  We analyze cubic spin 3 interaction in AdS space using the higher spin
extension of string-theoretic sigma-model constructed in our previous work,
which low energy limit is described by AdS vacuum. We find that, in the leading
order of the cosmological constant, the spin 3 correlator on the AdS4 string
theory side reproduces the structure of 3 point function of composite
operators, quadratic in free fields, in the dual vector model. The cancellation
of terms violating higher spin holography is related to the value of the
Liouville background charge in four dimensions.
