Soluble CD44 isoforms in serum as potential markers of metastatic gastric carcinoma

Production and characterization of a peptide-based monoclonal antibody against CD44 variant 6

The gene that codes for the CD44 family members consists of 20 exons, nine of which encode the standard form of the molecule. The other exons can be inserted in various combinations into the membrane proximal region of the extracellular domain of the protein, giving rise to variant isoforms (CD44v). CD44 variants, especially the CD44v6, have been reported to regulate tumor invasion, progression, and metastasis of carcinomas. Producing a high affinity monoclonal antibody against human CD44v6 provides a powerful tool to monitor and trace CD44v6 function in different biological fluids. In this study, a synthetic peptide from CD44v6 was conjugated to keyhole limpet hemocyanin (KLH) and injected into BALB/c mice. Splenocytes from the immunized mice were fused with murine SP2/0 myeloma cells followed by selection of antibody producing hybridoma cells. After screening of hybridoma colonies by ELISA, high affinity antibodies were selected and purified by affinity chromatography. Western blot, immunocytochemistry, and flow cytometry experiments were used to characterize the antibodies. Six stable hybridoma cell lines, designated as 1H1, 1H2, 2A12, 2G11, 3H3, and 3H7, were obtained. Flow cytometry and immunocytochemistry results showed that the new monoclonal antibodies recognized CD44v6 on the cell surface. This novel panel of anti-CD44v6 antibodies has the potential for investigating the role of CD44v6 in cancer pathogenesis.

Correlation of CD44v6 expression with ovarian cancer progression and recurrence

Background

Previously some groups demonstrated that CD44 variant 6 (CD44v6) is correlated with progression and metastasis of ovarian cancer. However, a number of other groups failed to find such an association. Moreover, epithelial ovarian cancer is known to easily metastasize to distinct sites such as the pelvic and abdominal cavities, but the potential association of CD44v6 expression with site-specific metastasis of ovarian cancer has not been explored. This study sought to evaluate the expression of CD44 standard (CD44s) and CD44v6 in primary, metastatic and recurrent epithelial ovarian cancer to explore the potential association of CD44s and CD44v6 with tumor progression and recurrence.

Methods

Tumor specimens were procured from patients with advanced (FIGO III, G3) and recurrent ovarian serous adenocarcinoma. CD44s and CD44v6 expression in the tumor tissues was evaluated by real-time RT-PCR and Western blot. Moreover, serum soluble CD44s or CD44v6 concentrations of early stage (FIGO I, G1), advanced (FIGO III, G3) and recurrent ovarian serous adenocarcinoma patients were determined by enzyme-linked immunosorbent assays (ELISA). CD44v6 expression in a different set of tumor samples on an ovarian cancer tissue chip was evaluated by immunohistochemistry (IHC) and the correlation of CD44v6 expression with clinicopathologic features was analyzed. Finally, the effects of knockdown of CD44v6 in SKOV3 cells on cell adhesion, invasion and migration were assessed.

Results

The expression of CD44v6, but not CD44s, is up-regulated in recurrent ovarian serous cancer compared to advanced primary tumor. CD44v6 expression is also preferentially increased in the tumor at the abdominal cavity metastasis site of advanced diseases. Consistently, serum soluble CD44v6 levels of recurrent ovarian cancer were higher than those of early stage and advanced primary diseases. The IHC data demonstrate that CD44v6 expression is correlated with clinicopathologic features and tumor progression. Lastly, knockdown of CD44v6 decreases the adhesion and migration but not invasion capacities of SKOV3 cells.

Conclusions

CD44v6 expression levels are associated with epithelial ovarian cancer progression, metastasis and relapse. Moreover, serum soluble CD44v6 may be used as a potential marker for identifying tumor relapse. Finally, CD44v6 may play a role in ovarian cancer metastasis by mediating tumor cell adhesion and migration.

