Comparative expression analysis of isolated human adipocytes and the human adipose cell lines LiSa-2 and PAZ6.

OBJECTIVE: To obtain insight in the extent to which the human cell lines LiSa-2 and PAZ6 resemble isolated primary human adipocytes. DESIGN: A combination of cDNA subtraction (representative difference analysis; RDA) and cDNA microarray analysis was used to select adipose specific genes to compare isolated (pre-)adipocytes with (un)differentiated LiSa-2 and PAZ6 cells. MEASUREMENTS: RDA was performed on adipose tissue against lung tissue. A total of 1400 isolated genes were sequenced and cDNA microarray technology was used for further adipose related gene selection. 30 genes that were found to be enriched in adipose tissue were used to compare isolated human adipocytes and LiSa-2 and PAZ6 cells in the differentiated and undifferentiated states. RESULTS: RDA and microarray analysis resulted in the identification of adipose enriched genes, but not in adipose specific genes. Of the 30 most differentially expressed genes, as expected, most were related to lipid metabolism. The second category consisted of methyltransferases, DNMT1, DNMT3a, RNMT and SHMT2, of which the expression was differentiation dependent and higher in differentiated adipocytes. Using the 30 adipose expressed genes, it was found that isolated adipocytes on one hand, and PAZ6 and LiSa-2 adipocytes on the other, differ primarily in lipid metabolism. Furthermore, LiSa-2 cells seem to be more similar to isolated adipocytes than PAZ6 cells. CONCLUSION: The LiSa-2 cell line is a good model for differentiated adipocytes, although one should keep in mind that the lipid metabolism in these cells deviates from the in vivo situation Furthermore, our results imply that methylation may have an important function in terminal adipocyte differentiation.

Carboxypeptidase E and thrombospondin-1 are differently expressed in subcutaneous and visceral fat of obese subjects.

The aim of this study was to identify candidate genes for visceral obesity by screening for genes strongly differentially expressed between human subcutaneous and visceral adipose depots. A cDNA microarray with human adipose-derived cDNAs was used as an initial screening to identify genes that are potentially differentially expressed between human subcutaneous and visceral abdominal fat tissues. For the two best candidates, carboxypeptidase E (CPE) and thrombospondin-1 (THBS1) (EST N72406), real-time RT-PCR was performed to confirm their depot specific expression in extremely obese individuals. Both genes appeared to be strongly differentially expressed, having a higher expression in the visceral depot than in the subcutaneous one. For THBS1, the difference in expression between the depots was greater in women than in men. The involvement of CPE and THBS1 in obesity allows us to suggest that the physiological processes controlled by these genes contribute to depot and gender-related differences in the metabolic complications of obesity.

Differential gene expression in white and brown preadipocytes.

White (WAT) and brown (BAT) adipose tissue are tissues of energy storage and energy dissipation, respectively. Experimental evidence suggests that brown and white preadipocytes are differentially determined, but so far not much is known about the genetic control of this determination process. The aim of this study was to identify differentially expressed genes involved in brown and white preadipocyte development. Using representational difference analysis (cDNA RDA) and DNA microarray screening, we identified four genes with higher expression in white preadipocytes (three different complement factors and delta-6 fatty acid desaturase) and seven genes with higher expression levels in brown preadipocytes, of which three are structural genes implicated in cell adhesion and cytoskeleton organization (fibronectin, alpha-actinin-4, metargidin) and four that might function in gene transcription and protein synthesis (vigilin, necdin, snRNP polypeptide A, and a homolog to human hepatocellular carcinoma-associated protein). The expression profile of these genes was analyzed during preadipocyte differentiation, upon beta-adrenergic stimulation, and in WAT and BAT tissue in vivo compared with references genes such as peroxisome proliferator-activated receptor-gamma (PPARgamma), uncoupling protein 1 (UCP1), cytochrome c oxidase.

The application of DNA microarrays in gene expression analysis.

DNA microarray technology is a new and powerful technology that will substantially increase the speed of molecular biological research. This paper gives a survey of DNA microarray technology and its use in gene expression studies. The technical aspects and their potential improvements are discussed. These comprise array manufacturing and design, array hybridisation, scanning, and data handling. Furthermore, it is discussed how DNA microarrays can be applied in the working fields of: safety, functionality and health of food and gene discovery and pathway engineering in plants.

Evaluation of soluble CD44v6 as a potential serum marker for head and neck squamous cell carcinoma.

