Invadopodia proteins, cortactin, N-WASP and WIP differentially promote local invasiveness in ameloblastoma

A comparative immunohistochemical analysis of cortactin in orthokeratinized odontogenic cyst (OOC), sporadic odontogenic keratocyst (OKC), and syndromic OKC

OBJECTIVES

To evaluate and compare the immunohistochemical expression of cortactin in the epithelial lining of orthokeratinized odontogenic cyst (OOC), sporadic odontogenic keratocyst (OKC), and syndromic OKC.

METHODS

Formalin-fixed paraffin-embedded tissue blocks of histopathologically diagnosed cases of OOC, OKC, syndromic OKC, normal buccal mucosa (NBM), and oral squamous cell carcinoma (OSCC) were examined for immunohistochemical expression of cortactin. Clear brown cytoplasmic and membranous staining was considered positive.

RESULTS

A statistically significant difference was observed between OOC and syndromic OKC (p<0.001), as well as between sporadic OKC and syndromic OKC (p<0.001). Although not statistically significant, the expression of cortactin was slightly higher in the basal layer of NBM (mean=0.47), OOC (mean=0.27), sporadic OKC (mean=0.47) syndromic OKC (mean=1.53), and OSCC (mean=0.67) than in the parabasal layers of NBM (mean=0.27), OOC (mean=0.20), sporadic OKC (mean=0.47), syndromic OKC (mean=1.27), and OSCC (mean=0.60).

CONCLUSION

The expression of cortactin in the basal layer may suggest the formation of invadopodia in the basal layer where the invasion mechanism occurs. This finding is further supported by the higher localization of cortactin in areas of epithelial budding and daughter cysts in syndromic OKC, thereby reaffirming its possible association with recurrence.

Inhibition of invadopodia formation by diosgenin in tumor cells

Diosgenin is a type of steroid extracted from the rhizome of Dioscorea plants. In traditional Chinese medicine, Dioscorea has the effect of ‘eliminating phlegm, promoting digestion, relaxing tendons, promoting blood circulation and inhibiting malaria’. Recent studies have confirmed that diosgenin exhibits a number of pharmacological effects, including antitumor activities. Through its antitumor effect, diosgenin is able to block tumor progression and increase the survival rate of patients with cancer; ultimately improving their quality of life. However, the mechanism underlying its pharmacological action remains unclear. Once tumor cells reach a metastatic phase, it can be fatal. Increased migration and invasiveness are the hallmarks of metastatic tumor cells. Invadopodia formation is key to maintaining the high migration and invasive ability of tumor cells. Invadopodia are a type of membrane structure process rich in filamentous-actin and are common in highly invasive tumor cells. In addition to actin, numerous actin regulators, including cortical actin-binding protein (Cortactin), accumulate in invadopodia. Cortactin is a microfilament actin-binding protein with special repetitive domains that are directly involved in the formation of the cortical microfilament actin cell skeleton. Cortactin is also one of the main substrates of intracellular Src-type tyrosine protein kinases and represents a highly conserved family of intracellular cortical signaling proteins. In recent years, great progress has been made in understanding the role of Cortactin and its molecular mechanism in cell motility. However, the diosgenin-Cortactin-invadopodia mechanism is still under investigation. Therefore, the present review focused on the current research on the regulation of invadopodia by diosgenin via Cortactin.

Effects of butyric acid, a bacterial metabolite, on the migration of ameloblastoma mediated by laminin 332

Ameloblastoma is a benign tumor that develops in the jawbone. Occasionally, however, it may become malignant and metastasize to other tissues. Although it has been suggested that various cytokines and several adhesion factors may play a role in its malignant transformation, the details have not been elucidated. In this context, it has been reported that butyric acid produced by periodontopathic bacteria causes progression of malignant tumors occurring in the mouth via podoplanin. However, the influence of butyric acid on ameloblastoma has not been clarified. In the present study, therefore, the expression of various cytokines and adhesion factors in ameloblastoma upon stimulation with butyric acid or cytokines was investigated using real-time reverse-transcription polymerase chain reaction. Three cell lines (HAM1, HAM2 and HAM3) established from the same ameloblastoma were used in the experiments. It was found that the expression of mRNAs for epidermal growth factor (EGF) and transforming growth factor beta 1 (TGFβ1) was increased in HAM2 and HAM3, respectively, upon stimulation with butyric acid. In addition, stimulation with EGF and TGFβ1 led to an increase in the expression of laminin β-3 mRNA in the respective cell lines. These results suggest that butyric acid may be involved in ameloblastoma exacerbation through the expression of laminin 332 (LM332) via EGF and TGFβ1 produced by ameloblastoma itself.

Nanobody click chemistry for convenient site-specific fluorescent labelling, single step immunocytochemistry and delivery into living cells by photoporation and live cell imaging

While conventional antibodies have been an instrument of choice in immunocytochemistry for some time, their small counterparts known as nanobodies have been much less frequently used for this purpose. In this study we took advantage of the availability of nanobody cDNAs to site-specifically introduce a non-standard amino acid carrying an azide/alkyne moiety, allowing subsequent Cu(I)-catalyzed Azide-Alkyne Click Chemistry (CuAAC). This generated a fluorescently labelled nanobody that can be used in single step immunocytochemistry as compared to conventional two step immunocytochemistry. Two strategies were explored to label nanobodies with Alexa Fluor 488. The first involved enzymatic addition of an alkyne-containing peptide to nanobodies using sortase A, while the second consisted of incorporating para-azido phenylalanine at the nanobody C-terminus. Through these approaches, the fluorophore was covalently and site-specifically attached. It was demonstrated that cortactin and β-catenin, cytoskeletal and adherens junction proteins respectively, can be imaged in cells in this manner through single step immunocytochemistry. However, fixation and permeabilization of cells can alter native protein structure and form a dense cross-linked protein network, encumbering antibody binding. It was shown that photoporation prior to fixation not only allowed delivery of nanobodies into living cells, but also facilitated β-catenin nanobody Nb86 imaging of its target, which was not possible in fixed cells. Pharmacological inhibitors are lacking for many non-enzymatic proteins, and it is therefore expected that new biological information will be obtained through photoporation of fluorescent nanobodies, which allows the study of short term effects, independent of gene-dependent (intrabody) expression.

