Low Pre-Transplant Caveolin-1 Serum Concentrations Are Associated with Acute Cellular Tubulointerstitial Rejection in Kidney Transplantation

Acute and chronic transplant rejections due to alloreactivity are essential contributors to graft loss. However, the strength of alloreactivity is biased by non-immunological factors such as ischemia reperfusion injury (IRI). Accordingly, protection from IRI could be favorable in terms of limiting graft rejection. Caveolin-1 (Cav-1) is part of the cell membrane and an important regulator of intracellular signaling. Cav-1 has been demonstrated to limit IRI and to promote the survival of a variety of cell types including renal cells under stress conditions. Accordingly, Cav-1 could also play a role in limiting anti-graft immune responses. Here, we evaluated a possible association between pre-transplant serum concentrations of Cav-1 and the occurrence of rejection during follow-up in a pilot study. Therefore, Cav-1-serum concentrations were analyzed in 91 patients at the time of kidney transplantation and compared to the incidence of acute and chronic rejection. Higher Cav-1 levels were associated with lower occurrence of acute cellular tubulointerstitial rejection episodes.

Caveolin-1 promotes invasion and metastasis by upregulating Pofut1 expression in mouse hepatocellular carcinoma

Caveolin-1 (Cav-1) is an important structural protein of caveolae and plays an oncogene-like role by influencing protein glycosylation in hepatocellular carcinoma (HCC) cells. However, the mechanism by which Cav-1 promotes invasion and metastasis capacity has not been completely clarified. In this study, we demonstrate that Pofut1 is a fucosyltransferase induced by Cav-1. Mouse Hepa1-6 HCC cells lacking Cav-1 expression exhibited low transcription levels of Pofut1, whereas strong Pofut1 expression was found in high-metastasis-potential Hca-F cells with high levels of Cav-1. Cav-1 activated MAPK signaling and promoted phosphorylation of the transcription factors CREB, Sp1, HNF4A and c-Myc, which bound to the Pofut1 promoter region to induce its transcription. As Notch signaling receptors can be modified with O-fucose by Pofut1, we further showed that Cav-1-induced upregulation of Pofut1 expression activated the Notch pathway and thus enhanced invasion and metastasis by mouse HCC cells in vitro and in vivo. Collectively, our findings reveal a novel mechanism by which Cav-1 promotes tumor metastasis by upregulating expression of Pofut1, suggesting that Cav-1 may function as a new biomarker for HCC.

Mechanisms through Which Hypoxia-Induced Caveolin-1 Drives Tumorigenesis and Metastasis in Hepatocellular Carcinoma

In solid tumors, hypoxia triggers an aberrant vasculogenesis, enhances malignant character, and elevates metastatic risk. The plasma membrane organizing protein caveolin-1 (Cav1) is increased in a variety of cancers, including hepatocellular carcinoma (HCC), where it contributes to metastatic capability. However, the reason for elevation of Cav1 in tumor cells and the mechanistic basis for its contributions to metastatic risk are not fully understood. Here, we show that in HCC cells, hypoxia elevates expression of Cav1, which then acts through the calcium-binding protein S100P to promote metastasis. Hypoxic regions of HCC xenografts displayed elevated expression of Cav1. Hypoxia promoted HCC cell migration and invasion and distant pulmonary metastases, whereas Cav1 silencing abolished these effects. Gene expression profiling revealed that hypoxia-induced Cav1 functioned as a positive regulator of S100P via activation of the NF-κB pathway. S100P elevation under hypoxic conditions was abrogated by silencing of Cav1 or NF-κB function. Conversely, restoring S100P in Cav1-silenced cells rescued the migratory potential of HCC cells along with tumor formation and lung metastasis. In clinical specimens of HCC, we observed S100P overexpression to correlate with venous invasion, microsatellites, direct liver invasion, and absence of tumor encapsulation. Collectively, our findings demonstrated how hypoxia-induced expression of Cav1 in HCC cells enhances their invasive and metastatic potential. Cancer Res; 76(24); 7242-53. ©2016 AACR.

Caveolin and cavin family members: dual roles in cancer

Caveolae are specialized plasma membrane subdomains with distinct lipid and protein compositions, which play an essential role in cell physiology through regulation of trafficking and signaling functions. The structure and functions of caveolae have been shown to require the proteins caveolins. Recently, members of the cavin protein family were found to be required, in concert with caveolins, for the formation and function of caveolae. Caveolins have a paradoxical role in the development of cancer formation. They have been involved in both tumor suppression and oncogenesis, depending on tumor type and progress stage. High expression of caveolins and cavins leads to inhibition of cancer-related pathways, such as growth factor signaling pathways. However, certain cancer cells that express caveolins and cavins have been shown to be more aggressive and metastatic because of their increased potential for anchorage-independent growth. Here, we will survey the functional roles of caveolins and of different cavin family members in cancer regulation.

Caveolin-1 up-regulates integrin α2,6-sialylation to promote integrin α5β1-dependent hepatocarcinoma cell adhesion

The alterations of integrin glycosylation play a crucial role in tumor metastasis. Our previous studies indicated that caveolin-1 promoted the expression of the key α2,6-sialytransferase ST6Gal-I and fibronectin-mediated adhesion of mouse hepatocarcinoma cell. Herein, we investigated the role of α2,6-sialylated α5-integrin in the adhesion of mouse hepatocarcinoma H22 cell. We demonstrated that caveolin-1 up-regulated cell surface α2,6-linked sialic acid via stimulating ST6Gal-I transcription. Cell surface α2,6-sialylation was required for integrin α5β1-dependent cell adhesion to fibronectin, and an increase in α2,6-linked sialic acid on α5-subunit facilitated fibronectin-mediated focal adhesion kinase phosphorylations, suggesting that α2,6-sialylated α5-subunit promoted integrin α5β1-dependent cell adhesion.

