Tumor marker aquaporin 2 protein and application thereof

Abstract

Disclosed are a tumour marker aquaporin 2 protein and an application thereof, belonging to the fields of tumour detection and molecular targeted therapy. The present invention comprises applications of the aquaporin 2 protein in the following functions: (1) as a new tumour marker used for the early diagnosis and prognostic determination of malignant tumours including head and neck squamous cell carcinoma, kidney cancer and prostate cancer; (2) inhibiting tumour cell proliferation; (3) inhibiting tumour cell migration; (4) inhibiting animal transplant tumour model growth. Targeted therapy which uses the aquaporin 2 protein as a biomarker, as in the present invention, provides new ideas for the treatment of malignant tumours such as head and neck squamous cell carcinoma, kidney cancer and prostate cancer.

Description

TUMOR MARKER AQUAPORIN 2 PROTEIN AND APPLICATION THEREOF TECHNICAL FIELD The present invention pertains to the fields of tumor detection and molecular targeted therapy and more specifically, relates to a transmembrane protein AQUAPORIN 2 ("AQP2" for short) and the use thereof. BACKGROUND ART Tumors are currently the most serious diseases endangering human health. Studies have found that the generation of tumors is a complex process of gradual accumulation of gene mutations, and the development of modern medical technology and molecular biology has brought tumor treatment into the era of individualization which has greatly increased the tumor remission rate. Therefore, finding specific targets is crucial for early diagnosis, treatment and prognosis of tumors and a key bottleneck restricting the clinical efficacy of tumor treatments. Head and neck cancer includes neck tumors (thyroid tumors, etc.), ENT tumors (larynx cancer, nasopharyngeal cancer, paranasal sinus cancer, etc.) and oral and maxillofacial tumors (tongue cancer, gum cancer, cheek cancer, etc.). More than 90% of head and neck tumors are squamous cell carcinoma. Head and neck squamous cell carcinoma is the sixth most common cancer in the world, with more than 500,000 new cases worldwide each year, and a 5-year survival rate of less than 40%. At present, treatment methods mainly include radiotherapy, chemotherapy and surgery, all with poor clinical prognosis. Therefore, in depth study of the pathogenesis of head and neck squamous cell carcinoma and discovery of new biomarkers are of great significance for the targeted therapy of head and neck squamous cell carcinoma and the prognosis of patients. Kidney cancer, also known as renal cell carcinoma, originates from renal tubular epithelial cells and is the most common renal parenchymal malignancy. There are about 208,500 new cases globally every year, and the incidence in China is about 4.5 / 100,000. At present, the etiology of kidney cancer is not clear, and most patients with kidney cancer are not sensitive to radiotherapy and chemotherapy in clinical treatment and must rely on surgery for treatment. Therefore, improving the accuracy of early diagnosis is helpful for the timely treatment of kidney cancer patients. Prostate cancer refers to epithelial malignant tumors that occur in the prostate and mainly include adenocarcinoma (acinar adenocarcinoma), ductal adenocarcinoma, urothelial carcinoma, squamous cell carcinoma and adenosquamous carcinoma. The incidence increases with age and reaches a peak at 70 to 80 years old. There are obvious regional and racial differences in the incidence of prostate cancer. According to statistics, the incidence of prostate cancer is the lowest in Chinese and highest in Europeans. In recent years, with the improvement of living conditions and the prolongation of life expectancy, the incidence of prostate cancer in China has also increased. Tumor metastasis and invasion are important features of malignant tumors and the main culprits of most tumor recurrences. Studies have found that tumor metastasis and invasion is a continuous dynamic process involving multiple genes, of which proto-oncogenes and cancer suppressor genes play an equally important role. The effects of a large number of proto-oncogenes such as PTEN, MYC, RAS, PIK3CA and AKT1 in malignant tumors including head and neck squamous cell carcinoma have been revealed in depth, while studies on tumor suppressor genes except TP53 have been rarely reported. With the help of bioinformatics methods such as high-throughput screening and big data analysis, the discovery of tumor suppressor genes with important functions is critical for understanding the pathogenesis of tumors and for developing more comprehensive diagnosis and treatment plans. Aquaporin-2 (AQP2), a member of the aquaporin family, is mainly distributed in the luminal membrane and intracellular vesicles of chief cells of the collecting