Specialized Roles for Actin in Osteoclasts: Unanswered Questions and Therapeutic Opportunities

Osteoclasts are cells of the hematopoietic lineage that are specialized to resorb bone. In osteoclasts, the actin cytoskeleton engages in at least two unusual activities that are required for resorption. First, microfilaments form a dynamic and structurally elaborate actin ring. Second, microfilaments bind vacuolar H⁺-ATPase (V-ATPase) and are involved in forming the V-ATPase-rich ruffled plasma membrane. The current review examines these two specialized functions with emphasis on the identification of new therapeutic opportunities. The actin ring is composed of substructures called podosomes that are interwoven to form a cohesive superstructure. Studies examining the regulation of the formation of actin rings and its constituent proteins are reviewed. Areas where there are gaps in the knowledge are highlighted. Microfilaments directly interact with the V-ATPase through an actin binding site in the B2-subunit of V-ATPase. This binding interaction is required for ruffled membrane formation. Recent studies show that an inhibitor of the interaction blocks bone resorption in pre-clinical animal models, including a model of post-menopausal osteoporosis. Because the unusual actin-based resorption complex is unique to osteoclasts and essential for bone resorption, it is likely that deeper understanding of its underlying mechanisms will lead to new approaches to treat bone disease.

Hematopoietic lineage cell-specific protein 1 (HS1), a hidden player in migration, invasion, and tumor formation, is over-expressed in ovarian carcinoma cells

Hematopoietic lineage cell-specific protein 1 (HS1), which is the hematopoietic homolog of cortactin, is an actin-binding protein and Lyn substrate. It is upregulated in several cancers and its expression level is associated with increased cell migration, metastasis, and poor prognosis. Here we investigated the expression and roles of HS1 in ovarian carcinoma cells. We analyzed the expression of HS1 in 171 ovarian cancer specimens and determined the association between HS1 expression and clinicopathological characteristics, including patient outcomes. In patients with stage II-IV disease, positive HS1 expression was associated with significantly worse overall survival than negative expression (P < 0.05). HS1 was localized in invadopodia in some ovarian cancer cells and was required for invadopodia formation. Migration and invasion of ovarian cancer cells were suppressed by down-regulation of HS1, but increased in cells that over-expressed exogenous HS1. Furthermore, ovarian cancer cells that expressed HS1 shRNA exhibited reduced tumor formation in a mouse xenograft model. Finally, we found that tyrosine phosphorylation of HS1 was essential for cell migration and invasion. These findings show that HS1 is a useful biomarker for the prognosis of patients with ovarian carcinoma and is a critical regulator of cytoskeleton remodeling involved in cell migration and invasion.

Crosstalk between WIP and Rho family GTPases

Through actin-binding proteins such as the neural Wiskott-Aldrich syndrome protein (N-WASP) and WASP-interacting protein (WIP), the Rho family GTPases RhoA, Rac1 and Cdc42 are major modulators of the cytoskeleton. (N-)WASP and WIP control Rho GTPase activity in various cell types, either by direct WIP/(N-)WASP/Cdc42 or potential WIP/RhoA binding, or through secondary links that regulate GTPase distribution and/or transcription levels. WIP helps to regulate filopodium generation and participates in the Rac1-mediated ruffle formation that determines cell motility. In neurons, lack of WIP increases dendritic spine size and filamentous actin content in a RhoA-dependent manner. In contrast, WIP deficiency in an adenocarcinoma cell line significantly reduces RhoA levels. These data support a role for WIP in the GTPase-mediated regulation of numerous actin-related cell functions; we discuss the possibility that this WIP effect is linked to cell proliferative status.

VCA nanobodies target N-WASp to reduce invadopodium formation and functioning

Invasive cancer cells develop small actin-based protrusions called invadopodia, which perform a primordial role in metastasis and extracellular matrix remodelling. Neural Wiskott-Aldrich syndrome protein (N-WASp) is a scaffold protein which can directly bind to actin monomers and Arp2/3 and is a crucial player in the formation of an invadopodium precursor. Expression modulation has pointed to an important role for N-WASp in invadopodium formation but the role of its C-terminal VCA domain in this process remains unknown. In this study, we generated alpaca nanobodies against the N-WASp VCA domain and investigated if these nanobodies affect invadopodium formation. By using this approach, we were able to study functions of a selected functional/structural N-WASp protein domain in living cells, without requiring overexpression, dominant negative mutants or siRNAs which target the gene, and hence the entire protein. When expressed as intrabodies, the VCA nanobodies significantly reduced invadopodium formation in both MDA-MB-231 breast cancer and HNSCC61 head and neck squamous cancer cells. Furthermore, expression of distinct VCA Nbs (VCA Nb7 and VCA Nb14) in PC-3 prostate cancer cells resulted in reduced overall matrix degradation without affecting MMP9 secretion/activation or MT1-MMP localisation at invadopodial membranes. From these results, we conclude that we have generated nanobodies targeting N-WASp which reduce invadopodium formation and functioning, most likely via regulation of N-WASp—Arp2/3 complex interaction, indicating that this region of N-WASp plays an important role in these processes.