Expression of CD74, the receptor for macrophage migration inhibitory factor, in non-small cell lung cancer

Pharmacological inhibition of macrophage migration inhibitory factor interferes with the proliferation and invasiveness of squamous carcinoma cells

Recent clinical observations and experimental studies of our group indicate that macrophage migration inhibitory factor (MIF) may contribute to tumor progression in head and neck squamous cell carcinomas (HNSCC). The present study was undertaken to examine the effects of the irreversible MIF inhibitor 4-iodo-6-phenylpyrimidine (4-IPP) on proliferation and invasiveness of the squamous carcinoma cell line SCCVII. Cell counting, crystal violet assay and flow cytometry were used to analyze the effects of 4-IPP on SCCVII cell growth. The impact of 4-IPP on cell invasiveness was assessed by Boyden chamber assay. Knockdown of the MIF receptor CD74 was achieved by transduction with lentiviral vectors encoding anti-CD74 shRNAs. As shown by immunofluorescence staining, SCCVII cells express both MIF and CD74. Decreased MIF immunoreactivity as a result of exposure to 4-IPP suggested a covalent modification of the cytokine. 4-IPP inhibited SCCVII cell proliferation and invasiveness. Moreover, the cytostatic effect of 4-IPP was enhanced by CD74 knockdown. The inhibitory effects of 4-IPP on cell proliferation and invasiveness strongly suggest that MIF is involved in proliferative activity and invasive properties of squamous carcinoma cells. In conclusion, MIF inhibition may open possibilities for target-directed treatment of head and neck squamous cell carcinoma.

High CD74 expression correlates with ZAP70 expression in B cell chronic lymphocytic leukemia patients

Chronic lymphocytic leukemia (CLL) is the most common leukemia in adults in Western countries. It is characterized by heterogeneous clinical course of the disease and new prognostic factors are still needed. CD74 plays an important role in signal transduction in B cell proliferation and survival pathway. CD74 expression has been shown in solid tumors and has been connected with poor prognosis and tumor progression. The aim of the study was to evaluate the expression of CD74 in chronic lymphocytic leukemia patients with combination with other known prognostic factors. Expression of CD74 was determined in 90 patients and 28 healthy controls. CD74 expression was significantly higher in CLL group than in controls. There was positive correlation between CD74 and ZAP70 expression (p = 0.008). High expression of CD74 was positively correlated with more advanced stage of the disease (p = 0.02). No correlation was shown between CD74 and sex, mutational status IgVH and time to first treatment.

Functional disruption of macrophage migration inhibitory factor (MIF) suppresses proliferation of human H460 lung cancer cells by caspase-dependent apoptosis

Background

Macrophage migration inhibitory factor (MIF) is important in regulating cell proliferation and apoptosis in both normal and cancerous cells, and may be important in cancer progression and metastasis. In human non-small cell lung cancer (NSCLC), the underlying mechanisms responsible for MIF-dependent regulation of cellular proliferation, and cell death remain poorly appreciated.

Methods

The human H460 lung cancer cell-line was treated with an optimally determined dose of 50 pmol/ml MIF siRNA, following which cell proliferation, cell cycle and apoptosis were analyzed. Additionally, known pathways of apoptosis including expression of Annexin-V, enhanced production of caspases-3 and −4 and expression of the Akt signaling protein were assessed in an attempt to provide insights into the signaling pathways involved in apoptosis following disruption of MIF expression.

Results

Specific siRNA sequences markedly decreased MIF expression in H460 cells by 2 to 5-fold as compared with the negative control. Moreover, MIF miRNA dampened not only cellular proliferation, but increased the frequency of apoptotic cells as assessed by cell-surface Annexin-V expression. Entry of cells into apoptosis was partly dependent on enhanced production of caspases −3 and −4 while not affecting the expression of either caspase-8 or the Akt signaling pathway.

Conclusions

In a model of NSCLC, knockdown of MIF mRNA expression dampened H460 proliferation by mechanisms partly dependent on entry of cells into apoptosis and enhanced production of caspase-3 and −4. MIF expression may thus be important in NSCLC progression. Targeting MIF may have clinical utility in the management of human lung cancer.

