This project focuses on the important but under-studied role of the P-TEFb-dependent transcription elongation machinery in human breast cancer progression. It aims to test the hypothesis that transcription elongation is a key regulatory step in breast cancer development, and that targeting P-TEFb can be an effective strategy to block breast cancer progression. During the current reporting period, we have established all the required biological assays and generated several key cell lines that either stably overexpress components of active P-TEFb complexes or knock down components of the inhibitory complex. These cell lines will be tested in various EMT, cancer stemness and invasion assays as originally proposed. We are also investigating the activity of a novel CDK9 inhibitor in blocking the expression of various transcription factors that control cell growth and EMT. By establishing these key reagents and experimental conditions, we are laying a solid foundation and making excellent progress toward achieving the stated goals of the project in the next reporting period.