Despite longstanding interest by nephrologists and physiologists, the molecular identities of membrane water channels remained elusive until recognition of CHIP, a 28-kDa channel-forming integral membrane protein from human red blood cells originally referred to as "CHIP28." CHIP functions as an osmotically driven, water-selective pore; 1) expression of CHIP conferred Xenopus oocytes with markedly increased osmotic water permeability but did not allow transmembrane passage of ions or other small molecules; 2) reconstitution of highly purified CHIP into proteoliposomes permitted determination of the unit water permeability, i.e., 3.9 x 10(9) water molecules.channel subunit-1 x s-1. Although CHIP exists as a homotetramer in the native red blood cell membrane, site-directed mutagenesis studies suggested that each subunit contains an individually functional pore that may be reversibly occluded by mercurial inhibitors reacting with cysteine-189. CHIP is a major component of both apical and basolateral membranes of water-permeable segments of the nephron, where it facilitates transcellular water flow during reabsorption of glomerular filtrate. CHIP is also abundant in certain other absorptive or secretory epithelia, including choroid plexus, ciliary body of the eye, hepatobiliary ductules, gall bladder, and capillary endothelia. Distinct patterns of CHIP expression occur at these sites during fetal development and maturity. Similar proteins from other mammalian tissues and plants were later shown to transport water, and the group is now referred to as the "aquaporins." Recognition of CHIP has provided molecular insight into the biological phenomenon of osmotic water movement, and it is hoped that pharmacological modulation of CHIP function may provide novel treatments of renal failure and other clinical problems.

Purpose: To evaluate aberrant promoter hypermethylation of candidate tumor suppressor genes as a means to detect epigenetic alterations specific to solid tumors, including head and neck squamous cell carcinoma (HNSCC). Experimental Design: Using promoter regions identified via a candidate gene and discovery approach, we evaluated the ability of an expanded panel of CpG-rich promoters known to be differentiallyhypermethylatedin HNSCCindetectionof promoterhypermethylationin serum and salivary rinses associated with HNSCC.We did preliminary evaluation via quantitative methylation-specific PCR (Q-MSP) using a panel of 21genes in a limited cohort of patients with HNSCC and normal controls. Using sensitivity and specificity for individual markers as criteria, we selected panels of eight and six genes, respectively, for use in salivary rinse and serum detection and tested these in an expanded cohort including up to 211patients with HNSCC and 527 normal controls. Results: Marker panels in salivary rinses showed improved detection when compared with single markers, including a panel with 35% sensitivity and 90% specificity and a panel with 85% sensitivity and 30% specificity. A similar pattern was noted in serum panels, including a panel with 84.5% specificity with 50.0% sensitivity and a panel with sensitivity of 81.0% with specificity of 43.5%.We also noted that serum and salivary rinse compartments showed a differential pattern of methylation in normal subjects that influenced the utility of individual markers. Conclusions: Q-MSP detection of HNSCC in serum and salivary rinses using multiple targets offers improved performance when compared with single markers. Compartment-specific methylation in normal subjects affects the utility of Q-MSP detection strategies.

Aquaporins (AQPs) are important in controlling water permeability. As AQP1 is known as a serum-responsive gene, we hypothesized that AQP expression may be involved in the development of human cancer. By reverse transcriptase-polymerase chain reaction analysis, expression of AQPs 1, 3, and 5 was found in seven colon and colorectal cancer cell lines. Western blot analysis confirmed their expression in four of these cell lines. In situ hybridization demonstrated that during colorectal carcinogenesis, the expression of AQPs 1 and 5 was induced in early-stage disease (early dysplasia) and maintained through the late stages of colon cancer development. Expression of AQPs 1 and 5 was maintained even in metastatic lesions in the liver. These findings demonstrate that the expression of several AQPs is found in tumor cells and is associated with an early stage of colorectal cancer development. These novel observations suggest that multiple AQP expression may be advantageous to tumorigenesis, which may lead to a better understanding of colorectal carcinogenesis.