HSP72 and gp96 in gastroenterological cancers

Heat shock protein 72 (HSP72) and glycoprotein 96 (gp96) are highly expressed in cancer tissues. Recent studies indicate the possible roles of HSP72 and gp96 in the development and progression of gastrointestinal carcinomas but detailed mechanisms are still ambiguous. Human esophageal cancer, gastric cancer, colon cancer and liver cancer are common gastrointestinal malignant carcinomas in the world. The studies indicated that there existed a significant correlation between the expression of HSP72, gp96 and the development and progression of digestive carcinomas. HSP72 and gp96 expression were significantly associated with the presence of tumor infiltration, lymph node and remote metastasis. Interestingly, studies have found that HSP72 chaperoned alpha-fetoprotein (AFP), HBx in hepatocellular carcinoma, and CD44 in colonic carcinomas. The further researches demonstrated that HSP72-AFP or gp96-AFP recombined vaccine could elicit specific anti-tumor immunity. The high-level expression of HSP72 and gp96 may be not only used as diagnostic or prognostic markers for gastrointestinal carcinomas but also as better immunotherapeutic vaccines in the cancers.

The Role of CD44 in the Pathogenesis, Diagnosis, and Therapy of Gastric Cancer

CD44 is a transmembrane glycoprotein and surface receptor for hyaluronan that is involved in the response of cells to their microenvironment. CD44 splice variants play roles in carcinogenesis, differentiation, and lymph node metastasis and are predictive of the prognosis for various carcinomas, including gastric cancer. Current data suggest that gastric tissue stem cells and gastric cancer stem cells both express the splice variant, CD44v9. Overall, the data regarding the alterations that occur in CD44 and its splice variants in response to acute and chronic infection with Helicobacter pylori are scant and poorly elucidated in terms of possible changes in expression that occur in gastric cancer precursor lesions, such as chronic atrophic gastritis, pyloric metaplasia and intestinal metaplasia. In this study, we discuss the available data and suggest which new data would likely be useful in clinical practice. We also discuss the potential for CD44-targeted therapeutic strategies in gastric cancer. CD44 and its splice variants are positively associated with the initiation and progression of gastric cancer and may also play important roles in diagnosis, therapy and prognosis. CD44 research has been active but fragmented, and it may offer new therapeutic approaches to gastric cancer.

The Role of CD44 in the Pathogenesis, Diagnosis, and Therapy of Gastric Cancer

CD44 is a transmembrane glycoprotein and surface receptor for hyaluronan that is involved in the response of cells to their microenvironment. CD44 splice variants play roles in carcinogenesis, differentiation, and lymph node metastasis and are predictive of the prognosis for various carcinomas, including gastric cancer. Current data suggest that gastric tissue stem cells and gastric cancer stem cells both express the splice variant, CD44v9. Overall, the data regarding the alterations that occur in CD44 and its splice variants in response to acute and chronic infection with Helicobacter pylori are scant and poorly elucidated in terms of possible changes in expression that occur in gastric cancer precursor lesions, such as chronic atrophic gastritis, pyloric metaplasia and intestinal metaplasia. In this study, we discuss the available data and suggest which new data would likely be useful in clinical practice. We also discuss the potential for CD44-targeted therapeutic strategies in gastric cancer. CD44 and its splice variants are positively associated with the initiation and progression of gastric cancer and may also play important roles in diagnosis, therapy and prognosis. CD44 research has been active but fragmented, and it may offer new therapeutic approaches to gastric cancer.

Expression and prognostic relevance of CD44v6 in stage I non-small cell lung carcinoma

PURPOSE

Expression of CD44 and its variants has been shown to be relevant to tumor progression in various human malignancies. We evaluated the expression of CD44v6 in the primary lesions of stage I non-small cell lung cancer (NSCLC) and correlated the expression level to its prognosis.

METHODS

The expression of CD44v6, measured by immunohistochemistry, was assessed in the tumor specimens from 190 patients with stage I NSCLC. Each slide was assigned a score: the average of the score of tumor cells staining multiplied by the score of staining intensity. And depending on the cut-off score based on receiver operating characteristic (ROC) curve analysis, the CD44v6 expression was categorized into high- and low-level groups, which were then correlated directly with the clinical outcomes.

RESULTS

The high expression of CD44v6 was detected more frequently in the squamous cell carcinoma (38 of 71 patients, 53.5%) than in the other types of carcinoma (p < 0.05). The Kaplan-Meier survival curves showed that high level expression of CD44v6 indicated a better post-operative survival (p = 0.006), especially for stage IB disease (p = 0.049) and squamous cell carcinoma (p = 0.029). The multivariate analysis also confirmed that the expression of CD44v6 was an independent prognostic indicator (p = 0.011).