duct, and is an antidiuretic hormone-sensitive aquaporin. Current studies have found that AQP2 is mainly expressed in kidney tissue and is involved in the pathological processes of diseases such as neurological diabetes insipidus and polycystic kidney disease. However, the expression and functions of AQP2 in tumors have not been reported in the literature. This study discovered for the first time the expression level and potential biological functions of AQP2 in different types of tumors, which is important for the development of the application value of AQP2 in tumor detection and treatment. SUMMARY OF THE INVENTION According to an aspect of the invention, there is provided use of a transmembrane protein as a tumor marker, wherein the transmembrane protein is AQUAPORIN 2, and its amino acid sequence is as set forth in SEQ ID NO.2 and wherein the tumor is head and neck squamous cell carcinoma or kidney cancer. According to another aspect of the invention, there is provided a method for detecting tumor marker, wherein the tumor is head and neck squamous cell carcinoma or kidney cancer and the detection method is any of a and b: (a) detecting gene expression of transmembrane protein AQUAPORIN 2 in tissue or cells by a PCR method; (b) detecting gene expression of transmembrane protein AQUAPORIN 2 in tissue or cells by a Western blot method. To address the existing problem that malignant tumors such as head and neck squamous cell carcinoma do not have closely related biomarkers, the present invention provides a tumor marker AQP2 protein which has then been used in tumor detection and treatment. Through bioinformatics methods, clinical tumor samples and biological function experiments, new biomarkers closely related to the occurrence, development and metastasis of head and neck squamous cell carcinoma, kidney cancer and prostate cancer were discovered. The present invention adopts the following technical solution: Application of a transmembrane protein in the preparation of tumor treatment drugs or the use as a tumor marker, wherein the marker is transmembrane protein AQP2, and its amino acid sequence is shown in SEQ ID NO.2. Preferably, tumors that this tumor marker is used to detect include head and neck squamous cell carcinoma, kidney cancer and prostate cancer. In some embodiments, a kit for detecting the expression of the foregoing marker is provided, wherein the detection kit includes a specific primer pair designed for the nucleotide sequence encoding AQP2 (shown in SEQ ID NO. 1). * Preferably, reagents for detecting biomarker expression can be used as tools for prognosis of tumor subjects. The method of prognosis described herein includes: obtaining a test sample from a tumor; determining the expression level of the biomarker in the test sample; and analyzing the expression level to generate a risk score, which can be used to provide a prognosis for the subject. It should be noted that the test samples used in the prognosis are fresh, frozen, or paraffin-fixed and - embedded tissue. Preferably, the foregoing detection reagents are reagents containing anti-AQP2 protein antibody and can also be composition detection reagents containing anti-AQP2 protein antibody. In some embodiments, a method for detecting the foregoing biomarker is provided, wherein specific primers are designed, a PCR method is used to detect the expression quantity of transmembrane protein AQP2 in tissue cells, and the primer sequences are shown in SEQ ID NO. 3 and SEQ ID NO. 4. In some embodiments, a recombinant vector achieving overexpression of the transmembrane protein AQP2 is provided, wherein the recombinant vector can be applied in the preparation of drugs for treating tumors. Preferably, the recombinant vector is an overexpression plasmid, lentivirus or cell line containing the nucleotide sequence shown in SEQ ID NO. 1 and having the following functions (a1) to (a3): (a1) inhibiting tumor growth; (a2) inhibiting proliferation of tumor cells; (a3) inhibiting migration of tumor cells. Compared with the prior art, the present invention has the following advantages: (1) For the first time, it was found that transmembrane protein AQP2 played an important role in tumor diagnosis, prognosis and treatment, and could be used as a tumor marker of head and neck squamous cell carcinoma, kidney cancer and prostate cancer. (2) The present invention found that the expression levels of transmembrane protein AQP2 in head and neck squamous cell carcinoma cells, kidney cancer cells and prostate cancer cells were significantly lower than that in normal epithelial cells, and AQP2 overexpression could significantly inhibit the proliferation, migration and in vivo tumor growth of head and neck squamous cell carcinoma cells, kidney cancer cells and prostate cancer cells, which demonstrates the importance of AQP2 