Promoter hypermethylation accompanied by gene silencing is a common feature of human cancers. We identified previously several new tumor suppressor genes based on pharmacologic unmasking of the promoter region and detection of reexpression on microarray analysis. In this study, we modified the selection of candidates from our previous microarray data by excluding genes that showed basal expression in cancer cell lines. With the new method, we found novel methylated genes with 90% accuracy. Among these 33 novel methylated genes that we identified in esophageal squamous cell carcinoma (ESCC) cell lines, N-methyl-D-aspartate receptor type 2B (NMDAR2B) was of particular interest. NMDAR2B was methylated in 95% of primary human ESCC tissue specimens and 12 ESCC cell lines by sequence analysis. NMDAR2B expression was silenced in all 12 ESCC cell lines and was reactivated by the demethylating agent 5-aza-2V-deoxycytidine. Moreover, reintroduction of the gene was accompanied by marked Ca 2+ -independent apoptosis in ESCC cell lines, suggesting that NMDAR2B can suppress tumor growth. Thus, NMDAR2B promoter methylation is common in ESCC, abrogating gene transcription and leading to cellular resistance to apoptosis.

The aquaporins represent a family of transmembrane water channel proteins that play a major role in trans-cellular and transepithelial water movement. Most tumors have been shown to exhibit high vascular permeability and interstitial fluid pressure, but the transport pathways for water within tumors remain unknown. Here, we tested 10 non-small cell lung cancer cell lines of various origins by reverse transcriptase-polymerase chain reaction and Western blot analysis and identified clear expression of aquaporin 1 (AQP1) in seven cell lines. We next examined the distribution of the AQP1 protein in several types of primary lung tumors (16 squamous cell carcinomas, 21 adenocarcinomas, and 7 bronchoalveolar carcinomas) by immunohistochemical staining. AQP1 was overexpressed in 62% (13 of 21) and 75% (6 of 8) of adenocarcinoma and bronchoalveolar carcinoma, respectively, whereas all cases of squamous cell carcinoma and normal lung tissue were negative. Forced expression of full-length AQP1 cDNA in NIH-3T3 cells induced many phenotypic changes characteristic of transformation, including cell proliferation-enhancing activity by the MTT assay and anchorage-independent growth in soft agar. Although further details on the molecular function of AQP1 related to tumorigenesis remain to be elucidated, our results suggest a potential role of AQP1 as a novel therapeutic target for the management of lung cancer.

The aquaporins (AQP) are water channel proteins playing a major role in transcellular and transepithelial water movement. Recently, the role of AQPs in human carcinogenesis has become an area of great interest. Here, by immunohistochemistry (IHC), we have found an expression of AQP5 protein in 35.3% (IHC-score: ≥1, 144/408) of the resected NSCLC tissue samples. Cases with AQP5-positive status (IHC-score: ≥2) displayed a higher rate of tumor recurrence than negative ones in NSCLC (54.7% vs. 35.1%, p = 0.005) and worse disease-free survival (p = 0.033; OR = 1.52; 95%CI:1.04−2.23). Further in vitro invasion assay using BEAS-2B and NIH3T3 cells stably transfected with overexpression constructs for full length wild-type AQP5 (AQP5) and its two mutants, N185D which blocks membrane trafficking and S156A which blocks phosphorylation on Ser156, showed that AQP5 induced cell invasions while both mutants did not. In BEAS-2B cells, the expression of AQP5 caused a spindle-like and fibroblastic morphologic change and losses of cell-cell contacts and cell polarity. Only cells with AQP5, not either of two mutants, exhibited a loss of epithelial cell markers and a gain of mesenchymal cell markers. In a human SH3-domains protein array, cellular extracts from BEAS-2B with AQP5 showed a robust binding activity to SH3-domains of the c-Src, Lyn, and Grap2 C-terminal. Furthermore, in immunoprecipitation assay, activated c-Src, phosphorylated on Tyr416, showed a stronger binding activity to cellular extracts from BEAS-2B with AQP5 compared with N185D or S156A mutant. Fluorescence in situ hybridization (FISH) analysis failed to show evidence of genomic amplification, suggesting AQP5 expression as a secondary event. Based on these clinical and molecular observations, we conclude that AQP5, through its phosphorylation on Ser156 and subsequent interaction with c-Src, plays an important role in NSCLC invasion and, therefore, may provide a unique opportunity for developing a novel therapeutic target as well as a prognostic marker in NSCLC.