Down-regulation of CD74 inhibits growth and invasion in clear cell renal cell carcinoma through HIF-1α pathway

OBJECTIVES

To investigate the expression and function of CD74 in normal renal tissue and clear cell-renal cell carcinoma (ccRCC), as well as related renal tubule epithelial lines. We also analyzed the association between clinicopathological characteristics of ccRCCs and the expression levels of CD74.

METHODS

Immunostaining of CD74 was performed in 107 patients' renal tissue and cell lines. We evaluated the association between clinicopathological characteristics of ccRCC and CD74 levels using image analysis. CD74 expression levels were also analyzed by Western blot. Lentivirus-mediated CD74 knockdown inhibited the growth and invasion, of ccRCC cell lines 786-O in vitro and in vivo. Cell proliferation, apoptosis, and invasion as well as HIF-1α pathway-related proteins, were estimated by Western blot. All experiments were repeated at least 3 times.

RESULTS

Immunostaining and image analysis showed strong immunoreactions of CD74 in all patients' ccRCC tissue and malignant cell lines, while CD74 expression levels were associated with tumor grade (P = 0.013). Western blot indicated that ccRCC tissue and malignant cell lines expressed higher levels of CD74 and hypoxia inducible factor 1α (HIF-1α) than adjacent normal renal tissue and normal cell HK-2. Vitro and vivo tests demonstrated that lentivirus-mediated CD74 knockdown inhibited the proliferation of ccRCC cell lines, induced G1/S arrest and apoptosis, and inhibited invasion. Inhibition of CD74 resulted in down-regulation of HIF-1α pathway proteins.

CONCLUSIONS

CD74 was overexpressed in human ccRCCs and associated with tumor grade, and inhibition of CD74 produced ccRCC proliferation arrest, induced apoptosis, and inhibited invasion, which impinged on HIF-1α pathway-related proteins. It might represent a potential therapeutic target for ccRCC.

Negative regulation of AMP-activated protein kinase (AMPK) activity by macrophage migration inhibitory factor (MIF) family members in non-small cell lung carcinomas

AMP-activated protein kinase (AMPK) is a nutrient- and metabolic stress-sensing enzyme activated by the tumor suppressor kinase, LKB1. Because macrophage migration inhibitory factor (MIF) and its functional homolog, d-dopachrome tautomerase (d-DT), have protumorigenic functions in non-small cell lung carcinomas (NSCLCs) but have AMPK-activating properties in nonmalignant cell types, we set out to investigate this apparent paradox. Our data now suggest that, in contrast to MIF and d-DTs AMPK-activating properties in nontransformed cells, MIF and d-DT act cooperatively to inhibit steady-state phosphorylation and activation of AMPK in LKB1 wild type and LKB1 mutant human NSCLC cell lines. Our data further indicate that MIF and d-DT, acting through their shared cell surface receptor, CD74, antagonize NSCLC AMPK activation by maintaining glucose uptake, ATP production, and redox balance, resulting in reduced Ca(2+)/calmodulin-dependent kinase kinase β-dependent AMPK activation. Combined, these studies indicate that MIF and d-DT cooperate to inhibit AMPK activation in an LKB1-independent manner.

CD74 expression is increased in high-grade, invasive urothelial carcinoma of the bladder

This study aimed to identify the clinicopathological features of bladder cancer patients with high CD74 expression, as milatuzumab humanized anti-CD74 antibody is being evaluated in clinical trials for hematological malignancies. Expression of CD74 was examined in 342 urothelial carcinomas of the bladder, and two urothelial carcinoma cell lines by immunohistochemistry and western blotting, respectively. CD74 was overexpressed in 192 (56.1%) of the 342 cancer tissues, although it was not expressed in the cancer cell lines. CD74 staining was intense in tumor cells and inflammatory cells in the tumor stroma, but not in normal urothelium. CD74 expression was significantly associated with older age at diagnosis (≥ 68 years, P=0.048), high World Health Organization grade (P=0.019), advanced stages (P=0.001) and non-papillary growth pattern (P=0.040). CD74 expression was also correlated with the absence of tumor-infiltrating inflammatory cells (P<0.001) and the presence of tumor-associated inflammatory cells (P=0.017). However, CD74 expression was not related to recurrence-free and overall survivals in primary and subgroup analyses. In conclusion, urothelial bladder carcinomas with high CD74 expression are characterized by older age, high World Health Organization grade, non-papillary growth and advanced stages.