Caveolin-1 up-regulates ST6Gal-I to promote the adhesive capability of mouse hepatocarcinoma cells to fibronectin via FAK-mediated adhesion signaling

Caveolin-1 is a major structural protein of caveolae and plays important functions in tumorigenesis and development. Hca-F and Hepa1-6 are mouse hepatocarcinoma cell lines with high and low malignant potential, respectively. Our previous studies revealed that caveolin-1 promoted cell invasion by up-regulating the glycosylation of matrix metalloproteinase inducer CD147 of Hepa1-6 and Hca-F cells. However, the roles of caveolin-1 in cell-ECM adhesion and the mechanisms involved remain unknown. This study showed that caveolin-1 overexpression in Hepa1-6 cells up-regulated sialyltransferase ST6Gal-I expression and activated FAK-mediated adhesion signaling, and down-regulation of ST6Gal-I attenuated caveolin-1-induced increase in the adhesive ability of Hepa1-6 cells to fibronectin. Conversely, caveolin-1 knockdown in Hca-F cells inhibited ST6Gal-I expression and FAK signaling-mediated cell adhesion to fibronectin. Re-expression of wild-type caveolin-1 or ST6Gal-I rescued the decreased ST6Gal-I expression and adhesion of Hca-F cells caused by caveolin-1 silencing. Further studies indicated that caveolin-1 might regulate ST6Gal-I expression through caveolin-1 scaffolding domain. Taken together, these results demonstrate for the first time that caveolin-1 can up-regulate ST6Gal-I expression and further contribute to promoting mouse hepatocarcinoma cell adhesion to fibronectin by activating FAK-mediated adhesion signaling.

Curcumin inhibits the migration and invasion of mouse hepatoma Hca-F cells through down-regulating caveolin-1 expression and epidermal growth factor receptor signaling

Mouse hepatoma cellular carinoma cell line (Hca-F) cells have highly invasive and lymphatic metastasis potential in vitro and in vivo. Curcumin (diferuloylmethane) is an active component of the spice turmeric and has a diversity of antitumor activities. However, there is no available information to address the effects of curcumin on migration and invasion of mouse hepatoma Hca-F cells. In this study, we found that curcumin exerted a concentration- and time-dependent inhibitory effect on the migration and invasion of Hca-F cells in vitro. Curcumin inhibited the expression of the tumor promoter caveolin-1 (Cav-1) in Hca-F cells. Up-regulation of Cav-1 expression by pcDNA3.1/Cav-1 plasmid was able to reverse the curcumin-induced antimigration and anti-invasion effects in vitro. Curcumin down-regulated the expression of cluster of differntiation (CD)147, matrix metalloproteinase 2, and matrix metalloproteinase 9 and inhibited the phosphorylation of epidermal growth factor receptor (EGFR), the phosphoinositilde 3-kinase (PI3K)/protein kinase B (Akt), p38 mitogen-activated protein kinase (MAPK), and p44/42MAPK in Hca-F cells. Taken together, our findings suggest that curcumin can suppress the migratory and invasive ability of mouse hepatoma Hca-F cells, and this action is mediated through a novel mechanism involving inactivation of Cav-1 and EGFR signaling pathways.

Caveolin-1: role in cell signaling

Caveolins (Cavs) are integrated plasma membrane proteins that are complex signaling regulators with numerous partners and whose activity is highly dependent on cellular context. Cavs are both positive and negative regulators of cell signaling in and/or out of caveolae, invaginated lipid raft domains whose formation is caveolin expression dependent. Caveolins and rafts have been implicated in membrane compartmentalization; proteins and lipids accumulate in these membrane microdomains where they transmit fast, amplified and specific signaling cascades. The concept of plasma membrane organization within functional rafts is still in exploration and sometimes questioned. In this chapter, we discuss the opposing functions of caveolin in cell signaling regulation focusing on the role of caveolin both as a promoter and inhibitor of different signaling pathways and on the impact of membrane domain localization on caveolin functionality in cell proliferation, survival, apoptosis and migration.

Impairment of transforming growth factor beta signaling in caveolin-1-deficient hepatocytes: role in liver regeneration

Caveolin-1 (Cav-1) is the main structural protein of caveolae and plays an important role in various cellular processes such as vesicular transport, cholesterol homeostasis, and signal transduction pathways. The expression and functional role of Cav-1 have been reported in liver and in hepatocyte cell lines, in human cirrhotic liver, and in hepatocellular carcinomas. Previous studies demonstrated that Cav-1 was dispensable for liver regeneration, because Cav-1(-/-) animals survived and fully regenerated liver function and size after partial hepatectomy. In this study, we have investigated the mechanisms by which the lack of Cav-1 accelerates liver regeneration after partial hepatectomy. The data show that transforming growth factor beta (TGF-beta) signaling is impaired in regenerating liver of Cav-1(-/-) mice and in hepatocytes derived from these animals. TGF-beta receptors I and II do not colocalize in the same membrane fraction in the hepatocytes derived from Cav-1(-/-) mice, as Smad2/3 signaling decreased in the absence of Cav-1 at the time that the transcriptional corepressor SnoN accumulates. Accordingly, the expression of TGF-beta target genes, such as plasminogen activator inhibitor-1, is decreased due to the presence of the high levels of SnoN. Moreover, hepatocyte growth factor inhibited TGF-beta signaling in the absence of Cav-1 by increasing SnoN expression. Taken together, these data might help to unravel why Cav-1-deficient mice exhibit an accelerated liver regeneration after partial hepatectomy and add new insights on the molecular mechanisms controlling the initial commitment to hepatocyte proliferation.