumors, indicating that Bif-1 is a tumor suppressor. The study highlights the role of Bif-1 in autophagy and tumorigenesis, and its potential as a therapeutic target for cancer treatment.