  The supersymmetric grand unified theory where the $SU(5)$ gauge symmetry is
broken by the Hosotani mechanism provides a natural solution to the so-called
doublet-triplet splitting problem. At the same time, this model derives a
general and distinctive prediction that is testable at TeV scale collider
experiments. To be more concrete, adjoint chiral supermultiplets with masses
around TeV scale appear. Since these additional fields originate from a
higher-dimensional gauge supermultiplet, our model is highly predictive. We
study especially the Higgs sector and show that our model is discriminative
from the others by precision measurements of the couplings and masses. Namely,
we may get a hint of the breaking mechanism of the grand unification at future
collider experiments.
