CKLFSF2 is highly expressed in testis and can be secreted into the seminiferous tubules

Current Opinions on the Relationship Between CMTM Family and Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a typically malignant tumor in the digestive system. The mortality of HCC ranks third place in the world, second only to lung cancer and colorectal cancer. For the characteristics of high invasiveness, high metastasis, high recurrence rate as well as short survival time, HCC treatment has always been difficult in clinical practice. Many causes have contributed to the appearance of these features, including insidious onset, high degree of malignancy, lack of effective early molecular diagnostic markers, and disease prediction models. The human chemokine-like factor superfamily (CMTMs) is a new gene family consisting of CKLF and CMTM1-CMTM8. CMTMs have a marvel domain which can activate and chemotaxis immune cells. Many studies have reported that CMTMs are involved in the regulation of cell growth and development, and play an important role in the malignant progression of the immune system and reproductive system, especially in the development of tumors. In this review, we summarized the structure and function of the human CMTMs, the relationship between its family members and HCC, the prognostic value, potential functions, and mechanisms in HCC. CMTMs could provide a new diagnostic and therapeutic target in clinical practice for patients with HCC.

CMTM6 and CMTM4 as two novel regulators of PD-L1 modulate the tumor microenvironment

The tumor microenvironment (TME) plays crucial roles in regulating tumor occurrence, progress, metastasis and drug resistance. However, it remains largely elusive how the components of TME are regulated to govern its functions in tumor biology. Here, we discussed how the two novel functional proteins, chemokine-like factor (CKLF)-like MARVEL transmembrane domain-containing 6 (CMTM6) and CMTM4, which involved in the post-translational regulation of PD-L1, modulate the TME functions. The roles of CMTM6 and CMTM4 in regulating TME components, including immune cells and tumor cells themselves were discussed in this review. The potential clinical applications of CMTM6 and CMTM4 as biomarkers to predict therapy efficacy and as new or combined immunotherapy targets are also highlighted. Finally, the current hot topics for the biological function of CMTM6/4 and several significant research directions for CMTM6/4 are also briefly summarized in the review.

Chemokines and NSCLC: Emerging role in prognosis, heterogeneity, and therapeutics

Lung cancer persists to contribute to one-quarter of cancer-associated deaths. Among the different histologies, non-small cell lung cancer (NSCLC) alone accounts for 85% of the cases. The development of therapies involving immune checkpoint inhibitors and angiogenesis inhibitors has increased patients' survival probability and reduced mortality rates. Developing targeted therapies against essential genetic alterations also translates to better treatment strategies. But the benefits still seem farfetched due to the development of drug resistance and refractory tumors. In this review, we have highlighted the interplay of different tumor microenvironment components, essentially discussing the chemokine families (CC, CXC, C, and CX3C) that regulate the tumor biology in NSCLC and promote tumor growth, metastasis, and associated heterogeneity. The development of therapeutics and prognostic markers is a complex and multipronged approach. However, some essential chemokines can act as critical players for being considered potential prognostic markers and therapeutic targets.

Chemokine-like factor-like MARVEL transmembrane domain-containing family in autoimmune diseases

The chemokine-like factor (CKLF)-like MARVEL transmembrane domain-containing family (CMTM) is widely expressed in the immune system. Abnormal expression of CMTM is associated with the development of various diseases. This article summarizes the relevant research on the role of the CMTM family in immune disorders. This information will increase our understanding of pathogenesis and identify promising targets for the diagnosis and treatment of autoimmune diseases. The CMTM family is highly expressed in peripheral blood mononuclear cells. CKLF1 may be involved in the development of arthritis through its interaction with C-C chemokine receptor 4. CKLF1 is associated with the pathogenesis of lupus nephritis and psoriasis. Both CMTM4 and CMTM5 are associated with the pathogenesis of systemic lupus erythematosus. CMTM1, CMTM2, CMTM3, and CMTM6 play a role in rheumatoid arthritis, systemic sclerosis, Sjögren syndrome, and anti-phospholipid syndrome, respectively. The CMTM family has been implicated in various autoimmune diseases. Further research on the mechanism of the action of CMTM family members may lead to the development of new treatment strategies for autoimmune diseases.