While overexpression of several aquaporins (AQPs) has been reported in different types of human cancer, the role of AQPs in carcinogenesis has not been clearly defined. Here, by immunochemistry, we have found expression of AQP5 protein in 62.8% (59/94) of resected colon cancer tissue samples as well as association of AQP5 with liver metastasis. We then demonstrated that overexpression of human AQP5 (hAQP5) induces cell proliferation in colon cancer cells. Overexpression of wild-type hAQP5 increased proliferation and phosphorylation of extracellular signal-regulated kinase-1/2 in HCT116 colon cancer cells whereas these phenomena in hAQP5 mutants (N185D and S156A) were diminished, indicating that both membrane association and serine/threonine phosphorylation of AQP5 are required for proper function. Interestingly, overexpression of AQP1 and AQP3 showed no differences in extracellular signal-regulated kinase-1/2 phosphorylation, suggesting that AQP5, unlike AQP1, may be involved in signal transduction. Moreover, hAQP5-overexpressing cells showed an increase in retinoblastoma protein phosphorylation through the formation of a nuclear complex with cyclin D1 and CDK4. Small interfering RNA analysis confirmed that hAQP5 activates the Ras signaling pathway. These data not only describe the induction of hAQP5 expression during colorectal carcinogenesis but also provide a molecular mechanism for colon cancer development through the interaction of hAQP5 with the Ras/extracellular signal-regulated kinase/retinoblastoma protein signaling pathway, identifying hAQP5 as a novel therapeutic target.

Purpose: Aberrant promoter hypermethylation of several known or putative tumor suppressor genes occurs frequently during the pathogenesis of lung cancers and is a promising marker for cancer detection. We investigated the feasibility of detecting aberrant DNA methylation in the bronchoalveolar lavage (BAL) samples of lung cancer patients.Experimental Design: We examined the tumor and the matched BAL DNA for aberrant methylation of eight gene promoters (CDH1, APC, MGMT, RASSF1A, GSTP1, p16, RAR-␤2, and ARF) from 31 patients with primary lung tumors by quantitative fluorogenic real-time PCR. BAL from 10 age-matched noncancer patients was used as a control.Results: Promoter hypermethylation of at least one of the genes studied was detected in all 31 lung primary tumors; 27 (87%) CDH1, 17 (55%) APC, 14 (45%) RASSF1A, 12 (39%) MGMT, 7 (23%) p16, 3 (10%) GSTP1, 3 (10%) RAR-␤2, and 0 (0%) ARF. Methylation was detected in CDH1 (48%), APC (29%), RASSF1A (29%), MGMT (58%), p16 (14%), GSTP1 (33%), RAR-␤2 (0%), and ARF (0%) of BAL samples from matched methylation-positive primary tumors, and in every case, aberrant methylation in BAL DNA was accompanied by methylation in the matched tumor samples. BAL samples from 10 controls without evidence of cancer revealed no methylation of the MGMT, GSTP1, p16, ARF, or RAR-␤2 genes whereas methylation of RASSF1, CDH1, and APC was detected at low levels. Overall, 21 (68%) of 31 BAL samples from cancer patients were positive for aberrant methylation.Conclusion: Our findings suggest that promoter hypermethylation in BAL can be detected in the majority of lung cancer patients. This approach needs to be evaluated in large early detection and surveillance studies of lung cancer.