CD44 expression patterns in breast and colon tumors: a PCR-based study of splice variants

Less demand on stem cell marker-positive cancer cells may characterize metastasis of colon cancer

BACKGROUND

CD44 and CD133 are stem cell markers in colorectal cancer (CRC). CD44 has distinctive isoforms with different oncological properties like total CD44 (CD44T) and variant CD44 (CD44V). Clinical significance of such markers remains elusive.

METHODS

Sixty colon cancer were examined for CD44T/CD44V and CD133 at mRNA level in a quantitative PCR, and clarified for their association with clinicopathological factors.

RESULTS

(1) Both CD44T and CD44V showed higher expression in primary colon tumors than in non-cancerous mucosas (p<0.0001), while CD133 was expressed even in non-cancerous mucosa and rather decreased in the tumors (p = 0.048). (2) CD44V expression was significantly associated with CD44T expression (R = 0.62, p<0.0001), while they were not correlated to CD133 at all in the primary tumors. (3) CD44V/CD44T expressions were significantly higher in right colon cancer than in left colon cancer (p = 0.035/p = 0.012, respectively), while CD133 expression were not (p = 0.20). (4) In primary tumors, unexpectedly, CD44V/CD44T/CD133 mRNA expressions were not correlated with aggressive phenotypes, but CD44V/CD44T rather significantly with less aggressive lymph node metastasis/distant metastasis (p = 0.040/p = 0.039, respectively). Moreover, both CD44V and CD133 expressions were significantly decreased in liver metastasis as compared to primary tumors (p = 0.0005 and p = 0.0006, respectively).

CONCLUSION

Our transcript expression analysis of cancer stem cell markers did not conclude that their expression could represent aggressive phenotypes of primary and metastatic tumors, and rather represented less demand on stem cell marker-positive cancer cells.

OSM-induced CD44 contributes to breast cancer metastatic potential through cell detachment but not epithelial-mesenchymal transition

Background

Hormone receptor status in human breast cancer cells is a strong indicator of the aggressiveness of a tumor. Triple negative breast cancers (TNBC) are aggressive, difficult to treat, and contribute to high incidences of metastasis by possessing characteristics such as increased tumor cell migration and a large presence of the transmembrane protein, cluster of differentiation 44 (CD44) on the cell membrane. Estrogen receptor-positive (ER+) cells are less aggressive and do not migrate until undergoing an epithelial-mesenchymal transition (EMT).

Methods

The relationship between EMT and CD44 during metastatic events is assessed by observing changes in EMT markers, tumor cell detachment, and migration following cytokine treatment on both parental and CD44 knockdown human breast tumor cells.

Results

ER+ T47D and MCF-7 human breast cancer cells treated with OSM demonstrate increased CD44 expression and CD44 cleavage. Conversely, ER- MDA-MB-231 human breast cancer cells do not show a change in CD44 expression nor undergo EMT in the presence of OSM. In ER+ cells, knockdown expression of CD44 by shRNA did not prevent EMT but did change metastatic processes such as cellular detachment and migration. OSM-induced migration was decreased in both ER+ and ER- cells with shCD44 cells compared to control cells, while the promotion of tumor cell detachment by OSM was decreased in ER+ MCF7-shCD44 cells, as compared to control cells. Interestingly, OSM-induced detachment in ER- MDA-MB-231-shCD44 cells that normally don't detach at significant rates.

Conclusion

OSM promotes both EMT and tumor cell detachment in ER+ breast cancer cells. Yet, CD44 knockdown did not affect OSM-induced EMT in these cells, while independently decreasing OSM-induced cell detachment. These results suggest that regulation of CD44 by OSM is important for at least part of the metastatic cascade in ER+ breast cancer.

Isolation of All CD44 Transcripts in Human Epidermis and Regulation of Their Expression by Various Agents

CD44, a cell surface proteoglycan, is involved in many biological events. CD44 transcripts undergo complex alternative splicing, resulting in many functionally distinct isoforms. To date, however, the nature of these isoforms in human epidermis has not been adequately determined. In this study, we isolated all CD44 transcripts from normal human epidermis, and studied how their expressions are regulated. By RT-PCR, we found that a number of different CD44 transcripts were expressed in human epidermis, and we obtained all these transcripts from DNA bands in agarose and acrylamide gels by cloning. Detailed sequence analysis revealed 18 CD44 transcripts, 3 of which were novel. Next, we examined effects of 10 different agents on the expression of CD44 transcripts in cultured human keratinocytes, and found that several agents, particularly epidermal growth factor, hydrogen peroxide, phorbol 12-myristate 13-acetate, retinoic acid, calcium and fetal calf serum differently regulated their expressions in various patterns. Furthermore, normal and malignant keratinocytes were found to produce different CD44 transcripts upon serum stimulation and subsequent starvation, suggesting that specific CD44 isoforms are involved in tumorigenesis via different CD44-mediated biological pathways.

Demonstration of a melanoma-specific CD44 alternative splicing pattern that remains qualitatively stable, but shows quantitative changes during tumour progression

The role of CD44 in the progression of human melanoma has mostly been characterised by qualitative changes in expression of its individual variable exons. These exons however, may be expressed to form a number of molecules, the alternative splice variants of CD44, which may be structurally and functionally different. Using real-time PCR measurements with variable exon specific primers we have determined that all are expressed in human melanoma. To permit comparison between different tumours we identified a stable CD44 variable exon (CD44v) expression pattern, or CD44 ‘fingerprint’. This was found to remain unchanged in melanoma cell lines cultured in different matrix environments. To evaluate evolution of this fingerprint during tumour progression we established a scid mouse model, in which the pure expression pattern of metastatic primary tumours, circulating cells and metastases, non-metastatic primary tumours and lung colonies could be studied. Our analyses demonstrated, that although the melanoma CD44 fingerprint is qualitatively stable, quantitative changes are observed suggesting a possible role in tumour progression.

