CD44 and neoplasm: To determine if CD81 reintroduction rescues tumor cluster formation, we also assessed the clustering efficiency of CD81KO MDA-MB-231 cells when overexpressed with CD81 (HA tagged) which restored tumor clustering close to WT cells, whereas HACD81d mutant failed to do so (Figure 4—figure supplement 4D), suggesting CD81 binding with CD44 is important for functions of tumor cluster formation.