Promising noninvasive cellular phenotype in prostate cancer cells knockdown of matrix metalloproteinase 9

Hyaluronic Acid Interacting Molecules Mediated Crosstalk between Cancer Cells and Microenvironment from Primary Tumour to Distant Metastasis

Hyaluronic acid (HA) is a prominent component of the extracellular matrix, and its interactions with HA-interacting molecules (HAIMs) play a critical role in cancer development and disease progression. This review explores the multifaceted role of HAIMs in the context of cancer, focusing on their influence on disease progression by dissecting relevant cellular and molecular mechanisms in tumour cells and the tumour microenvironment. Cancer progression can be profoundly affected by the interactions between HA and HAIMs. They modulate critical processes such as cell adhesion, migration, invasion, and proliferation. The TME serves as a dynamic platform in which HAIMs contribute to the formation of a unique niche. The resulting changes in HA composition profoundly influence the biophysical properties of the TME. These modifications in the TME, in conjunction with HAIMs, impact angiogenesis, immune cell recruitment, and immune evasion. Therefore, understanding the intricate interplay between HAIMs and HA within the cancer context is essential for developing novel therapeutic strategies. Targeting these interactions offers promising avenues for cancer treatment, as they hold the potential to disrupt critical aspects of disease progression and the TME. Further research in this field is imperative for advancing our knowledge and the treatment of cancer.

The Potential of Extracellular Matrix- and Integrin Adhesion Complex-Related Molecules for Prostate Cancer Biomarker Discovery

Prostate cancer is among the top five cancer types according to incidence and mortality. One of the main obstacles in prostate cancer management is the inability to foresee its course, which ranges from slow growth throughout years that requires minimum or no intervention to highly aggressive disease that spreads quickly and resists treatment. Therefore, it is not surprising that numerous studies have attempted to find biomarkers of prostate cancer occurrence, risk stratification, therapy response, and patient outcome. However, only a few prostate cancer biomarkers are used in clinics, which shows how difficult it is to find a novel biomarker. Cell adhesion to the extracellular matrix (ECM) through integrins is among the essential processes that govern its fate. Upon activation and ligation, integrins form multi-protein intracellular structures called integrin adhesion complexes (IACs). In this review article, the focus is put on the biomarker potential of the ECM- and IAC-related molecules stemming from both body fluids and prostate cancer tissue. The processes that they are involved in, such as tumor stiffening, bone turnover, and communication via exosomes, and their biomarker potential are also reviewed.

Hyaluronic acid-functionalized lipoplexes and polyplexes as emerging nanocarriers for receptor-targeted cancer therapy

Cancer is an intricate disease that develops as a response to a combination of hereditary and environmental risk factors, which then result in a variety of changes to the genome. The cluster of differentiation (CD44) is a type of transmembrane glycoprotein that serves as a potential biomarker for cancer stem cells (CSC) and viable targets for therapeutic intervention in the context of cancer therapy. Hyaluronic acid (HA) is a linear polysaccharide that exhibits a notable affinity for the CD44 receptor. This characteristic renders it a promising candidate for therapeutic interventions aimed at selectively targeting CD44-positive cancer cells. Treating cancer via non-viral vector-based gene delivery has changed the notion of curing illness through the incorporation of therapeutic genes into the organism. The objective of this review is to provide an overview of various hyaluronic acid-modified lipoplexes and polyplexes as potential drug delivery methods for specific forms of cancer by effectively targeting CD44.

CD44 in Bone Metastasis Development: A Key Player in the Fate Decisions of the Invading Cells?

A participant in key developmental processes, the adhesion glycoprotein CD44 is also expressed in several types of malignancies and can promote metastasis. In addition, the expression of CD44 isoforms in different types of cancer such as prostate and breast cancers may facilitate bone metastases by enhancing tumorigenicity, osteomimicry, cell migration, homing to bone, and anchorage within the bone specialized domains. Moreover, there is evidence that the CD44-ICD fragments in breast cancer cells may promote the cells' osteolytic nature. Yet the mechanisms by which CD44 and its downstream effectors promote the establishment of these cells within the bone are not fully elucidated. In this review, we summarize the current data on the roles played by CD44 in cancer progression and bone metastasis and the possible effects of its interaction with the different components of the bone marrow milieu.