Histiocytoid breast carcinoma: Solid variant of invasive lobular carcinoma with decreased expression of both E-cadherin and CD44 epithelial variant

Histiocytoid breast carcinoma (HBC) is a rare type of breast carcinoma with morphologic characteristics resembling those of histiocytes. Described herein are cytological and histological findings in a case of HBC. Fine-needle aspiration cytology revealed numerous loosely cohesive tumor cells with abundant foamy to granular cytoplasm and bland-appearing nuclei. The resected tumor exhibited a solid growth pattern instead of classic invasive lobular patterns observed in most reported cases of HBC. However, distinct intracytoplasmic lumina and Pagetoid extension to ducts suggested that this tumor was a variant of invasive lobular carcinoma. To determine the cause of the loose cellular cohesiveness of this HBC, its expression of the epithelium-related cell adhesion molecules E-cadherin and CD44v8-10 (CD44 epithelial variant) was examined. Immunohistochemically, E-cadherin was not detected, similar to most lobular carcinomas. Furthermore, competitive reverse transcription-polymerase chain reaction (RT-PCR) analyses among alternatively spliced variants of CD44 revealed that the ratio of expression of CD44v8-10 to that of CD44v10 (dominant variant in leukocytes) was lower than that for the reference breast carcinoma samples. It is concluded that the present case of HBC was a solid variant of invasive lobular carcinoma exhibiting foamy to granular cytoplasmic change. Decreased expression of both E-cadherin and CD44 epithelial variant may be responsible for the loose cellular cohesiveness observed in HBC.

CD44 variant 6 in endometrioid carcinoma of the uterus: its expression in the adenocarcinoma component is an independent prognostic marker

The expression of variant isoforms of CD44 (CD44v) correlates with the metastatic potential of various carcinomas. In endometrial cancer, however, the significance of CD44v-expression as a prognostic indicator has not been fully investigated, nor has it been compared with that of p53, estrogen receptor or Ki67. Surgical material consisted of 14 atypical endometrial hyperplasias (AEH) and 163 endometrial carcinomas (EC). Expression of CD44s, v3 and v6 in carcinoma tissue, and other prognostic markers were immunohistochemically evaluated. The expression in the squamous differentiation was strictly excluded for the evaluation of immunohistochemistry, because the significance was different from that in the adenocarcinoma component. CD44s was frequently expressed in AEH and EC. On the other hand, CD44v3- and v6-positivities were rare or nonexistent in AEH, but were observed in 8 and 35% of EC, respectively. CD44v3-expression correlated significantly with histologic grade and lymph node metastasis. However, there was no correlation between CD44v6 expression and any clinicopathologic factor, nor were other prognostic markers expressed. Univariate analysis revealed that each CD44 was a prognostic determinant in the patients with EC. However, employing multivariate analysis, there were only three independent factors: p53 overexpression, CD44v6 expression and myometrial invasion. CD44v6 expression in the adenocarcinoma component may directly affect the behavior of carcinoma and the prognosis of patients with EC.

CD44 variant exons in leukemia and lymphoma

CD44 is a cell surface glycoprotein expressed on different cell types that functions in lymphocyte activation and homing, extracellular matrix adhesion and cellular migration. CD44 is encoded by a single gene composed of at least 20 exons. The standard CD44 protein (CD44S or CD44H) is the hematopoietic form of CD44 in lymphoid cells. Variant isoforms (designated from v1 to v10) are formed by addition of new exons to the extracellular domain. High levels of CD44v6 expression has been observed in some tumors and are associated with metastatic spread. The aim of the present study was to investigate and evaluate expression of the CD44v6 and v6-containing variants as a possible marker in chronic myeloid leukemia and lymphoma by reverse transcription-polymerase chain reaction. CD44 exon v6 was detected in all patients and all individuals in the control group. CD44v6-v10 mRNA was observed in 25 patients but in none of the subjects in the control group. CD44v6/v9-10, CD44v6-v7, CD44v6/v10 transcripts were detected in 11, 6, and 2 patients, respectively. CD44v6-7/v9-10 transcripts were not observed in either the patients or the healthy individuals. We conclude that CD44v6-v10 expression may be associated with hematologic malignancies.

Detection of malignant cells in pleural fluid or ascites by CD44v8-10/CD44v10 competitive RT-PCR

BACKGROUND

CD44 is a cell surface adhesion molecule which has been implicated in various biologic functions as lymphocyte homing and activation, cellular migration and extracellular matrix adhesion. Over-expression of CD44v8-10 has been found in several cancers and is considered to be associated with tumor progression and metastasis. Recently, a novel molecular method, CD44v8-10/CD44v10 competitive reverse transcription-polymerase chain reaction(RT-PCR) has been developed for detecting cancer cells over-expressing CD44v8-10.

METHODS

We analyzed from benign and malignant pleural effusion and ascites by CD44 competitive RT-PCR and compared to the conventional cytology.

RESULTS

The CD44 competitive RT-PCR analysis showed that all the 24 samples associated with benign disease presented a predominant expression of the CD44v10 transcript (v8-10/v10 ratio: 0.126-0.948), whereas 6 of 7 malignant pleural samples associated with cytology positive cancer expressed the CD44v8-10 transcript (v8-10/v10 ratio > 1.00).

CONCLUSION

These results indicate that CD44 competitive RT-PCR assay is a useful and adjunct to cytological examination in cancer diagnosis, especially in detecting exfoliated cancer cells in pleural effusion.

Molecular characterization of minimal residual cancer cells in patients with solid tumors

The failure to reduce the mortality of patients with solid tumors is mainly a result of the early dissemination of cancer cells to secondary sites, which is usually missed by conventional diagnostic procedures used for tumor staging. PCR was shown to be superior to conventional techniques in detecting circulating tumor cells and micrometastases allowing the identification of one tumor cell in up to 10(7) normal cells in various sources such as blood, bone marrow, lymph nodes, urine or stool. The methods used are based on the detection of either genomic alterations in oncogenes and tumor suppressor genes or on the mRNA expression of tissue-specific and tumor-associated genes. The additional implementation of techniques for cancer cell purification had a significant impact on analytical sensitivity and specificity of MRCC detection. For patients with e.g. melanoma, breast, colorectal or prostate cancer it was demonstrated that the presence of disseminated cancer cells defines a subgroup of patients with reduced time to recurrence. The possibility to use easily accessible body fluids as a source for MRCC detection enables longitudinal observations of the disease. In this review we discuss the potential of molecular characterization of MRCC as a tool to improve prognostication, therapy selection and drug targeting as well as therapy monitoring.