CONCLUSIONS

CD44v6 might be correlated with histogenesis of NSCLC, and its decreased expression may be an adverse prognostic indicator for the patients with stage I NSCLC, especially for those with stage IB diseases. Patients of this subgroup might need adjuvant therapy additionally.

The emerging role of splicing factors in cancer

Recent progress in global sequence and microarray data analysis has revealed the increasing complexity of the human transcriptome. Alternative splicing generates a huge diversity of transcript variants and disruption of splicing regulatory networks is emerging as an important contributor to various diseases, including cancer. Current efforts to establish the dynamic repertoire of transcripts that are generated in health and disease are showing that many cancer-associated alternative-splicing events occur in the absence of mutations in the affected genes. A growing body of evidence reveals changes in splicing-factor expression that correlate with cancer development, progression and response to therapy. Here, we discuss how recent links between cancer and altered expression of proteins implicated in splicing regulation are bringing the splicing machinery to the fore as a potential target for anticancer treatment.

Knockdown of contactin-1 expression suppresses invasion and metastasis of lung adenocarcinoma

Numerous genetic changes are associated with cancer cell metastasis and invasion. In search for key regulators of invasion and metastasis, a panel of lung cancer cell lines with different invasive ability was screened. The gene for contactin-1 was found to play an essential role in tumor invasion and metastasis. Suppression of contactin-1 expression abolished the ability of lung adenocarcinoma cells to invade Matrigel in vitro as well as the polymerization of filamentous-actin and the formation of focal adhesion structures. Furthermore, knockdown of contactin-1 resulted in extensive inhibition of tumor metastasis and in increased survival in an animal model. RhoA but not Cdc42 or Rac1 was found to serve a critical role in contactin-1-mediated invasion and metastasis. Contactin-1-specific RNA interference resulted in loss of metastatic and invasive capacity in both in vitro and in vivo models. This loss was overturned by constitutive expression of the active form of RhoA. Contactin-1 was differentially expressed in tumor tissues, and its expression correlated with tumor stage, lymph node metastasis, and patient survival. Contactin-1 is proposed to function importantly in the invasion and metastasis of lung adenocarcinoma cells via RhoA-mediated mechanisms.

Regulation of CD44 alternative splicing by SRm160 and its potential role in tumor cell invasion

The multiple isoforms of the transmembrane glycoprotein CD44 are produced by alternative RNA splicing. Expression of CD44 isoforms containing variable 5 exon (v5) correlates with enhanced malignancy and invasiveness of some tumors. Here we demonstrate that SRm160, a splicing coactivator, regulates CD44 alternative splicing in a Ras-dependent manner. Overexpression of SRm160 stimulates inclusion of CD44 v5 when Ras is activated. Conversely, small interfering RNA (siRNA)-mediated silencing of SRm160 significantly reduces v5 inclusion. Immunoprecipitation shows association of SRm160 with Sam68, a protein that also stimulates v5 inclusion in a Ras-dependent manner, suggesting that these two proteins interact to regulate CD44 splicing. Importantly, siRNA-mediated depletion of CD44 v5 decreases tumor cell invasion. Reduction of SRm160 by siRNA transfection downregulates the endogenous levels of CD44 isoforms, including v5, and correlates with a decrease in tumor cell invasiveness.

Role of VEGF and CD44v6 in differentiating benign from malignant ascites

AIM: To detect the vascular endothelial growth factor (VEGF) and soluble splice variant 6 of CD44 (sCD44v6) levels in ascites and to explore their role in differentiating benign from malignant ascites.

METHODS: Cirrhotic ascites (n = 36), tuberculosis ascites (n = 8) and malignant ascites (n = 23) were collected and studied. Concentrations of soluble VEGF and sCD44v6 in various kinds of ascites (n = 67) were measured using a sandwich enzyme-linked immunoadsorbent assay.

