  Motivated by D-brane scenarios, we consider a non-supersymmetric model based
on the gauge symmetry U(3)_CxU(3)_LxU(3)_R$ which is equivalent to the SU(3)^3
``trinification'' model supplemented by three U(1)s. Two U(1) combinations are
anomalous while the third U(1)_Z' is anomaly free and contributes to the
hypercharge generator. This hypercharge embedding correspods to
sin^2\theta_W=6/19 in the case of full gauge coupling unification. The U(3)^3
symmetry is broken down to the Standard Model by vev's of two (1,3,\bar3)-
scalar multiplets supplemented by two Higgs fields in (1,3,1) and (1,1,3)
representations. The latter break U(1)_Z' and provide heavy masses to the extra
lepton doublets. Fermions belong to (3,\bar 3,1)+(\bar 3,1,3)+ (1,3,\bar 3)
representations as in the trinification model. The model predicts a natural
quark-lepton hierarchy, since quark masses are obtained from tree-level
couplings, while charged leptons receive masses from fourth order Yukawa terms,
as a consequence of the extra abelian symmetries. Light Majorana neutrino
masses are obtained through a see-saw type mechanism operative at the SU(3)_R
breaking scale of the order M_R\ge 10^9 GeV.