Novel evaluation of the expression patterns CD44 and MMP9 proteins in intracranial meningiomas and their relationship to the overall survival

Background

Meningiomas are common primary brain neoplasms. CD44 is a cell surface glycoprotein receptor that is involved in matrix-mediated cell signaling and cell–matrix adhesion. Matrix metalloproteinase-9 (MMP-9) plays important role in angiogenesis and tumor invasion. The expression of CD44 protein membranous and cytoplasmic (CD44M and CD44C) has been reported in several tumors (such as lobular carcinoma, renal cell carcinoma, sinonasal melanoma, and lymphoma) except CNS tumors.

Methods

This study addressed the expression of CD44M and CD44C and MMP9 proteins in intracranial meningiomas and their relationship to overall survival. The expression patterns of CD44M&C and MMP-9 proteins were examined in 32 cases of benign meningiomas, 12 cases of atypical meningiomas, and 6 cases of anaplastic meningiomas using immunohistochemical staining methods.

Results

There was more evidence of CD44M expression in atypical and anaplastic meningioma (p =  < 0.001). Interestingly, Spearman correlation analyses revealed significant positive correlation between CD44M and MMP9 protein (r = 0.572, p =  < 0.001) in spite of the negative correlation between MMP9 and CD44 score (r = − 0.035 p = 0.405). There was a significant association between Ki67 protein expression and the grade of meningiomas (p < 0.001) and gender (p = 0.026). There was a significant correlation between overall survival (OS) and age, gender, tumor grade, and Ki-67.

Conclusions

Extensive CD44M expression in high-grade meningioma may reflect a tendency toward more invasive power of meningioma cells into surrounding structures (dura, bone, and brain).CD44M/MMP-9 axis presented by this study is open for future investigations.

Hyaluronic Acid: Known for Almost a Century, but Still in Vogue

Hyaluronic acid (HA) has a special position among glycosaminoglycans. As a major component of the extracellular matrix (ECM). This simple, unbranched polysaccharide is involved in the regulation of various biological cell processes, whether under physiological conditions or in cases of cell damage. This review summarizes the history of this molecule's study, its distinctive metabolic pathway in the body, its unique properties, and current information regarding its interaction partners. Our main goal, however, is to intensively investigate whether this relatively simple polymer may find applications in protecting against ionizing radiation (IR) or for therapy in cases of radiation-induced damage. After exposure to IR, acute and belated damage develops in each tissue depending upon the dose received and the cellular composition of a given organ. A common feature of all organ damage is a distinct change in composition and structure of the ECM. In particular, the important role of HA was shown in lung tissue and the variability of this flexible molecule in the complex mechanism of radiation-induced lung injuries. Moreover, HA is also involved in intermediating cell behavior during morphogenesis and in tissue repair during inflammation, injury, and would healing. The possibility of using the HA polymer to affect or treat radiation tissue damage may point to the missing gaps in the responsible mechanisms in the onset of this disease. Therefore, in this article, we will also focus on obtaining answers from current knowledge and the results of studies as to whether hyaluronic acid can also find application in radiation science.

Invadopodia play a role in prostate cancer progression

Background

Invadopodia, actin-rich structures that release metallo-proteases at the interface with extra-cellular matrix, in a punctate manner are thought to be important drivers of tumour invasion. Invadopodia formation has been observed in-vitro and in-vivo in numerous metastatic cell lines derived from multiple tumour types. However, prostate cancer cell lines have not been routinely reported to generate invadopodia and the few instances have always required external stimulation.

Methods

In this study, the invasive potential of primary prostate adenocarcinoma cell lines, which have never been fully characterised before, was investigated both in-vitro invadopodia assays and in-vivo zebrafish dissemination assay. Subsequently, circulating tumour cells from prostate cancer patients were isolated and tested in the invadopodia assay.

Results

Retention of E-cadherin and N-cadherin expression indicated a transitional state of EMT progression, consistent with the idea of partial EMT that has been frequently observed in aggressive prostate cancer. All cell lines tested were capable of spontaneous invadopodia formation and possess a significant degradative ability in-vitro under basal conditions. These cell lines were invasive in-vivo and produced visible metastasis in the zebrafish dissemination assay. Importantly we have proceeded to demonstrate that circulating tumour cells isolated from prostate cancer patients exhibit invadopodia-like structures and degrade matrix with visible puncta. This work supports a role for invadopodia activity as one of the mechanisms of dissemination employed by prostate cancer cells.

Conclusion

The combination of studies presented here provide clear evidence that invadopodia activity can play a role in prostate cancer progression.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09424-4.

