Dexamethasone resets stable association of nuclear Snail with LSD1 concomitant with transition from EMT to partial EMT.

Cancer cells utilize epithelial to mesenchymal transition (EMT) during invasion and metastasis. This program has intermediate cell states with retained epithelial and gained mesenchymal features together, referred to as partial EMT. Histone demethylase LSD1 forms a complex with the EMT master transcription factor Snail to modify histone marks and regulate target gene expression. However, little is known about the formation of this complex during the Snail-dependent transition between partial EMT and EMT. Here we visualized the nuclear complex of Snail and LSD1 as foci signals using proximity ligation assay. We demonstrated that the nuclear foci numbers varied with the transition of exogenous Snail-dependent partial EMT to EMT. Furthermore, we found that long exposure to dexamethasone could revert exogenous Snail-dependent EMT to partial EMT. In this reversion, the nuclear foci numbers also returned to previous levels. Therefore, we concluded that Snail might select partial EMT or EMT by altering its association with LSD1.

The squamous cell carcinoma cell line OM-1 retains both p75-dependent stratified epithelial progenitor potential and cancer stem cell properties.

The low-affinity nerve growth factor receptor p75 is a stratified epithelial stem/progenitor marker of human epithelia. We found OM-1, a human squamous cell carcinoma (SCC) cell line, showed distinct cells with p75 cluster, especially located at the center of a growing colony in a monolayer culture. A cell with p75 cluster was surrounded by cytokeratin 14- and cytokeratin 13-expressing cells that settled at the outer margin of the colony. OM-1 cells were also capable of forming tumor spheres in a cell suspension culture, an ability which was attenuated by the inhibition of p75-signaling. Intriguingly, we also found a p75-negative cell population from a growing culture of OM-1 that re-committed to become p75-clustering cells. These results indicated the possibility that SCC with epithelial multi-layering capacity can exploit the p75-dependent stratified epithelial progenitor property for the cancer stemness.

TGF-ß1 induces amoeboid-to-mesenchymal transition of CD44high oral squamous cell carcinoma cells via miR-422a downregulation through ERK activation and Cofilin-1 phosphorylation.

BACKGROUND: The objective of this study was to clarify the molecular mechanism of amoeboid-to-mesenchymal transition (AMT) of CD44high oral squamous cell carcinoma (OSCC) cells. METHODS: Morphology and expression of mesenchymal genes were investigated in CD44high OSCC cells (CD44high OM-1 cells) cultured on laminin-coated soft silicone gel. Additionally, microarray analysis was performed to investigate microRNA (miRNA) expression inhibited by transforming growth factor-ß1 (TGF-ß1) in CD44high OM-1 cells. RESULTS: When CD44high OM-1 cells were cultured on 2.0-kPa laminin-coated silicone gel, the cells exhibited an amoeboid-like round morphology. Cofilin-1 expression was found in the nucleus and cytoplasm of amoeboid-like CD44high OM-1 cells. The invasive capacity was significantly reduced after Cofilin-1 knockdown. Additionally, Cofilin-1 knockdown cells had an irregularly extended shape. Phosphorylated Cofilin-1 was significantly upregulated by TGF-ß1. Additionally, TGF-ß1 enhanced N-cadherin and Snail mRNA expression and induced a spindle-shaped morphology. ERK1/2 phosphorylation was induced by TGF-ß1. Microarray analysis revealed that miR-422a exhibited the greatest downregulation (fold change: 0.22) in the presence of TGF-ß1. Importantly, TGF-ß1-inhibited miR-422a expression was recovered by the ERK inhibitor or ERK1/2 knockdown. Additionally, miR-422a inhibitor-transfected CD44high OM-1 cells exhibited high N-cadherin and Snail mRNA expression. Furthermore, Cofilin-1 knockdown and miR-422a inhibition induced a spindle cell morphology. CONCLUSION: Cofilin-1 is involved in the invasive ability of CD44high OSCC cells. TGF-ß1 contributes to AMT by downregulation of miR-422a via ERK activation and Cofilin-1 phosphorylation. Our findings suggest that miR-422a and Cofilin-1 play major roles in the maintenance of amoeboid-like CD44high cells.

Effect of hydrogel stiffness on morphology and gene expression pattern of CD44high oral squamous cell carcinoma cells.

