Galectin-1 confers resistance to doxorubicin in hepatocellular carcinoma cells through modulation of P-glycoprotein expression

Galectin-1 (GAL1), a β-galactoside-binding protein abundantly expressed in the tumor microenvironment, has emerged as a key mechanism of chemoresistance developed by different tumors. Although increased expression of GAL1 is a hallmark of hepatocellular carcinoma (HCC) progression, aggressiveness and metastasis, limited information is available on the role of this endogenous lectin in HCC resistance to chemotherapy. Moreover, the precise mechanisms underlying this effect are uncertain. HCC has evolved different mechanisms of resistance to chemotherapy including those involving the P-glycoprotein (P-gp), an ATP-dependent drug efflux pump, which controls intracellular drug concentration. Here, we investigated the molecular mechanism underlying GAL1-mediated chemoresistance in HCC cells, particularly the involvement of P-gp in this effect. Our results show that GAL1 protected HepG2 cells from doxorubicin (DOX)- and sorafenib-induced cell death in vitro. Accordingly, GAL1-overexpressing HepG2 cells generated DOX-resistant tumors in vivo. High expression of GAL1 in HepG2 cells reduced intracellular accumulation of DOX likely by increasing P-gp protein expression rather than altering its membrane localization. GAL1-mediated increase of P-gp expression involved activation of the phosphatidylinositol-3 kinase (PI3K) signaling pathway. Moreover, 'loss-of-function' experiments revealed that P-gp mediates GAL1-driven resistance to DOX, but not to sorafenib, in HepG2 cells. Conversely, in PLC/PRF/5 cells, P-gp protein expression was undetectable and GAL1 did not control resistance to DOX or sorafenib, supporting the critical role of P-gp in mediating GAL1 effects. Collectively, our findings suggest that GAL1 confers chemoresistance in HCC through mechanisms involving modulation of P-gp, thus emphasizing the role of this lectin as a potential therapeutic target in HCC.

MicroRNAs contribute to ATP-binding cassette transporter- and autophagy-mediated chemoresistance in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) has an elevated mortality rate, largely because of high recurrence and metastasis. Additionally, the main obstacle during treatment of HCC is that patients usually develop resistance to chemotherapy. Cancer drug resistance involves many different mechanisms, including alterations in drug metabolism and processing, impairment of the apoptotic machine, activation of cell survival signaling, decreased drug sensitivity and autophagy, among others. Nowadays, miRNAs are emerging as master regulators of normal physiology- and tumor-related gene expression. In HCC, aberrant expression of many miRNAs leads to chemoresistance. Herein, we particularly analyzed miRNA impact on HCC resistance to drug therapy. Certain miRNAs target ABC (ATP-binding cassette) transporter genes. As most of these miRNAs are downregulated in HCC, transporter levels increase and intracellular drug accumulation decrease, turning cells less sensitive to death. Others miRNAs target autophagy-related gene expression, inhibiting autophagy and acting as tumor suppressors. Nevertheless, due to its downregulation in HCC, these miRNAs do not inhibit autophagy or tumor growth and, resistance is favored. Concluding, modulation of ABC transporter and/or autophagy-related gene expression or function by miRNAs could be determinant for HCC cell survival under chemotherapeutic drug treatment. Undoubtedly, more insights on the biological processes, signaling pathways and/or molecular mechanisms regulated by miRNAs are needed. Anyway, miRNA-based therapy together with conventional chemotherapeutic drugs has a great future in cancer therapy.

Contribution of galectin-1, a glycan-binding protein, to gastrointestinal tumor progression