Extracellular matrix and its therapeutic potential for cancer treatment

The extracellular matrix (ECM) is one of the major components of tumors that plays multiple crucial roles, including mechanical support, modulation of the microenvironment, and a source of signaling molecules. The quantity and cross-linking status of ECM components are major factors determining tissue stiffness. During tumorigenesis, the interplay between cancer cells and the tumor microenvironment (TME) often results in the stiffness of the ECM, leading to aberrant mechanotransduction and further malignant transformation. Therefore, a comprehensive understanding of ECM dysregulation in the TME would contribute to the discovery of promising therapeutic targets for cancer treatment. Herein, we summarized the knowledge concerning the following: (1) major ECM constituents and their functions in both normal and malignant conditions; (2) the interplay between cancer cells and the ECM in the TME; (3) key receptors for mechanotransduction and their alteration during carcinogenesis; and (4) the current therapeutic strategies targeting aberrant ECM for cancer treatment.

The Role of the Metzincin Superfamily in Prostate Cancer Progression: A Systematic-Like Review

Prostate cancer remains a leading cause of cancer-related morbidity in men. Potentially important regulators of prostate cancer progression are members of the metzincin superfamily of proteases, principally through their regulation of the extracellular matrix. It is therefore timely to review the role of the metzincin superfamily in prostate cancer and its progression to better understand their involvement in this disease. A systematic-like search strategy was conducted. Articles that investigated the roles of members of the metzincin superfamily and their key regulators in prostate cancer were included. The extracted articles were synthesized and data presented in tabular and narrative forms. Two hundred and five studies met the inclusion criteria. Of these, 138 investigated the role of the Matrix Metalloproteinase (MMP) subgroup, 34 the Membrane-Tethered Matrix Metalloproteinase (MT-MMP) subgroup, 22 the A Disintegrin and Metalloproteinase (ADAM) subgroup, 8 the A Disintegrin and Metalloproteinase with Thrombospondin Motifs (ADAMTS) subgroup and 53 the Tissue Inhibitor of Metalloproteinases (TIMP) family of regulators, noting that several studies investigated multiple family members. There was clear evidence that specific members of the metzincin superfamily are involved in prostate cancer progression, which can be either in a positive or negative manner. However, further understanding of their mechanisms of action and how they may be used as prognostic indicators or molecular targets is required.

siRNA-mediated silencing of CD44 delivered by Jet Pei enhanced Doxorubicin chemo sensitivity and altered miRNA expression in human breast cancer cell line (MDA-MB468)

CD44, as a superficial cellular glycoprotein, is an essential factor in cell-cell and cell-matrix interaction. The CD44 expression level has been substantially up-regulated in breast cancer, and this upregulation facilitates tumor proliferation and angiogenesis. This study aims to evaluate the combination therapy of Jet Pei/CD44-specific-siRNA/doxorubicin in breast cancer MDA-MB468 cell line. The MTT assay, wound healing test, colony formation assay, DAPI staining, and flow cytometry were performed to investigate the tumoral cell viability, migration, clonogenesis, and apoptosis progression. The quantitative real-time PCR (qRT-PCR) was performed to demonstrate the CD44 expression level. Finally, the effect of CD44 silencing on the expression of VEGF, CXCR4, MMP9, and MiR-142-3p was measured. The combination of CD44-specific-siRNA with doxorubicin decreased tumoral metastasis, proliferation, invasion, and migration, and increased apoptosis in MDA-MB468 cells. In conclusions, CD44 can serve as a therapeutic target in breast cancer. Moreover, the combination therapy of CD44-specific-siRNA with doxorubicin can be a promising treatment for patients with breast cancer.

Identification of sequence-specific interactions of the CD44-intracellular domain with RUNX2 in the transcription of matrix metalloprotease-9 in human prostate cancer cells

Aim

The Cluster of differentiation 44 (CD44) transmembrane protein is cleaved by γ-secretase, the inhibition of which blocks CD44 cleavage. This study aimed to determine the biological consequence of CD44 cleavage and its potential interaction with Runt-related transcription factor (RUNX2) in a sequence-specific manner in PC3 prostate cancer cells.

Methods

Using full-length and C-terminal deletion constructs of CD44-ICD (D1-D5) expressed as stable green fluorescent protein-fusion proteins in PC3 cells, we located possible RUNX2-binding sequences.

Results

Chromatin immunoprecipitation assays demonstrated that the C-terminal amino acid residues between amino acids 671 and 706 in D1 to D3 constructs were indispensable for sequence-specific binding of RUNX2. This binding was minimal for sequences in the D4 and D5 constructs. Correspondingly, an increase in matrix metalloprotease-9 (MMP-9) expression was observed at the mRNA and protein levels in PC3 cells stably expressing D1-D3 constructs.