The stiffness of extracellular matrix (ECM) has been associated with tumor growth, phenotypic plasticity, and invasion through modulation of the intracellular signaling pathway. However, the effect of ECM stiffness on oral cancer stem cells (CSCs) has not been fully elucidated. Therefore, we preliminarily investigated changes in phenotype and gene expression in CD44 positive-oral squamous cell carcinoma (OSCC) cells (i.e., CD44high OM-1 cells) that were cultured on laminin-coated hydrogel with various degrees of stiffness. Mesenchymal-like morphology was observed when cells were cultured on 4.0 kPa laminin-coated hydrogel; amoeboid-like morphology was observed when cells were cultured on 1.0 kPa and 0.5 kPa laminin-coated hydrogel. These results indicated that CD44high OM-1 cells underwent mesenchymal to amoeboid transition (MAT) when cultured on laminin-coated softer hydrogel. E-cadherin and ESA mRNA expression levels were significantly reduced in CD44high OM-1 cells cultured on 0.5 and 1.0 kPa laminin-coated hydrogel, compared with their levels in control cells cultured in laminin-coated dishes. Significant changes in CD44 mRNA expression were not found in CD44high OM-1 cells that were cultured on different stiff hydrogels, compared with expression in control cells. Microarray analysis revealed that expression of cofilin, an intracellular actin-modulating protein, was increased by 8.19-fold in amoeboid-like CD44high OM-1 cells, compared with mesenchymal-like CD44high OM-1 cells; this suggested that cofilin was associated with MAT in CD44high OSCC cells. Further studies are needed to clarify the relationship between cofilin and invasion ability in CD44high amoeboid-like OSCC cells.

Preoperative oral health care reduces postoperative inflammation and complications in oral cancer patients.

The records of 70 patients with oral cancer who were treated at a single institution between 2008 and 2014 were reviewed. The body temperature, white blood cell count, and C-reactive protein (CRP) levels were compared between those who had received preoperative oral care (oral care group) and those who had not received any (non-oral care group). When the patients were divided into those who underwent minimally invasive surgery and those who underwent severely invasive surgery, the mean CRP level in the early postoperative period was lower in the oral care group as compared with the non-oral care group in those who underwent minimally invasive surgery as well as those who underwent severely invasive surgery. However, the mean CRP level was most evidently reduced in the severely invasive group on days 1 and 3-5. However, no significant differences were observed with regard to the percentage of postoperative infectious complications (for example, surgical site infection, anastomotic leak and pneumonia) between the oral care (13.6%) and non-oral care (20.8%) groups, though a reduced prevalence of postoperative complications following preoperative oral care was noted. The results of the present study suggest that preoperative oral care can decrease inflammation during the early postoperative stage in patients with oral cancer who undergo severely invasive surgery.

CD44(high) /ALDH1(high) head and neck squamous cell carcinoma cells exhibit mesenchymal characteristics and GSK3ß-dependent cancer stem cell properties.

BACKGROUND: CD44 and aldehyde dehydrogenase 1 (ALDH1) have been shown to be useful markers for identification of cancer stem cells (CSCs). We previously reported that glycogen synthase kinase 3ß (GSK3ß) is involved in regulation of the self-renewal ability of head and neck squamous cell carcinoma (HNSCC) CSCs. The purpose of the present study was to clarify the role of GSK3ß in CD44(high) /ALDH1(high) HNSCC cells. METHODS: Cells with greater expression of CD44 and higher ALDH1 enzymatic activity were FACS sorted from the OM-1 HNSCC cell line. The self-renewal ability of CD44(high) /ALDH1(high) cells was then examined using a tumor sphere formation assay. mRNA expressions of the stem cell markers Sox2, Oct4, and Nanog, as well as GSK3ß were evaluated by real-time RT-PCR. RESULTS: CD44(high) /ALDH1(high) cells exhibited higher tumor sphere forming ability and increased expression of stem cell markers as compared with CD44(high) /ALDH1(low) cells. Interestingly, spindle-shaped cells positive for vimentin were found in the CD44(high) /ALDH1(high) but not the CD44(high) /ALDH1(low) cell population. In addition, the ALDH1 activity and sphere forming ability of CD44(high) /ALDH1(high) cells was significantly inhibited by GSK3ß knockdown. On the other hand, CD44(high) /ALDH1(low) cells exhibited high epidermal growth factor receptor (EGFR) expression and increased cell growth. CONCLUSIONS: Our results show that GSK3ß plays a major role in maintenance of stemness of CD44(high) /ALDH1(high) HNSCC cells. Additionally, they indicate a close relationship between CSC and mesenchymal characteristics in HNSCC.

