The tetraspanins CD151 and Tspan8 are essential exosome components for the crosstalk between cancer initiating cells and their surrounding

Tspan8 and CD151 are metastasis-promoting tetraspanins and a knockdown (kd) of Tspan8 or CD151 and most pronounced of both tetraspanins affects the metastatic potential of the rat pancreatic adenocarcinoma line ASML. Approaching to elaborate the underlying mechanism, we compared ASML(wt), -CD151(kd) and/or Tspan8(kd) clones. We focused on tumor exosomes, as exosomes play a major role in tumor progression and tetraspanins are suggested to be engaged in exosome targeting. ASML-CD151/Tspan8(kd) cells poorly metastasize, but regain metastatic capacity, when rats are pretreated with ASML(wt), but not ASML-CD151(kd) and/or -Tspan8(kd) exosomes. Both exosomal CD151 and Tspan8 contribute to host matrix remodelling due to exosomal tetraspanin-integrin and tetraspanin-protease associations. ASML(wt) exosomes also support stroma cell activation with upregulation of cytokines, cytokine receptors and proteases and promote inflammatory cytokine expression in hematopoietic cells. Finally, CD151-/Tspan8-competent exosomes support EMT gene expression in poorly-metastatic ASML-CD151/Tspan8(kd) cells. These effects are not seen or are weakened using ASML-CD151(kd) or -Tspan8(kd) exosomes, which is at least partly due to reduced binding/uptake of CD151- and/or Tspan8-deficient exosomes. Thus, CD151- and Tspan8-competent tumor exosomes support matrix degradation, reprogram stroma and hematopoietic cells and drive non-metastatic ASML-CD151/Tspan8(kd) cells towards a motile phenotype.