Introduction of antisense CD44S CDNA down-regulates expression of overall CD44 isoforms and inhibits tumor growth and metastasis in highly metastatic colon carcinoma cells

We created antisense CD44 transfectants using LS174T, a colon adenocarcinoma cell line and assessed the effects of overall CD44 down-regulation on colorectal tumor growth and metastasis. The expression of antisense CD44s (the standard form of CD44) cDNA markedly inhibited the overall expression of CD44 variants. In vitro studies showed a significantly reduced ability of the stable antisense transfectants (LS174TAS1 and LS174TAS2) to bind hyaluronate and osteopontin, ligands for CD44. These cells developed tumors more slowly than controls (parental LS174T and mock transfectants) when the cells were subcutaneously injected into SCID mice. However, in vitro proliferation assays demonstrated no significant difference between the antisense transfectants and the controls on a hyaluronate-coated surface, suggesting the participation of ligands other than hyaluronate in tumor growth in vivo. Intrasplenic injection of parental LS174T cells produced colonies in the liver in 10 of 11 mice, whereas mice injected with the antisense transfectants were completely free of metastasis. In peritoneal dissemination, the weight of nodules and amount of ascites were significantly reduced in LS174TAS1 and AS2 compared with the controls. In vitro adhesion assays between the transfectants or controls and human peritoneal mesothelial cells revealed that the binding of LS174T cells to mesothelial cells was partly mediated by CD44-hyaluronate interaction. These data suggest that CD44-hyaluronate interaction plays a crucial role in peritoneal dissemination in colorectal carcinoma. The results of our study demonstrate the possible application of antisense CD44s to the treatment of colorectal carcinoma.

Clear cell carcinoma of the ovary: characterization of its CD44 isoform repertoire

OBJECTIVE

CD44 is a cell surface receptor implicated in tumor metastases. We have previously shown that there is a loss of CD44 splice control in clear cell carcinoma (CCCa) of the ovary. Our aim is to characterize the expression of CD44-3v, -5v, -7v, and -10v in clear cell ovarian tumors and to determine their prognostic value.

METHODS

Twenty-two cases of ovarian CCCa were studied for CD44-3v, -5v, -7v, and -10v expression by immunocytochemistry.

RESULTS

The primary tumors showed expression of CD44-3v, -5v, -7v, and -10v in 44, 55, 61, and 39% of the cases, respectively. We were able to compare the expression of CD44 in the primary tumor and metastatic sites from the same patient in 7 cases (metastatic sites n = 16). We observed decreased immunoreactivity of CD44-3v, -5v, -7v, and -10v in 67, 100, 93, and 92% of the sites, respectively. CD44-3v and -10v expression was absent in 100% of the nonaffected contralateral ovaries while -7v and -10v were expressed in 1/11 (9%) of them. When CD44-10v was not expressed in the primary tumor, only 18% of the women recurred or died of disease; in contrast, of the cases where it was present, 71% of the women recurred or died of disease (P = 0.049).

CONCLUSIONS

There is aberrant alternative mRNA splicing in the development of CCCa of the ovary when compared to the contralateral nonaffected ovary. The expression of CD44-10v correlates with survival. Larger series are needed to further understand the role of CD44 isoforms in ovarian cancer metastases.

CD44 interaction with tiam1 promotes Rac1 signaling and hyaluronic acid-mediated breast tumor cell migration

In this study we have explored the interaction between CD44 (the hyaluronic acid (HA)-binding receptor) and Tiam1 (a guanine nucleotide exchange factor) in metastatic breast tumor cells (SP1 cell line). Immunoprecipitation and immunoblot analyses indicate that both the CD44v3 isoform and the Tiam1 protein are expressed in SP1 cells and that these two proteins are physically associated as a complex in vivo. Using an Escherichia coli-derived calmodulin-binding peptide-tagged Tiam1 fragment (i.e. the NH(2)-terminal pleckstrin homology (PHn) domain and an adjacent protein interaction domain designated as PHn-CC-Ex, amino acids 393-738 of Tiam1) and an in vitro binding assay, we have detected a specific binding interaction between the Tiam1 PHn-CC-Ex domain and CD44. Scatchard plot analysis indicates that there is a single high affinity CD44 binding site in the PHn-CC-Ex domain of Tiam1 with an apparent dissociation constant (K(d)) of 0.2 nM, which is comparable with CD44 binding (K(d) = approximately 0.13 nM) to intact Tiam1. These findings suggest that the PHn-CC-Ex domain is the primary Tiam1-binding region for CD44. Most importantly, the binding of HA to CD44v3 of SP1 cells stimulates Tiam1-catalyzed Rac1 signaling and cytoskeleton-mediated tumor cell migration. Transfection of SP1 cells with Tiam1cDNA promotes Tiam1 association with CD44v3 and up-regulates Rac1 signaling as well as HA/CD44v3-mediated breast tumor cell migration. Co-transfection of SP1 cells with PHn-CC-Ex cDNA and Tiam1 cDNA effectively inhibits Tiam1 association with CD44 and efficiently blocks tumor behaviors. Taken together, we believe that the linkage between CD44v3 isoform and the PHn-CC-EX domain of Tiam1 is required for HA stimulated Rac1 signaling and cytoskeleton-mediated tumor cell migration during breast cancer progression.

