Nuclear factor-kappaB-dependent expression of metastasis suppressor KAI1/CD82 gene in lung cancer cell lines expressing mutant p53

KAI1/CD82 has been shown to be a metastasis suppressor for several human cancers, and a recent study revealed that wild-type tumor suppressor p53 can directly activate KAI1/CD82 gene expression. However, the response of KAI1/CD82 expression in cancer cells to exogenous stimulants has not been investigated. The present study examined whether tumor necrosis factor (TNF), which mediates many of the cellular responses associated with inflammatory reactions or cancer progression, can affect the KAI1/CD82 expression in lung cancer cells and, if so, whether nuclear factor (NF)-kappaB, a key molecule in TNF-mediated gene expression, is involved in the mechanism of KAI1/CD82 induction. Our results demonstrated that expression of KAI1/CD82 in PC-14 cells expressing mutant p53 could be augmented by TNF-alpha, and that transfer of the gene for a specific inhibitor of NF-kappaB, IkappaB alphaSR (mutant IkappaB alpha; NF-kappaB super-repressor), into PC-14 cells could inhibit this augmentation. The amount of NF-kappaB in the nucleus of PC-14/IkappaB alphaSR cells correlated well with KAI1/CD82 mRNA and protein expression. In addition, IkappaB alphaSR gene transfer inhibited the spontaneous expression of KAI1/CD82 protein in KAI1/CD82-high-expressing RERF-LC-OK cells, which contain a mutant-type p53. These observations indicate that NF-kappaB activation may play a role in the regulation of KAI1/CD82 expression in lung cancer cells independently of wild-type p53, and suggest that KAI1/CD82 expression may be regulated by interaction with the host microenvironment.     

KAI1/CD82的表达与乳腺癌转移、预后的关系

目的探讨KAI1/CD82在乳腺癌进展中的作用及其在预后判断中的价值。方法采用免疫组化方法对60例有临床和随访资料的乳腺癌组织进行KAI1/CD82蛋白表达的研究。以15例良性乳腺瘤,15例正常乳腺组织作对照,分析与临床病理指标的关系。结果在乳腺癌原发灶中KAI1/CD82阳性表达41．66%,较正常乳腺组织（80%）、良性乳腺瘤（73．33%）明显减少（P＜0．01、P＜0．05）。KAI1/CD82在有淋巴结转移、周围组织侵润、远处脏器转移肿瘤中表达显著降低（P＜0．01、P＜0．05、P＜0．05）,生存5年以上者的KAI1/CD82蛋白阳性表达率59．38%,明显高于生存时间不超过5年者21．43%（P＜0．01）。患者的术后复发情况与KAI1/CD82表达无关。结论KAI1/CD82的异常表达可能参与了乳腺癌的恶性进展。检测KAI1/CD82的表达对判断肿瘤的侵袭、转移及乳腺癌患者预后有一定的参考价值。     

KAI1/CD82在原发性乳腺癌中的表达及其临床意义

目的:探讨KAI1/CD82在乳腺癌中的表达及其临床意义。方法:采用RT-PCR和免疫组化方法对69例原发性乳腺癌组织、癌旁组织和区域淋巴结组织中KAI1 mRNA和CD82蛋白的表达进行研究。结果:在69例原发性乳腺癌中,癌旁组织中KAI1基因在区域淋巴结转移阴性组和区域淋巴结转移阳性组的mRNA表达无显著性差异(P>0.05)。癌组织和区域淋巴结组织中KAI1基因在区域淋巴结转移阴性组和区域淋巴结转移阳性组的mRNA表达有显著差异(P<0.05)。CD82表达与临床病理类型以及PR表达无相关性(P>0.05),而与临床分期、组织学分级、区域淋巴结转移、远处转移、ER表达有相关性(P<0.05)。结论:KAI1/CD82的表达与乳腺癌的转移及某些临床病理因素有关,具有一定的临床指导意义。     

An alternatively spliced KAI1 mRNA is expressed at low levels in human bladder cancers and bladder cancer cell lines and is not associated with invasive behaviour