Chemokine-Like Factor-Like MARVEL Transmembrane Domain-Containing Family in Hepatocellular Carcinoma: Latest Advances

Chemokine-like factor (CKLF)-like MARVEL transmembrane domain-containing family (CMTMs) is a new gene family, consisting of CKLF and CMTM1 to CMTM8, which plays an important role in hematopoiesis system, autoimmune diseases, male reproduction etc. Abnormal expression of CMTMs is also associated with tumor genesis, development and metastasis. In this review, we briefly describe the characteristics of CMTM family, outline its functions in multiple kinds of carcinomas, and summarize the latest research on their roles in hepatocellular carcinoma which are mainly related to the expression, prognostic effect, potential functions, and mechanism of action. The CMTM family is expected to provide new ideas and targets for HCC diagnosis and treatment.

Identification of Serum CMTM2 as a Potential Biomarker for HBV-Related Disorders

Substantial advance supports that CMTM2 serve as an important performer in physiological and pathological processes. However, very little is clear about the relationship between CMTM2 and HBV-related disorders. Here, for the first time, we explore that whether or not serum CMTM2 is involved in HBV-related diseases. We found that CMTM2 values were significantly lower in patients compared to healthy control (p <0.001), using ELISA assay. Furthermore, serum CMTM2 levels were negatively correlated with HBV DNA levels in CHB patients but not correlated with the serum levels of ALT and AST. Serum CMTM2 concentrations were not correlated with the serum levels of ALT, AST and HBV DNA load in HBLC and HCC patients. In addition, analysis of the ROC curve indicated that CMTM2 levels were significantly associated with the diagnostic value of HBV-related disorders. Finally, downregulation of CMTM2 was observed in HBV-infected cell model. CMTM2 degradation could be attributed to HBx-activated Lys48 (K48)-linked polyubiquitination, which was abolished by treatment with the proteasome inhibitor MG132. HBV infection suppresses CMTM2 expression by activating ubiquitin-proteasome system. Serum CMTM2 levels can be adopted as an effective indicator of the pathogenesis of HBV-related disorders.

Identification and validation of novel DNA methylation markers for early diagnosis of lung adenocarcinoma

Lung cancer has the highest mortality of all cancers worldwide. Epigenetic alterations have emerged as potential biomarkers for early diagnosis of various cancer tissue types. To identify methylation markers for early diagnosis of lung adenocarcinoma, we aimed to integrate genome‐wide DNA methylation and gene expression data from The Cancer Genome Atlas. To this end, we first examined the global DNA methylation pattern of lung adenocarcinoma and investigated the relationship between DNA methylation subtypes and clinical features. We then extracted differentially methylated and expressed genes, and adopted feature selection techniques to determine the final methylation markers. The performance of the markers in predicting lung adenocarcinoma was evaluated on three independent datasets from Gene Expression Omnibus. Protein levels of marker genes were validated by immunohistochemistry, and their biological function was further verified in vivo. We identified three novel methylation markers in lung adenocarcinoma including cg08032924, cg14823851, and cg19161124, mapping to CMTM2, TBX4, and DPP6, respectively. Validating these results on three independent datasets indicated that the three markers can achieve extremely high sensitivity and specificity in distinguishing lung adenocarcinoma from normal samples. Immunohistochemistry quantification results confirmed that markers are weakly expressed in human lung adenocarcinoma, and CMTM2 decreased tumor growth of mouse Lewis lung carcinoma in vivo. Overall, our study identified three novel methylation markers in lung adenocarcinoma which may contribute toward an improved diagnosis potentially leading to a better outcome for patients with lung adenocarcinoma.

Down-Regulated CMTM2 Promotes Epithelial-Mesenchymal Transition in Hepatocellular Carcinoma

Background

Our recent study identified that human chemokine-like factor (CKLF)-like MARVEL transmembrane domain-containing family member 2 (CMTM2) was deregulated in hepatocellular carcinoma (HCC) tissues and posed as a potential tumor suppressor. However, the mechanism of CMTM2 in HCC occurrence and development has not been well elaborated.

Materials and Methods

The expression of CMTM2 was knocked-down by RNA interruption in Huh-7 and SMMC7721 cells. Cell proliferation ability was detected by CCK8 test and colony formation assay. The cell invasion and migration were measured by wound healing and Transwell assay.