Molecular detection of low-level disease in patients with cancer

The accurate detection of low-level disease in patients with cancer is essential to improve the staging of disease and consequently to define appropriate treatment strategies. Most methods currently used for staging are based on imaging studies and histological and immunocytochemical analysis of tissues such as bone marrow aspirates, or antibody assays for marker proteins secreted into the circulation. These methods have limited sensitivity. However, assays for nucleic acid-based markers may be valuable tools for the sensitive detection, assessment, and monitoring of disease status in asymptomatic cancer patients. Application of these methods may allow the early detection of cancer, when the tumour burden is smaller and the disease potentially more curable. The last decade has seen the application of polymerase chain reaction (PCR)-based methods to the detection of tumour in a wide variety of compartments, including peripheral blood, bone marrow, lymph nodes, urine, sputum, faeces, pancreatic juice, and more recently plasma. Molecular detection of disease by PCR has targeted DNA and RNA markers, including mutations, microsatellites, and tissue-specific gene expression. It is likely that these molecular methods will provide important clinical information, though their current clinical utility remains unclear. The current status of nucleic acid-based assays for the detection and assessment of disease status in the management of patients with solid tumours is reviewed.

Prognostic value of CD44 expression in invasive squamous cell carcinoma of the vulva

OBJECTIVE

CD44 is a cell adhesion molecule that binds extracellular matrix. CD44 isoforms arising from alternative mRNA splicing are implicated in tumor metastases. The aim of our study is to investigate the expression of CD44 splice variants and its correlation to lymph node metastases and disease-free survival in squamous cell carcinoma (SCC) of the vulva.

METHODS

Thirty-five cases of SCC of the vulva were evaluated for CD44 splice variants -3v, -4v, -5v, and -7v expression by immunocytochemistry. When available one nonmetastatic lymph node (LN) was also studied. In cases with LN metastases, the metastatic LN as well as a nonmetastatic LN from the same patient were evaluated.

RESULTS

All CD44 variants studied were expressed in all epithelium: normal, dysplastic, and SCC. CD44 variants showed decreased immunostaining in the tumor cells when compared to normal epithelium. Furthermore, intensity of expression of the CD44 isoforms changed within the tissue containing invasive cancer. Interestingly, CD44-4v expression was downregulated in the most differentiated cells within the carcinoma, mainly in patients who had disease recurrence or died of disease (P = 0.004). Confirming prior publications, CD44-5v and -7v expression did not correlate with survival. One hundred percent of metastatic tumors to LNs were immunoreactive with CD44-3v and only 1/30 normal LN had CD44-3v expression. Eighty percent of metastatic tumors to LNs were immunoreactive for CD44-4v. However, 3 LNs without tumor were also immunoreactive with CD44-4v.

CONCLUSION

CD44-4v is a potential molecular marker of disease recurrence in vulvar carcinoma. A larger multiinstitutional study is needed to evaluate the specificity of CD44-3v expression in LN metastasis. If a larger scale study confirms our findings, a CD44-3v antibody could be used for radioimmunoimaging of occult lymph node metastases in patients with vulvar cancer.

Expression of CD44 adhesion molecules in nonpapillary renal cell carcinoma and normal kidneys

OBJECTIVES

To analyze the relationship between the alterations in the expression of the CD44 gene in nonpapillary renal cell carcinoma (RCC) and several clinicopathologic factors.

METHODS

The expression of the CD44 gene in 10 human RCC cell lines, 60 nonpapillary RCC tumor samples, and 15 normal kidney samples was investigated by reverse-transcription polymerase chain reaction (RT-PCR) using a set of primers capable of amplifying all CD44 variant isoforms. The results were analyzed with respect to several clinicopathologic factors.

RESULTS

Nine of the 10 human RCC cell lines predominantly expressed the standard CD44 isoform (CD44s); CD44v10 was the major isoform in the 10th RCC cell line. The 15 normal kidney samples revealed the identical CD44 gene expression pattern; that is, CD44s, CD44v8-10, and CD44v10 were detectable in normal kidneys, and among them, CD44s was expressed most dominantly. In the 60 nonpapillary RCC samples, CD44s, CD44v8-10, and CD44v10 were the major isoforms in 46 (77%), 11 (18%), and 3 (5%) cases, respectively. Furthermore, the incidence of the predominant expression of CD44v8-10 in high-stage RCC was significantly higher than that in low-stage RCC. CD44s was more frequently expressed as a major isoform in clear cell RCC than in other histologic types of RCC.

CONCLUSIONS

The results of this study show that the alternative splicing pattern of CD44 gene in RCC is different in each histologic type of RCC and suggest that CD44v8-10 upregulation in the progression of nonpapillary RCC is important.

Adhesion proteins in the biology of breast cancer: contribution of CD44

One of the most important features of tumor cell invasion is the ability to establish or modulate adhesion to other cells or to an extracellular matrix, a process mediated by a large number of adhesion proteins. This review examines how CD44 participates in malignant transformation and progression of the breast epithelium. CD44 is a family of cell adhesion glycoproteins generated by alternative splicing of up to 10 variant exons. Discrete CD44 isoforms are overexpressed in different human cancers, including breast cancer. Recent studies, including our own, have shown that CD44 is involved in two of the three steps of the invasive cascade: adhesion to the extracellular matrix and motility. The overexpression of one of the CD44 variants, CD44v6, is a significant component in the malignant transformation of the breast epithelium and its use as a prognostic marker is presently investigated.