Conclusion

These results provide biochemical evidence for the possible sequence-specific CD44-ICD/RUNX2 interaction and its functional relationship to MMP-9 transcription in the promoter region.

Role of αVβ3 in Prostate Cancer: Metastasis Initiator and Important Therapeutic Target

In prostate cancer, distant organ metastasis is the leading cause of patient death. Although the mechanism of malignant tumor metastasis is unclear, studies have confirmed that integrin αVβ3 plays an important role in this process. In prostate cancer, αVβ3 mediates adhesion, invasion, immune escape and neovascularization through interactions with different ligands. Among these ligands and in addition to proteins that are directly related to tumor invasion, other proteins that contain the RGD structure could also bind to αVβ3 and cause a number of biological effects. In this article, we summarized the ligand and downstream proteins related to αVβ3-mediated prostate cancer metastasis as well as some diagnostic and therapeutic measures targeting αVβ3.

Invadopodia: clearing the way for cancer cell invasion

The invasive nature of many cancer cells involves the formation of F-actin-based, lipid-raft-enriched membrane protrusions known as invadopodia or, more broadly, invadosomes. Invadopodia are specialized adhesive structures arising from ventral cell surface within cell-extracellular matrix (ECM) contacts and concentrate high proteolytic activities that allow cells to overcome the dense scaffold of local microenvironment, comprising a natural barrier to cell spreading. This degradative activity distinguishes invadopodia from other adhesive structures like focal adhesions, lamellipodia or filopodia, and is believed to drive cancer progression.

Elevated MMP9 expression in breast cancer is a predictor of shorter patient survival

PURPOSE

MMP9 is a matricellular protein associated with extracellular matrix (ECM) remodelling, that promotes tumour progression, and modulates the activity of cell adhesion molecules and cytokines. This study aims to assess the prognostic value of MMP9 and its association with cytoskeletal modulators in early-stage invasive breast cancer (BC).

METHODS

MMP9 expression was evaluated by immunohistochemistry using a well-characterised series of primary BC patients with long-term clinical follow-up. Association with clinicopathological factors, patient outcome and ECM remodelling BC-biomarkers were investigated. METABRIC dataset, BC-GenExMiner v4.0 and TCGA were used for the external validation of MMP9 expression. GSEA gene enrichment analyses were used to evaluate MMP9 associated pathways.

RESULTS

MMP9 immunopositivity was observed in the stroma and cytoplasm of BC cells. Elevated MMP9 protein levels were associated with high tumour grade, high Nottingham Prognostic Index, and hormonal receptor negativity. Elevated MMP9 protein expression correlated significantly with cytokeratin 17 (Ck17), Epidermal Growth Factor Receptor (EGFR), proliferation (Ki67) biomarkers, cell surface adhesion receptor (CD44) and cell division control protein 42 (CDC42). Cytoplasmic MMP9 expression was an independent prognostic factor associated with shorter BC-specific survival. In the external validation cohorts, MMP9 expression was also associated with poor patients' outcome. Transcriptomic analysis confirmed a positive association between MMP9 and ECM remodelling biomarkers. GSEA analysis supports MMP9 association with ECM and cytoskeletal pathways.

CONCLUSION

This study provides evidence for the prognostic value of MMP9 in BC. Further functional studies to decipher the role of MMP9 and its association with cytoskeletal modulators in BC progression are warranted.

The chemokine CCL7 regulates invadopodia maturation and MMP-9 mediated collagen degradation in liver-metastatic carcinoma cells

Liver metastases remain a major cause of death from gastrointestinal tract cancers and other malignancies, such as breast and lung carcinomas. Understanding the underlying biology is essential for the design of effective therapies. We previously identified the chemokine CCL7 and its receptor CCR3 as critical mediators of invasion and metastasis in lung and colon carcinoma cells. Here we show that the CCL7/CCR3 axis regulates a late stage in invadopodia genesis namely, the targeting of MMP-9 to the invadopodia complex, thereby promoting invadopodia maturation and collagen degradation. We show that this process could be blocked by overexpression of a dominant negative RhoA in highly invasive cells, while a constitutively active RhoA upregulated invadopodia maturation in CCL7-silenced and poorly invasive and metastatic cells and also enhanced their metastatic potential in vivo, collectively, implicating RhoA activation in signaling downstream of CCL7. Blockade of the ERK or PI3K pathways by chemical inhibitors also inhibited invadopodia formation, but affected the initiation stage of invadopodia genesis. Our data implicate CCL7/CCR3 signaling in invadopodia maturation and suggest that chemokine signaling acts in concert with extracellular matrix-initiated signals to promote invasion and liver metastasis.