Clinicopathological analysis of salivary gland carcinomas and literature review.

Malignant salivary gland tumors are rare and exhibit a broad spectrum of phenotypic heterogeneity. The objective of this study was to investigate prognostic factors in patients with salivary gland carcinomas and review the results in light of other reports. We retrospectively reviewed 40 patients with primary salivary gland carcinomas who were diagnosed and treated at our institution between 1991 and 2014. Of the 40 tumors, 19 (47.5%) were mucoepidermoid carcinomas, 11 (27.5%) were adenoid cystic carcinomas, 7 (17.5%) were acinic cell carcinomas, 2 (5.0%) were myoepithelial carcinomas and 1 (2.5%) was a squamous cell carcinoma. Clinically positive lymph nodes were present in 4 patients (10.0%). As regards clinical stage, 15 cases (37.5%) were stage I, 13 (32.5%) were stage II, 1 (2.5%) was stage III and 11 (27.5%) were stage IVA. The majority of the patients (97.5%) were treated with surgery, of whom 25 (62.5%) received surgery alone and 14 (35.0%) underwent surgery in combination with chemotherapy or chemotherapy and radiotherapy. The median follow-up time for all the patients was 48 months. The disease-specific survival rate at 5 years was 87.1%. We identified a significant correlation between poor survival rate and histological grade (intermediate/high), tumor size (T3/T4), lymph node metastasis (node-positive) and clinical stage (III/IV) using the Kaplan-Meier method (P<0.05 for each). In addition, the Cox proportional hazards regression analysis confirmed that lymph node metastasis and tumor size were independent prognostic factors for disease-specific survival (hazard ratio = 18.7 and 15.1, respectively; P=0.023 and 0.037, respectively). Furthermore, tumor size was found to be a predictive factor regarding recurrence in the multivariate logistic regression analysis (odds ratio = 8.35; P=0.025). Our results suggest that lymph node metastasis and tumor size are significant prognostic factors for patients with salivary gland carcinomas.

Role of receptor for hyaluronan-mediated motility (RHAMM) in human head and neck cancers.

The receptor for hyaluronan (HA)-mediated motility (RHAMM) is a HA-binding protein located in the cytoskeleton and centrosome. RHAMM has multiple functions that manifest with different cellular localizations, for example, modulation of growth factor receptor, regulation of cell signaling pathways, and mitotic spindle assembly. In addition, its increased expression has major roles in tumorigenesis and can induce genomic instability and cancer progression. In head and neck cancers, increased expression of RHAMM is associated with high proliferation of cancer cells and decreased survival. CD44, a cell-adhesion molecule and HA receptor, can modulate intracellular signaling by forming complexes with RHAMM to promote invasion and metastasis of cancer cells. In this review, we provide an overview of the biological functions of RHAMM in non-neoplastic cells and cancer cells, as well as its association with CD44, and also introduce studies that particularly implicate RHAMM in the pathogenesis of head and neck cancers.

Autocrine galectin-1 promotes collective cell migration of squamous cell carcinoma cells through up-regulation of distinct integrins.

We found that high galectin-1 (Gal-1) mRNA levels were associated with invasive squamous cell carcinoma (SCC) cells that expressed Snail, an epithelial-to-mesenchymal transition (EMT) regulator. Both Gal-1 overexpression and soluble Gal-1 treatment accelerated invasion and collective cell migration, along with activation of cdc42 and Rac. Soluble Gal-1 activated c-Jun N-terminal kinase to increase expression levels of integrins α2 and ß5, which were essential for Gal-1 dependent collective cell migration and invasiveness. Soluble Gal-1 also increased the incidence of EMT in Snail-expressing SCC cells; these were a minor population with an EMT phenotype under growing conditions. Our findings indicate that soluble Gal-1 promotes invasiveness through enhancing collective cell migration and increasing the incidence of EMT.

AKT primes snail-induced EMT concomitantly with the collective migration of squamous cell carcinoma cells.

