Sialic acid binding lectin (SBL) isolated from Rana catesbeiana oocytes is a multifunctional protein which has lectin activity, ribonuclease activity and antitumor activity. However, the mechanism of antitumor effects of SBL is unclear to date and the validity for human leukemia cells has not been fully studied. We report here that SBL shows cytotoxicity for some human leukemia cell lines including multidrug-resistant (MDR) cells. The precise mechanisms of SBL-induced apoptotic signals were analyzed by combinational usage of specific caspase inhibitors and the mitochondrial membrane depolarization detector JC-1. It was demonstrated that SBL causes mitochondrial perturbation and the apoptotic signal is amplified by caspases and cell death is executed in a caspase-dependent manner. The efficacy of this combinational usage was shown for the first time, to distinguish the apoptotic pathway in detail. SBL selectively kills tumor cells, is able to exhibit cytotoxicity regardless of P-glycoprotein expression and has potential as an alternative to conventional DNA-damaging anticancer drugs.

Malignant transformation is accompanied with aberrant glycosylation of proteins. Such changes in glycan structure also occur in the integrins, which are a large family of cell surface receptors for the extracellular matrix and play key roles in tumor progression. There is now increasing evidence that glycosylation of integrins affects cellular signaling and interaction with the extracellular matrix, receptor tyrosine kinases, and galectins, thereby regulating cell adhesion, motility, growth, and survival. Integrin α6β4 is a receptor for laminin-332 and the increased expression level is correlated with malignant progression and poor survival in various types of cancers. Recent studies have revealed that integrin α6β4 plays central roles in tumorigenesis and the metastatic process. In this review, we summarize our current understanding of the molecular mechanisms of tumor progression driven by integrin α6β4 and also discuss the modification of glycans on integrin β4 subunit to address the important roles of glycan in integrin-mediated tumor progression.

Malignant transformation is associated with aberrant -glycosylation, but the role of protein-glycosylation in cancer progression remains poorly defined. β4-integrin is a major carrier of -glycans and is associated with poor prognosis, tumorigenesis, and metastasis. Here,-glycosylation of β4-integrin contributes to the activation of signaling pathways that promote β4-dependent tumor development and progression. Increased expression of β1,6GlcNAc-branched -glycans was found to be colocalized with β4-integrin in human cutaneous squamous cell carcinoma tissues, and that the β1,6GlcNAc residue was abundant on β4-integrin in transformed keratinocytes. Interruption of β1,6GlcNAc-branching formation on β4-integrin with the introduction of bisecting GlcNAc by-acetylglucosaminyltransferase III overexpression was correlated with suppression of cancer cell migration and tumorigenesis. -Glycan deletion on β4-integrin impaired β4-dependent cancer cell migration, invasion, and growth and diminished tumorigenesis and proliferation The reduced abilities of β4-integrin were accompanied with decreased phosphoinositol-3 kinase (PI3K)/Akt signals and were restored by the overexpression of the constitutively active p110 PI3K subunit. Binding of galectin-3 to β4-integrin via β1,6GlcNAc-branched-glycans promoted β4-integrin-mediated cancer cell adhesion and migration. In contrast, a neutralizing antibody against galectin-3 attenuated β4-integrin -glycan-mediated PI3K activation and inhibited the ability of β4-integrin to promote cell motility. Furthermore, galectin-3 knockdown by shRNA suppressed β4-integrin-glycan-mediated tumorigenesis. These findings provide a novel role for -glycosylation of β4-integrin in tumor development and progression, and the regulatory mechanism for β4-integrin/PI3K signaling via the galectin-3--glycan complex.-Glycosylation of β4-integrin plays a functional role in promoting tumor development and progression through PI3K activation via the galectin-3--glycan complex. .

Malignant mesothelioma is a highly aggressive tumor with poor prognosis. An effective drug for treatment of malignant mesothelioma is greatly needed. Sialic acid-binding lectin (SBL) isolated from oocytes of Rana catesbeiana is a multifunctional protein which has lectin activity, ribonuclease activity and antitumor activity, so it could be developed as a new type of anticancer drug. The validity of SBL for treatment of malignant mesothelioma was assessed using three malignant mesotheliomas and a non-malignant mesothlial cell line. Effectiveness of combinatorial treatment of SBL and tumor necrosis factor-related apoptosis inducing ligand (TRAIL) was also elucidated and characterized. SBL induced tumor-selective cytotoxicity that was attributed to induction of apoptosis. Combinatorial treatment of SBL and TRAIL showed synergistic apoptosis-inducing effect. Additional experiments revealed that Bid was the mediating molecule for the synergistic effect in SBL and TRAIL. These results suggested that SBL could be a promising candidate for the therapeutics for malignant mesothelioma. Furthermore, the combinatorial treatment of SBL and TRAIL could be an effective regimen against malignant mesothelioma.

Despite significant advances in the understanding of cancer biology, cancer is still a leading cause of death worldwide. Expression of the tumor microenvironment component, osteopontin, in tumor tissues, plasma, and serum, has been shown to be associated with a poor prognosis and survival rate in various human cancers. Recent studies suggest that osteopontin drives tumor development and aggressiveness using various strategies. In this review, we first provide an overview of how osteopontin promotes tumor progression, such as tumor growth, invasion, angiogenesis, and immune modulation, as well as metastasis and chemoresistance. Next, we address how the functional activities of osteopontin are modulated by the interaction with integrins and CD44 receptors, but also by the post-translational modification, such as proteolytic processing by several proteases, phosphorylation, and glycosylation. Then, we review how osteopontin activates tumor-associated macrophages (TAMs) and cancer-associated fibroblasts (CAFs), and functions as an immunosuppressor by regulating immune surveillance and immune checkpoint in the tumor microenvironment. Finally, we discuss the potential applications of osteopontin as a biomarker and as a therapeutic target.