  The effective potential for the Aharonov-Bohm phase $\theta_H$ in the fifth
dimension in GUT inspired $SO(5)\times U(1) \times SU(3)$ gauge-Higgs
unification is evaluated to show that dynamical electroweak symmetry breaking
takes place with $\theta_H \not= 0$, the 4D Higgs boson mass 125$\,$GeV being
generated at the quantum level. The cubic and quartic self-couplings
$(\lambda_3, \lambda_4)$ of the Higgs boson are found to satisfy universal
relations, i.e. they are determined, to high accuracy, solely by $\theta_H$,
irrespective of values of other parameters in the model. For $\theta_H=0.1$
($0.15$), $\lambda_3$ and $\lambda_4$ are smaller than those in the standard
model by 7.7% (8.1%) and 30% (32%), respectively.