Serum biomarker profiles as diagnostic tools in lung cancer

BACKGROUND

Computed tomography (CT) scanning has emerged as an effective means of early detection for lung cancer. Despite marked improvement over earlier methodologies, the low level of specificity demonstrated by CT scanning has limited its clinical implementation as a screening tool. A minimally-invasive biomarker-based test that could further characterize CT-positive patients based on risk of malignancy would greatly enhance its clinical efficacy.

METHODS

We performed an analysis of 81 serum proteins in 92 patients diagnosed with lung cancer and 172 CT-screened control individuals. We utilize a series of bioinformatics algorithms including Metropolis-Monte Carlo, artificial neural networks, Naïve Bayes, and additive logistic regression to identify multimarker panels capable of discriminating cases from controls with high levels of sensitivity and specificity in distinct training and independent validation sets.

RESULTS

A three-biomarker panel comprised of MIF, prolactin, and thrombospondin identified using the Metropolis-Monte Carlo algorithm provided the best classification with a %Sensitivity/Specificity/Accuracy of 74/90/86 in the training set and 70/93/82 in the validation set. This panel was effective in the classification of control individuals demonstrating suspicious pulmonary nodules and stage I lung cancer patients.

CONCLUSIONS

The selected serum biomarker panel demonstrated a high diagnostic utility in the current study and performance characteristics which compare favorably with previous reports. Further advancements may lead to the development of a diagnostic tool useful as an adjunct to CT-scanning.

CD74 and macrophage migration inhibitory factor as therapeutic targets in gastric cancer

AIM

To investigate the relationship and molecular features of CD74/macrophage migration inhibitory factor (MIF)/Toll-like receptor 4 (TLR4) in gastric cancer.

METHODS

CD74, MIF and TLR4 expression in the paraffin-embedded sections of gastric cancer from 120 patients were detected by immunohistochemical staining. Knock down of CD74 expression in gastric cancer cell line MKN-45 was performed by lentivirus transduction and detected by Western blotting. MKN-45 cell proliferation assay under the stimulants was measured by the cell counting kit 8 (CCK8) assay and MIF concentration in the culture medium was detected by enzyme-linked immunosorbent assay. Surface staining of CD74 in the MKN-45 cell line under the stimulation of lipopolysaccharide (LPS) was measured by flow cytometry. MIF, CD74 and TLR4 co-localization in the MKN-45 cell line was performed by the immunoprecipitation.

RESULTS

CD74, MIF and TLR4 were found to be expressed in gastric cancer and increased significantly in the advanced stage, and were also associated with lymph node metastasis. Correlation analysis revealed that CD74 was positively correlated with MIF (r = 0.2367, P < 0.01) and both proteins were also associated with TLR4 (r = 0.4414, r = 0.5001, respectively, P < 0.01). LPS can significantly promote MKN-45 cell proliferation (3.027 ± 0.388 vs 4.201 ± 0.092, P < 0.05), induce MIF production (54.333 ± 2.906 pg/mL vs 29.667 ± 3.180 pg/mL, P < 0.01) and cell surface expression of CD74 (75.6% ± 4.046% vs 9.4% ± 0.964%, P < 0.01) at LPS concentration of 1 μg/mL compared to medium control. Knockdown of CD74 or using anti-CD74 and MIF antagonist ISO-1 significantly reduced LPS-induced MKN-45 cell proliferation (4.201 ± 0.092 vs 3.337 ± 0.087, 4.534 ± 0.222 vs 3.368 ± 0.290, 4.058 ± 0.292 vs 2.934 ± 0.197, respectively, P < 0.01). MIF, CD74 and TLR4 could co-localize in the MKN-45 cell line.

CONCLUSION

Upregulation of MIF, CD74 and TLR4 are associated with increasing clinical stage and provide an opportunity as novel gastric cancer chemoprevention and/or treatment strategy.