Levels of the KAI1 metastasis suppressor are reduced in advanced stages of many human cancers, leading to the loss of KAI1 function. A recent study has suggested that the loss of KAI1 function may also occur via alternative splicing of KAI1 mRNA which deletes an exon encoding a critical 28 amino acids from the protein. Using PCR, 20 bladder tumours at differing stage and grade, a non-tumourigenic urothelial cell line (SV-HUC-1) and 17 bladder cancer cell lines were examined for expression of this alternatively spliced (AS) KAI1 mRNA. Full-length KAI1 mRNA was present in all tumour samples and low levels of AS KAI1 mRNA in 15/20 samples. There was no association between the presence or absence of AS mRNA and clinicopathological characteristics of these tumours. Low levels of AS KAI1 mRNA were present in SV-HUC-1 and 14/17 bladder cancer cell lines. There was no association between the presence or absence of AS KAI1 mRNA and tumourigenicity, or in vivo invasive abilities of these cell lines. In all cell lines expressing AS KAI1 mRNA, levels were 3- to 5-fold lower than levels of wild-type mRNA, irrespective of wild-type mRNA levels. Low levels of an alternatively spliced form of KAI1 mRNA are present in most bladder cancer tumours and tumour cell lines, but are not associated with invasive behaviour.     

KAI1/CD82和E-cadherin在子宫内膜癌的表达

[目的]研究KAI1/CD82与E-cadherin在子宫内膜癌组织中的表达及其与临床病理参数的关系。[方法]采用免疫组织化学EnVision二步法检测76例子宫内膜癌,15例非典型增生子宫内膜和20例正常增生期子宫内膜组织中KAI1/CD82、E-cadherin的表达。[结果]KAI1/CD82在正常增生期子宫内膜、非典型增生内膜、子宫内膜癌的阳性表达率分别为95%、93.3%和60.5%;E-cadherin在正常增生期子宫内膜、非典型增生内膜、子宫内膜癌的异常表达率分别为0、6.67%和55.26%。KAI1/CD82在子宫内膜癌的表达与组织学分级、肌层浸润程度呈负相关(P=0.000,P=0.01)。E-cadherin在子宫内膜癌的表达与组织学分级及组织学类型有关。KAI1/CD82与E-cadherin在子宫内膜癌中的表达呈显著性相关(P<0.01)。[结论]KAI1/CD82表达下调和E-cadherin异常表达增高与子宫内膜癌的进展有关。     

KAI1/CD82 protein expression in primary prostate cancer and in BPH associated with cancer

Current prognostic methods in primary prostate cancer cannot accurately identify patients with clinically significant disease at highest risk of developing metastases. This study examined KAI1/CD82 metastasis suppressor expression by quantitative immunohistochemical analysis of benign prostatic hyperplasia (BPH) and prostate cancer specimens. Altogether, prostate cancers exhibited significant KAI1 overexpression compared to BPH not associated with cancer (P = 0.022). Increased KAI1 expression in well and moderately differentiated cancers, above levels seen in BPH, with decreased expression in poorly differentiated cancers was observed. Interestingly, KAI1 expression in BPH associated with cancers was significantly higher than in BPH not associated with cancer (P = 0.009). Thus, KAI1 overexpression may restrain onset and early stage prostate cancer development, whilst its loss may predispose the patient to more aggressive cancer behaviour. Altered KAI1 expression in prostate cancers and BPH associated with cancer may have important diagnostic roles.     

KAI1/CD82在神经母细胞瘤组织中的表达及其与预后的关系

背景与目的KAI1/CD82是近年来发现的肿瘤转移抑制基因,它的失活与某些肿瘤的进展和浸润有关。本研究旨在通过检测KAI1/CD82蛋白在神经母细胞瘤中的表达,探讨其与神经母细胞瘤临床病理特征和预后的关系。方法用免疫组化EnVision法检测90例神经母细胞瘤瘤组织中KAI1/CD82蛋白的表达,结合临床资料与随访资料进行统计学分析。结果39.3%(11/28)节细胞神经母细胞瘤KAI1/CD82呈阳性表达,14.5%(9/62)神经母细胞瘤KAI1/CD82呈阳性表达(P=0.014)。KAI1/CD82的表达与神经母细胞瘤的分化程度呈显著性正相关,且KAI1/CD82的表达与临床分期呈显著性负相关(P=0.003)。结论KAI1/CD82表达的改变是神经母细胞瘤发生的早期事件,其表达下调是神经母细胞瘤分化和转移的一个潜在标志。此标记物可能作为临床评估预后的综合指标之一。     

Expression of KAI1/CD82 in distant metastases from estrogen receptor-negative breast cancer

