RPS6KB1 and neoplasm: Furthermore, xenograft tumour studies in nude mice showed that the p-4E-BP1 levels were downregulated in vivo upon H19 overexpression and that p-4E-BP1 levels were increased in H19 knockdown tumours; mTORC1-mediated S6K1 phosphorylation, however, was not affected by H19 expression or knockdown (Figs. 3c, d).