Results

We found that the cell proliferation was significantly increased by interruption of CMTM2 expression, both in Huh-7 and SMMC7721 cells. Moreover, down-regulated CMTM2 could promote the invasion and migration ability of HCC cells through inducing the epithelial-mesenchymal transition (EMT) process. We further discovered that both the expression of CMTM2 and the EMT-associated marker E-cadherin were decreased in the same thirty cases of HCC tissues compared with the corresponding adjacent non-tumor tissues. Pearson correlation test showed that there was a significantly positive correlation between CMTM2 and E-cadherin in HCC tissues (P<0.05).

Conclusion

Based on the results of cell model and HCC tissues, our study suggests that down-regulated CMTM2 promotes HCC metastasis through inducing the EMT process.

Goat CMTM2: mRNA expression profiles of different alternative spliced variants and associations analyses with growth traits

CKLF like MARVEL transmembrane domain containing 2 (CMTM2) plays crucial roles in spermiogenesis, skeletogenous, growth, and development through PI3K/Akt and other pathways. The purpose of this study was to explore the expression profile and variation of different spliced CMTM2 gene in Shaanbei white cashmere goats, as well as to find the relationships between a CMTM2 promoter region 14 bp genetic variant and growth traits in 1366 Shaanbei white cashmere goats. In this study, we identified alternative CMTM2 splicing and detected the effects of the spliced variants on mRNA expression levels in tissues. Meanwhile, an unreported spliced variant of CMTM2 in goat was identified using in CDS cloning and RT-PCR, namely, CMTM2-AS2. Compared with the normal transcript (CMTM2-AS1), the novel variant had the higher expression level in muscle and liver tissues, indicating that it plays an effective role in growth traits. Furthermore, a 14 bp deletion was detected within CMTM2 promoter region, and the different genotypes were significantly associated with growth traits (e.g., body length, circumference of cannon bone) in the large group of 1366 individuals in Shaanbei white cashmere goats. We found that the body length of the individuals with II (n = 571) genotype had better phenotypes than those with DD (n = 118) and ID (n = 650) genotypes. These results have direct guiding significance for goat breeding in the future and provide a new idea for studying the characteristics and functions of CMTM2 gene in goats.

Downregulated CMTM2 Poses Potential Clinical Significance in Hepatocellular Carcinoma

This study aimed to investigate the expression and clinical significance of chemokine-like factor-like MARVEL transmembrane domain-containing family member 2 (CMTM2) in hepatocellular carcinoma (HCC) tissues. Bioinformatics analysis showed that CMTM2 was downregulated in HCC tissues and correlated with vascular invasion of HCC patients. The immunohistochemistry (IHC) method found that CMTM2 expression was negative in 29/75 (38.67%) cases of HCC tissues and 13/75 (17.33%) cases of paracancerous tissues, also showed a significantly lower expression of CMTM2 in HCC tissues than the paired paracancerous tissues (p < 0.05). Moreover, CMTM2 expression was significantly correlated with tumor grade of HCC patients (p < 0.05), but had no relationship with other clinicopathological features. In addition, multivariate logistic regression analysis indicated that tumor grade was an independent risk factor for CMTM2 expression. The survival time of HCC patients between high and low expression of CMTM2 had no difference by bioinformatics analysis, but the IHC result showed that the negative expression of CMTM2 was related to a poor prognosis of HCC patients. Further COX regression analysis showed that CMTM2 expression was an independent protective factor for the prognosis of HCC patients. We identify that CMTM2 is downregulated in HCC tissues and correlated with the prognosis of HCC patients, suggesting a potential tumor suppressor role of CMTM2 in HCC progression.

Research Advances in CKLF-like MARVEL Transmembrane Domain-containing Family in Non-small Cell Lung Cancer

CKLF-like MARVEL transmembrane domain-containing member (CMTM) is a new gene family first cloned and reported in 2001. The CMTM family consists of nine members including CKLF and CMTM1-CMTM8, which are located on different chromosomes. Besides exhibiting extensive chemotactic activity, the CMTM family plays an important role in the hematopoiesis system, the immune system, the cardiovascular system and the male reproductive system. Recent in-depth research has also revealed that CMTM is closely associated with the genesis, development and metastasis of tumors, displaying opposing activities in diverse human tumors. In this review, we discuss the structural and functional characteristics of the CMTM family and summarize latest research findings of the relationship between several CMTM members and non-small cell lung cancer.

