Rudhira-mediated microtubule stability controls TGFβ signaling during mouse vascular development

The Transforming Growth Factor {beta} (TGF{beta}) signaling pathway is critical for survival, proliferation, and cell migration, and is tightly regulated during cardiovascular development. Smads, key effectors of TGF{beta} signaling, are sequestered by microtubules (MTs) and need to be released for pathway function. Independently, TGF{beta} signaling also stabilizes MTs. Molecular details and the in vivo relevance of this cross-regulation remain unclear, understanding which is important in complex biological processes such as cardiovascular development. Here, we use rudhira/Breast Carcinoma Amplified Sequence 3 (BCAS3), a MT-associated, endothelium-restricted and developmentally essential proto-oncogene, as a pivot to decipher cellular mechanisms in bridging TGF{beta} signaling and MT stability. We show that Rudhira regulates TGF{beta} signaling in vivo, during mouse cardiovascular development, and in endothelial cells in culture. Rudhira associates with MTs and is essential for the activation and release of Smad2/3 from MTs. Consequently, Rudhira depletion attenuates Smad2/3- dependent TGF{beta} signaling thereby impairing cell migration. Interestingly, Rudhira is also a transcriptional target of Smad2/3-dependent TGF{beta} signaling essential for TGF{beta}-induced MT stability. Our study identifies an immediate early physical role and a slower, transcription-dependent role for Rudhira in cytoskeleton-TGF{beta} signaling crosstalk. These two phases of control could facilitate temporally-and spatially restricted targeting of the cytoskeleton and/or TGF{beta} signaling in vascular development and disease. Significance statementThe developmental TGF{beta} pathway is essential for cell migration, cell-cell communication, adhesion, apoptosis, and matrix remodeling. Dysregulation of TGF{beta} signaling leads to aberrant vascular patterning and angiogenesis during mouse embryogenesis. Pathway activation involves phosphorylation and nuclear transport of Smads. Microtubules sequester Smads in the cytoplasm, thereby inhibiting TGF{beta} signaling. Conversely, TGF{beta} signaling stabilizes microtubules. However, the molecular components involved, and biological relevance of this cross-regulation remain unclear. We show that the oncoprotein Rudhira/BCAS3 facilitates Smad-MT dissociation upon ligand-mediated TGF{beta} receptor activation. Interestingly, Smad-dependent TGF{beta} signaling activation enhances rudhira transcription, essential for microtubule stabilization during cardiovascular development. This dual regulation of TGF{beta} signaling and microtubule stability by Rudhira allows sustained temporal control essential for development, and its dysregulation has pathological outcomes.