Highly specific and sensitive detection of malignancy in urine samples from patients with urothelial cancer by CD44v8-10/CD44v10 competitive RT-PCR

CD44 is a widely expressed cell surface adhesion molecule in which various isoforms arise from alternative RNA splicing mechanism. Overexpression of specific CD44 splice variant, i.e., CD44v8-10, has been found in several human malignancies and is considered to be associated with tumor progression and metastasis. We have demonstrated a novel molecular approach, CD44v8-10/CD44v10 competitive reverse transcription-polymerase chain reaction (CC-RT-PCR) for the detection of cancer cells overexpressing CD44v8-10 by the measurement of the transcriptional level of CD44v8-10 relative to that of CD44v10 (v8-10/v10 ratio). In this study, we initially examined the expression of CD44 splice variants in human urothelial cancers and their adjacent normal urinary tissues by RT-PCR. Any CD44 variant isoforms were barely detectable in normal urinary tissues, whereas CD44v8-10 was predominantly expressed in 23 of the 30 (77%) urothelial cancer specimens. We then applied CC-RT-PCR to spontaneously voided urine samples from patients with 80 urothelial cancer and 50 various benign urologic diseases. The CC-RT-PCR analysis revealed that all of the samples associated with benign diseases presented a predominant expression of the CD44v10 transcript (the v8-10/v10 ratios = 0.00-0.87), whereas 62 of the 80 samples associated with urothelial cancers mostly expressed the CD44v8-10 transcript (the v8-10/v10 ratios > 1.00). In addition, the positivity rate obtained by the CC-RT-PCR analysis was high regardless of the pathological grade of the urothelial cancers, although the sensitivity of the cytological examination declined with decreasing tumor grade. Our findings suggest strongly that CC-RT-PCR is a non-invasive useful tool for the diagnosis of urine samples from patients with urothelial cancer.

Overexpression of CD44 variants 6 and 7 in human endometrial cancer

OBJECTIVES

The expression of CD44 V6, V7, and V10 in normal endometrium and endometrial cancer was compared.

METHODS

Using reverse transcription polymerase chain reaction (RT-PCR) blot analysis, the expression of mRNA containing CD44 V6, V7, and V10 was determined in 19 normal endometrium and 27 endometrial cancer samples. Immunohistochemical staining of CD44 V6 and V7 was performed in the same samples.

RESULTS

In RT-PCR analysis, the CD44 variant forms containing V6 and V7 exons were expressed in 96 and 93% of endometrial cancer tissues, respectively. These proportions were significantly higher than those in normal endometrium (V6, 63%; V7, 58%) (P < 0.01). CD44 V10 was expressed in 96% of endometrial cancers and 89% of normal endometrial samples. In immunohistochemical staining, CD44 V6 and V7 were detected in 48 and 61% of endometrial cancers and in 26 and 42% of normal endometrial samples, respectively. Neither of these differences was significant. No correlation was found between the expression of CD44 variants and any clinicopathological features.

CONCLUSION

CD44 V6 and V7 were expressed in a significantly larger proportion of endometrial cancers than normal endometrial samples. However, they were also expressed in a considerable proportion of normal endometria. These findings suggest that CD44 V6 and V7 play roles in normal endometrial function and overexpression of CD44 V6 and V7 is not related to the metastatic potential of endometrial cancer.

Decreased expression of CD44 splicing variants in advanced colorectal carcinomas

CD44v6 expression appears to be associated with adverse prognosis and propensity for metastasis in patients with colorectal cancer. However, expression of CD44 variants in different tumour stages has been poorly characterised. CD44 variant expression was investigated in normal colonic mucosa (n = 36), colorectal adenomas (n = 15), carcinomas (n = 62) and metastases (n = 6) by reverse transcriptase-polymerase chain reaction (RT-PCR) and Southern blotting with exon-specific probes. High frequencies of CD44 standard (CD44s) and CD44 epithelial (CD44e) were observed in normal and neoplastic tissue. CD44v2 was seen predominantly in adenomas (27%) and UICCI carcinomas (29%). CD44v5 expression was low in normal mucosa (3%), higher in adenomas and carcinomas (29-33%), independent of tumour stage. CD44v6 expression was low in normal mucosa (6%) and higher in adenomas (47%) and carcinomas (42%). Surprisingly, a significant decrease of CD44v6 was observed in metastatic primary tumours (8%) and metastases (17%) (UICCIV) (P < or = 0.05). Therefore, the concept of CD44v6 conferring metastatic potential to malignant cells cannot be supported by our data.

Correlation of CD44 expression with proliferative activity of normal human breast epithelial cells in culture

A number of studies have shown that certain variant isoforms of CD44 are overexpressed in human breast cancer, suggesting their use as indicators of the presence of malignant cells. We now show that CD44 isoform mRNA and protein expression is upregulated in normal human breast epithelial cells (HBEC) when these cells are stimulated to proliferate in culture. Reverse transcription-PCR analysis of cultured normal HBEC revealed complex patterns of CD44 mRNA expression that were indistinguishable from patterns previously shown to be characteristic of tissue samples containing malignant HBEC. CD44v6-expressing cells were identified in cultures generated from FACS-purified populations of either normal luminal (CALLA-MUC-1+) or myoepithelial (CALLA+MUC-1-) cells, even though immunohistochemical analysis of normal breast tissue sections confirmed CD44v6 expression to be limited to the myoepithelium in vivo. Increased expression of both CD44v mRNA and protein in cultured populations of normal HBEC was shown to correlate positively with the proportion of cells that were proliferating (Ki-67+) independent of cell density. These results indicate that activation of CD44 variant isoform expression in HBEC occurs as a normal response to factors that stimulate their proliferation and suggests caution in the use of this marker to identify malignant cells.

No evidence for cancer-related CD44 splice variants in primary and metastatic colorectal cancer

The expression of alternatively spliced CD44 adhesion molecules has been implicated in the pathogenesis and metastasis of colorectal cancer. Using a new set of primers for exon-specific reverse transcription-polymerase chain reaction (RT-PCR) we delineated the exact exon composition of CD44 mRNAs in normal colorectal mucosa, including isolated colonic crypts, in colorectal carcinomas and in their hepatic metastases. In addition, the surface expression of CD44 isoforms was analysed by immunohistochemistry. We identified by RT-PCR eight variant transcripts expressed in colorectal carcinomas and their metastases, but also constitutively in normal colorectal epithelia. In the normal colorectal epithelium, the surface expression of CD44 standard and variant molecules was restricted to proliferating cells at the bottom of the crypts. Despite expression of these transcripts in colorectal cancers and their metastases, monoclonal antibodies specific for standard or variant epitopes encoded by exons v5 and v6 stained only a few neoplastic lesions. These data point to a differentiation-specific CD44 expression and splicing pattern in proliferating colorectal epithelia. However, they do not support a cancer- or metastasis-specific CD44 splicing pattern. Instead, cell surface availability of CD44 epitopes was reduced rather than increased in primary tumours and particularly in liver metastases.