Integrated Analyses of Phenotype and Quantitative Proteome of CMTM4 Deficient Mice Reveal Its Association with Male Fertility

The chemokine-like factor (CKLF)-like MARVEL transmembrane domain-containing family (CMTM) is a gene family that has been implicated in male reproduction. CMTM4 is an evolutionarily conserved member that is highly expressed in the testis. However, its function in male fertility remains unknown. Here, we demonstrate that CMTM4 is associated with spermatogenesis and sperm quality. Using Western blotting and immunohistochemical analyses, we found CMTM4 expression to be decreased in poor-quality human spermatozoa, old human testes, and testicular biopsies with nonobstructive azoospermia. Using CRISPR-Cas9 technology, we knocked out the Cmtm4 gene in mice. These Cmtm4 knockout (KO) mice showed reduced testicular daily sperm production, lower epididymal sperm motility and increased proportion of abnormally backward-curved sperm heads and bent sperm midpieces. These mice also had an evident sub-fertile phenotype, characterized by low pregnancy rates on prolonged breeding with wild type female mice, reduced in vitro fertilization efficiency and a reduced percentage of acrosome reactions. We then performed quantitative proteomic analysis of the testes, where we identified 139 proteins to be downregulated in Cmtm4-KO mice, 100 (71.9%) of which were related to sperm motility and acrosome reaction. The same proteomic analysis was performed on sperm, where we identified 3588 proteins with 409 being differentially regulated in Cmtm4-KO mice. Our enrichment analysis showed that upregulated proteins were enriched with nucleosomal DNA binding functions and the downregulated proteins were enriched with actin binding functions. These findings elucidate the roles of CMTM4 in male fertility and demonstrates its potential as a promising molecular candidate for sperm quality assessment and the diagnosis or treatment of male infertility.

The expression of CKLFSF2B is regulated by GATA1 and CREB in the Leydig cells, which modulates testicular steroidogenesis

CKLFSF is a protein family that serves as a functional bridge between chemokines and members of the transmembrane 4 superfamily (TM4SF). In the course of evolution, CKLFSF2 has evolved as two isoforms, namely CKLFSF2A and CKLFSF2B, in mice. CKLFSF2A, also known as CMTM2A and ARR19, is expressed in the testis and is important for testicular steroidogenesis. CKLFSF2B is also known to be highly expressed in the testis. In the prepubertal stage, CKLFSF2B is expressed only in Leydig cells, but it is highly expressed in haploid germ cells and Leydig cells in adult testis. CKLFSF2B is naturally processed inside the cell at its C-terminus to yield smaller proteins compared to its theoretical size of ≈25 kDa. The Cklfsf2b gene is regulated by GATA-1 and CREB protein, binding to their respective binding elements present in the 2-kb upstream promoter sequence. In addition, the overexpression of CKLFSF2B inhibited the activity of the Nur77 promoter, which consequently represses the promoter activity of Nur77-target steroidogenic genes such as P450c17, 3β-HSD, and StAR in MA-10 Leydig cells. Adenovirus-mediated overexpression of CKLFSF2B in primary Leydig cells isolated from adult mice shows a repression of steroidogenic gene expression and consequently testosterone production. Moreover, intratesticular injection of CKLFSF2B-expressing adenovirus in adult mice clearly had a repressive effect compared to the control injected with only GFP-expressing adenovirus. Altogether, these findings suggest that CKLFSF2B might be involved in the development and function of Leydig cells and regulate testicular testosterone production by fine-tuning the expression of steroidogenic genes.

Co-expression of sperm membrane proteins CMTM2A and CMTM2B is essential for ADAM3 localization and male fertility in mice

Chemokines are signaling proteins that are secreted to induce chemotaxis during an immunological response. However, the functions of transmembrane-type chemokine-like factor (CKLF) and the CMTM (CKLF-like MARVEL transmembrane domain containing) protein family remain to be determined. In this study, we focused on the testis-specific mouse CMTM gene cluster (Cmtm1, Cmtm2a and Cmtm2b) and generated CRISPR/Cas9-mediated mutant mice to examine their physiological functions. Although Cmtm1 mutant mice were fertile, Cmtm2a and Cmtm2b double mutant mice had defects in male fertility due to impaired sperm function. We found that co-expression of sperm membrane proteins CMTM2A and CMTM2B is required for male fertility and affects the localization of the sperm membrane protein ADAM3 in regulating sperm fertilizing ability.