for tumor growth and metastasis and suggests that AQP2 has the potential to be a target for drug design. For example, antitumor substances targeting AQP2 (containing overexpression plasmid vector, lentivirus or transgenic cell line encoding nucleotide) can be used to prepare drugs against head and neck squamous cell carcinoma, kidney cancer and prostate cancer. (3) The present invention uses GAPDH as an internal reference gene to detect the expression level of AQP2. It is found that the expression quantities of AQP2 protein in head and neck squamous cell carcinoma cells SCC4, kidney cancer cells 786-O, and prostate cancer cells DU145 were significantly reduced, which proves that AQP2 can be used as a new biomarker to diagnose malignant tumors including head and neck squamous cell carcinoma, kidney cancer and prostate cancer. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is the comparison of the expression quantities of AQP2 gene in head and neck squamous cell carcinoma tissue and paracancer tissue of human. The data is from TCGA database; Fig. 2 is the comparison of the expression quantities of AQP2 gene in papillary cell renal carcinoma tissue and paracancer tissue of human. The data is from TCGA database; Fig. 3 is the comparison of the expression quantities of AQP2 gene in clear cell renal carcinoma tissue and paracancer tissue of human. The data is from TCGA database; Fig. 4 is the comparison of the expression quantities of AQP2 gene in chromophobe cell renal carcinoma tissue and paracancer tissue of human. The data is from TCGA database; Fig. 5 is the comparison of the expression quantities of AQP2 gene in prostate cancer tissue and paracancer tissue of human. The data is from TCGA database; Fig. 6 is the comparison of the expression quantities of AQP2 gene in three types of tumor cells and normal cells; Fig. 7 is the comparison of the AQP2 protein expression quantities of AQP2 gene in three types of tumor cells and normal cells; Fig. 8 is the map of a lentiviral overexpression vector of AQP2; Fig. 9 shows the effect of overexpression AQP2 on the expression quantities of AQP2 gene and protein in head and neck squamous cell carcinoma cells; Fig. 10 shows the effect of overexpression AQP2 on the expression quantities of AQP2 gene and protein in kidney cancer cells; Fig. 11 shows the effect of overexpression AQP2 on the expression quantities of AQP2 gene and protein in prostate cancer cells; Fig. 12 shows the effect of overexpression AQP2 on the proliferation ability of head and neck squamous cell carcinoma cells SCC4; Fig. 13 shows the effect of overexpression AQP2 on the proliferation ability of kidney cancer cells 786-O; Fig. 14 shows the effect of overexpression AQP2 on the proliferation ability of prostate cancer cells DU145. Fig. 15 shows the effect of overexpression AQP2 on the in vivo tumor growth of head and neck squamous cell carcinoma cells SCC4; Fig. 16 shows the effect of overexpression AQP2 on the in vivo tumor growth of kidney cancer cells 786-O; Fig. 17 shows the effect of overexpression AQP2 on the in vivo tumor growth of prostate cancer cells DU145. DETAILED DESCRIPTION The present invention will be further described below in conjunction with specific embodiments. Embodiment 1 Expression profile microarray analysis of AQP2 in different human tumor tissues and paracancer tissues The Cancer Genome Atlas (TCGA) Program was jointly initiated by the National Cancer Institute (NCI) and the National Human Genome Research Institute (NHGRI) of the United States in 2006. It applies genome analysis techniques based on large-scale sequencing to conduct large-scale experiments on 36 types of cancers. The Genome Characterization Center (GCC) of TCGA compares tumors and normal tissues to look for gene mutations, amplifications or deletions associated with each cancer or subtype to help understand the molecular mechanisms of cancer and improve scientific understanding of cancer pathogenesis at the molecular level. The whole gene expression profile data and clinical information of 36 tumors and their paracancer tissues were downloaded by the TCGA standard method, R language (3.1.1 version) software was used to filter away the tumor types not containing AQP2 expression information, and AP2 expression was detected in 20 types of tumors. Table 1. Analysis of expression levels of AQP2 in different tumors in TCGA database [Image disponible dans le document PDF, Image available in the PDF document] [Image disponible dans le document PDF, Image available in the PDF document] [Image disponible dans le document PDF, Image available in the PDF document] Graphpad Prism7 was used to carry out statistical analyses on the expression levels of AQP2 in 20 types of tumor tissues and corresponding paracancer tissues. All data underwent statistical t test, *<semantics>P<annotation