Utilization of polymerase chain reaction technology in the detection of solid tumors

BACKGROUND

Most cancer detection tests currently performed are based on either antibody assays to a marker protein with altered expression in cancer patients or on imaging studies to identify characteristic lesions. Generally, for a positive result, these detection assays require that a tumor have a significant volume of cancer cells. Advances in diagnostic techniques and technology may allow for cancer detection at earlier stages, when the tumor burden is smaller and potentially more curable. The molecular techniques of polymerase chain reaction (PCR) and reverse transcriptase PCR (RT-PCR) are highly sensitive methods for detecting a small number of cancer cells. Over the past few years, numerous clinical studies have used PCR techniques to detect physical alterations of genes, such as mutations, deletions, translocations and amplification, the presence of oncogenic viruses, and the expression of genes specific to tissue, cancer, and metastasis. The current status of PCR as a method for detecting marker genes in the management of solid tumors is reviewed.

METHODS

A review of the literature on the clinical utility of PCR and RT-PCR in the detection of solid tumor micrometastasis was conducted.

RESULTS

Amplification by PCR is a highly sensitive method to determine gene expression. A single cell expressing a tumor marker among 10-100 million lymphocytes can be detected by the PCR assay. This approach has been used to detect tumor cells in approximately 18 different solid tumor types, with melanoma and carcinoma of the breast and prostate the most widely investigated to date. PCR-based assays have been used to detect cancer cells in biopsies of solid tissue, lymph nodes, bone marrow, peripheral blood, and other body fluids. Several studies have reported a high specificity and sensitivity of tumor marker detection and a high correlation between PCR results and the presence of metastatic disease. However, in a few studies, PCR assays have not consistently demonstrated a higher sensitivity and specificity of detection than traditional modalities for many types of cancer. There has been a wide range in sensitivity and specificity among the studies, which may be partly attributed to the lack of uniformity among the PCR protocols used in different studies.

CONCLUSIONS

PCR can detect tumor marker-expressing cells that are otherwise undetectable by other means in patients with localized or metastatic cancer. Reports from various study groups have lacked uniformity in their protocols, and this has prevented adequate comparison. The clinical utility of this assay as a tool for the prognosis and management of cancer patients remains and area of active investigation. PCR is a powerful tool in the study of the biology of cancer metastasis and will likely serve as a useful adjunct to clinical decision-making in the future.

Utilization of polymerase chain reaction technology in the detection of solid tumors

BACKGROUND

Most cancer detection tests currently performed are based on either antibody assays to a marker protein with altered expression in cancer patients or on imaging studies to identify characteristic lesions. Generally, for a positive result, these detection assays require that a tumor have a significant volume of cancer cells. Advances in diagnostic techniques and technology may allow for cancer detection at earlier stages, when the tumor burden is smaller and potentially more curable. The molecular techniques of polymerase chain reaction (PCR) and reverse transcriptase PCR (RT-PCR) are highly sensitive methods for detecting a small number of cancer cells. Over the past few years, numerous clinical studies have used PCR techniques to detect physical alterations of genes, such as mutations, deletions, translocations and amplification, the presence of oncogenic viruses, and the expression of genes specific to tissue, cancer, and metastasis. The current status of PCR as a method for detecting marker genes in the management of solid tumors is reviewed.

METHODS

A review of the literature on the clinical utility of PCR and RT-PCR in the detection of solid tumor micrometastasis was conducted.

RESULTS

Amplification by PCR is a highly sensitive method to determine gene expression. A single cell expressing a tumor marker among 10-100 million lymphocytes can be detected by the PCR assay. This approach has been used to detect tumor cells in approximately 18 different solid tumor types, with melanoma and carcinoma of the breast and prostate the most widely investigated to date. PCR-based assays have been used to detect cancer cells in biopsies of solid tissue, lymph nodes, bone marrow, peripheral blood, and other body fluids. Several studies have reported a high specificity and sensitivity of tumor marker detection and a high correlation between PCR results and the presence of metastatic disease. However, in a few studies, PCR assays have not consistently demonstrated a higher sensitivity and specificity of detection than traditional modalities for many types of cancer. There has been a wide range in sensitivity and specificity among the studies, which may be partly attributed to the lack of uniformity among the PCR protocols used in different studies.

CONCLUSIONS

PCR can detect tumor marker-expressing cells that are otherwise undetectable by other means in patients with localized or metastatic cancer. Reports from various study groups have lacked uniformity in their protocols, and this has prevented adequate comparison. The clinical utility of this assay as a tool for the prognosis and management of cancer patients remains and area of active investigation. PCR is a powerful tool in the study of the biology of cancer metastasis and will likely serve as a useful adjunct to clinical decision-making in the future.

Molecular detection of cancer cells by competitive reverse transcription-polymerase chain reaction analysis of specific CD44 variant RNAs

BACKGROUND

CD44 is a cell surface glycoprotein implicated in such diverse biologic processes as lymphocyte activation and homing, extracellular matrix adhesion, and cellular migration. Primary transcripts of the CD44 gene can be alternatively spliced to produce a variety of messenger RNA (mRNA) species. The standard form of CD44 mRNA contains sequences from at least 20 genomic exons; variant mRNAs contain sequences from one or more additional exons (v1-10). Predominant expression of a specific CD44 variant, i.e., CD44v8-10, in several human carcinomas has been described previously. In this study, we developed a novel molecular approach for detecting cancer cells that overexpress CD44v8-10 mRNA.