CMTM8 inhibits the carcinogenesis and progression of bladder cancer

Bladder cancer is the most common tumor of the urinary tract. The incidence of bladder cancer has increased in the last few decades, thus novel molecular markers for early diagnosis and more efficacious treatment are urgently needed. Chemokine‑like factor (CKLF)‑like MARVEL transmembrane domain containing 8 (CMTM8) is downregulated in several types of cancers and is associated with tumor progression. However, CMTM8 expression has been unexplored in bladder cancer to date. Our results revealed that the expression of CMTM8 was negative in 46 of 74 (62.2%) bladder cancer samples via immunohistochemistry assay. CMTM8 downregulation was associated with advancing tumor stage and tumor grade. CMTM8 was successfully overexpressed by lentivirus in EJ and T24 cells, and the CCK‑8 and Transwell assays showed that CMTM8 overexpression decreased cell proliferation, migration and invasion in vitro. In tumor xenografts upregulation of CMTM8 inhibited tumor growth and lymph node metastasis in vivo. In conclusion, overexpression of CMTM8 in bladder cancer results in reduced malignant cell growth, migration and invasion, which could make it a potential therapeutic target in the treatment of bladder cancer.

CMTM4 is frequently downregulated and functions as a tumour suppressor in clear cell renal cell carcinoma

BACKGROUND

Chemokine-like factor (CKLF)-like MARVEL transmembrane domain-containing family (CMTM) is a gene family involved in multiple malignancies. CMTM4 is a member of this family and is located at chromosome 16q22.1, a locus that harbours a number of tumour suppressor genes. It has been defined as a regulator of cell cycle and division in HeLa cells; however, its roles in tumourigenesis remain poorly studied.

METHODS

An integrated bioinformatics analysis based on the array data from the GEO database was conducted to view the differential expression of CMTM4 across multiple cancers and their corresponding control tissues. Primary clear cell renal cell carcinoma (ccRCC) and the paired adjacent non-tumour tissues were then collected to examine the expression of CMTM4 by western blotting, immunohistochemistry, and quantitative RT-PCR. The ccRCC cell lines A498 and 786-O and the normal renal tubular epithelial cell line HK-2 were also tested for CMTM4 expression by western blotting. Cell Counting Kit-8 (CCK-8) and viable cell counting assays were used to delineate the growth curves of 786-O cells after CMTM4 overexpression or knockdown. Wound healing and transwell assays were performed to assess the cells' ability to migrate. The effects of CMTM4 on cellular apoptosis and cell cycle progression were analysed by flow cytometry, and cell cycle hallmarks were detected by western blotting and RT-PCR. The xenograft model in nude mice was used to elucidate the function of CMTM4 in tumourigenesis ex vivo.

RESULTS

By omic data analysis, we found a substantial downregulation of CMTM4 in ccRCC. Western blotting then confirmed that CMTM4 was dramatically reduced in 86.9 % (53/61) of ccRCC tissues compared with the paired adjacent non-tumour tissues, as well as in the 786-O and A498 ccRCC cell lines. Restoration of CMTM4 significantly suppressed 786-O cell growth by inducing G2/M cell cycle arrest and p21 upregulation, and cell migration was also inhibited. However, knockdown of CMTM4 led to a completely opposite effect on these cell behaviours. Overexpression of CMTM4 also markedly inhibited the tumour xenograft growth in nude mice.

CONCLUSIONS

CMTM4 is downregulated and exhibits tumour-suppressor activities in ccRCC, and could be exploited as a target for ccRCC treatment.

CMTM5 is reduced in prostate cancer and inhibits cancer cell growth in vitro and in vivo

PURPOSE

A novel tumor suppressor CKLF-like MARVEL transmembrane domain-containing member 5 (CMTM5) is reduced or undetectable in many kinds of cancers and inhibits tumor cells' malignant features. To explore its role in prostate cancer (PCa), we detected its expression patterns in prostate tissues and PCa cells, and determined its anti-proliferation functions in PCa cells in vitro and in vivo.