In this study, we found that wounding of a confluent monolayer of squamous cell carcinoma (SCC) cells induced epithelial-mesenchymal transition (EMT) specifically at the edge of the wound. This process required the combined stimulation of TGFß, TNFα, and PDGF-D. Such a combined cytokine treatment of confluent monolayers of the cells upregulated the expression levels of Snail and Slug via PI3K. The PI3K downstream effector, AKT, was dispensable for the upregulation of Snail and Slug, but essential for enabling EMT in response to upregulation of Snail and Slug.

Expression of receptor for hyaluronan-mediated motility (RHAMM) in ossifying fibromas.

Fibro-osseous lesions of the jaw are poorly understood because of a significant overlap of clinical, radiological and histological features among the various types, though they present distinct patterns of disease progression. An ossifying fibroma is associated with significant cosmetic and functional disturbances, as it shows expansive proliferation. Thus, it is important to establish a specific marker, as well as clearly elucidate its etiology for diagnosis and proper treatment. We previously established immortalized cell lines from human ossifying fibromas of the jaw and found that they highly expressed the receptor for hyaluronan (HA)-mediated motility (RHAMM). In this study, we examined the expression of RHAMM mRNA in 65 fibro-osseous lesions, including ossifying fibroma, fibrous dysplasia and osseous dysplasia, as well as 5 normal jaws, using real-time RT-PCR and immunohistochemistry assays. RHAMM mRNA and protein expression were significantly elevated in the ossifying fibroma specimens. These results suggest that detection of upregulated RHAMM expression in an ossifying fibroma assists with differential diagnosis and has a key role in elucidation of its pathophysiology.

Snail promotes Cyr61 secretion to prime collective cell migration and form invasive tumor nests in squamous cell carcinoma.

We previously identified genes associated with Snail-mediated squamous cell carcinoma (SCC) invasiveness, in which we observed significant elevation of Cyr61 expression. In this study, SCC cell lines overexpressing Cyr61 exhibited constitutive activation of Rho A and upregulated invasiveness without the disruption of homophilic cell attachment. Humoral Cyr61 enhanced further production of endogenous Cyr61 by SCC cells, which stimulated collective cell migration and the development of an invasive tumor nest. We propose a Cyr61-dependent model for the development of invasive SCC nest, whereby a subset of tumor cells that highly produce Cyr61 may direct other tumor cells to undergo collective cell migration, resulting in a formation of primary SCC mass.

Overexpression of receptor for hyaluronan-mediated motility (RHAMM) in MC3T3-E1 cells induces proliferation and differentiation through phosphorylation of ERK1/2.

Receptor for hyaluronan (HA)-mediated motility (RHAMM) was first described as a soluble HA binding protein released by sub-confluent migrating cells. We previously found that RHAMM was highly expressed and plays an important role in proliferation in the human cementifying fibroma (HCF) cell line, which we previously established. HCF is a benign fibro-osseous neoplasm of the jaw and is composed of fibrous tissue containing varying amounts of mineralized material. However, the pathogenesis of HCF is not clear. In this paper, we examined the roles of RHAMM in osteoblastic cells. We generated RHAMM-overexpressing MC3T3-E1 cells and examined the cell proliferation and differentiation of osteoblastic cells. In MC3T3-E1 cells, overexpressing RHAMM was located intracellular and activated ERK1/2. Interestingly, the ERK1/2 activated by RHAMM overexpression promoted cell proliferation and suppressed the differentiation of osteoblastic cells. Our findings strongly suggest that RHAMM may play a key role in the osteoblastic differentiation process. The rupture of balance from differentiation to proliferation induced by RHAMM overexpression may link to the pathogenesis of bone neoplasms such as HCF.

PGE2 targets squamous cell carcinoma cell with the activated epidermal growth factor receptor family for survival against 5-fluorouracil through NR4A2 induction.