In recent years, the measurement of soluble CD44 levels in the circulation of patients with malignant diseases has been introduced as a new and simple diagnostic tool for the detection of human cancer. The high CD44v6 expression in head and neck squamous cell carcinoma (HNSCC) would enable the use of soluble CD44v6 proteins present in the circulation of HNSCC patients as a marker of disease. In the present study, we determined CD44v6 plasma levels using a domain-specific ELISA in healthy volunteers, non-cancer patients, and HNSCC patients before and after surgical removal of the tumor. A difference between the CD44v6 plasma levels of HNSCC patients and controls could not be observed. Moreover, surgical removal of the tumor did not result in a reduction of the CD44v6 plasma level in the HNSCC patients. In addition, the spectrum of soluble v6-containing CD44 proteins present in the plasma of HNSCC patients and controls was determined by immunoprecipitation experiments, but again, tumor-related isoforms could not be distinguished in patient samples. Additional experiments to unravel the biological source of these circulating proteins indicated surprisingly that the v6-containing proteins present in the circulation of healthy individuals are only released in part, if at all, by activated lymphocytes or other nucleated blood cells. Most circulating CD44v6 proteins seem to be derived from the normal epithelial cell compartments, including breast cells, colon cells, and squamous cells. Taken together, these data do not support the use of soluble CD44v6 as a tumor marker in HNSCC or any other tumor type that has developed from tissues producing soluble isoforms.

Characterization of CD44v6 isoforms in head-and-neck squamous-cell carcinoma.

CD44 splice variants, especially those containing the v6 domain, are assumed to play a critical role in the malignant progression of many human tumors. This concept was based on (i) the aberrant expression of CD44v6 in malignant cells, often encoded by alternatively spliced transcripts, and (ii) the absence of CD44v6 expression in corresponding normal tissues. Remarkably, data on CD44v6 expression in squamous cells do not support this hypothesis: the v6 domain is highly expressed in normal squamous tissues and down-regulation has been described in the majority of squamous-cell carcinomas of the head and neck (HNSCC). In this study, we have compared the expression of v6 in normal oral mucosa and HNSCC in a qualitative and quantitative way. Immuno-histochemistry was performed with 3 different anti-v6 antibodies (U36, U39 and VFF18) on a large panel of HNSCC cell lines and tumors. The v6-encoding splice variants were characterized by screening a cDNA library of a human HNSCC cell line and by RT-PCR on HNSCC cell lines, microdissected normal mucosa and primary as well as metastatic HNSCC tissue. The results revealed that there is no, or only marginal, down-regulation of CD44v6 in HNSCC. About 97% of the primary HNSCC tumors exhibited a high and homogeneous staining pattern (U36, 270/277; U39, 268/277 tumors with more than 50% positive cells). Furthermore, the v6-containing CD44 splice variants present in HNSCC primary tumors and metastases were identical to those expressed in normal mucosa. Our data indicate that v6-containing CD44 splice variants do not play a role in the malignant progression of HNSCC.

Sequence variation in the monoclonal-antibody-U36-defined CD44v6 epitope.

Monoclonal antibody (mAb) U36 was developed for the treatment of minimal residual disease of head and neck squamous cell carcinoma (HNSCC). The mAb-U36-defined antigen was characterized by cDNA cloning, and was shown to be identical to the keratinocyte-specific CD44 splice variant epican. The epitope recognized by mAb U36 was shown to be located in the v6 domain. Two amino acids within the epitope appeared to differ from the sequences that have been described in literature. The sequence of the epitope appeared to contain glutamic acid at position 367 and lysine at position 374, while valine and arginine respectively have been described before. Interestingly, another anti-CD44v6 antibody with possible clinical application, VFF18, recognizes an epitope in the same area. With respect to the applicability of these antibodies for tumor targeting, this variation might have an influence on antibody-antigen interaction and mAb accumulation in the tumor. Furthermore, this observation raised the question whether the different epitopes are related to the malignant behavior of tumor cells. In this paper we determine the relative affinity of mAb U36 for the variant epitope sequences by tumor cell binding assays using synthetic peptides for competition. The presence of glutamic acid instead of valine at position 367 caused strong competition. Further evaluation showed that the published valine variant does not exist in vivo, and is the result of a sequencing artefact. The effect of substitution of lysine for arginine at position 374 had no effect on the binding of mAb U36 to the cells. This amino acid variation was shown to be due to allelic polymorphism. There was no trend towards allelic imbalance in tumor cells as compared to normal cells.

Monoclonal antibody U36, a suitable candidate for clinical immunotherapy of squamous-cell carcinoma, recognizes a CD44 isoform.

At present, tumor-targeting with monoclonal antibodies (MAbs) is among the most promising novel adjuvant-therapy modalities for the treatment of patients with minimal residual disease of head-and-neck squamous-cell carcinoma (HNSCC). For this purpose we developed MAb U36, recognizing a 200-kDa antigen expressed on the outer cell surface of squamous-cell carcinomas and their normal counterparts. Clinical radioimmunoscintigraphy (RIS) and biodistribution studies have shown that the MAb-U36-defined antigen is a suitable target molecule for antibody-based therapy of head-and-neck cancer. In the present study we further characterized the antigen by cDNA cloning. The cDNA was isolated by expression cloning in COS-7 cells. Sequence analysis and database searching revealed that the MAb-U36-defined antigen is identical to the squamous-cell-specific CD44 splice variant epican. The epitope recognized by MAb U36 was mapped by screening overlapping synthetic peptides of the epican-specific region encoded by exon 7-11 (v3-v7), and appeared to be located in the v6 domain. The applicability of MAb U36 for targeting human tumors of various origin expressing the CD44v6 domain is discussed.