Lorena Aguilar

E-cadherin determines Caveolin-1 tumor suppression or metastasis enhancing function in melanoma cells

The role of caveolin‐1 (CAV1) in cancer is highly controversial. CAV1 suppresses genes that favor tumor development, yet also promotes focal adhesion turnover and migration of metastatic cells. How these contrasting observations relate to CAV1 function in vivo is unclear. Our previous studies implicate E‐cadherin in CAV1‐dependent tumor suppression. Here, we use murine melanoma B16F10 cells, with low levels of endogenous CAV1 and E‐cadherin, to unravel how CAV1 affects tumor growth and metastasis and to assess how co‐expression of E‐cadherin modulates CAV1 function in vivo in C57BL/6 mice. We find that overexpression of CAV1 in B16F10 (cav‐1) cells reduces subcutaneous tumor formation, but enhances metastasis relative to control cells. Furthermore, E‐cadherin expression in B16F10 (E‐cad) cells reduces subcutaneous tumor formation and lung metastasis when intravenously injected. Importantly, co‐expression of CAV1 and E‐cadherin in B16F10 (cav‐1/E‐cad) cells abolishes tumor formation, lung metastasis, increased Rac‐1 activity, and cell migration observed with B16F10 (cav‐1) cells. Finally, consistent with the notion that CAV1 participates in switching human melanomas to a more malignant phenotype, elevated levels of CAV1 expression correlated with enhanced migration and Rac‐1 activation in these cells.

The Interaction of Classical Complement Component C1 with Parasite and Host Calreticulin Mediates Trypanosoma cruzi Infection of Human Placenta

Background 9 million people are infected with Trypanosoma cruzi in Latin America, plus more than 300,000 in the United States, Canada, Europe, Australia, and Japan. Approximately 30% of infected individuals develop circulatory or digestive pathology. While in underdeveloped countries transmission is mainly through hematophagous arthropods, transplacental infection prevails in developed ones. Methodology/Principal Findings During infection, T. cruzi calreticulin (TcCRT) translocates from the endoplasmic reticulum to the area of flagellum emergence. There, TcCRT acts as virulence factor since it binds maternal classical complement component C1q that recognizes human calreticulin (HuCRT) in placenta, with increased parasite infectivity. As measured ex vivo by quantitative PCR in human placenta chorionic villi explants (HPCVE) (the closest available correlate of human congenital T. cruzi infection), C1q mediated up to a 3–5-fold increase in parasite load. Because anti-TcCRT and anti-HuCRT F(ab′)2 antibody fragments are devoid of their Fc-dependent capacity to recruit C1q, they reverted the C1q-mediated increase in parasite load by respectively preventing its interaction with cell-bound CRTs from both parasite and HPCVE origins. The use of competing fluid-phase recombinant HuCRT and F(ab′)2 antibody fragments anti-TcCRT corroborated this. These results are consistent with a high expression of fetal CRT on placental free chorionic villi. Increased C1q-mediated infection is paralleled by placental tissue damage, as evidenced by histopathology, a damage that is ameliorated by anti-TcCRT F(ab′)2 antibody fragments or fluid-phase HuCRT. Conclusions/Significance T. cruzi infection of HPCVE is importantly mediated by human and parasite CRTs and C1q. Most likely, C1q bridges CRT on the parasite surface with its receptor orthologue on human placental cells, thus facilitating the first encounter between the parasite and the fetal derived placental tissue. The results presented here have several potential translational medicine aspects, specifically related with the capacity of antibody fragments to inhibit the C1q/CRT interactions and thus T. cruzi infectivity.

Comparative in vivo antiangiogenic effects of calreticulin from Trypanosoma cruzi and Homo sapiens sapiens

Angiogenesis is a complex multi-step process of neovascularization arising from preexisting blood vessels whose generation is regulated by pro- and anti-angiogenic factors. Both Trypanosoma cruzi calreticulin (TcCRT) and its human counterpart (HuCRT) are antiangiogenic. This is the first report where the TcCRT and HuCRT anti-angiogenic properties are compared in vivo. In the chick embryonic chorioallantoid membrane assay (CAM) and at equimolar concentrations, TcCRT displayed significantly higher antiangiogenic activities than its human counterpart. LPS had marginal effects at the concentrations present in the recombinant protein preparations and the TcCRT antiangiogenic effects were largely inhibited by specific polyclonal antibodies, thus, reinforcing the fact that the observed TcCRT effects can be attributed to the parasite-derived molecule and not to the endotoxin. The antiangiogenic TcCRT effects correlate with its anti-tumor in vivo effects, as recently shown in our laboratory.

Caveolin-1 in Melanoma Progression

Cancer is a leading cause of death world wide and mortality due to this group of diseases has doubled in the last 20 years. With an estimated 3 million cases, skin cancer is currently the third most common human malignancy and global incidence is rising at an alarming rate due to environmental changes. Within that category, melanomas represent the least common, but most dangerous form accounting for the majority of skin cancer-related deaths. In general terms, cancer evolves as the consequence of a multi-factorial process that involves the loss of a cell’s ability to respond in an appropriate fashion to cues provided by the microenvironment. The development of such aberrant, autonomous behavior is caused by both genetic mutations and epigenetic mechanisms. Particularly relevant in the context of melanoma are the Ras/Raf/MEK/Erk, PI3K/PTEN and NF-kB signaling pathways. The Wnt/┚-catenin patway is also implicated, but it s role still remains unclear. Depending on whether changes result in a “gain of function” or a “loss of function”, the molecules involved are classified as either oncogenes or tumor suppressors, examples important in melanomas being NRas and B-Raf or PTEN, respectively. More recently, a new group of molecular participants has begun to emerge, which, depending on the cellular context, display the ability to either block tumor development or favor progression. Very little is still known about the underlying mechanisms that might explain such “ambiguous” behavior. In this respect, work from our laboratory has focused on the study of a scaffolding protein called caveolin-1. This protein is implicated in a large number of cellular processes, including caveolae formation and vesicular transport, cholesterol transport and the regulation of signal transduction. With respect to tumor development, initial reports implicated caveolin-1 as a tumor suppressor. For instance, caveolin-1 expression is reduced in several human tumors including lung, mammary, colon, ovarian carcinoma and sarcomas, as wells as osteosarcomas and re-expression of the protein can reverse characteristics associated with the transformed phenotype. However, evidence to the contrary is also available showing that caveolin-1 promotes more aggressive traits in tumor cells, such as metastasis and multidrug resistance. Importantly, in human melanoma patients high levels of caveolin-1 are detected in exosomes found in the plasma and some data available associate caveolin-1 expression with increased metastatic potential in different human melanoma cell lines. In this chapter, we summarize data available in the literature highlighting the ambiguity of caveolin-1 function in cancer development. Mechanisms that might explain one or the other