METHODS

After finding that CD44v8-10 was predominantly expressed in non-small-cell lung and bladder carcinomas and that CD44v10 was predominantly expressed in leukocytes, we developed a competitive reverse transcription-polymerase chain reaction assay (CC-RT-PCR) that allows quantification of the relative expression of these two mRNA species in clinical specimens (i.e., determination of a v8-10/v10 ratio). CC-RT-PCR analysis was applied to pleural effusion specimens from patients with benign or malignant lung diseases as well as to spontaneously voided urine samples from patients with benign or malignant urologic diseases.

RESULTS

Fifty two of 54 samples from patients with benign diseases expressed CD44v10 predominantly (v8-10/v10 ratio < or = 0.65), whereas 46 of 61 samples from patients with malignant diseases expressed CD44v8-10 predominantly (v8-10/v10 ratio > 1.00) (two-sided P < .001). CC-RT-PCR detected predominant expression of CD44v8-10 in cytologically negative samples from 11 patients who were later diagnosed with malignant disease.

CONCLUSIONS

CC-RT-PCR analysis of CD44v8-10 expression could be an important adjunct to cytologic examination in cancer diagnosis, especially in detecting exfoliated cancer cells in pleural effusions and urine.

CD44 splice variants as prognostic markers in colorectal cancer

BACKGROUND

Splice variants of CD44 play a causal role in the metastatic spread of pancreatic carcinoma in the rat. In previous studies we have shown that homologues of these CD44 isoforms (CD44v6) are overexpressed during colorectal tumorigenesis in man and that CD44v6 overexpression is associated with an unfavorable prognosis in this disease. In the present study we have assessed the prognostic significance of CD44 variants containing exon v5. In addition, we have used a panel of different antibodies against CD44v6 and applied a combined scoring system to improve its value as prognosticator.

METHODS

Expression of CD44 variants was studied by immunohistochemistry on frozen tissue sections, and the prognostic value of the CD44 variant expression was assessed using univariate and multivariate analysis.

RESULTS

Our studies show that expression of CD44v6, but not CD44v5, has significant prognostic value. Analysis of CD44v6 expression by means of a combined scoring system, on the basis of a panel of three different monoclonal antibodies (mAbs), makes CD44v6 a highly significant prognostic marker that is independent of Dukes stage, tumor grade, or tumor localization.

CONCLUSION

Assessment of CD44v6 expression by a combination of mAbs yields an independent prognosticator that may be of value in identifying patients with a high propensity to develop distant metastasis.

Molecular pathogenesis of colorectal cancer

The enormous progress made in the identification of genes that are involved in colon carcinogenesis has provided the foundation for further understanding the biology of both normal and cancer cells and for targeted therapeutic strategies. In one sense, the genes described in this review are only the building blocks of a larger puzzle that constitutes the integrated metabolic function of a cell. The current challenge is to understand the functional role of these genes in normal cellular physiology and make the connections between pathways that knit together integrated cellular homeostasis. A complete understanding of the regulatory pathways, and the synthesis and modifications of the proteins involved, will provide novel targets for therapeutic agents.

CD44 isoforms with exon v6 and metastasis of primary N0M0 breast carcinomas

New isoforms of CD44 with alternatively spliced exons have recently been described. Expression of exon v6 seems to be of particular interest. It has indeed been associated with poorer outcome of breast cancer patients with node invasion at diagnosis. However, no data were available for patients N0M0 (with neither metastasis nor node invasion at diagnosis). Moreover, previous statistical analyses were realized using immunohistochemical methods to detect CD44v6 expression although several variants with exon v6 have been described. We investigated expression of isoforms containing CD44v6 using an RT-PCR approach and a panel of 25 normal breast specimens, 10 mammary fibroadenomas, 8 cystic samples and 52 primary breast tumors (38 invasive N0M0). Normal breasts, fibroadenomas, and cysts all express the same variant, A (with exon v6 only), while several transcripts are amplified in tumors. Expression of variants other than A correlates with acquisition of a malignant phenotype. Invasive cancers also express additional variants in comparison with in situ carcinomas. Metastasis capacities seem to be associated with transcription of variants other than A but also with no transcription of some of them, variants D (with exons v6 and v10) and L (with exons v6 to v10). Expression of variants D and L correlates with higher percentages of disease-free survival and better outcome. Expression of CD44 splice variants with exon v6, as detected by RT-PCR, might be a useful prognostic factor for breast cancer. However, since the series size is small, our results need to be confirmed by later studies on a larger number of patients.

Coexpression of CD44 variant (v10/ex14) and CD44S in human mammary epithelial cells promotes tumorigenesis

CD44 is the major hyaluronan cell surface receptor and functions as an adhesion molecule in many different cell types, including human breast epithelial cells. The coexpression of certain CD44 variants (CD44v), such as CD44v (v10/ex14), with CD44s (standard form) appears to be closely associated with human breast tumor metastasis. In this study we have established a stable transfection of CD44v (v10/ex14) cDNA into nontumorigenic human breast epithelial cells (HBL100) which contain endogenous CD44s. Our results indicate that coexpression of both CD44v (v10/ex14) and CD44s alters the following important biological properties of these cells: 1) there is a significant reduction in hyaluronic acid (HA)-mediated cell adhesion; 2) there is an increased migration capability in collagen-matrix gel; and 3) these cells constitutively produce certain angiogenic factors and effectively promote tumorigenesis in athymic nude mice. These findings suggest that coexpression of CD44v (v10/ex14) and CD44s may trigger the onset of cell transformation required for breast cancer development.

