Why can an end-centered unit cell not be cubic? What is the highest possible symmetry for this type of unit cell?

The crystal system of a compound with unit cell dimensions $\mathrm{a}=0.387 \mathrm{nm}, \mathrm{b}=0.387 \mathrm{nm}$ and $\mathrm{c}=0.504 \mathrm{nm}$ and $\mathrm{\alpha }=\mathrm{\beta }=90°$ and $\mathrm{\gamma }=120°$ is