PI3K regulates branch initiation and extension of cultured mammary epithelia via Akt and Rac1 respectively

Abstract

The tree-like architecture of the mammary gland is generated by branching morphogenesis, which is regulated by many signals from the microenvironment. Here we examined how signaling downstream of phosphoinositide 3-kinase (PI3K) regulates different steps of mammary branching using three-dimensional culture models of the mammary epithelial duct. We found that PI3K was required for both branch initiation and elongation. Activated Akt was enhanced at branch initiation sites where its negative regulator, PTEN, was blocked by signaling via Sprouty2 (SPRY2); inhibiting Akt prevented branch initiation. The pattern of SPRY2 expression, and thus of Akt activation and branch initiation, was controlled by mechanical signaling from endogenous cytoskeletal contractility. In contrast, activated GTP-bound Rac1 localized to the leading edge of nascent branches and was required for branch elongation. These data suggest that the PI3K network integrates mechanical and biochemical signaling to control branching morphogenesis of mammary epithelial cells.

Regulation of tissue morphodynamics: an important role for actomyosin contractility

“…In a 3D model of mammary branching morphogenesis, tissue regions under higher mechanical stress (~0.1 kPa) show changes in gene expression [39] and molecular signaling [40], resulting in multicellular invasion into the surrounding matrix [41]. Additionally, contractility within the tissue generates surrounding mechanical heterogeneities [42] and locally aligns matrix fibrils to instruct ductal elongation [43].…”

Topography Design Concept of a Tissue Engineering Scaffold for Controlling Cell Function and Fate Through Actin Cytoskeletal Modulation

“…13,63,64 On this scale, the formation of actin stress fibers is promoted or limited for the adjustment of the mechanical homeostasis between the cell and ECM mainly in response to a change in the cell peripheral curvature defined by the topographical features.…”

“…The resulting collective migration forms a multicellular spherical acinus or tube inside a structural constraint with a curved surface. 63,64,119 Control of cell migration through actin modulation has been well characterized based on contact guidance by means of simple synthetic 2.5D microtopographical features, such as parallel ridges and grooves, 73,96,[120][121][122][123][124] arrays of micropillars, 14,22,80,81 and asymmetric microchannels (Fig. 5B).…”

Inhibition of Sprouty2 polarizes macrophages toward an M2 phenotype by stimulation with interferon γ andPorphyromonas gingivalislipopolysaccharide

“…The interaction between Grb2 and RTK is prevented and RTK signaling is inhibited as a result of the interaction between Spry2 and Grb2 21, 38. In addition to the Ras/ERK pathway, Spry2 can also suppress the PI3K/AKT signaling pathway by promoting the activation and stability of phosphatase and tensin homolog (PTEN) 39, 40, 41. In contrast, loss of Spry2 protein results in hyper‐activation of PI3K/AKT signaling to drive cell proliferation and invasion 42.…”