METHODS

The expression of CMTM5 in prostate tissue microarray, specimens and cell lines was evaluated by immunohistochemistry and Western blot, respectively. After being transfected with CMTM5 adenovirus or vector, the proliferation and migration of DU145 cells were detected by MTT assay and transwell assay, respectively. Furthermore, the effects of CMTM5 on tumor growth were performed in nude mice xenograft in vivo.

RESULTS

We found CMTM5 was reduced in PCa tissues and cells compared with BPH tissues, and its expression in PCa tissues was related to the Gleason score. Moreover, after being transfected with adenovirus, ectopic expression of CMTM5-v1 in DU145 cells led to significant inhibition of cell proliferation and migration compared with the control, which may be attributed to decreased Akt activity. Finally, restoration of CMTM5 significantly suppressed tumor growth in vivo.

CONCLUSIONS

These results indicate that CMTM5 is down-regulated in PCa and exhibit tumor suppressor activities in androgen-independent PCa cells. Loss of CMTM5 protein may be contributed to the development of PCa and it is a potential therapeutic target for castration-resistant prostate cancer.

CMTM3 inhibits human testicular cancer cell growth through inducing cell-cycle arrest and apoptosis

Human CMTM3 has been proposed as a putative tumor suppressor gene. The loss of CMTM3 has been found in several carcinomas. However, the regulation of CMTM3 expression and its function in tumor progression remain largely unknown. Here, we investigated the regulation of CMTM3 expression, function and molecular mechanism in human testicular cancer cells. CMTM3 was frequently downregulated or silenced in testicular cancer cell lines and tumor tissues but highly expressed in normal testis tissues. The re-expression of CMTM3 significantly suppressed the colony formation, proliferation, and migration capacity of testicular cancer cells by inducing a G2 cell cycle arrest and apoptosis. Moreover, the re-expression of CMTM3 activated the transcription of p53, induced p53 accumulation, up-regulated the expression of p21, and increased the cleavage of caspase 9, 8, 3, and PARP. The downregulation of CMTM3 in clinical tumor tissues was associated with the methylation of a single CpG site located within the Sp1/Sp3-responsive region of the core promoter. These results indicate that CMTM3 can function as tumor suppressor through the induction of a G2 cell cycle arrest and apoptosis. CMTM3 is thus involved in testicular cancer pathogenesis, and it is frequently at least partially silenced by the methylation of a single, specific CpG site in tumor tissues.

A novel 3p22.3 gene CMTM7 represses oncogenic EGFR signaling and inhibits cancer cell growth

Deletion of 3p12-22 is frequent in multiple cancer types, indicating the presence of critical tumor-suppressor genes (TSGs) at this region. We studied a novel candidate TSG, CMTM7, located at the 3p22.3 CMTM-gene cluster, for its tumor-suppressive functions and related mechanisms. The three CMTM genes, CMTM6, 7 and 8, are broadly expressed in human normal adult tissues and normal epithelial cell lines. Only CMTM7 is frequently silenced or downregulated in esophageal and nasopharyngeal cell lines, but uncommon in other carcinoma cell lines. Immunostaining of tissue microarrays for CMTM7 protein showed its downregulation or absence in esophageal, gastric, pancreatic, liver, lung and cervix tumor tissues. Promoter CpG methylation and loss of heterozygosity were both found contributing to CMTM7 downregulation. Ectopic expression of CMTM7 in carcinoma cells inhibits cell proliferation, motility and tumor formation in nude mice, but not in immortalized normal cells, suggesting a tumor inhibitory role of CMTM7. The tumor-suppressive function of CMTM7 is associated with its role in G1/S cell cycle arrest, through upregulating p27 and downregulating cyclin-dependent kinase 2 (CDK2) and 6 (CDK6). Moreover, CMTM7 could promote epidermal growth factor receptor (EGFR) internalization, and further suppress AKT signaling pathway. Thus, our findings suggest that CMTM7 is a novel 3p22 tumor suppressor regulating G1/S transition and EGFR/AKT signaling during tumor pathogenesis.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 5: intercellular junctions and contacts between germs cells and Sertoli cells and their regulatory interactions, testicular cholesterol, and genes/proteins associated with more than one germ cell generation

