PTEN-Dependent Stabilization of MTSS1 Inhibits Metastatic Phenotype in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) presents at metastatic stage in over 50% of patients. With a survival rate of just 2.7% for patients presenting with distant disease, it is imperative to uncover novel mechanisms capable of suppressing metastasis in PDAC. Previously, we reported that the loss of metastasis suppressor protein 1 (MTSS1) in PDAC cells results in significant increase in cellular migration and invasion. Conversely, we also found that overexpressing MTSS1 in metastatic PDAC cell lines corresponds with not only decreased metastatic phenotype, but also greater overall survival. While it is known that MTSS1 is downregulated in late-stage PDAC, the mechanism behind that loss has not yet been elucidated. Here, we build off our previous findings to present a novel regulatory mechanism for the stabilization of MTSS1 via the tumor suppressor protein phosphatase and tensin homolog (PTEN). We show that PTEN loss in PDAC cells results in a decrease in MTSS1 expression and increased metastatic potential. Additionally, we demonstrate that PTEN forms a complex with MTSS1 in order to stabilize and protect it from proteasomal degradation. Finally, we show that the inflammatory tumor microenvironment, which makes up over 90% of PDAC tumor bulk, is capable of downregulating PTEN expression through secretion of miRNA-23b, potentially uncovering a novel extrinsic mechanism of MTSS1 regulation. Collectively, these data offer new insight into the role and regulation of MTSS1 in suppressing tumor cell invasion and migration and help shed light as to what molecular mechanisms could be leading to early cell dissemination in PDAC.