Exosomal LINC00355 derived from cancer-associated fibroblasts promotes bladder cancer cell proliferation and invasion by regulating miR-15a-5p/HMGA2 axis

We have previously demonstrated that exosomes derived from cancer-associated fibroblasts (CAFs) promote bladder cancer (BC) cell proliferation and invasion by transferring LINC00355. In this study, the molecular mechanisms underlying the pro-bladder cancer action of exosomal LINC00355 were explored. CAFs were obtained from BC tumor tissues, and normal fibroblasts (NFs) were obtained from adjacent normal tissues. Human BC cell lines (T24 and 5367) were incubated with NF-Exo (exosomes from NFs), CAF-Exo (exosomes from CAFs), CAF^si-Ctrl-Exo (exosomes from si-Ctrl-transfected CAFs), and CAF^si-LINC00355-Exo (exosomes from si-LINC00355-transfected CAFs). BC cell proliferation and invasion were evaluated by MTT and Transwell assays, respectively. The interaction between miR-15a-5p and LINC00355 or HMGA2 was examined by online bioinformatics analysis and luciferase activity assay. Results showed that HMGA2 is a direct target of miR-15a-5p, and LINC00355 functions as a sponge of miR-15a-5p to upregulate HMGA2 expression. The promoting effects of CAF-Exo on HMGA2 expression, cell proliferation, and cell invasion were hindered when LINC00355 expression was inhibited in BC cells. These promoting effects were also hindered when miR-15a-5p was overexpressed or HMGA2 was silenced in BC cells. In conclusion, exosomal LINC00355 derived from CAFs promotes BC cell proliferation and invasion by regulating miR-15a-5p/HMGA2 axis.