Nomogram Incorporating CD44v6 and Clinicopathological Factors to Predict Lymph Node Metastasis for Early Gastric Cancer

Background

Treatment strategy for early gastric cancer depends on the probability of lymph node metastasis. The aim of this study is to develop a nomogram predicting lymph node metastasis in early gastric cancer using clinicopathological factors and biomarkers.

Methods

A literature review was performed to identify biomarkers related to lymph node metastasis in gastric cancer. Seven markers were selected and immunohistochemistry was performed in 336 early gastric cancer tissues. Based on the multivariable analysis, a prediction model including clinicopatholgical factors and biomarkers was developed, and benefit of adding biomarkers was evaluated using the area under the receiver operating curve and net reclassification improvement. Functional study in gastric cancer cell line was performed to evaluate mechanism of biomarker.

Results

Of the seven biomarkers studied, α1 catenin and CD44v6 were significantly associated with lymph node metastasis. A conventional prediction model, including tumor size, histological type, lymphatic blood vessel invasion, and depth of invasion, was developed. Then, a new prediction model including both clinicopathological factors and CD44v6 was developed. Net reclassification improvement analysis revealed a significant improvement of predictive performance by the addition of CD44v6, and a similar result was shown in the internal validation using bootstrapping. Prediction nomograms were then constructed based on these models. In the functional study, CD44v6 was revealed to affect cell proliferation, migration and invasion.

Conclusions

Overexpression of CD44v6 was a significant predictor of lymph node metastasis in early gastric cancer. The prediction nomograms incorporating CD44v6 can be useful to determine treatment plans in patients with early gastric cancer.

Cyclodextrin mediated delivery of NF-κB and SRF siRNA reduces the invasion potential of prostate cancer cells in vitro

Prostate cancer is the most common cancer in men of the western world. To date, no effective treatment exists for metastatic prostate cancer and consequently, there is an urgent need to develop new and improved therapeutics. In recent years, the therapeutic potential of RNA interference (RNAi) has been extensively explored in a wide range of diseases including prostate cancer using numerous gene delivery vectors. The aims of this study were to investigate the ability of a non-viral modified cyclodextrin (CD) vector to deliver siRNA to the highly metastatic PC-3 prostate cancer cell line, to quantify the resulting knockdown of the two target genes (RelA and SRF) and to study the effects of the silencing on metastasis. Data from a Matrigel in vitro invasion assay indicated that the silencing of the target genes achieved by the CD vector resulted in significant reductions (P=0.0001) in the metastatic potential of these cells. As the silencing of these target genes was shown not to have a negative impact on cell viability, we hypothesise that the mechanism of invasion inhibition is due, in part, to the significant reduction observed (P⩽0.0001) in the level of pro-inflammatory cytokine, MMP9, which is known to be implicated in the metastasis of prostate cancer.

Alternative CD44 splicing identifies epithelial prostate cancer cells from the mesenchymal counterparts

An epithelial to mesenchymal transition (EMT) has been shown to be a necessary precursor to prostate cancer metastasis. Additionally, the differential expression and splicing of mRNAs has been identified as a key means to distinguish epithelial from mesenchymal cells by qPCR, western blotting and immunohistochemistry. However, few markers exist to differentiate between these cells by flow cytometry. We previously developed two cell lines, PC3-Epi (epithelial) and PC3-EMT (mesenchymal). RNAseq was used to determine the differential expression of membrane proteins on PC3-Epi/EMT. We used western blotting, qPCR and flow cytometry to validate the RNAseq results. CD44 was one of six membrane proteins found to be differentially spliced between epithelial and mesenchymal PC3 cells. Although total CD44 was positive in all PC3-Epi/EMT cells, PC3-Epi cells had a higher level of CD44v6 (CD44 variant exon 6). CD44v6 was able to differentiate epithelial from mesenchymal prostate cancer cells using either flow cytometry, western blotting or qPCR.

INPP4B suppresses prostate cancer cell invasion

BACKGROUND

INPP4B and PTEN dual specificity phosphatases are frequently lost during progression of prostate cancer to metastatic disease. We and others have previously shown that loss of INPP4B expression correlates with poor prognosis in multiple malignancies and with metastatic spread in prostate cancer.

