Fibronectin controls cap-dependent translation through β1 integrin and eukaryotic initiation factors 4 and 2 coordinated pathways

Fibronectin (FN) is a major matrix protein involved in multiple processes. Little is known about how adhesion to FN affects the translational machinery. We show that in fibroblasts adhesion to FN triggers translation through the coordinated regulation of eukaryotic initiation factors (ell's) 4F and 2 and is impaired by blocking beta 1 integrin engagement. FN-stimulated translation has unique properties: (i) it is highly sensitive to the inhibition of phosphaticlylinositol 3-kinase (PI3K), but not to the inhibition of mammalian target of rapamycin, downstream of PI3K; (ii) there is no synergy between serum-stimulated translation and FN-dependent translation; (iii) FN-dependent translation, unlike growth factor-stimulated translation, does not lead to increased translocation of 5' terminal oligopyrimidine tract mRNAs to polysomes; and (iv) cells devoid of attachment to matrix show an impairment of initiation of translation accompanied by phosphorylation of elF2 alpha, which cannot be reverted by active PI3K. These findings indicate that integrins may recruit the translational machinery in a unique way and that FN-dependent translation cannot be blocked by mammalian target of rapamycin inhibition.