Interstitial flow in and around tumor tissue affects the mechanical microenvironment to modulate tumor cell growth and metastasis. We investigated the roles of flow-induced shear stress in modulating cell cycle distribution in four tumor cell lines and the underlying mechanisms. In all four cell lines, incubation under static conditions for 24 or 48 h led to G0/G1 arrest; in contrast, shear stress (12 dynes/cm 2 ) induced G2/M arrest. The molecular basis of the shear effect was analyzed, and the presentation on molecular mechanism is focused on human MG63 osteosarcoma cells. Shear stress induced increased expressions of cyclin B1 and p21 CIP1 and decreased expressions of cyclins A, D1, and E, cyclin-dependent protein kinases (Cdk)-1, -2, -4, and -6, and p27 KIP1 as well as a decrease in Cdk1 activity. Using specific antibodies and small interfering RNA, we found that the shear-induced G2/M arrest and corresponding changes in G2/M regulatory protein expression and activity were mediated by ␣v␤3 and ␤1 integrins through bone morphogenetic protein receptor type IA-specific Smad1 and Smad5. Shear stress also down-regulated runt-related transcription factor 2 (Runx2) binding activity and osteocalcin and alkaline phosphatase expressions in MG63 cells; these responses were mediated by ␣v␤3 and ␤1 integrins through Smad5. Our findings provide insights into the mechanism by which shear stress induces G2/M arrest in tumor cells and inhibits cell differentiation and demonstrate the importance of mechanical microenvironment in modulating molecular signaling, gene expression, cell cycle, and functions in tumor cells.M echanical microenvironment plays important roles in modulating tissue development, maintenance, and remodeling and in cellular responses and functions (1). Interstitial fluid flow in and around tissue affects the mechanical microenvironment, including the shear stress and pressure force acting on the cell surface and the tethering force acting on cell-matrix connections (2). These interstitial flow-induced forces can modulate tumor metastasis and invasion as well as anticancer drug delivery (3).Although the influence of interstitial fluid flow on tumor pathobiology and drug delivery has been studied, the effect of the flow-induced shear force on tumor cells has not been much explored. Compressive forces have been shown to inhibit tumor cell growth (4) and up-regulate adhesion molecules (5). A recent study reported that tumor cell proliferation is affected by intratumoral pressure and that activation of mitogen-activated protein kinases and nuclear antigen Ki-67 is involved in this mechanical modulation (6). Although these results show that mechanical forces can modulate tumor cell responses, the detailed mechanisms by which mechanical stimuli are transduced into cellular signaling to regulate tumor cell gene expression and functions remain unclear.Integrins have been implicated as mechanosensors in many types of cells seeded on extracellular matrix (ECM) (7), but their role in modulating mechanical responses of...

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Atherosclerosis, a vascular pathology responsible for most cardiovascular‐related morbidity and mortality, develops predictably in regions of the arterial tree in which wall shear stresses are generated by complex patterns of blood flow. It has been recognized that hemodynamic characteristics determine the location of lesions and contribute to the pathogenesis of atherosclerosis. The key cells involved in atherogenesis include vascular endothelial cells (ECs) and smooth muscle cells (SMCs). Recent evidence suggests that laminar blood flow in the straight part of the arterial tree and high shear stress modulate cellular signaling and EC function, and protect against atherogenesis. In contrast, disturbed flow in bifurcations of the arterial tree and the associated oscillatory low shear stress enhance leukocyte infiltration of the arterial wall and thus are atherogenic. However, little is known about the effect of disturbed flow on ECs, especially on their interactions with SMCs, whose phenotypic switching is significantly implicated in atherosclerosis and neointimal lesion formation. Our recent studies using microRNA (miR) assay, in vitro EC‐SMC co‐culture flow system, experimental animal models, and human specimens from patients with coronary artery disease (CAD) have identified several miRs to be involved in the formation and progression of atherosclerosis. Among these miRs, miR‐146a and 10a play atheroprotective roles in ECs against atherogenesis induced by disturbed flow. MiR‐451, by targeting Rab5a, inhibits vascular SMC proliferation and inflammation and suppresses injury‐induced neointimal lesion formation. Our findings help the discovery of new target biomarkers and elucidation of functional mechanisms underlying atherosclerosis, thereby facilitating the development of new approaches for therapeutic interventions.Support or Funding InformationThis work was supported by grants from the Ministry of Science and Technology in Taiwan (grant numbers: MOST‐106‐2633‐B‐009‐001, 105‐2321‐B‐400‐007, 106‐3114‐Y‐043‐021)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Vascular endothelial cells (ECs) are exposed to different patterns of blood flow (disturbed vs. laminar) and the associated shear stresses (oscillatory [OSS] vs. pulsatile [PSS]), which lead to differential EC responses. We investigated the roles of classes I and II histone deacetylases (HDACs, i.e., HDAC‐1/2/3 and HDAC‐5/7, respectively) in regulating NF‐E2‐related factor‐2 (Nrf2) and Krüppel‐like factor‐2 (KLF2), two important transcription factors that govern many shear‐responsive genes, and cell cycle in ECs in response to OSS. Application of OSS (0.5±4 dynes/cm2) to ECs up‐regulated both classes I and II HDACs and their nuclear accumulations, whereas PSS (12±4 dynes/cm2) induced phosphorylation‐dependent nuclear export of class II HDACs. OSS induced the association of HDAC‐1/2/3 with Nrf2 and HDAC‐3/5/7 with myocyte enhancer factor‐2, and the deacetylations of these HDACs led to down‐regulations of the antioxidant gene NAD(P)H quinone oxidoreductase‐1 (NQO1) and KLF2 in ECs. Transfecting ECs with HDAC‐1/2/3‐ and HDAC‐3/5/7‐specific small interfering RNAs eliminated the OSS‐induced down‐regulations of NQO1 and KLF2, respectively. OSS up‐regulated cyclin A and phospho‐retinoblastoma and down‐regulated p21CIP1 in ECs and hence their proliferation; these effects are mediated by HDAC‐1/2/3. The OSS‐induced HDAC signaling and EC responses are mediated by phosphatidylinositol 3‐kinase/Akt. Immunohistochemical examinations of the experimentally stenosed rat abdominal aorta showed high levels of HDAC‐2/3/5 in the EC layer at post‐stenotic sites, where OSS occurs. Our findings indicate the importance of different HDACs in regulating endothelial oxidative, inflammatory, and proliferative responses to disturbed flow with OSS.