RESUMEN
Tumor-derived exosomes are emerging mediators of cancer cachexia, a kind of multifactorial syndrome characterized by serious loss of skeletal muscle mass and function. Our previous study had showed that microRNAs in exosomes of C26 colon tumor cells were involved in induction of muscle atrophy. Here, we focus on studying proteins in tumor-derived exosomes which might also contribute to the development of cancer cachexia. Results of comparing the protein profiles of cachexic C26 exosomes and non-cachexic MC38 exosomes suggested that growth differentiation factor 15 (GDF-15) was rich in C26 exosomes. Western blotting analysis confirmed the higher levels of GDF-15 in C26 cells and C26 exosomes, compared with that of MC38 cells. Results of animal study also showed that GDF-15 was rich in tumor tissues, serum exosomes, and gastrocnemius (GA) muscle tissues of C26 tumor-bearing mice. GDF-15 protein could directly induce muscle atrophy of cultured C2C12 myotubes via regulating Bcl-2/caspase-3 pathways. What's more, overexpression of GDF-15 in MC38 cells could increase the potency of MC38 conditioned medium or exosomes in inducing muscle atrophy. Knockdown of GDF-15 in C26 cells decreased the potency of C26 conditioned medium or exosomes in inducing muscle atrophy. These results suggested that GDF-15 in tumor-derived exosomes could contribute to induction of muscle atrophy and also supported the possibility of targeting GDF-15 in treatment of cancer cachexia.
RESUMEN
Tumor-derived exosomes are emerging mediators of cancer cachexia. Clarifying the regulation of exosome biogenesis and finding possible targets for cancer cachexia therapy are important and necessary. In the present study, systemic analysis of the roles of STAT3 in controlling exosome biogenesis of murine C26 colon tumor cells and its contribution to the development of cancer cachexia is conducted. The genetic manipulation of STAT3 expression, STAT3 knockout (KO) or overexpression (OE), significantly affected the exosome biogenesis and also the potency of C26 conditioned medium (CM) in inducing muscle atrophy and lipolysis in vitro. The genetic manipulation of STAT3 expression caused change in phosphorylation of PKM2 and glycolysis. PKM2/SNAP23 pathway was involved in regulation of exosome biogenesis by STAT3 genetic manipulation as well as by STAT3 inhibitors in C26 cells. Mice inoculated with STAT3 knockout or overexpression C26 cells exhibited ameliorated or aggravated cancer cachexia symptoms, with a positive correlation with the serum exosome and IL-6 levels. The STAT3/PKM2/SNAP23 pathway was affected in C26 tumor tissues with genetic manipulation of STAT3 expression. The capacity of exosome biogenesis of different human cancer cells also exhibited a positive correlation with the activation of STAT3/PKM2/SNAP23 pathway. The research presented here confirms that STAT3 plays a critical role in regulating biogenesis of tumor-derived exosomes which could contribute to cancer cachexia development.