encoding="application / x-tex">P< / annotation>< / semantics><0.05 means significant difference, and **<semantics>P<annotation encoding="application / x-tex">P< / annotation>< / semantics><0.01 means very significant difference. The specific analysis results are shown in Table 1. Compared with the corresponding paracancer tissues, AQP2 showed significant low expression in head and neck squamous cell carcinoma (Fig. 1), three renal carcinoma subtypes (papillary cell renal carcinoma, clear cell renal carcinoma, chromophobe renal carcinoma, Fig. 2 to Fig. 4) and prostate cancer (Fig. 5). Embodiment 2 In this embodiment, a fluorescent quantitative PCR method was used to detect the expression quantities of AQP2 in tumor cells and normal epithelial cells. 1. Materials Head and neck squamous cell carcinoma cells SCC4 and human normal oral epithelial cells HIOEC, kidney cancer cells 786-O and human renal epithelial cells HEK293T, prostate cancer cells DU145 and human normal prostate epithelial cells RWPE-1; the above cells were all purchased from U.S. ATCC Cell Repository. 2. Methods 2.1 Extraction of total RNA in tumor cells and normal epithelial cells After the foregoing six types of cells were cultured in a 37 DEG C 5% CO2 incubator until the density was 90%, they were digested and collected by trypsin, the cells were re-suspended in a culture solution and counted under a microscope, the concentration of the cells was adjusted to 5×105 cells / mL, and then the cell suspension after concentration adjustment was inoculated to 6- well plates, 2mL per well, and further cultured in the 37 DEG C 5% CO2 incubator for 24 h. Extraction of the total RNA in head and neck squamous cell carcinoma cells SCC4 and human normal oral epithelial cells HIOEC, kidney cancer cells 786-O and human renal epithelial cells HEK293T, prostate cancer cells DU145 and human normal prostate epithelial cells RWPE-1, respectively was carried out according to the TrizolTM manual of Life Technologies. The purity and concentration of the extracted RNA was quantified by the NanoDropTM ND-1000 nucleic acid quantifier, and the integrity of the extracted RNA was ensured through quality inspection by agarose. 2.2 Synthesis of first-strand cDNA by reverse transcription of RNA TaKaRa kit PrimeScriptTM RT kit with gDNA Eraser (Perfect Real Time) was used to reverse transcribe the extracted total RNA thereby synthesizing cDNA. This kit contains gDNAEraser DNase and can effectively remove mingled genomic DNA. 2.3 Real-time quantitative PCR Design specific primers according to the nucleotide sequences of AQP2 and GAPDH were used with the TaKaRa kit SYBR® Premix Ex TaqTM II (TliRNaseH Plus) to carry out the PCR reaction. The forward primer and reverse primer of AQP2 are SEQ ID NO. 3 and SEQ ID NO. 4, and the forward primer and reverse primer of GAPDH are SEQ ID NO. 5 and SEQ ID NO. 6. The reaction system is shown in the table below: Table 2. PCR reaction system [Image disponible dans le document PDF, Image available in the PDF document] After mixing the above components evenly, real-time quantitative PCR was carried out according to the following procedure: Initially denature at 95 DEG C for 30 s at 40 cycles; 95 DEG C for 5 s and 60 DEG C for 30 s. The specificity of the reaction was determined according to the melting curve and the mRNA expression quantity of AQP2 was calculated according to Formula 2-DDCt. The result is shown in Fig. 6. Compared with the normal human epithelial cells, the expression of AQP2 in head and neck squamous cell carcinoma cells SCC4, kidney cancer cells 786-O and prostate cancer cells DU145 were reduced significantly, consistent with the analysis results of clinical samples. Embodiment 3 In this embodiment, the Western blot method was used to detect the expression quantities of AQP2 protein in tumor cells and normal epithelial cells. Trypsin was used to digest and collect the six types of cells in Embodiment 2 when the growth density reached 90%. A culture solution was used to re-suspend the cells for multiplication culture, and then the cells were collected when the confluence was 80%. The mixture was centrifuged, the supernatant was discarded, and the pellet was rinsed with PBS twice. RIPA lysis buffer was added followed by lysis on ice for 20 min. Centrifugation at 12,000 g for 10 min allowed for collection of the supernatant. 