PTRF/cavin-1 and MIF proteins are identified as non-small cell lung cancer biomarkers by label-free proteomics

With the completion of the human genome sequence, biomedical sciences have entered in the “omics” era, mainly due to high-throughput genomics techniques and the recent application of mass spectrometry to proteomics analyses. However, there is still a time lag between these technological advances and their application in the clinical setting. Our work is designed to build bridges between high-performance proteomics and clinical routine. Protein extracts were obtained from fresh frozen normal lung and non-small cell lung cancer samples. We applied a phosphopeptide enrichment followed by LC-MS/MS. Subsequent label-free quantification and bioinformatics analyses were performed. We assessed protein patterns on these samples, showing dozens of differential markers between normal and tumor tissue. Gene ontology and interactome analyses identified signaling pathways altered on tumor tissue. We have identified two proteins, PTRF/cavin-1 and MIF, which are differentially expressed between normal lung and non-small cell lung cancer. These potential biomarkers were validated using western blot and immunohistochemistry. The application of discovery-based proteomics analyses in clinical samples allowed us to identify new potential biomarkers and therapeutic targets in non-small cell lung cancer.

Correlation of macrophage migration inhibitory factor gene polymorphism with the risk of early-stage cervical cancer and lymphatic metastasis

Associations of functional single nucleotide polymorphisms in MIF-173G/C with early stage cervical cancer were investigated in a hospital-based case-control study on 250 patients with cervical cancer prior to surgery (including 49 cases with and 201 cases without lymphatic metastasis) and 147 healthy controls. The polymorphism was assessed using restriction fragment length polymorphism polymerase chain reaction, and the MIF serum concentration was examined using the enzyme-linked immunosorbent assay to analyze the correlation between the polymorphism and the MIF serum concentration. Carriers of the variant C allele in MIF-173 were at a significantly higher risk of cervical cancer compared to carriers of the wild-type allele (aOR=1.508; 95% CI, 1.128-2.016, p=0.05). The GC and CC genotypes may be the causative factors for cervical cancer (aOR=1.851; 95% CI, 1.132-3.027, p=0.013). Individuals with the GC+CC genotype and C allele at the MIF-173G/C site were at a significantly higher risk of cervical cancer and lymphatic metastasis. The risk of lymphatic metastasis in early stage cervical cancer was increased more than 1.6 times in patients with the CC and GC genotypes compared with those with the GG genotype. The genotype distribution and allele frequency of MIF-173G/C were statistically significant in the well-, moderately and poorly differentiated groups (P<0.05). Compared to the GG genotype and G allele, patients with GC and CC genotypes and C allele exhibited a lower degree of differentiation and a higher degree of malignancy. A significant difference was observed in MIF serum concentrations among the various subgroups (P<0.05). The early cervical cancer, lymphatic metastasis and poorly differentiated groups exhibited higher MIF levels in serum. Moreover, patients with the CC genotype exhibited higher MIF serum concentration, which could increase the risk of early stage cervical cancer and lymphatic metastasis. The results presented in this study provide the first evidence that the genetic polymorphism MIF-173 is associated with cervical cancer in humans. Detection of MIF serum concentration and genotyping may be used as biomarkers for early diagnosis and therapy for cervical cancer.

Expression of macrophage migration inhibitory factor and CD74 in cervical squamous cell carcinoma

OBJECTIVE

Macrophage migration inhibitory factor (MIF) and CD74 emerge as important players in pathogenesis and angiogenesis of several types of malignant tumors. The purpose of this study was to evaluate the expression of MIF and CD74 in cervical squamous cell carcinoma and explore the potential roles they play in cervical tumor angiogenesis.

METHODS

Macrophage migration inhibitory factor and CD74 expression was assessed by immunohistochemistry in 209 cases with various degrees of cervical epithelial lesions, including 40 normal cervical epithelia, 43 mild cervical intraepithelial neoplasia 1 (CIN 1), 41 moderate-severe cervical intraepithelial neoplasia (CIN 2 to 3), and 85 cervical squamous cell carcinomas (SCCs). CD34 staining was used for counting microvessel density. Semiquantitative reverse transcription polymerase chain reaction and Western blot were used to detect messenger RNA and protein levels of MIF and CD74 in normal and malignant cervical tissues and cervical cancer cell lines SiHa and C-33A. The concentration of vascular endothelial growth factor (VEGF) in the conditioned media of cervical cancer cells was analyzed by enzyme-linked immunosorbent assay.

RESULTS

Immunohistochemical analysis showed that MIF and CD74 expression was significantly higher in CIN than in the normal samples and higher in SCC than in CIN. The overexpression of MIF was correlated with deep stromal infiltration but not with the other clinicopathologic features of SCC. Correlation analyses revealed that MIF was positively related to CD74, and both protein levels were associated with microvessel density. Exogenous MIF induced VEGF secretion in SiHa and C-33A cells in a dose-dependent manner, which can be inhibited by MIF-specific inhibitor (ISO-1) or anti-CD74 antibody.