RESULTS: VEGF and sCD44v6 levels in malignant ascites were 640.74 ± 264.81 pg/mL and 89.22 ± 38.20 ng/mL, respectively, both of which were significantly higher than those in cirrhotic ascites and tuberculous ascites (q = 18.98, 11.89 and q = 8.92, 5.09; P < 0.01). However, the levels of VEGF and sCD44v6 in cirrhotic and tuberculous ascites had no significant difference (q = 0.48, 0.75; P > 0.05). Furthermore, VEGF levels in malignant ascites in patients with ovarian cancer were higher than those with gastric and colon cancer (q = 5.03, 6.79; P < 0.01, respectively). But differences of VEGF levels between gastric and colon cancer were not significant (q = 1.90, P > 0.05). Whereas, sCD44v6 levels in malignant ascites from patients with ovarian, gastric and colon cancer had no significant difference (q = 0.06, 0.91, 0.35; P > 0.05, respectirely). In comparison with cirrhotic and tuberculous ascites, when the upper limit of its VEGF mean levels 119.44 pg/mL (70.90 ± 48.54) and sCD44v6 mean levels 63.59 ng/mL (44.42 ± 19.17) was taken as the minimum cutoff limit, the sensitivity and specificity of VEGF and sCD44v6 of this assay to the diagnos is of malignant ascites were 91.3%, 90.9% and 73.9%, 88.7% respectively.

CONCLUSION: Elevated levels of VEGF and sCD44v6 may be useful in differential diagnosis of benign and malignant ascites.

Expression of CD44v6 in advanced gastric cancer and its relationship to hematogenous metastasis and long-term prognosis

BACKGROUND AND OBJECTIVES

Variants of CD44 have been proposed to be important in promoting tumor progression and metastasis. We attempted to determine the expression of CD44v6 product in advanced gastric cancer and to evaluate its prognostic value.

METHODS

The expression of CD44v6 was analyzed immunohistochemically in advanced gastric cancers using monoclonal antibody, 44-2V. We investigated the relationship between CD44v6 expression and prognosis in 201 gastric cancer patients.

RESULTS

Ninety-five (47.3%) of 201 cancer tissues expressed CD44v6. The expression of CD44v6 protein was significantly higher in differentiated, adenocarcinoma than in diffuse type carcinoma. The CD44v6-positive cancers were more frequently associated with hematogenous metastasis. There was no significant correlation between CD44v6 immunoreactivity, and prognosis among the combined cases. Among patients with differentiated adenocarcinoma, however, the prognosis was significantly poorer in patients with CD44v6-positive tumors than in those with CD44v6-negative tumors.

CONCLUSIONS

CD44v6 protein may have an important role in hematogenous metastasis, and may be a biologic marker of prognostic significance in differentiated type gastric cancers.

Splicing regulation as a potential genetic modifier

Inherited diseases are associated with profound phenotypic variability, which is affected strongly by genetic modifiers. The splicing machinery could be one such modifying system, through a mechanism involving splicing motifs and their interaction with a complex repertoire of splicing factors. Mutations in splicing motifs and changes in levels of splicing factors can result in different splicing patterns. Changes in the level of normal transcripts or in the relative pattern of different mRNA isoforms affect disease expression, leading to phenotypic variability. Here, we discuss the splicing machinery in terms of its significance in disease severity and its potential role as a genetic modifier.

Serum CD44 levels preceding the diagnosis of non-Hodgkin's lymphoma

Serum CD44 (s-CD44) concentrations were measured in sera taken from 49 individuals who were diagnosed with non-Hodgkin's lymphoma 0.9 to 7.2 years after taking the blood sample, and from 49 controls matched for age. The serum samples had been collected in conjunction of the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) study, which evaluated the influence of vitamin supplementation on cancer prevention. S-CD44 was measured using chemiluminescence enzyme immunoassay. S-CD44 concentrations of the cases were significantly elevated before the diagnosis of lymphoma when compared to the serum levels found in the controls (median, 447 ng/mL; range, 108-780 ng/mL vs. median, 364 ng/mL; range, 53-660 ng/mL; p=0.012). Individuals who were later diagnosed with high grade lymphoma according to the Kiel classification (n=21) had significantly higher values than the controls 0.9-4.0 years before the diagnosis, but such a difference could not be detected if serum samples had been taken more than 4 years before the diagnosis. The s-CD44 levels were not significantly elevated among individuals who were later diagnosed with low grade malignant non-Hodgkin's lymphoma (n=25) as compared to their controls. The prediagnostic s-CD44 levels in cases and controls overlapped markedly, and a value higher than the highest value found among the controls (660 ng/mL) was found only in 5 (10%) samples taken from individuals who were later diagnosed with lymphoma. We conclude that serum CD44 may be elevated a few years preceding the diagnosis of non-Hodgkin's lymphoma, but the levels overlap markedly with those found in individuals without lymphoma.