1XSDS loading buffer was added, the sample was mixed well by pipetting, and then degenerated by boiling for 5 min. Total protein was separated by 10% SDS-PAGE gel, then transferred onto a PVDF membrane. The membrane was block with 5% BSA at room temperature for 2 h, then incubated with AQP2 antibody (abeam) overnight at 4 DEG C, before being washed with TBST 3 times. The membrane was then incubated with a secondary antibody at room temperature for 1 h and then washed with TBST three times. The Western blot was developed with an ECL supersensitive chemiluminescence solution, and the Tannon imaging system was used to form images with GAPDH used as an internal reference to compare the expression levels of AQP2 protein in different cells. The results are shown in Fig. 7 and are consistent with AQP2 mRNA expression differences. The expression quantities of AQP2 protein in head and neck squamous cell carcinoma cells SCC4, kidney cancer cells 786-O and prostate cancer cells DU145 were reduced significantly. Embodiment 4 In this embodiment, the preparation of AQP2 overexpression vector and the detection of virus transfection efficiency were conducted. Full-length cDNA for AQP2 was synthesized (see SEQ ID NO. 1 for the specific sequence) and introduced to plvx-CMV-ZsGreen 1 plasmid (see Fig. 8 for the atlas). Co-transfer of the above plasmid, the packaging plasmid psPAX2 and the envelope plasmid pMD2.G into 293T cells was performed to generate virus. After 48 hours of transfection, the viral supernatant of the cells was collected and used to infect SCC4 head and neck squamous cell carcinoma cells, 786-Okidney cancer cells and DU145 prostate cancer cells, respectively. After 48 hours of infection, cells were screen with puromycin for two weeks to obtain a cell line that stably promoted AQP2 gene expression. At that point, collection of the total RNA and total protein of the blank vectors and overexpression vectors of the three types of cells was carried out, so that the expression changes of AQP2 gene and protein could be compared by qPCR (the specific method is the same as that in Embodiment 2) and Western blot method (the specific method is the same as that in Embodiment 3). The results are shown in Fig. 9 to Fig. 11. Overexpression of AQP2 caused the expression quantities of AQP2 gene and protein in head and neck squamous cell carcinoma cells SCC4 (Fig. 9), kidney cancer cells 786-O (Fig. 10) and prostate cancer cells DU145 (Fig. 11) to increase significantly. Embodiment 5 This embodiment shows the effect of overexpression of AQP2 on the proliferation ability of human tumor cells. Trypsin was used to digest and collect head and neck squamous cell carcinoma cells SCC4, kidney cancer cells 786-O and prostate cancer cells DU145 after they had been stably transfected empty vectors and AQP2-overexpressed cells in a 37 DEG C 5% CO2 incubator until the density was 90%. At that point, cells were re-suspended in a culture solution, cells were then counted under a microscope, before adjusting the cell concentration to 3.0×104 cells / mL. The cell suspension was then inoculated to 96-well plates, 100µL per well, and cultured in a 37 DEG C 5% CO2 incubator for 24h, 48h and 72h, respectively. At that point, 20µL of 5 mg / mL MTT was added to each well of the 96-well plates, and culturing was continued for 4 h. The culture medium was aspirated away and 100 µL of DMSO was added for dissolution. ELIASA was used to detect absorbance at detection wavelength 570 nm and reference wavelength 630 nm to calculate proliferation inhibition (PI) according to the following formula: PI (%) =1- drug group / negative group The test was independently repeated three times. The results obtained from the test were expressed with mean±SD, a statistical t test was done, the comparison of two or more groups of data adopted One-way ANOVA, statistical significance was expressed with value <semantics>P<annotation encoding="application / x-tex">P< / annotation>< / semantics>, <semantics>P<0.05<annotation encoding="application / x-tex">P < 0.05< / annotation>< / semantics> means significant difference, and <semantics>P<0.01<annotation encoding="application / x-tex">P < 0.01< / annotation>< / semantics> means very significant difference. The results are shown in Fig. 12 to Fig. 14. Compared with empty vector cells (plvx-crtl), the proliferation speed of the cells with overexpression of AQP2 (plvx-AQP2) (head and neck squamous cell carcinoma cells SCC4 (Fig. 12), kidney cancer cells 786-O (Fig. 14) and prostate cancer cells DU145 (Fig. 15)) was obviously reduced. This indicates that overexpression of AQP2 can significantly inhibit the proliferation of head and neck squamous cell carcinoma cells SCC4, kidney cancer cells 786-O and prostate cancer cells DU145 and further verifies the importance of AQP2 as a cancer suppressor gene. Embodiment 6 This embodiment shows the effect of overexpression of AQP2 on the migration ability of human tumor cells. Head and neck squamous cell carcinoma cells SCC4, kidney cancer cells 786-O and prostate cancer cells DU145 were inoculated to transwell cells, 100 µL per well, after they stably transfected empty vectors and AQP2-overexpressed cells. 