We found a linear correlation between the Prostaglandin E(2) (PGE(2)) amount and the NR4A2 expression in oral squamous cell carcinoma (SCC) tissues through a statistical analysis among 41 clinical cases. In SCC cell lines, PGE(2) receptor (EP) ligation by exogenous PGE(2) promoted the NR4A2 expression in the cAMP/protein kinase A (PKA)-dependent manner. The process required a nature of SCC cell represented by constitutive activated epidermal growth factor receptor (EGFR) family. Targeted inactivation of the EGFRs interfered the PGE(2)-dependent NR4A2 expression. The PGE(2)-dependent NR4A2 induction is essential for the resistance to anti-cancer drug-induced apoptosis especially in SCC cells which showed constitutive EGFRs activity via autocrine epiregulin, a ligand for EGFRs. Conversely, SCC cells which lack epiregulin expression in their nature could gain the ability to promote the NR4A2 expression in response to PGE(2) and attain the resistance to anti-cancer drug-induced apoptosis under the existence of exogenous epiregulin. These findings suggest that susceptibility of SCC to anti-cancer drug could be compromised when PGE(2) was delivered in the microenvironment of SCC cells supported by constitutive EGFR family activities as their nature.

RHAMM/ERK interaction induces proliferative activities of cementifying fibroma cells through a mechanism based on the CD44-EGFR.

We have previously established immortalized cells (HCF) from cementifying fibroma of the jaw bone. Here, we found that the receptor for hyaluronan (HA)-mediated motility (RHAMM) and epiregulin, a ligand for the epidermal growth factor receptor (EGFR), were highly expressed in HCF cells in comparison with osteoblasts by conducting a microarray analysis. The cell growth of HCF cells was significantly decreased by the knockdown of RHAMM using small interfering RNA (siRNA). RHAMM was associated with extracellular signal-regulated kinase (ERK) and essential for ERK phosphorylation. HCF cells had characteristic growth mechanisms in which epiregulin functions in an extracellular autocrine loop. Interestingly, exogenous HA induced the phosphorylation of EGFR, which was mainly dependent on CD44. The results raise the novel idea that the EGFR may activate Raf-MEK-ERK signaling in response to the binding of HA to CD44. Moreover, RHAMM was able to associate with TPX2 in the nucleus and was required for HA-induced activation of the Aurora A kinase. The results suggest that RHAMM has a predominant role in the cell cycle in HCF. Here, we report the new machinery by which RHAMM/ERK interaction induces the proliferative activity of cementifying fibroma cells via a specific signaling pathway through the CD44-EGFR axis.

Nodal lymphangiogenesis and metastasis: Role of tumor-induced lymphatic vessel activation in extramammary Paget's disease.

Nodal lymphangiogenesis promotes distant lymph node (LN) metastasis in experimental cancer models. However, the role of nodal lymphangiogenesis in distant metastasis and in the overall survival of cancer patients remains unknown. Therefore, we investigated mechanisms that might facilitate regional and distant LN metastasis in extramammary Paget's disease (EMPD). We retrospectively analyzed the impact of tumor-induced lymphatic vessel activation on the survival of 116 patients, the largest cohort with EMPD studied to date. Nodal lymphangiogenesis was significantly increased in metastatic, compared with tumor-free, LNs (P = 0.022). Increased lymphatic invasion within regional LNs was significantly associated with distant metastasis in LN (P = 0.047) and organs (P = 0.003). Thus, invasion within regional LNs is a powerful indicator of systemic tumor spread and reduced patient survival in EMPD (P = 0.0004). Lymphatic vessels associated with tumors expressed stromal cell-derived factor-1 (SDF-1), whereas CXCR4 was expressed on invasive Paget cells undergoing epithelial-mesenchymal transition (EMT)-like process. A431 cells overexpressing Snail expressed increased levels of CXCR4 in the presence of transforming growth factor-beta1. Haptotactic migration assays confirmed that Snail-induced EMT-like process promotes tumor cell motility via the CXCR4-SDF-1 axis. Sinusoidal lymphatic endothelial cells and macrophages expressed SDF-1 in subcapsular sinuses of lymph nodes before Paget cell arrival. Our findings reveal that EMT-related features likely promote lymphatic metastasis of EMPD by activating the CXCR4-SDF-1 axis.

Overexpression of the receptor for hyaluronan-mediated motility, correlates with expression of microtubule-associated protein in human oral squamous cell carcinomas.

