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Original Article |
Correspondence to: Erik H.J. Danen, Division of Cell Biology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands, Tel:(3120) 512-1934 Fax:(3120) 512-1944 E-mail:edanen{at}nki.nl.
In cellular transformation, activated forms of the small GTPases Ras and RhoA can cooperate to drive cells through the G1 phase of the cell cycle. Here, we show that a similar but substrate-regulated mechanism is involved in the anchorage-dependent proliferation of untransformed NIH-3T3 cells. Among several extracellular matrix components tested, only fibronectin supported growth factorinduced, E2F-dependent S phase entry. Although all substrates supported the mitogen-activated protein kinase (MAPK) response to growth factors, RhoA activity was specifically enhanced on fibronectin. Moreover, induction of cyclin D1 and suppression of p21Cip/Waf occurred specifically, in a Rho-dependent fashion, in cells attached to fibronectin. This ability of fibronectin to stimulate both Ras/MAPK- and RhoA-dependent signaling can explain its potent cooperation with growth factors in the stimulation of cell cycle progression.
Key Words: fibronectin, cell adhesion, G1 cell cycle, integrin, Rho
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