The tetraspanin protein superfamily member KAI1 suppresses tumor growth and metastasis in animal models and is downregulated in various human malignancies. In breast cancer, KAI1 is preferentially lost in estrogen receptor (ER)-positive tumors. Interestingly, most ER-negative primary breast cancers retain KAI1 expression. This study aimed to evaluate whether or not KAI1 is downregulated during progression to metastasis of these carcinomas. Expression of KAI1, ER, progesterone receptor, c-ErbB2, and Ki67 was analyzed in tissue microarrays comprising a large collection of distant organ metastases from human breast cancers ( n  = 92) by immunohistochemistry. Results were compared with a previously characterized set of primary breast tumors ( n  = 209). Immunoreactivity for KAI1 was observed in one-third of the metastases and was associated with lack of ER expression ( P  = 0.005). The high frequency of KAI1-positive cases in ER-negative primary tumors was maintained in ER-negative metastases. Expression of KAI1 was also observed in MDA-MB-468 and SK-BR-3, two ER-negative breast cancer cell lines of metastatic origin. Moreover, a reanalysis of independent microarray gene expression data indicated maintenance of KAI1 mRNA expression in metastases from ER-negative breast cancers. Furthermore, in a series of matched pairs of mammary carcinomas and metachronous distant metastases, all metastases from KAI1-positive/ER-negative primary tumors were KAI1-positive as well. Collectively, these findings demonstrate that the expression of KAI1 is maintained during progression to metastasis in a large proportion of ER-negative mammary carcinomas. This has significant implications for the use of KAI1 as a clinical marker and the understanding of the metastatic process in human breast cancer. ( Cancer Sci 2009; 100: 1767–1771)     

KAI1 COOH-terminal interacting tetraspanin (KITENIN), a member of the tetraspanin family, interacts with KAI1, a tumor metastasis suppressor, and enhances metastasis of cancer

We cloned recently an alternatively spliced variant of KAI1 mRNA that lacked exon 7 at the COOH-terminal region and showed differences in metastasis suppression when compared with the wild-type KAI1. These findings indicated that the COOH-terminal region of KAI1 is critical for its metastasis suppressor function. In this study, we isolated a cDNA clone of VANGL1, a member of the tetraspanin protein family, which interacted specifically with the COOH-terminal cytoplasmic domain of KAI1 in the yeast two-hybrid system. We renamed it KAI1 COOH-terminal interacting tetraspanin (KITENIN). We found that KITENIN-overexpressing CT-26 mouse colon cancer cells showed increased tumorigenicity and early hepatic metastasis in vivo, as well as increased invasiveness and adhesion to fibronectin in vitro compared with parental cells. Moreover, increased levels of KITENIN were observed in a human gastric tumor and its metastatic tissues, compared with the normal adjacent mucosa. Our results indicate that KITENIN promotes adhesion and invasion of cancer cells in vitro and in vivo, and suggest that KITENIN participates in the regulation of the tumor formation and metastasis by interacting with KAI1, a metastasis suppressor and antisense KITENIN strategy that can be used to inhibit metastasis in various cancers.     

胃腺癌组织中KAI1/CD82蛋白的表达及其意义

目的 探讨KAI1／CD82蛋白在胃腺癌组织中表达及其与胃癌生物学行为的关系。方法应用免疫组织化学技术S-P法检测68例胃腺癌组织中KAI1／CD82蛋白的表达，以20例非肿瘤性胃黏膜组织作对照。对随访14个月～13年的35例做生存分析。结果 68例胃腺癌组织KAI1／CD82蛋白阳性表达率为26、5％（18／68），对照组胃黏膜组织阳性表达率95．0％（19／20）；高／中分化胃腺癌KAI1／CD82蛋白阳性表达率较低分化者为高，分别为41．4％（12／29）、15．4％（6／39），P〈0．05；无淋巴结转移胃腺癌的KAI1／CD82蛋白阳性表达率较有淋巴结转移者为高，分别为45.5％（10／22）、5.3％（8／46），P〈0.05；侵及黏膜及黏膜下层、肌层和浆膜层胃腺癌KAI1／CD82蛋白阳性表达率分别为66、7％（4／6）、34.8％（8／23）、15.4％（6／39），P〈0.05。KAI1／CD82蛋白在Ⅰ～Ⅱ期胃腺癌阳性表达率为37.0％（17／46），在Ⅲ～Ⅳ期胃腺癌中阳性表达率为13.6％（1／22），P〈0.05。KAI1／CD82蛋白阳性患者术后1、3、5、7、10年生存率分别为100.0％（7／7）、85.7％（6／7）、57.1％（4／7）、42.9％（3／7）和28．6％（2／7），而KAI1／CD82阴性患者术后生存率分别为89、3％（25／28）、42、9％（12／28）、14．3％（14／28）、7．1％（2／28）和3、6％（1／28）。KAI1／CD82蛋白阳性患者术后1、3、5、7和10年生存率比KAI1／CD82阴性患者术后1、3、5、7和10年生存率显著提高，P〈0．05。结论 KAI1／CD82蛋白在胃腺癌的表达与肿瘤浸润深度、分化程度、临床分期及淋巴结转移有关，与患者性别、年龄无关。检测KAI1／CD82蛋白有助于临床评估病情，判断预后。     