Identification and characterization of CD44RC, a novel alternatively spliced soluble CD44 isoform that can potentiate the hyaluronan binding activity of cell surface CD44

Soluble CD44 proteins generated by proteolytic cleavage or aberrant intron retention have been shown to antagonize the ligand binding activity of the corresponding cell surface receptor, inducing apoptosis and inhibiting tumor growth. Interestingly, such findings appear to contradict recent studies demonstrating a correlation between the presence of high levels of soluble CD44 in the serum of cancer patients and poor prognosis. In the present study, we report the cloning of a novel, naturally occurring, differentially expressed, soluble CD44 isoform, designated CD44RC, which, in contrast to previously described soluble CD44 proteins, can dramatically enhance the hyaluronan binding activity of cell surface CD44. Sequence analysis suggests that CD44RC is generated by an alternative splicing event in which the 3' end of CD44 exon 2 is spliced into an internal splice acceptor site present within exon 18, altering reading frame and giving rise to a soluble protein with a unique COOH terminus. Functional studies suggest that CD44RC enhances hyaluronan binding by adhering to chondroitin sulfate side-chains attached to cell surface CD44, generating a multivalent complex with increased avidity for hyaluronan.

Soluble CD44: quantification and molecular repartition in plasma of patients with colorectal cancer

Based on the important role of CD44 in tumour progression and metastasis, we evaluated, in a prospective study, plasma-soluble CD44 (sCD44) as a serum marker in colorectal cancer. Blood plasma specimens from 89 patients with colorectal neoplasm, 22 patients with a gastrointestinal disease and 23 healthy donors were analysed for quantitation (ELISA assay) and purification of sCD44. The concentration of sCD44, indicating the concentration of all isoforms, was significantly higher in patients with colorectal cancer and intestinal disease than in normal individuals, but no significant differences were found between the two groups. We found no association between plasma levels and staging of the colorectal cancer patients according to Astler and Coller. A two-step batch purification combining ion exchange and immunoaffinity chromatography, followed by Western blot analysis, revealed a complex pattern with a major band corresponding to the standard form of CD44 and minor bands that may correspond to larger variant forms. No particular sCD44 isoform was clearly associated with anatomopathological or biological information.

Soluble CD44 variant 6 as a prognostic indicator in patients with colorectal cancer

The expression of CD44v6 is well known as a useful marker of tumor progression and prognosis in colorectal cancer. In this study, we evaluated the serum levels of soluble CD44 splice variants containing exon v6 (sCD44v6) and examined the histological expression of CD44v6 in patients with colorectal cancer. Serum samples were obtained from 44 primary colorectal cancer patients before surgery. We used enzyme-linked immunosorbent assay to determine the serum levels of sCD44v6. The expression of CD44v6 was examined by immunohistochemical staining of the primary tumors obtained from the same patients. Both the serum concentration of sCD44v6 and the expression of CD44v6 were significantly associated with lymph node metastasis (p < 0.05). Furthermore, the serum level of sCD44v6 was higher in those patients with CD44v6-positive tumor tissues (154.4 +/- 34.8 ng/ml) than in those with CD44v6-negative ones (130.7 +/- 32.3 ng/ml; p < 0.05). The 5-year survival rate was significantly lower in patients with high serum levels of sCD44v6 (52.4%) than in those with low levels of sCD44v6 (78.0%; p < 0.05), and it was also significantly lower in patients with CD44v6-positive cancer (42.1%) than in those with CD44v6-negative cancer (84%; p < 0. 01). We concluded that preoperative elevation in the serum levels of sCD44v6 might be a prognostic indicator for patients with colorectal cancer.

Molecular studies into the role of CD44 variants in metastasis in gastric cancer

CD44, an integral membrane glycoprotein expressed by many cell types, serves as the principal transmembrane hyaluronate receptor and might be a determinant of metastatic and invasive behaviour in carcinomas. The generation of CD44 splice variants might be linked closely with gastric carcinoma tumorigenesis and differentiation. Some studies have reported that the magnitude of CD44 variant synthesis at the protein level correlates with lymph node metastasis. A number of studies have examined the possible mechanism of involvement of the CD44 variant in tumour metastasis. Most studies have reported that the regulation of CD44 binding to hyaluronate results from glycosylation of variably spliced exons. Direct hyaluronate binding studies of CD44 V4-V7 isoforms transfected into the human gastric carcinoma cell line, SC-M1, have indicated that the V4-V7 isoforms themselves, in addition to glycosylation, can alter hyaluronate binding.

