14 In this study, we demonstrate that the interaction between HCC and stroma plays a key role in tumor progression, and that in patients this interaction occurs in more advanced disease. We based our conclusions on the following data: (1) CAFs stimulated proliferation, migration and invasion of HCC cells; (2) HCC cells secreted LPA, which promoted transdifferentiation

of PTFs to a CAF-like myofibroblastic phenotype through the up-regulation of genes related to a contractile phenotype; (3) MK-8669 in vivo this recruitment and transdifferentiation was blocked by inhibiting LPA secretion; (4) PTFs coinjected with HCC cells accelerated tumor growth and progression, but an LPA inhibitor blocked PTF transdifferentiation Buparlisib in vitro and slowed HCC growth and progression; and (5) patients with higher LPA concentrations had larger, metastatic HCC and worse survival. Myofibroblasts have recently been implicated in HCC progression,15

but the molecular mechanisms regulating the interaction between HCC and cells and myofibroblasts are still unknown. We demonstrate for the first time that LPA is involved in the reciprocal cross-talk between HCC cells and resident fibroblasts, leading to tumor progression. In particular, HCC cells activate resident fibroblasts (PTFs), which acquire a contractile capability and express α-SMA, sustained by the up-regulation of specific contractile-related genes giving rise to a myofibroblast-like phenotype. This occurs through a paracrine mechanism, because HCC cells secrete LPA and PTFs express LPA receptors that are absent in HCC cells. LPA is implicated in different malignancies and has recently been shown

to induce HCC cell invasion by increasing the production of matrix metalloproteinase-9.12 Once PTFs have assumed a myofibroblast-like phenotype, in coculture experiments they increase the proliferation, migration, and invasion of HCC cells in vitro and promote tumoral progression in vivo. We did not investigate mediators of the back cross-talk from myofibroblasts Lck toward HCC cells, but the central role of LPA is further demonstrated by the fact that by blocking LPA with a pharmacological inhibitor or with ATX-silencing, the increased proliferation, migration and invasion of HCC cells is abrogated. In vivo, this is even more striking, because after treating animals with an LPA inhibitor, we found a down-regulation of the genes supporting the myofibroblast phenotype and a lower number of activated PTFs, whereas HCC progression decreased. LPA is seen to have a central role in orchestrating the tumor–stroma interaction. This finding is consistent with a previous work showing an alteration of the phospholipid in HCC, where ATX displays a crucial role in the inflammatory peritumoral reaction by interacting with the tumor necrosis factor α/nuclear factor κB pathway.