KAI1/CD82的表达与大肠腺癌的相关性分析

目的　初探KAI1/CD82在大肠腺癌组织中的表达。方法　采用免疫组织化学方法 (S -P法 ) ,对 2 41例大肠腺癌组织中KAI1/CD82的表达水平进行半定量研究 ,并探讨其与 2 41例大肠腺癌病理学分级及转移、浸润的相关性。结果　大肠腺癌组织中KAI1/CD82的表达与病理学分级、浸润深度、淋巴结及血道转移呈负相关 (P <0 0 1)。结论　大肠腺癌组织中KAI1/CD82的表达可作为评估肿瘤细胞的转移潜能的一个指标。     

Adenoviral transduction of MRP-1/CD9 and KAI1/CD82 inhibits lymph node metastasis in orthotopic lung cancer model

Conventional therapies still remain less effective for metastasis of lung cancer, thus leading to a poor prognosis for this disorder. Although the processes involved in metastasis have not yet been clearly elucidated, our previous studies have shown that higher expression levels of MRP-1/CD9 and KAI1/CD82 in cancer cells are significantly correlated with less metastatic potency. To determine whether the gene transfer of these tetraspanins into lung tumor cells may be a useful strategy to regulate metastasis, we adopted an orthotopic lung cancer model produced by the intrapulmonary implantation of Lewis lung carcinoma (LLC) cells and evaluated the metastatic growth in the mediastinal lymph nodes using two different methods of gene delivery as follows: (a) the implantation of LLC cells preinfected with adenovirus encoding either MRP-1/CD9 cDNA, KAI1/CD82 cDNA, or LacZ gene into the mouse lung and (b) the intratracheal administration of these adenoviruses into the mice orthotopically preimplanted with LLC cells. In both cases, we found that the delivery of either MRP-1/CD9 or KAI1/CD82 cDNA dramatically reduced the metastases to the mediastinal lymph nodes in comparison with those of LacZ gene delivery, without affecting the primary tumor growth at the implanted site. These results reemphasize the important role of MRP-1/CD9 and KAI1/CD82 in the suppression of the metastatic process and also show the feasibility of gene therapy when using these tetraspanins for lung cancer to prevent metastasis to the regional lymph nodes. This strategy may therefore be clinically applicable as a prophylactic treatment to suppress the occurrence of lymph node metastasis.     

Motility-related protein (MRP-1/CD9) and KAI1/CD82 expression inversely correlate with lymph node metastasis in oesophageal squamous cell carcinoma

Although the mechanisms of action of the transmembrane superfamilies, motility-related protein-1 (MRP-1/CD9) and KAI1/CD82, are not well known, they are reported to suppress the metastasis of several kinds of cancers. The suppression of cell motility by MRP-1/CD9 may cause suppression of the metastasis. As we could not find any reports concerning the expression of MRP-1/CD9 and KAI1/CD82 in oesophageal cancers we investigated their expression in oesophageal specimens. We conducted immunohistochemical staining for MRP1/CD9 against 108 cases of oesophageal squamous cell carcinoma using anti-MRP-1/CD9 monoclonal antibody M31-15, and for KAI1/CD82 against 104 cases using anti-KAI1/CD82 monoclonal antibody C33. To investigate the gradual expression of MRP-1/CD9 and KAI1/CD82, 24 oesophageal dysplasias were immunohistochemically stained using the same method and then investigated. The expression of both MRP-1/CD9 and KAI1/CD82 were positive on the cell membranes of normal oesophageal epithelial cells, but reduced or negative in the cancer cells. Reduced MRP-1/CD9 expressions significantly correlated to tumour depth (P = 0.0009). We found a significantly greater number of reduced or negative expression of MRP-1/CD9 and KAI1/CD82 in lymph node metastatic cases (P = 0.0003 and P= 0.0129, respectively), but not in distant metastatic cases. The 5-year survival rate of MRP-1/CD9-negative and reduced patients was significantly worse than those of positive patients (n = 108, curative cases, RO). Few cases remained KAI1/CD82-positive (9.6%; 10/104) in oesophageal cancer. Twenty (83.3%) and twenty-two (91.7%) cases out of 24 dysplasias were defined as KAI1/CD82-positive and MRP1/CD9-positive, respectively. The decrease in MRP-1/CD9 and KAI1/CD82 expression may facilitate lymph node metastasis in oesophageal squamous cell carcinomas. Knowing the status of the expression of MRP-1/CD9 appears helpful in predicting the prognosis for each patient.     

