Sara Strömberg

A Human Protein Atlas for Normal and Cancer Tissues Based on Antibody Proteomics

Antibody-based proteomics provides a powerful approach for the functional study of the human proteome involving the systematic generation of protein-specific affinity reagents. We used this strategy to construct a comprehensive, antibody-based protein atlas for expression and localization profiles in 48 normal human tissues and 20 different cancers. Here we report a new publicly available database containing, in the first version, ∼400,000 high resolution images corresponding to more than 700 antibodies toward human proteins. Each image has been annotated by a certified pathologist to provide a knowledge base for functional studies and to allow queries about protein profiles in normal and disease tissues. Our results suggest it should be possible to extend this analysis to the majority of all human proteins thus providing a valuable tool for medical and biological research.

A cis-acting regulatory mutation causes premature hair graying and susceptibility to melanoma in the horse

In horses, graying with age is an autosomal dominant trait associated with a high incidence of melanoma and vitiligo-like depigmentation. Here we show that the Gray phenotype is caused by a 4.6-kb duplication in intron 6 of STX17 (syntaxin-17) that constitutes a cis-acting regulatory mutation. Both STX17 and the neighboring NR4A3 gene are overexpressed in melanomas from Gray horses. Gray horses carrying a loss-of-function mutation in ASIP (agouti signaling protein) had a higher incidence of melanoma, implying that increased melanocortin-1 receptor signaling promotes melanoma development in Gray horses. The Gray horse provides a notable example of how humans have cherry-picked mutations with favorable phenotypic effects in domestic animals.

ZBED6, a novel transcription factor derived from a domesticated DNA transposon regulates IGF2 expression and muscle growth.

This study identifies a previously uncharacterized protein, encoded by a domesticated DNA transposon, called ZBED6 that regulates the expression of the insulin-like growth factor 2 (IGF2) gene, and possibly numerous others, in all placental mammals including human.

Analysis of Protein Expression in Cell Microarrays: A Tool for Antibody-based Proteomics

Tissue microarray (TMA) technology provides a possibility to explore protein expression patterns in a multitude of normal and disease tissues in a high-throughput setting. Although TMAs have been used for analysis of tissue samples, robust methods for studying in vitro cultured cell lines and cell aspirates in a TMA format have been lacking. We have adopted a technique to homogeneously distribute cells in an agarose gel matrix, creating an artificial tissue. This enables simultaneous profiling of protein expression in suspension- and adherent-grown cell samples assembled in a microarray. In addition, the present study provides an optimized strategy for the basic laboratory steps to efficiently produce TMAs. Presented modifications resulted in an improved quality of specimens and a higher section yield compared with standard TMA production protocols. Sections from the generated cell TMAs were tested for immunohistochemical staining properties using 20 well-characterized antibodies. Comparison of immunoreactivity in cultured dispersed cells and corresponding cells in tissue samples showed congruent results for all tested antibodies. We conclude that a modified TMA technique, including cell samples, provides a valuable tool for high-throughput analysis of protein expression, and that this technique can be used for global approaches to explore the human proteome.

Mutation spectra of epidermal p53 clones adjacent to basal cell carcinoma and squamous cell carcinoma

Abstract:  Foci of normal keratinocytes overexpressing p53 protein are frequently found in normal human skin. Such epidermal p53 clones are common in chronically sun‐exposed skin and have been suggested to play a role in skin cancer development. In the present study, we have analyzed the prevalence of p53 mutations in epidermal p53 clones from normal skin surrounding basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). Using laser‐assisted microdissection, 37 epidermal p53 clones adjacent to BCC (21) and SCC (16) were collected. Genetic analysis was performed using a multiplex/nested polymerase chain reaction followed by direct DNA sequencing of p53 exons 2–11. In total, 21 of 37 analyzed p53 clones consisted of p53‐mutated keratinocytes. The identified mutations were located in p53 exons 4–8, corresponding to the sequence‐specific DNA‐binding domain. All mutations were missense, and 78% displayed a typical ultraviolet signature. The frequency of p53 mutations was similar in skin adjacent to BCC compared to SCC. The presented data confirm and extend previous knowledge on the genetic background of epidermal p53 clones. The mutation spectra found in epidermal p53 clones resemble that of non‐melanoma skin cancer. Approximately, 40% of the epidermal p53 clones lacked an underlying p53 mutation, suggesting that other genetic events in genes up‐ or downstream of the p53 gene can generate foci of normal keratinocytes overexpressing p53 protein.

Transcriptional profiling of melanocytes from patients with vitiligo vulgaris

Vitiligo is a complex, polygenic disorder characterized by patchy loss of skin pigmentation due to abnormal melanocyte function. Both genetic and environmental etiological factors have been proposed for vitiligo and lack of molecular markers renders difficulties to predict development and progression of the disease. Identification of dysregulated genes has the potential to unravel biological pathways involved in vitiligo pathogenesis, facilitating discovery of potential biomarkers and novel therapeutic approaches. In this study, we characterized the transcriptional profile of melanocytes from vitiligo patients. Oligonucleotide microarrays containing ∼16 000 unique genes were used to analyse mRNA expression in melanocytes from vitiligo patients and age‐matched healthy controls. In total, 859 genes were identified as differentially expressed. A substantial number of these genes were involved in (i) melanocyte development, (ii) intracellular processing and trafficking of tyrosinase gene family proteins, (iii) packing and transportation of melanosomes, (iv) cell adhesion and (v) antigen processing and presentation. In conclusion, our results show a significantly different transcription profile in melanocytes from vitiligo patients compared with controls. Several genes of potential importance for the pathogenesis and development of vitiligo were identified. Our data indicate that autoimmunity involving melanocytes may be a secondary event in vitiligo patients caused by abnormal melanocyte function.

