RSU1 and neoplasm: Based on these results, we hypothesized that in highly invasive MDA-MB-231-LM2 cells, depletion of RSU-1L triggers the activation of the truncated RSU-1-X1 isoform to compensate for the loss of RSU-1L function and for this reason its depletion promotes tumor spheroid invasion rather than inhibits it (Fig. 2).