Gastrointestinal cancer is a group of tumors that affect multiple sites of the digestive system, including the stomach, liver, colon and pancreas. These cancers are very aggressive and rapidly metastasize, thus identifying effective targets is crucial for treatment. Galectin-1 (Gal-1) belongs to a family of glycan-binding proteins, or lectins, with the ability to cross-link specific glycoconjugates. A variety of biological activities have been attributed to Gal-1 at different steps of tumor progression. Herein, we summarize the current literature regarding the roles of Gal-1 in gastrointestinal malignancies. Accumulating evidence shows that Gal-1 is drastically up-regulated in human gastric cancer, hepatocellular carcinoma, colorectal cancer and pancreatic ductal adenocarcinoma tissues, both in tumor epithelial and tumor-associated stromal cells. Moreover, Gal-1 makes a crucial contribution to the pathogenesis of gastrointestinal malignancies, favoring tumor development, aggressiveness, metastasis, immunosuppression and angiogenesis. We also highlight that alterations in Gal-1-specific glycoepitopes may be relevant for gastrointestinal cancer progression. Despite the findings obtained so far, further functional studies are still required. Elucidating the precise molecular mechanisms modulated by Gal-1 underlying gastrointestinal tumor progression, might lead to the development of novel Gal-1-based diagnostic methods and/or therapies.

Hierarchical and selective roles of galectins in hepatocarcinogenesis, liver fibrosis and inflammation of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) represents a global health problem. Infections with hepatitis B or C virus, non-alcoholic steatohepatitis disease, alcohol abuse, or dietary exposure to aflatoxin are the major risk factors to the development of this tumor. Regardless of the carcinogenic insult, HCC usually develops in a context of cirrhosis due to chronic inflammation and advanced fibrosis. Galectins are a family of evolutionarily-conserved proteins defined by at least one carbohydrate recognition domain with affinity for β-galactosides and conserved sequence motifs. Here, we summarize the current literature implicating galectins in the pathogenesis of HCC. Expression of "proto-type" galectin-1, "chimera-type" galectin-3 and "tandem repeat-type" galectin-4 is up-regulated in HCC cells compared to their normal counterparts. On the other hand, the "tandem-repeat-type" lectins galectin-8 and galectin-9 are down-regulated in tumor hepatocytes. The abnormal expression of these galectins correlates with tumor growth, HCC cell migration and invasion, tumor aggressiveness, metastasis, postoperative recurrence and poor prognosis. Moreover, these galectins have important roles in other pathological conditions of the liver, where chronic inflammation and/or fibrosis take place. Galectin-based therapies have been proposed to attenuate liver pathologies. Further functional studies are required to delineate the precise molecular mechanisms through which galectins contribute to HCC.

Novel roles of galectin-1 in hepatocellular carcinoma cell adhesion, polarization, and in vivo tumor growth

Galectin-1 (Gal-1), a widely expressed β-galactoside-binding protein, exerts pleiotropic biological functions. Gal-1 is up-regulated in hepatocarcinoma cells, although its role in liver pathophysiology remains uncertain. We investigated the effects of Gal-1 on HepG2 hepatocellular carcinoma (HCC) cell adhesion and polarization. Soluble and immobilized recombinant Gal-1 (rGal-1) promoted HepG2 cell adhesion to uncoated plates and also increased adhesion to laminin. Antibody-mediated blockade experiments revealed the involvement of different integrins as critical mediators of these biological effects. In addition, exposure to rGal-1 markedly accelerated the development of apical bile canaliculi as shown by TRITC-phalloidin labeling and immunostaining for multidrug resistance associated-protein 2 (MRP2). Notably, rGal-1 did not interfere with multidrug resistance protein 1/P-glycoprotein or MRP2 apical localization, neither with transfer nor secretion of 5-chloromethylfluorescein diacetate through MRP2. Stimulation of cell adhesion and polarization by rGal-1 was abrogated in the presence of thiodigalactoside, a galectin-specific sugar, suggesting the involvement of protein-carbohydrate interactions in these effects. Additionally, Gal-1 effects were abrogated in the presence of wortmmanin, PD98059 or H89, suggesting involvement of phosphoinositide 3-kinase (PI3K), mitogen-activated protein kinase and cyclic adenosine monophosphate-dependent protein kinase signaling pathways in these functions. Finally, expression levels of this endogenous lectin correlated with HCC cell adhesion and polarization and up-regulation of Gal-1-favored growth of hepatocarcinoma in vivo.

CONCLUSION

Our results provide the first evidence of a role of Gal-1 in modulating HCC cell adhesion, polarization, and in vivo tumor growth, with critical implications in liver pathophysiology.