Serum concentration of CD44 variant 6 and its relation to prognosis in patients with gastric carcinoma

BACKGROUND

The expression of variant isoforms of CD44 is correlated with the ability of tumor cells to metastasize in some clinical carcinomas. In this study, the serum concentration of soluble splice isoforms of CD44 that shared exon variant 6 (sCD44v6) were measured and the histologic expression of CD44v6 in tumors from patients with gastric carcinoma examined.

METHODS

Serum samples were obtained from 102 patients with primary gastric carcinoma before surgery and serum levels of sCD44v6 were determined with an enzyme-linked immunoadsorbent assay. The expression of CD44v6 in tumors was examined by immunohistochemical staining.

RESULTS

Both the serum concentration of sCD44v6 and its expression in tumors were associated significantly with the depth of invasion of the tumor, lymph node metastasis, and clinical stage in patients with diffuse type gastric carcinoma. Among patients with gastric carcinoma, the serum level of sCD44v6 was higher in those with CD44v6 positive tumor cells than in those with CD44v6 negative tumor cells. The serum level of sCD44v6 was a prognostic indicator in patients with diffuse type gastric carcinoma, as was the histologic expression of CD44v6. However, neither CD44v6 nor sCD44v6 was a predictor of survival time in patients with intestinal type gastric carcinoma.

CONCLUSIONS

It appears that CD44v6 and sCD44v6 are related to the progression of diffuse type gastric carcinoma. An elevated serum level of sCD44v6 may be useful as a prognostic indicator in patients with diffuse type gastric carcinoma.

Soluble CD44 and CD44v6 serum levels in patients with colorectal cancer are independent of tumor stage and tissue expression of CD44v6

OBJECTIVES

Tissue overexpression of CD44 variants, especially CD44v6, and elevated serum concentrations of soluble CD44 variants (sCD44) have been demonstrated in patients with colorectal cancer and several other tumors. Our aim was to evaluate the clinical value of their measurement in colorectal cancer.

METHODS

To examine the suitability of sCD44 and sCD44v6 as tumor markers in colorectal cancer these parameters were analyzed in serum of patients with colorectal cancer, inflammatory bowel disease, chronic renal failure, and controls. Tissue expression of CD44v6 in colorectal carcinomas was investigated by reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

sCD44 and sCD44v6 levels were significantly elevated in most of the patient groups (medians, sCD44: 330-709 ng/ml; sCD44v6: 125-160 ng/ml) compared to controls (sCD44: 346 ng/ml; sCD44v6: 106.5 ng/ml). No difference was seen between colorectal cancer patients of different UICC (Union Internationale Contre le Cancer) stages and between patients with CD44v6-positive or -negative primary tumors.

CONCLUSIONS

sCD44 and sCD44v6 concentrations showed no correlation to tumor burden or CD44v6 tissue expression. Sensitivity and specificity were low, compared to CEA. Therefore, in our view sCD44 and sCD44v6 measurement in screening or follow-up of patients with colorectal cancer is of very little clinical value.

Hyaluronate binding assay study of transfected CD44 V4-V7 isoforms into the human gastric carcinoma cell line SC-M1

The potential human metastasis molecule CD44 and its isoforms V5 and V6 are overexpressed in human gastric carcinoma. Among the numerous extracellular matrix components, hyaluronate, a CD44 ligand, is of increasing interest in relation to its role in cancer cell development and invasion. By using the dynabead separation method, the SC-M1 cell line was separated into V5 and V6 isoform-positive and -negative populations. The V5 and V6 isoform-negative populations exhibited significantly higher hyaluronate binding activity than the corresponding positive cells. The hyaluronate binding activity of V5 and V6-positive cells could be restored by pretreatment with anti-CD44 V5 and V6 monoclonal antibodies (MAbs). In addition, transfection of aVV5 and V6-negative cells decreased their hyaluronate binding activity to the levels of CD44 V5 and V6-positive cells. Cells transfected with V5 and V6 recovered their hyaluronate binding activity after pretreatment with MAbs against V5 and V6. These data suggest that cell adhesion involving hyaluronate can be regulated by multiple mechanisms, one of which involves alternative splicing of CD44 isoforms.