CONCLUSION

Overexpression of MIF and CD74 in SCC and its precancerous lesions and the up-regulation of VEGF secretion in cervical cancer cells indicate that MIF and CD74 may play critical roles in the pathogenesis and angiogenesis of cervical cancer.

Lung cancer diagnosis from proteomic analysis of preinvasive lesions

Early detection may help improve survival from lung cancer. In this study, our goal was to derive and validate a signature from the proteomic analysis of bronchial lesions that could predict the diagnosis of lung cancer. Using previously published studies of bronchial tissues, we selected a signature of nine matrix-assisted laser desorption ionization mass spectrometry (MALDI MS) mass-to-charge ratio features to build a prediction model diagnostic of lung cancer. The model was based on MALDI MS signal intensity (MALDI score) from bronchial tissue specimens from our 2005 published cohort of 51 patients. The performance of the prediction model in identifying lung cancer was tested in an independent cohort of bronchial specimens from 60 patients. The probability of having lung cancer based on the proteomic analysis of the bronchial specimens was characterized by an area under the receiver operating characteristic curve of 0.77 (95% CI 0.66-0.88) in this validation cohort. Eight of the nine features were identified and validated by Western blotting and immunohistochemistry. These results show that proteomic analysis of endobronchial lesions may facilitate the diagnosis of lung cancer and the monitoring of high-risk individuals for lung cancer in surveillance and chemoprevention trials.

CD74: an emerging opportunity as a therapeutic target in cancer and autoimmune disease

INTRODUCTION

CD74, also known as the invariant chain, participates in several key processes of the immune system, including antigen presentation, B-cell differentiation and inflammatory signaling. Despite being described more than 3 decades ago, new functions and novel interactions for this evolutionarily conserved molecule are still being unraveled. As a participant in several immunological processes and an indicator of disease in some conditions, it has potential as a therapeutic target.

AREAS COVERED

The relationship between the structure of CD74 variants and their physiological functions is detailed in this review. The function of CD74 in several cell lineages is examined with a focus on the interactions with cathepsins and, in an inflammatory milieu, the pro-inflammatory cytokine macrophage migratory inhibitory factor. The role of CD74 signaling in inflammatory and carcinogenic processes is outlined as is the use of CD74 as a therapeutic target (in cancer) and tool (as a vaccine).

EXPERT OPINION

CD74 has several roles within the cell and throughout the immune system. Most prominent amongst these are the complex relationships with MIF and cathepsins. Modulation of CD74 function shows promise for the effective amelioration of disease.

Interaction between lung cancer cells and astrocytes via specific inflammatory cytokines in the microenvironment of brain metastasis

The incidence of brain metastasis is increasing, however, little is known about molecular mechanism responsible for lung cancer-derived brain metastasis and their development in the brain. In the present study, brain pathology was examined in an experimental model system of brain metastasis as well as in human brain with lung cancer metastasis. In an experimental model, after 3–6 weeks of intracardiac inoculation of human lung cancer-derived (HARA-B) cells in nude mice, wide range of brain metastases were observed. The brain sections showed significant increase in glial fibrillary acidic protein (GFAP)-positive astrocytes around metastatic lesions. To elucidate the role of astrocytes in lung cancer proliferation, the interaction between primary cultured mouse astrocytes and HARA-B cells was analyzed in vitro. Co-cultures and insert-cultures demonstrated that astrocytes were activated by tumor cell-oriented factors; macrophage migration inhibitory factor (MIF), interleukin-8 (IL-8) and plasminogen activator inhibitor-1 (PAI-1). Activated astrocytes produced interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and interleukin-1 β (IL-1β), which in turn promoted tumor cell proliferation. Semi-quantitative immunocytochemistry showed that increased expression of receptors for IL-6 and its subunits gp130 on HARA-B cells. Receptors for TNF-α and IL-1β were also detected on HARA-B cells but down-regulated after co-culture with astrocytes. Insert-culture with astrocytes also stimulated the proliferation of other lung cancer-derived cell lines (PC-9, QG56, and EBC-1). These results suggest that tumor cells and astrocytes stimulate each other and these mutual relationships may be important to understand how lung cancer cells metastasize and develop in the brain.

