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Tuberous sclerosis complex 2 (TSC2), or tuberin, is a pivotal regulator of the mechanistic target of rapamycin signaling pathway that controls cell survival, proliferation, growth, and migration. Loss of Tsc2 function manifests in organ-specific consequences, the mechanisms of which remain incompletely understood. Recent single cell analysis of the kidney has identified ATP-binding cassette G2 (Abcg2) expression in renal proximal tubules of adult mice as well as a in a novel cell population. The impact in adult kidney of Tsc2 knockdown in the Abcg2-expressing lineage has not been evaluated. We engineered an inducible system in which expression of truncated Tsc2, lacking exons 36-37 with an intact 3= region and polycystin 1, is driven by Abcg2. Here, we demonstrate that selective expression of Tsc2fl36-37 in the Abcg2pos lineage drives recombination in proximal tubule epithelial and rare perivascular mesenchymal cells, which results in progressive proximal tubule injury, impaired kidney function, formation of cystic lesions, and fibrosis in adult mice. These data illustrate the critical importance of Tsc2 function in the Abcg2- expressing proximal tubule epithelium and mesenchyme during the development of cystic lesions and remodeling of kidney parenchyma. [ABSTRACT FROM AUTHOR]

Transforming growth factor-β (TGF-β) and hepatocyte growth factor (HGF) play key roles in regulating the response to renal injury but are thought to mediate divergent effects on cell behavior. However, how TGF-β signaling alters the response to HGF in epithelia, the key site of HGF signaling in the injured kidney, is not well studied. Contrary to our expectation, we showed that deletion of the TGF-β type II receptor in conditionally immortalized proximal tubule (PT) cells impaired HGF-dependent signaling. This reduced signaling was due to decreased transcription of c-Met, the HGF receptor, and the TGF-β-dependent c-Met transcription and increased response to HGF in PT cells were mediated by the Notch pathway. The interactions of TGF-β, HGF, and Notch pathways had biologically significant effects on branching morphogenesis, cell morphology, migration, and proliferation. In conclusion, epithelial TGF-β signaling promotes HGF signaling in a Notchdependent pathway. These findings suggest that TGF-β modulates PT responses not only by direct effects, but also by affecting other growth factor signaling pathways. [ABSTRACT FROM AUTHOR]