  We report on the temperature and electric field driven evolution of the
magnetoresistance lineshape at an interface between Ni/AlO$_x$ and Nb-doped
SrTiO$_3$. This is manifested as a superposition of the Lorentzian lineshape
due to spin accumulation and a parabolic background related to tunneling
anisotropic magnetoresistance (TAMR). The characteristic Lorentzian line shape
of the spin voltage is retrieved only at low temperatures and large positive
applied bias. This is caused by the reduction of electric field at large
positive applied bias which results in a simultaneous reduction of the
background TAMR and a sharp enhancement in spin injection. Such mechanisms to
tune magnetoresistance are uncommon in conventional semiconductors.