Expression profiling of microdissected cell populations selected from basal cells in normal epidermis and basal cell carcinoma

Background Basal cell carcinomas (BCCs) are prevalent tumours with uniform histology that develop without any known precursor lesion. Alterations in the sonic hedgehog–patched1 signalling pathway are accepted as necessary events for tumorigenesis, and mutations in the patched1 gene are frequently present in tumours.

A fluid cover medium provides superior morphology and preserves RNA integrity in tissue sections for laser microdissection and pressure catapulting.

Laser microdissection and pressure catapulting has become a powerful tool to obtain homogeneous cell populations from tissue samples in nearly all fields of biomedical research. The isolated cells can be subsequently used for the analysis of proteins, DNA or RNA. However, the method requires physical access to the tissue surface and the sections therefore need to be air‐dried and uncovered. The consequence is poor morphology, which severely reduces the potential of the technique, especially in non‐homogeneous tissues or tissues with infiltrating immune cells. To overcome this limitation, a fluid cover medium was developed and the effects on frozen and paraffin wax‐embedded tissue morphology were evaluated. The cover medium improved the morphology such that it was almost comparable to sections overlaid with glass coverslips. Moreover, the laser microdissection procedure was facilitated, since the medium allowed larger areas of tissues to be laser pressure‐catapulted. Neither the isolation of proteins nor the extraction of genomic DNA was adversely affected by the use of the fluid cover medium. No significant differences in RNA quantity and integrity were detected by TaqMan real‐time PCR for GAPDH, and microchip electrophoresis, between covered and uncovered tissue sections. In conclusion, this method provides considerably improved morphology for laser microdissection and pressure catapulting techniques without affecting RNA‐dependent downstream applications. This not only facilitates established procedures, but will also extend the application to tissues that require superior morphological resolution. Copyright

SOX10 expression in superficial spreading and nodular malignant melanomas

SOX10 is a transcription factor expressed in nerve cells and melanocytes. The aim of this study was to investigate the protein expression pattern of SOX10 in malignant melanoma tumors and to analyze whether the results correlated with clinical parameters and the proliferation marker Ki-67. Furthermore, proliferation and migration were analyzed in three different cell lines employing SOX10 small interfering RNA-mediated silencing. Expression patterns were determined in 106 primary tumors and 39 metastases in addition to 16 normal skin samples and six benign nevi employing immunohistochemistry and tissue microarrays. The immunohistochemical staining was evaluated manually and with an automated algorithm. SOX10 was strongly expressed in the benign tissues, but for the malignant tumors superficial spreading melanomas stained stronger than nodular malignant melanomas (P=0.008). The staining intensity was also inversely correlated with T-stage (Spearmans ρ=−0.261, P=0.008). Overall survival and time to recurrence were significantly correlated with SOX10 intensity, but not in multivariate analysis including T-stage. With the automated algorithm there was an inverse correlation between the SOX10 staining intensity and the proliferation marker, Ki-67 (ρ=−0.173, P=0.02) and a significant difference in the intensity signal between the benign tissues, the primary tumors and the metastases where the metastases stained the weakest (P≤0.001). SOX10 downregulation resulted in variable effects on proliferation and migration rates in the melanoma cell lines. In conclusion, the SOX10 intensity level differed depending on the tissue studied and SOX10 might have a role in survival. No conclusion regarding the role of SOX10 for in-vitro proliferation and migration could be drawn.

Selective Expression of Syntaxin-7 Protein in Benign Melanocytes and Malignant Melanoma

To search for proteins expressed in human melanocytes and melanoma, we employed an antibody-based proteomics strategy to screen for protein expression in tissue microarrays containing normal tissues, cancer tissues and cell lines. Syntaxin-7 (STX7) was identified as a novel protein, not previously characterized in cells of melanocytic lineage, displaying a cell type-specific protein expression pattern. In tumor tissues, STX7 was expressed in malignant melanoma and lymphoma. The protein was further characterized regarding subcellular localization, specificity, tissue distribution pattern and potential as a diagnostic and prognostic marker using cell lines and tissue microarrays containing normal skin, melanocytic nevi and primary and metastatic melanoma. STX7 was expressed in normal melanocytes, various benign melanocytic nevi, atypical nevi and malignant melanoma. Analysis in two independent melanoma cohorts demonstrated STX7 expression in nearly all investigated tumors, although at varying levels (> 90% positive tumors). The expression level of STX7 protein was inversely correlated to tumor stage, suggesting that decreased expression of STX7 is associated with more aggressive tumors. In conclusion, we present protein profiling data for a novel protein showing high sensitivity and specificity for cells of the melanocytic lineage. The presented antibody-based proteomics approach can be used as an effective strategy to identify novel tumor markers and evaluate their potential clinical relevance.