0.6 mL of complete medium containing 10% FBS was added to the transwell cells to stimulate cell migration, before culturing in 5% CO2 at 37 DEG C for 24 h. The medium in the wells was discarded, and cells were fixed with 90% alcohol at room temperature for 30 min, then stain with 0.1% crystal violet at room temperature for 10 min. The samples were rinsed with clear water, the non-migrated cells were gently wiped off the upper layer with a cotton swab, and cells were observed under a microscope. Four fields of view were selected to take pictures and count. The migration inhibition rate (MIR) was calculated according to the following formula: [Image disponible dans le document PDF, Image available in the PDF document] where Ntest is the number of migrated cells in the test group (plvx-AQP2) and Ncontrol is the number of migrated cells in the blank control group (plvx-ctrl). The test was independently repeated three times. The results obtained from the test were expressed with mean±SD, statistical t test was done, the comparison of two or more groups of data adopted One-way ANOVA, statistical significance was expressed with value <semantics>P<annotation encoding="application / x-tex">P< / annotation>< / semantics>, <semantics>P<0.05<annotation encoding="application / x-tex">P < 0.05< / annotation>< / semantics> means significant difference, and <semantics>P<0.01<annotation encoding="application / x-tex">P < 0.01< / annotation>< / semantics> means very significant difference. Table 3 Inhibitory effect of overexpression of AQP2 on the migration ability of human tumor cells [Image disponible dans le document PDF, Image available in the PDF document] In the table: * means <semantics>P<0.05<annotation encoding="application / x-tex">P<0.05< / annotation>< / semantics>, **means <semantics>P<0.01<annotation encoding="application / x-tex">P<0.01< / annotation>< / semantics>. The results are as shown in Table 3. After AQP2 expression was upregulated, the migration abilities of head and neck squamous cell carcinoma cells SCC4, kidney cancer cells 786-O and prostate cancer cells DU145 were obviously reduced. Embodiment 7 This embodiment shows the effect of overexpression of AQP2 on the in vivo growth of human tumor cells. Cultured head and neck squamous cell carcinoma cells SCC4, kidney cancer cells 786-O and prostate cancer cells DU145 after they stably transfected empty vectors and AQP2-overexpressed cells, and digested with a 0.25% pancreatin solution. The cell suspension was centrifuged at 1,000 rpm for 5 min after termination of digestion, and then cells were re-suspend in a serum-free DMEM culture medium, before counting the cells and adjusting cell concentration to <semantics>5×107<annotation encoding="application / x-tex">5\times10^7< / annotation>< / semantics> cells / ml; (2) Each nude mouse (female mice at the age of 4-6 weeks and with a weight of 14-16 g were ordered and adaptively reared for 1 week in an SPF animal breeding room) was inoculated with 100 µl of the cell suspension of the corresponding group in the left armpit, and the number of cells injected was <semantics>5×106<annotation encoding="application / x-tex">5 \times 10^6< / annotation>< / semantics>; (3) After inoculation, the tumor growth at the inoculation sites of nude mice was closely observed. The volume of the transplanted tumor was measured and recorded every two days. The calculation formula of tumor volume (TV) is shown below: [Image disponible dans le document PDF, Image available in the PDF document] where, a is the length of the transplanted tumor (mm), and b is the width of the transplanted tumor (mm). Compared with the empty vector control group (plvx-ctrl), the cells with overexpression of AQP2 (plvx-AQP2) (head and neck squamous cell carcinoma cells SCC4 (Fig. 15), kidney cancer cells 786-O (Fig. 16) and prostate cancer cells DU145 (Fig. 17)) showed a lower tumor growth rate and obviously reduced in-vivo tumorigenicity in nude mice, indicating that overexpression of AQP2 can inhibit the in vivo growth ability of malignant tumor cells.

Claims

1. Use of a transmembrane protein as a tumor marker, wherein the transmembrane protein is AQUAPORIN 2, and its amino acid sequence is set forth in SEQ ID NO.2 and wherein the tumor is head and neck squamous cell carcinoma or kidney cancer.

2. A method for detecting a tumor marker, wherein the tumor is head and neck squamous cell carcinoma or kidney cancer and the detection method is any of a and b: (a) detecting gene expression of transmembrane protein AQUAPORIN 2 in tissue or cells by a PCR method; (b) detecting gene expression of transmembrane protein AQUAPORIN 2 in tissue or cells by a Western blot method.

3. The detection method according to claim 2, wherein the PCR method includes a specific primer pair designed for SEQ ID NO. 1 sequence.

4. The detection method according to claim 3, wherein the specific primer pair includes SEQ ID NO. 3 and SEQ ID NO. 4.