In the testis, cell adhesion and junctional molecules permit specific interactions and intracellular communication between germ and Sertoli cells and apposed Sertoli cells. Among the many adhesion family of proteins, NCAM, nectin and nectin-like, catenins, and cadherens will be discussed, along with gap junctions between germ and Sertoli cells and the many members of the connexin family. The blood-testis barrier separates the haploid spermatids from blood borne elements. In the barrier, the intercellular junctions consist of many proteins such as occludin, tricellulin, and claudins. Changes in the expression of cell adhesion molecules are also an essential part of the mechanism that allows germ cells to move from the basal compartment of the seminiferous tubule to the adluminal compartment thus crossing the blood-testis barrier and well-defined proteins have been shown to assist in this process. Several structural components show interactions between germ cells to Sertoli cells such as the ectoplasmic specialization which are more closely related to Sertoli cells and tubulobulbar complexes that are processes of elongating spermatids embedded into Sertoli cells. Germ cells also modify several Sertoli functions and this also appears to be the case for residual bodies. Cholesterol plays a significant role during spermatogenesis and is essential for germ cell development. Lastly, we list genes/proteins that are expressed not only in any one specific generation of germ cells but across more than one generation.

Identification and characterization of CMTM4, a novel gene with inhibitory effects on HeLa cell growth through Inducing G2/M phase accumulation

Human CMTM is a novel gene family consisting of CKLF and CMTM1-8. CMTM4 is the most conserved gene and has three RNA splicing forms designated as CMTM4-v1, -v2 and -v3, but in many types of tissue and cell lines, only CMTM4-v1 and -v2 could be detected. CMTM4-v2 is the full length cDNA product, which has been highly conserved during evolution. CMTM4-v1 and -v2 are broadly expressed in normal types of tissue. They are distributed on the cell membrane and across the cytoplasm in a speckled pattern. Overexpression of CMTM4-v1 and -v2 can inhibit HeLa cell growth via G2/M phase accumulation without inducing apoptosis. Therefore, CMTM4 might be an important gene involved in cell growth and cell cycle regulation.

CMTM5 exhibits tumor suppressor activities and is frequently silenced by methylation in carcinoma cell lines

PURPOSE

CMTM5 (CKLF-like MARVEL transmembrane domain containing member 5) is located at 14q11.2, a locus associated with multiple cancers. It has six RNA splicing variants with CMTM5-v1 as the major one. We explored its expression pattern in normal tissues and tumor cell lines, as well as its functions in carcinoma cells.

EXPERIMENTAL DESIGN

We evaluated CMTM5 expression by semiquantitative reverse transcription-PCR (RT-PCR) in normal tissues and carcinoma cell lines of cervical, breast, nasopharyngeal, lung, hepatocellular, esophageal, gastric, colon, and prostate. We further examined CMTM5 promoter methylation in these cell lines. We also analyzed CMTM5 expression after 5-aza-2'-deoxycytidine treatment and genetic demethylation and the functional consequences of restoring CMTM5 in HeLa and PC-3 cells.

RESULTS

CMTM5-v1 is broadly expressed in human normal adult and fetal tissues, but undetectable or down-regulated in most carcinoma cell lines. Its promoter methylation was detected in virtually all the silenced or down-regulated cell lines. The silencing of CMTM5 could be reversed by pharmacologic demethylation or genetic double-knockout of DNMT1 and DNMT3B, indicating methylation-mediated mechanism. Restoration of CMTM5-v1 suppressed carcinoma cell proliferation, migration, and invasion.

CONCLUSIONS

These results indicate that CMTM5 exhibits tumor suppressor activities, but with frequent epigenetic inactivation in carcinoma cell lines.

Expression and localization of CKLFSF2 in human spermatogenesis

AIM

To investigate the expression and subcellular localization of chemokine-like factor superfamily 2 (CKLFSF2) in human testis and its potential role in spermatogenesis.

METHODS

A specific polyclonal antibody against CKLFSF2 was raised. The expression and cellular localization of CKLFSF2 in the seminiferous tubules was checked by immunohistochemistry method. Also, in situ hybridization was applied to localize the mRNA distribution. The EGFP-CKLFSF2 fusion protein was expressed in COS-7 cells to localize its subcellular location in vitro. In addition, the abnormal expression of CKLFSF2 in testes of patients with male infertility was assayed by reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry methods.

