TrkB is responsible for EMT transition in malignant pleural effusions derived cultures from adenocarcinoma of the lung

Abstract

Lung cancer is the leading cause of cancer-related mortality worldwide. Recent evidence indicates that tumors contain a subpopulation of cancer stem cells (CSCs) that are responsible for tumor maintenance and spread. CSCs have recently been linked to the occurrence of epithelial-to-mesenchymal transition (EMT). Neurotrophins (NTs) are growth factors that regulate the biology of embryonic stem cells and cancer cells, but still little is known about the role NTs in the progression of lung cancer. In this work, we investigated the role of the NTs and their receptors using as a study system primary cell cultures derived from malignant pleural effusions (MPEs) of patients with adenocarcinoma of the lung. We assessed the expression of NTs and their receptors in MPE-derived adherent cultures vs. spheroids enriched in CSC markers. We observed in spheroids a selectively enhanced expression of TrkB, both at the mRNA and protein levels. Both K252a, a known inhibitor of Trk activity, and a siRNA against TrkB strongly affected spheroid morphology, induced anoikis and decreased spheroid forming efficiency. Treatment with neurotrophins reversed the inhibitory effect of K252a. Importantly, TrkB inhibition caused loss of vimentin expression as well as that of a set of transcription factors known to be linked to EMT. These ex vivo results nicely correlated with an inverse relationship between TrkB and E-cadherin expression measured by immunohistochemistry in a panel of lung adenocarcinoma samples. We conclude that TrkB is involved in full acquisition of EMT in lung cancer, and that its inhibition results in a less aggressive phenotype.

Malignant Pleural Effusion and ascites Induce Epithelial-Mesenchymal Transition and Cancer Stem-like Cell Properties via the Vascular Endothelial Growth Factor (VEGF)/Phosphatidylinositol 3-Kinase (PI3K)/Akt/Mechanistic Target of Rapamycin (mTOR) Pathway

“…We found here, from clinical specimens and in vitro experiments, that cancer cells in malignant PE/ascites underwent EMT and displayed a cancer stem cells phenotype, which could account for the poor prognosis. Here, besides confirming the phenomena described previously (9,19,20), we also found that malignant exudates had universal induction activity regardless of tumor type and origin. More importantly, we noted that non-CSCs could undergo EMT process and be directly converted into the CSC state when exposed to malignant PE/ascites; therefore, blocking the process in combination with conventional chemotherapies is critical to better control malignant PE/ascites.…”

“…Indeed, VEGF was reported to induce EMT in human pancreatic cancer cells (35). Previous investigations reported that cancer cell EMT and gain of CSC properties in malignant PE/ascites depended on TrkB and TGF-␤ signaling, respectively (9,45). TrkB is a well established regulator that promotes VEGF expression (46).…”

“…EMT and gain a stem cell phenotype within malignant PE/ascites (9,19,20). So far, however, there are no available strategies to inhibit these processes because the underlying mechanisms are barely understood.…”

Schwann cells promote EMT and the Schwann-like differentiation of salivary adenoid cystic carcinoma cells via the BDNF/TrkB axis

“…Increasing evidence suggests that EMT plays a crucial role in the acquisition of invasive and metastatic potential in a number of cancers, such as head and neck squamous cell carcinoma (21), breast cancer (24), pancreatic cancer (25) and lung cancer (26). Recent studies found that the BDNF/TrkB axis is involved in the EMT process in various cancers including SACC (8,21,27). Although the correlation between EMT and PNI has been rarely reported, it is plausible to infer that EMT plays an important role in the PNI process since it can confer tumor cells with increased migration and invasion abilities (8,10,11).…”

BDNF: An Oncogene or Tumor Suppressor?

“…What is of considerable interest is that the BDNF/TrkB pathway has been shown to mediate the resistance to anoikis of multiple cancers (9,18,(25)(26)(27)(28)(29). it was shown that in multiple cancers, metastatic tumor cells have up-regulated TrkB and BDNF compared to tumor cells that did not metastasize (18,26,29). Furthermore, tumor cells were resistant to anchorage-independent cell death, or anoikis, because TrkB activation resulted in constitutive pi3K activity and survival for the duration of the migration to neighboring tissues (18), supporting the pro-survival role of BDNF as tumor cells migrate.…”