Macrophage migration inhibitory factor promotes tumor growth in the context of lung injury and repair

RATIONALE

Tissue injury and repair involve highly conserved processes governed by mechanisms that can be co-opted in tumors. We hypothesized that soluble factors released during the repair response to lung injury would promote orthotopic tumor growth.

OBJECTIVES

To determine whether lung injury promoted growth of orthotopic lung tumors and to study the molecular mechanisms.

METHODS

We initiated lung injury in C57Bl6 mice using different stimuli, then injected Lewis lung carcinoma cells during the repair phase. We assessed tumor growth 14 days later. We measured tumor angiogenesis, cytokine expression, proliferation, and apoptosis.

MEASUREMENTS AND MAIN RESULTS

Regardless of the mechanism, injured lungs contained more numerous and larger tumors than sham-injured lungs. Tumors from injured lungs were no more vascular, but had higher levels of proliferation and reduced rates of apoptosis. The cytokine macrophage migration inhibitory factor (MIF) was highly expressed in both models of tissue injury. We observed no increase in tumor growth after lung injury in MIF knockout mice. We induced lung-specific overexpression of MIF in a double-transgenic mouse, and observed that MIF overexpression by itself was sufficient to accelerate the growth of orthotopic Lewis lung carcinoma tumors.

CONCLUSIONS

Lung injury leads to increased expression of the cytokine MIF, which results in protection from apoptosis and increased proliferation in orthotopic tumors injected after the acute phase of injury.

A role for NRAGE in NF-kappaB activation through the non-canonical BMP pathway

Background

Previous studies have linked neurotrophin receptor-interacting MAGE protein to the bone morphogenic protein signaling pathway and its effect on p38 mediated apoptosis of neural progenitor cells via the XIAP-Tak1-Tab1 complex. Its effect on NF-κB has yet to be explored.

Results

Herein we report that NRAGE, via the same XIAP-Tak1-Tab1 complex, is required for the phosphorylation of IKK -α/β and subsequent transcriptional activation of the p65 subunit of NF-κB. Ablation of endogenous NRAGE by siRNA inhibited NF-κB pathway activation, while ablation of Tak1 and Tab1 by morpholino inhibited overexpression of NRAGE from activating NF-κB. Finally, cytokine profiling of an NRAGE over-expressing stable line revealed the expression of macrophage migration inhibitory factor.

Conclusion

Modulation of NRAGE expression revealed novel roles in regulating NF-κB activity in the non-canonical bone morphogenic protein signaling pathway. The expression of macrophage migration inhibitory factor by bone morphogenic protein -4 reveals novel crosstalk between an immune cytokine and a developmental pathway.

Identification of potential therapeutic targets in human head & neck squamous cell carcinoma

Background

Human head and neck squamous cell carcinoma (HNSCC) is an aggressive and recurrent malignancy. Identification of unique or overexpressed cell-associated or cell surface antigens is critical for diagnosis and development of cancer vaccines and targeted therapies for HNSCC. We have used high throughput microarray technology to search for candidate targets in HNSCC.

Methods

Gene expression profiling in 17 HNSCC tumors and 3 normal tonsil tissues was performed by microarray. QRT-PCR analysis was performed to validate the microarray results. The five candidate genes were further characterized by immunohistochemical technique in surgical samples and tissue arrays.

Results

A total of 192 up-regulated genes at statistical significance of p < 0.01 and log2 ratio ≥ 1 were identified in HNSCC tumors compared to normal tissues. These genes belong to immune response, cell growth, cell cycle regulation, oncogenes, metabolism and others. Five potential novel target genes (FABP5, CD24, CD44, CD74, and HSP27) were identified, which were highly expressed in HNSCC tumor samples and tissue arrays. CD24, CD44, and CD74 proteins were expressed on the cell surface, and FABP5 and HSP27 proteins were predominantly expressed in the cytoplasm of HNSCC.

Conclusion

Five genes and their products may serve as a diagnostic biomarker or therapeutic target for HNSCC. While additional work is needed to elucidate the biological significance of these proteins, CD24 and CD74 expressed only in small proportion of cells indicating tumor heterogeneity and subtypes of tumor initiating cells (CD24+/CD44+) present in HNSCC.