RESULTS

Having a close correlation with spermatogenesis defects, CKLFSF2 was specifically expressed in meiotic and post-meiotic germ cells, which were localized to the endoplasmic reticulum (ER) near the Golgi apparatus.

CONCLUSION

CKLFSF2 could play important roles in the process of meiosis and spermiogenesis, and might be involved in the vesicular transport or membrane apposition events in the endoplasmic reticulum.

Characterization and Expression Profile of CMTM3/CKLFSF3

CMTM/CKLFSF is a novel family of proteins linking chemokines and TM4SF. In humans, these proteins are encoded by nine genes, CKLF and CMTM1-8/CKLFSF1-8. Here we report the characteristics and expression profile of CMTM3/CKLFSF3. Human CMTM3/CKLFSF3 has a high sequence identity among various species and similar characteristics as its mouse and rat homologues. Established by results both of RT-PCR and Quantitative Real-time PCR, the gene is highly transcribed in testis, leukocytes and spleen. For further verification, we generated a polyclonal antibody against human CMTM3/CKLFSF3 and found that the protein is highly expressed in the testis and some cells of PBMCs. Therefore, CMTM3/CKLFSF3 is an evolutionarily conserved gene that may have important roles in the male reproductive system and immune system. Further studies are necessary to validate its functions in the two systems.

Molecular cloning and identification of mouse Cklfsf2a and Cklfsf2b, two homologues of human CKLFSF2

Human chemokine-like factor superfamily (CKLFSF) is a novel gene family comprising CKLF and CKLFSF1-8. Among them, CKLFSF2 is highly expressed in testis and may play important roles in male reproduction. Besides, it is very active during evolution and has two counterparts in mouse. For further study, we cloned the two mouse genes by EST assembly and RT-PCR methods and designated them as mouse Cklfsf2a and Cklfsf2b. Their predicted open-reading frames (ORFs) that encode 169 and 210 amino acids, respectively, were obtained; and their predicted full-length molecular sizes that are approximately 1.2 kb for mCklfsf2a and 0.9 kb for mCklfsf2b were confirmed by Northern blot analysis. Mouse Cklfsf2a and Cklfsf2b show similarities with human CKLFSF2 in the expression patterns that are abundant in testis, hematopoietic and immune tissues; as well as in the chromosome localizations that neighbor CKLFSF1 and 3. Their putative protein products have 47.6 and 45.5% identities with hCKLFSF2, respectively; both of them contain four potential transmembrane regions and MARVEL domains, which are also similar with hCKLFSF2. Functionally, they all can affect the transcriptional activity of androgen receptor in PC-3 and HeLa cells, but mCklfsf2a is a repressor while mCklfsf2b and hCKLFSF2 are enhancers. Taken together, we conclude that mouse Cklfsf2a and Cklfsf2b are two homologues of human CKLFSF2. Studies on them would provide much help in further investigation of the latter.

A functional promoter region of the CKLFSF2 gene is located in the last intron/exon region of the upstream CKLFSF1 gene

The genes for CKLFSF1 (chemokine-like factor super family member 1) and CKLFSF2 (chemokine-like factor super family member 2) are very closely linked, within 312 bp of each other. Here, we present evidence that the last intron/exon region of the CKLFSF1 gene contains a novel eukaryotic promoter capable of directing the expression of the downstream gene, CKLFSF2. We identified two segments of the upstream region of the CKLFSF2 gene, 2146 bp (-2134/+12, relative to ATG +1) and 1483 bp (-2134/-652), that were capable of efficiently driving expression of a linked reporter gene upon transient transfection into several kinds of cell lines. The 1483 bp segment exhibited more than a two-fold increase in luciferase activity relative to the 2146 bp segment. By analyzing 5'-deletion mutants of the 1483 bp segment, we identified a 195 bp segment (-846/-625) located in the last intron/exon region of the CKLFSF1 gene that was critical for promoter activity. DNA decoy experiments revealed that a 122 bp (-846/-725) fragment markedly inhibited CKLFSF2 mRNA transcription. Furthermore, we found that the putative promoter region of the CKLFSF2 gene is separated from the transcription start site by about 500 bp. Accumulating reports suggest that introns have many functions, including the modulation of regulation and structure. This work provides evidence that a eukaryotic gene promoter sequence from one gene located in an intron/exon of another.