KAI1/CD82 expression as a prognosic factor in sporadic colorectal cancer

BACKGROUND: Since its identification as a suppressor gene for prostate cancer metastasis, down-regulation of KAI1/CD82 in a variety of malignancies has been reported. MATERIALS AND METHODS: Using immunohistochemistry, we examined KAI1/CD82 expression in surgical specimens obtained from 70 patients with advanced colorectal cancer and its correlation with clinicopathological factors, to clarify their prognostic significance. RESULTS: KAI1/CD82 expression was positive in 55% of the 70 colorectal cancers. There were statistically significant correlations between KAI1/CD82 expression and Dukes' stage, venous invasion, lymph node metastasis, tumor differentiation and liver metastasis. The significant correlation between KAI1/CD82 expression and outcome among patients with Dukes' C cancer (p=0.024) is particularly noteworthy. On multivariate analysis, KAI1/CD82 expression and Dukes' stage were identified as significant and independent prognostic factors (p=0.006 and 0.045, respectively). CONCLUSION: KAI1/CD82 expression closely correlates with clinicopathological factors for colorectal cancers. KAI1/CD82 expression appears to be a useful prognostic marker.     

MRP-1/CD9 and KAI1/CD82 expression in normal and various cancer tissues

As part of our evaluation of MRP-1/CD9 and KAI1/CD82 as prognostic predictors among patients with cancer, we have extended our studies to solid tumors of a variety of anatomical sites. Normal tissues were included for comparison. Immunohistochemical techniques were used throughout. Our results indicate that MRP-1/CD9 was strongly expressed by many normal tissues, including the epithelium of the gastrointestinal tract, alveolar epithelium of the lung, urothelium and smooth muscle. Expression was weak in the pituitary gland, spleen and hepatocytes, and absent in testes and spinal cord. KAI1/CD82 was also expressed by many normal tissues, but was absent in some MRP-1/CD9-positive tissues (e.g., smooth muscle, adrenal cortex, urothelium, myelin of peripheral nerves, epithelium of amnion). On the other hand, KAI1/CD82 was strongly expressed in spinal cord gray matter, which was MRP-1/CD9-negative. Expression of these glycoproteins was detected in almost all types of tumors examined. In certain cancers, MRP-1/CD9 and KAI1/CD82 positivity was inversely related to lymph node involvement. Whereas lymph node metastases were present in 22.2% of lung cancer patients whose tumors were MRP-1/CD9 and KAI1/CD82-positive, 65.5% of patients with MRP-1/CD9 and KAI1/CD82-reduced/negative tumors had lymph node metastases. A similar inverse relationship was seen in colon cancer and breast cancer patients with respect to MRP-1/CD9 expression. The present data, together with our previous results suggest that evaluating the MRP1/CD9 and KAI1/CD82 status of cancers of the lung, breast and colon may provide useful information on the metastatic potential of the tumors.     

CD82/KAI1基因蛋白在62例胃癌中的表达

[目的]探讨胃癌组织中抑癌基因CD82/KAI1蛋白的表达与胃癌临床生物学行为及预后的关系。[方法]采用免疫组织化学方法检测62例胃癌原发灶、阴性组织切缘中CD82/KAI1基因蛋白产物的表达。[结果]胃癌组织中KAI1蛋白阳性表达率为72.5%,显著低于阴性组织切缘的95.2%（P〈0.01）。KAI1蛋白在浸润深度的T3＋T4组（65.1%）较T1＋T2组（89.5%）;低分化组（20.5%）较高、中分化组（88.9%）;淋巴结转移组（59.1%）较无淋巴结转移组（94.4%）;TNM分期中的Ⅲ～Ⅳ期组（63.4%）较Ⅰ～Ⅱ期组表达（90.5%）均降低（P〈0.05）。胃癌组织中的KAI1蛋白表达与患者性别、年龄、肿瘤大小、Lauren分型无关,胃癌患者生存期5年以下组的胃癌组织中KAI1蛋白的表达水平明显低于生存期5年以上组（P〈0.05）。[结论]胃癌组织中KAI1基因蛋白表达降低与胃癌的侵袭、转移及临床病理进展有关。     