Receptor for hyaluronan-mediated motility (RHAMM) has previously been characterized as a cell surface receptor for hyaluronan and a microtubule-associated intracellular hyaluronan binding protein. We examined the expression of RHAMM mRNA in 43 oral squamous cell carcinomas (SCCs) and 7 normal gingivae by real-time RT-PCR. The expression level of RHAMM mRNA was significantly higher in oral SCCs than normal gingivae (P=0.0047). Forty out of 43 oral SCCs showed expression of RHAMM splice variant (48 bp deletion). We immunohistochemically confirmed the protein expression of RHAMM in oral SCCs with higher levels of RHAMM mRNA. Patients with oral SCC who had high RHAMM expression had shorter survival rates than patients with low expression. However, it was not statistically significant. It has been reported that RHAMM interacts with spindle assembly factors such as microtubule-associated protein (TPX2). To investigate the expression of microtubule-associated protein in oral SCCs, mRNA expression of TPX2 was also examined by real-time RT-PCR. The expression level of TPX2 mRNA was significantly higher in oral SCCs than normal gingivae (P=0.046). Furthermore, a significant correlation between the mRNA expression levels of TPX2 and RHAMM was recognized (P=0.011). The results indicate that there is a strong correlation between the mRNA expression levels of TPX2 and RHAMM in oral SCCs. Our observations suggest that the up-regulations of human RHAMM and TPX2 gene correlate with the malignant condition and might be linked to the increased or abnormal cell proliferation in human oral SCCs.

DeltaNp63alpha-dependent expression of Id-3 distinctively suppresses the invasiveness of human squamous cell carcinoma.

p63 is a member of the p53 family and DeltaNp63alpha is the dominant-expressing isoform of p63 in basal layer of normal stratified epithelium and human squamous cell carcinoma (SCC) cells. We have previously reported that down-regulation of p63 was accompanied with epithelial-to-mesenchymal transition (EMT) by Snail-expressing SCC cells, in which re-expression of DeltaNp63alpha diminished their invasiveness (Higashikawa K, Yoneda S, Tobiume K, Taki M, Shigeishi H, Kamata N. Snail-induced down-regulation of DeltaNp63alpha acquires invasive phenotype of human squamous cell carcinoma. Cancer Res 2007;67:9207-13). In this study, we found that DeltaNp63alpha positively regulated inhibitor of differentiation-3 (Id-3) expression. Id is a dominant negative regulator of E2A which is a transcriptional repressor of E-cadherin. Enforced expression of Id-3 was incapable of invoking E-cadherin expression in the SCC cells with EMT phenotype, whereas it significantly impaired their invasiveness with down-regulation of matrix-metalloproteinase-2 (MMP-2) expression. Reporter gene assay revealed that the Ets-1-induced MMP-2 promoter activity was suppressed by the Id-3, while the Id-3-dependent E-cadherin promoter activity was remarkably reduced in the presence of Snail. Furthermore, knockdown of p63 in SCC cells significantly decreased Id-3 expression, in which up-regulation of MMP-2 expression was concomitant with the acquired invasiveness. These findings propose a particular role of the off-signaling of the DeltaNp63alpha-Id-3 axis incident to Snail-mediated EMT for the MMP-2-dependent invasiveness in SCC cells.

Expression of TPX2 in salivary gland carcinomas.

TPX2 is a microtubule-associated protein and is required for microtubule formation at kinetochores in mammalian cells. The purpose of this study was to clarify the expression of TPX2 mRNA and correlation between TPX2 and clinicopathological factors in salivary gland carcinomas. The expression of TPX2 mRNA was investigated in 20 human salivary gland carcinomas (8 mucoepidermoid carcinomas, 7 adenoid cystic carcinomas, 5 acinic cell carcinomas) and 6 normal submandibular glands using real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR). The mean expression level of TPX2 mRNA was higher in mucoepidermoid carcinomas (0.53+/-0.51) than in normal submandibular glands (0.047+/-0.029); a significant association was found (Mann-Whitney U test, P=0.0067). The mean expression levels of TPX2 were also higher in acinic cell carcinomas (0.45+/-0.49) and adenoid cystic carcinomas (0.28+/-0.22) than in normal submandibular glands. Statistical correlations were found (Mann-Whitney U test, P=0.028 and P=0.003, respectively). Correlation between expression of TPX2 and receptor for hyaluronan-mediated motility (RHAMM) was also investigated in this study. A significant association was found between the mRNA expression levels of TPX and RHAMM (Pearson's correlation coefficient by rank test, P=0.020). These results indicate that human TPX2 mRNA is closely linked to increased or abnormal cell proliferation in malignant salivary gland tumors.