CD44 and the adhesion of neoplastic cells

CD44 is a family of transmembrane glycoproteins that act mainly as a receptor for hyaluronan. It can also bind some other extracellular matrix ligands (chondroitin sulphate, heparan sulphate, fibronectin, serglycin, osteopontin) with lower affinity. CD44 is encoded by a single gene containing 20 exons, 10 of which (v1-v10) are variant exons inserted by alternative splicing. The standard, ubiquitously expressed isoform of CD44, does not contain sequences encoded by these variant exons. Numerous variant isoforms of CD44 containing different combinations of exons v1-v10 inserted into the extracellular domain can be expressed in proliferating epithelial cells and activated lymphocytes. CD44 plays a significant role in lymphocyte homing. Both alternative splicing and glycosylation influence receptor function of the molecule, usually reducing its affinity to hyaluronan. The cytoplasmic domain of CD44 communicates with the cytoskeleton via ankyrin and proteins belonging to the ezrin-moesin-radixin family. Relatively little is known about the intracellular events following interactions of CD44 with its ligands. Some variant isoforms, especially those containing sequences encoded by v6-v10, are overexpressed in both human and animal neoplasms. In a rat pancreatic adenocarcinoma model one of the variant CD44 isoforms was proved to be determinant in the metastatic process. For some human neoplasms (carcinomas of the digestive tract, non-Hodgkin's lymphomas, thyroid carcinomas, and others) correlations have been made between the particular pattern of CD44 variants produced by neoplastic cells and clinicopathological parameters of tumours, such as grade, stage, presence of metastases, and survival. In vitro studies indicate that modifications of CD44 expression result in different ligand recognition and influence cell motility, invasive properties, and metastatic potential of experimental tumours. Investigation of CD44 neoexpression can be useful both in early cancer diagnosis and in predicting tumour behaviour. It can also contribute to better understanding of molecular mechanisms leading to neoplastic transformation.

CD44: structure, function, and association with the malignant process

CD44 is a ubiquitous multistructural and multifunctional cells surface adhesion molecule involved in cell-cell and cell-matrix interactions. Twenty exons are involved in the genomic organization of this molecule. The first five and the last 5 exons are constant, whereas the 10 exons located between these regions are subjected to alternative splicing, resulting in the generation of a variable region. Differential utilization of the 10 variable region exons, as well as variations in N-glycosylation, O-glycosylation, and glycosaminoglycanation (by heparan sulfate or chondroitin sulfate), generate multiple isoforms (at least 20 are known) of different molecular sizes (85-230 kDa). The smallest CD44 molecule (85-95 kDa), which lacks the entire variable region, is standard CD44 (CD44s). As it is expressed mainly on cells of lymphohematopoietic origin, CD44s is also known as hematopoietic CD44 (CD44H). CD44s is a single-chain molecule composed of a distal extracellular domain (containing, the ligand-binding sites), a membrane-proximal region, a transmembrane-spanning domain, and a cytoplasmic tail. The molecular sequence (with the exception of the membrane-proximal region) displays high interspecies homology. After immunological activation, T lymphocytes and other leukocytes transiently upregulate CD44 isoforms expressing variant exons (designated CD44v). A CD44 isform containing the last 3 exon products of the variable region (CD44V8-10, also known as epithelial CD44 or CD44E), is preferentially expressed on epithelial cells. The longest CD44 isoform expressing in tandem eight exons of the variable region (CD44V3-10) was detected in keratinocytes. Hyaluronic acid (HA), an important component of the extracellular matrix (ECM), is the principal, but by no means the only, ligand of CD44. Other CD44 ligands include the ECM components collagen, fibronectin, laminin, and chondroitin sulfate. Mucosal addressin, serglycin, osteopontin, and the class II invariant chain (Ii) are additional, ECM-unrelated, ligands of the molecule. In many, but not in all cases, CD44 does not bind HA unless it is stimulated by phorbol esters, activated by agonistic anti-CD44 antibody, or deglycosylated (e.g., by tunicamycin). CD44 is a multifunctional receptor involved in cell-cell and cell-ECM interactions, cell traffic, lymph node homing, presentation of chemokines and growth factors to traveling cells, and transmission of growth signals. CD44 also participates in the uptake and intracellular degradation of HA, as well as in transmission of signals mediating hematopoiesis and apoptosis. Many cancer cell types as well as their metastases express high levels of CD44. Whereas some tumors, such as gliomas, exclusively express standard CD44, other neoplasms, including gastrointestinal cancer, bladder cancer, uterine cervical cancer, breast cancer and non-Hodgkin's lymphomas, also express CD44 variants. Hence CD44, particularly its variants, may be used as diagnostic or prognostic markers of at least some human malignant diseases. Furthermore, it has been shown in animal models that injection of reagents interfering with CD44-ligand interaction (e.g., CD44s- or CD44v-specific antibodies) inhibit local tumor growth and metastatic spread. These findings suggest that CD44 may confer a growth advantage on some neoplastic cells and, therefore, could be used as a target for cancer therapy. It is hoped that identification of CD44 variants expressed on cancer but not on normal cells will lead to the development of anti-CD44 reagents restricted to the neoplastic growth.

Increased expression of CD44 variants in differentiated thyroid cancers

Expression of CD44 variants in thyroid tumors was analyzed by reverse transcription-polymerase chain reaction (RT-PCR) with a fluorescent image analyzer. Increased expression of CD44 variants compared with normal thyroid tissues was observed in most thyroid follicular tumors, especially in follicular carcinomas, poorly differentiated papillary carcinomas and some follicular adenomas. However, variants were hardly detectable in an anaplastic carcinoma. Analysis with restriction enzymes revealed that the major PCR product, consisting of variant bands, was derived from CD44E. Therefore, the expression of CD44E may be associated with the proliferation of differentiated thyroid cells.

Expression of CD44 splice variants in metastatic and non-metastatic mouse tumour cell lines

Different splice variants of the CD44 cell-surface molecule have been linked to metastasis formation in several animal and human cancers. We have used metastatic CSML-100 and non-metastatic CSML-0 mouse adenocarcinoma cell lines to determine whether variant CD44 molecules could be implicated in the different behaviour of these cells. Two CD44 splice variants containing exons v7-v10 and v8-v10 were detected in the non-metastatic CSML-0. Two other mouse cell lines, the normal mammary gland NMuMG and the mammary pre-neoplastic CL-S1 were also found to express these exons. A short (hematopoietic) CD44 isoform was expressed in the metastatic CSML-100 and three other mouse mammary tumour cell lines. Overexpression of v7-v10 and v8-v10 CD44 variants in CSML 100 cells did not decrease their metastatic potential.