喉鳞癌中KAI1/CD82、MRP1/CD9的表达及意义

目的探讨喉鳞癌中KAI1/CD82和MRP1/CD9的表达及意义。方法 采用实时荧光定量PCR法(RT-qPCR)及免疫组织化学技术检测100例喉鳞癌(Laryngeal squamous cell carcinoma, LSCC)组织及随机抽取30例相应癌旁非癌组组织中KAI1/CD82和MRP1/CD9的表达情况, 并分析二者与肿瘤临床病理参数的关系及对生存函数的影响。结果 在mRNA及蛋白水平上KAI1/CD82和MRP1/CD9表达结果基本是一致的, KAI1/CD82和MRP1/CD9在30例配对的LSCC中, 癌组织表达显著低于相应癌旁非癌组织, 其表达差异有统计学意义(P＜0.05);两者在TNM分期Ⅲ~Ⅳ、分化程度差、临床分期Ⅲ~Ⅳ、有淋巴结转移LSCC中的表达水平均低于在TNM分期Ⅰ~Ⅱ、分化程度良、临床分期Ⅰ~Ⅱ、无淋巴结转移LSCC患者(P＜0.05)。而在不同性别、不同年龄组、不同生长部位等LSCC患者的组织中其表达差异无统计学意义(P＞0.05);LSCC中KAI1/CD82蛋白阳性表达者中位生存期为78个月, 高于阴性表达者的48个月(χ²=6.98, P=0.008), LSCC中MRP1/CD9蛋白阳性表达者中位生存期为78个月, 高于阴性表达者的49个月(χ²=5.45, P=0.02);在LSCC中KAI1/CD82和MRP1/CD9蛋白的表达呈正相关(χ²=31.41, P＜0.01)。结论 KAI1/CD82和MRP1/CD9可能共同参与了LSCC的发生发展过程, 对LSCC的浸润和转移及预后评估具有一定的临床参考价值。KAI1/CD82、MRP1/CD9可以作为判断喉鳞癌浸润转移及预后的标记物。     

EWI2/PGRL associates with the metastasis suppressor KAI1/CD82 and inhibits the migration of prostate cancer cells

Cancer metastasis suppressor KAI1/CD82 belongs to the tetraspanin superfamily and inversely correlates with the metastatic potential of a variety of cancers. The mechanism of KAI1/CD82-mediated metastasis suppression remains unclear. In this study, we found a M(r) 68,00 cell-surface protein physically associated with KAI1/CD82 and named it KASP: a KAI1/CD82-associated surface protein. Distinctive from known KAI1/CD82 associations that usually occur in the context of "tetraspanin web," the KAI1/CD82-KASP association is likely to be direct because it is: (a) highly stoichiometric; (b) stabilized by chemical cross-linking; and (c) independent of cholesterol-enriched lipid rafts. Therefore, KASP is one of the major transmembrane proteins that associates with KAI1/CD82. Consistent with the wide distribution of KAI1/CD82, KASP is expressed ubiquitously in human tissues. Through peptide sequencing, KASP was identified as an immunoglobulin superfamily member called EWI2 or PGRL. Although EWI2/PGRL has been found to associate with tetraspanins CD9 and CD81, it forms distinct complexes with different tetraspanins, and its association with KAI1/CD82 could be independent of CD81 and CD9. Overexpression of EWI2/PGRL in Du145 metastatic prostate cancer cells inhibits cell migration on both fibronectin- and laminin-coated substratum, indicating that EWI2/PGRL directly regulates cell migration. Furthermore, EWI2/PGRL synergizes KAI1/CD82 in inhibiting cell migration, indicating that EWI2/PGRL is likely required for the function of KAI1/CD82. In summary, we identified a major KAI1/CD82-associated protein, EWI2/PGRL, that is important for KAI1/CD82-mediated suppression of cancer cell migration.