Human mesenchymal stem cells enhance autophagy of lung carcinoma cells against apoptosis during serum deprivation

Currently, some evidence suggests that human multipotential mesenchymal stems cells (hMSCs) aid tumor growth and metastasis. Nutrient deprivation and oxygen deficiency are representative characteristics of solid tumor microenvironment during the cancer development. Because the effects of hMSCs on tumors under stressful conditions have not been determined, we investigated the survival mechanisms used by stressed stromal cells on A549 and SPC-1 lung carcinoma cell lines in vitro and in vivo. An indirect culture system was used to investigate the effects of hMSCs on viability and apoptosis in starved carcinoma cells and focused on the role of autophagy in regulating the survival of carcinoma cells. The results showed that A549 and SPC-1 cells had higher viability when co-cultured with hMSCs and that this was mainly attributed to decreased apoptosis. Autophagosomes were analyzed using GFP-LC3 and electron microscopy, which showed that autophagy was significantly activated in the starved co-culture groups. However, the inhibition of autophagy by the autophagic inhibitor 3-MA significantly abrogated the apoptosis reduction in either single groups or co-culture groups under serum deprivation, which implied that the hMSCs protected against apoptosis by enhancing autophagy in lung carcinoma cells in vitro. We also observed that hMSCs promoted tumor initiation and growth in vivo. In conclusion, our study demonstrates that hMSCs can protect carcinoma cells from nutrient deprivation-induced apoptosis and promote tumor initiation and growth, and, interestingly, autophagy plays an important role in the survival of cancer cells.