PAK1 and neoplasm: However, a reduction in CD11c+ dendritic cells and MHC-II expression was observed in PAK1KO tumours, which was probably due to a compensatory mechanism, where PAK1 deletion led to upregulated PAK4 expression (Figure 4C), decreasing CD11c+ dendritic cells and reducing MHC-II expression; PAK4 deletion does not affect PAK1 expression in PAK4KO cell lines.