RESULTS

We demonstrate that de novo expression of INPP4B in highly invasive human prostate carcinoma PC-3 cells suppresses their invasion both in vitro and in vivo. Using global gene expression analysis, we found that INPP4B regulates a number of genes associated with cell adhesion, the extracellular matrix, and the cytoskeleton. Importantly, de novo expressed INPP4B suppressed the proinflammatory chemokine IL-8 and induced PAK6. These genes were regulated in a reciprocal manner following downregulation of INPP4B in the independently derived INPP4B-positive LNCaP prostate cancer cell line. Inhibition of PI3K/Akt pathway, which is highly active in both PC-3 and LNCaP cells, did not reproduce INPP4B mediated suppression of IL-8 mRNA expression in either cell type. In contrast, inhibition of PKC signaling phenocopied INPP4B-mediated inhibitory effect on IL-8 in either prostate cancer cell line. In PC-3 cells, INPP4B overexpression caused a decline in the level of metastases associated BIRC5 protein, phosphorylation of PKC, and expression of the common PKC and IL-8 downstream target, COX-2. Reciprocally, COX-2 expression was increased in LNCaP cells following depletion of endogenous INPP4B.

CONCLUSION

Taken together, we discovered that INPP4B is a novel suppressor of oncogenic PKC signaling, further emphasizing the role of INPP4B in maintaining normal physiology of the prostate epithelium and suppressing metastatic potential of prostate tumors.

INPP4B suppresses prostate cancer cell invasion

Background

INPP4B and PTEN dual specificity phosphatases are frequently lost during progression of prostate cancer to metastatic disease. We and others have previously shown that loss of INPP4B expression correlates with poor prognosis in multiple malignancies and with metastatic spread in prostate cancer.

Results

We demonstrate that de novo expression of INPP4B in highly invasive human prostate carcinoma PC-3 cells suppresses their invasion both in vitro and in vivo. Using global gene expression analysis, we found that INPP4B regulates a number of genes associated with cell adhesion, the extracellular matrix, and the cytoskeleton. Importantly, de novo expressed INPP4B suppressed the proinflammatory chemokine IL-8 and induced PAK6. These genes were regulated in a reciprocal manner following downregulation of INPP4B in the independently derived INPP4B-positive LNCaP prostate cancer cell line. Inhibition of PI3K/Akt pathway, which is highly active in both PC-3 and LNCaP cells, did not reproduce INPP4B mediated suppression of IL-8 mRNA expression in either cell type. In contrast, inhibition of PKC signaling phenocopied INPP4B-mediated inhibitory effect on IL-8 in either prostate cancer cell line. In PC-3 cells, INPP4B overexpression caused a decline in the level of metastases associated BIRC5 protein, phosphorylation of PKC, and expression of the common PKC and IL-8 downstream target, COX-2. Reciprocally, COX-2 expression was increased in LNCaP cells following depletion of endogenous INPP4B.

Conclusion

Taken together, we discovered that INPP4B is a novel suppressor of oncogenic PKC signaling, further emphasizing the role of INPP4B in maintaining normal physiology of the prostate epithelium and suppressing metastatic potential of prostate tumors.

Electronic supplementary material

The online version of this article (doi:10.1186/s12964-014-0061-y) contains supplementary material, which is available to authorized users.

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CD44 is a cell surface adhesion receptor that is highly expressed in many cancers and regulates metastasis via recruitment of CD44 to the cell surface. Its interaction with appropriate extracellular matrix ligands promotes the migration and invasion processes involved in metastases. It was originally identified as a receptor for hyaluronan or hyaluronic acid and later to several other ligands including, osteopontin (OPN), collagens, and matrix metalloproteinases. CD44 has also been identified as a marker for stem cells of several types. Beside standard CD44 (sCD44), variant (vCD44) isoforms of CD44 have been shown to be created by alternate splicing of the mRNA in several cancer. Addition of new exons into the extracellular domain near the transmembrane of sCD44 increases the tendency for expressing larger size vCD44 isoforms. Expression of certain vCD44 isoforms was linked with progression and metastasis of cancer cells as well as patient prognosis. The expression of CD44 isoforms can be correlated with tumor subtypes and be a marker of cancer stem cells. CD44 cleavage, shedding, and elevated levels of soluble CD44 in the serum of patients is a marker of tumor burden and metastasis in several cancers including colon and gastric cancer. Recent observations have shown that CD44 intracellular domain (CD44-ICD) is related to the metastatic potential of breast cancer cells. However, the underlying mechanisms need further elucidation.